source/nl.nlsw.Items.cs

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// __ _ ____ _ _ _ _ ____ ____ ____ ____ ____ ___ _ _ ____ ____ ____
// | \| |=== |/\| |___ | |--- |=== ==== [__] |--- | |/\| |--| |--< |===
//
/// @file nl.nlsw.Items.cs
/// @copyright Ernst van der Pols, Licensed under the EUPL-1.2-or-later
 
using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.Specialized;
using System.Globalization;
using System.Text;
using System.Text.RegularExpressions;
using System.Xml;
 
///
/// Base classes for collections of items with attributes properties.
///
/// @author Ernst van der Pols
/// @date 2022-10-22
/// @requires .NET Framework 4.5
///
namespace nl.nlsw.Items {
 
    /// Attributes (or parameters), i.e. key=value pairs
    /// The base class allows for multiple entries with the same key,
    /// using case insensitive CultureInvariant key comparison.
    public class Attributes : System.Collections.Specialized.NameValueCollection {
 
        /// Check if the attribute with the specified name contains the specified value.
        /// Uses a case-sensitive comparison.
        public bool HasValue(string name, string value) {
            string[] values = GetValues(name);
            if (values != null) {
                foreach (string v in values) {
                    if (String.Compare(v,value,StringComparison.Ordinal) == 0) {
                        return true;
                    }
                }
            }
            return false;
        }
 
        /// Check if the attribute with the specified name contains exactly the specified values.
        /// Uses a comparison as specified.
        public bool HasEqualValues(string name, string[] values, StringComparison comparison = StringComparison.Ordinal) {
            string[] vs = GetValues(name);
            if ((vs == null) ^ (values == null)) {
                return false;
            }
            if (vs != null) {
                if (vs.Length != values.Length) {
                    return false;
                }
                foreach (string v1 in vs) {
                    bool found = false;
                    foreach (string v2 in values) {
                        if (String.Compare(v1,v2,comparison) == 0) {
                            found = true;
                            break;
                        }
                    }
                    if (!found) {
                        return false;
                    }
                }
            }
            // both null or all strings match
            return true;
        }
 
        /// Check if the attribute with the specified name has exactly the same
        /// values in the other Attributes.
        /// Uses a case-sensitive comparison.
        public bool HasEqualValues(string name, Attributes other) {
            return HasEqualValues(name,other.GetValues(name),StringComparison.Ordinal);
        }
 
        /// Check if the attribute with the specified name has exactly the same
        /// values in the other Attributes.
        /// Uses a case-insensitive comparison.
        public bool HasEqualValuesIgnoreCase(string name, Attributes other) {
            return HasEqualValues(name,other.GetValues(name),StringComparison.OrdinalIgnoreCase);
        }
 
        /// Check if the attribute with the specified name contains the specified value.
        /// Uses a case-insensitive comparison.
        public bool HasValueIgnoreCase(string name, string value) {
            string[] values = GetValues(name);
            if (values != null) {
                foreach (string v in values) {
                    if (String.Compare(v,value,StringComparison.OrdinalIgnoreCase) == 0) {
                        return true;
                    }
                }
            }
            return false;
        }
 
        /// Add the value once to the attribute with the specified name.
        /// If the attribute already contains this value, it is not added again.
        /// Uses a case-sensitive comparison.
        public void AddOnce(string name, string value) {
            if (HasValue(name,value)) {
                return;
            }
            Add(name,value);
        }
 
        /// Add the value once to the attribute with the specified name.
        /// If the attribute already contains this value, it is not added again.
        /// Uses a case-insensitive comparison.
        public void AddOnceIgnoreCase(string name, string value) {
            if (HasValueIgnoreCase(name,value)) {
                return;
            }
            Add(name,value);
        }
 
        /// Remove the specified value from the specified attribute.
        /// Uses a case-insensitive value comparison.
        public void RemoveValue(string name, string value) {
            string[] values = GetValues(name);
            if ((values != null) && (value != null)) {
                Remove(name);
                for (int i = 0; i < values.Length; i++) {
                    if (String.Compare(values[i],value,StringComparison.Ordinal) != 0) {
                        Add(name,values[i]);
                    }
                }
            }
        }
 
        /// Remove the specified value from the specified attribute.
        /// Uses a case-insensitive value comparison.
        public void RemoveValueIgnoreCase(string name, string value) {
            string[] values = GetValues(name);
            if ((values != null) && (value != null)) {
                Remove(name);
                for (int i = 0; i < values.Length; i++) {
                    if (String.Compare(values[i],value,StringComparison.OrdinalIgnoreCase) != 0) {
                        Add(name,values[i]);
                    }
                }
            }
        }
 
        /// Counterpart of GetValues(), missing in the base class.
        public void SetValues(string name, string[] values) {
            if (values == null || values.Length == 0) {
                Remove(name);
            }
            else {
                Set(name,values[0]);
                for (int i = 1; i < values.Length; i++) {
                    Add(name,values[i]);
                }
            }
        }
    }
 
    ///
    /// A CompoundValue is a data value container that can represent a single "line"
    /// of a Comma-Separated-Values data file, as specified in RFC 4180.
    ///
    /// The class extends this specification to support nested CompoundValues as well,
    /// i.e. any value can be a comma-separated-value that (recursively) holds another
    /// list of comma-separated-values, surrounded by parentheses.
    /// This extension provides for a simple format for serializing an ordered, directed
    /// rooted tree of data nodes.
    ///
    /// The class is based on a generic object list. For serialization to string the ToString()
    /// operation of the objects are used. De-serialization builds a CompoundValue tree of strings.
    /// A nested CompoundValue has a link to is Parent CompoundValue.
    ///
    /// @see https://tools.ietf.org/html/rfc4180
    /// @see https://en.wikipedia.org/wiki/Comma-separated_values
    /// @see https://www.loc.gov/preservation/digital/formats/fdd/fdd000323.shtml
    /// @see https://en.wikipedia.org/wiki/Tree_(graph_theory)
    ///
    public class CompoundValue : global::System.Collections.Generic.List<object> {
        const char ValueSeparator = ',';
        const char DoubleQuote = '"';
        const char CompoundOpen = '(';
        const char CompoundClose = ')';
 
        /// Characters that require escaping
        public static readonly char[] Delimiters = {',','"','\r','\n',
            CompoundOpen,CompoundClose};
 
        /// The depth of this node in the tree.
        public int Depth {
            get {
                int result = 0;
                for (CompoundValue p = Parent; p != null; result++, p = p.Parent) {
                }
                return result;
            }
        }
 
        /// The parent node.
        public CompoundValue Parent { get; set; }
 
        /// Default Constructor (defines the parent)
        public CompoundValue(CompoundValue parent = null) {
            Parent = parent;
        }
 
        /// Initializing constructor
        public CompoundValue(string value) {
            FromString(value);
        }
 
        /// Get a value at the specified index, null if not present or index out-of-range.
        public object GetValue(int index) {
            if (index < Count) {
                return this[index];
            }
            return null;
        }
 
        /// Set the CompoundValue to the values in the list, array, or other enumerable
        /// @note List<T> has a constructor for IEnumerable, but no assignment
        public void FromEnumerable(IEnumerable list) {
            Clear();
            if (list != null) {
                foreach (object item in list) {
                    Add(item);
                }
            }
        }
 
        /// Set the CompoundValue to the (comma-separated) values specified in the string.
        /// @exception FormatException if the value has an invalid format
        public void FromString(string value) {
            Clear();
            if (string.IsNullOrEmpty(value)) {
                return;
            }
            CompoundValue current = this;
            int start = 0, position;
            for (; (position = value.IndexOfAny(Delimiters,start)) != -1; start = position + 1) {
                switch (value[position]) {
                case ValueSeparator:
                    current.Add(value.Substring(start,position - start));
                    break;
                case DoubleQuote:
                    if (position != start) {
                        // this delimiter must here be at start of field
                        throw new FormatException("unescaped DOUBLE-QUOTE character in CompoundValue");
                    }
                    start++;
                    {
                        // escaped value, scan for next DoubleQuote
                        position = value.IndexOf(DoubleQuote,start);
                        bool doubles = false;
                        while ((position >= 0) && ((position + 1) < value.Length) && (value[position + 1] == DoubleQuote)) {
                            // escaped DoubleQuote: needs to be replaced with single DoubleQuote
                            doubles = true;
                            position = value.IndexOf(DoubleQuote,position + 2);
                        }
                        if (position < 0) {
                            throw new FormatException("unclosed escaped CompoundValue (missing DOUBLE-QUOTE)");
                        }
                        string s = value.Substring(start);
                        if (doubles) {
                            s = s.Replace("\"\"","\"");
                        }
                        current.Add(s);
                    }
                    break;
                case CompoundOpen:
                    if (position != start) {
                        // this delimiter must here be at start of field
                        throw new FormatException(String.Format("unescaped '{0}' character in CompoundValue",CompoundOpen));
                    }
                    // increase nesting level
                    CompoundValue cv = new CompoundValue(current);
                    // set at this location
                    current.Add(cv);
                    // switch reading to nested level
                    current = cv;
                    break;
                case CompoundClose:
                    current.Add(value.Substring(start,position - start));
                    // decrease nesting level
                    if (current.Parent == null) {
                        throw new FormatException("unbalanced CompoundValue: closing delimiter without earlier opening delimiter");
                    }
                    current = current.Parent;
                    // skip the CompoundClose
                    position++;
                    // this delimiter must be followed by 1) nothing (end-of-line) or 2) comma
                    if ((position < value.Length) && (value[position] != ValueSeparator)) {
                        throw new FormatException(String.Format("missing value separator '{0}' after enquoted value",ValueSeparator));
                    }
                    break;
                case '\r':
                    throw new FormatException(String.Format("unescaped CARRIAGE RETURN character in CompoundValue",CompoundOpen));
                case '\n':
                    throw new FormatException(String.Format("unescaped LINEFEED character in CompoundValue",CompoundOpen));
                default:
                    throw new FormatException("unescaped CompoundValue delimiter encountered: "+value[position]);
                }
            }
            if (start < value.Length) {
                // no delimiters found, a single simple string has remained
                current.Add(value.Substring(start));
            }
            if (current != this) {
                throw new FormatException("unbalanced CompoundValue: opening delimiter without closing delimiter");
            }
        }
 
        /// Set the value at the specified index.
        /// If the index is outside the current list, the list is expanded to
        public void SetValue(int index, object value) {
            while (index >= Count) {
                Add(null);
            }
            this[index] = value;
        }
 
        ///
        /// Match the (text) value or the fields of the CompoundValue with the specified regular expression.
        /// @return the first successful match encountered, or null otherwise
        public static Match TextValueMatch(object value, System.Text.RegularExpressions.Regex regex) {
            Match result = null;
            if (value is CompoundValue) {
                for (int i = 0; i < ((CompoundValue)value).Count; i++) {
                    result = TextValueMatch(((CompoundValue)value)[i],regex);
                    if ((result != null) && result.Success) {
                        return result;
                    }
                }
            }
            else if (value != null) {
                result = regex.Match(value.ToString());
                if (result != null && result.Success) {
                    return result;
                }
            }
            // null encountered or no success
            return null;
        }
 
        ///
        /// Test whether the (compound) text value matches the regular expression.
        ///
        public static bool TextValueMatches(object value, System.Text.RegularExpressions.Regex regex) {
            Match m = TextValueMatch(value,regex);
            return (m != null) && m.Success;
        }
 
        /// Get the fields as a string, separated with the specified separator.
        /// Optionally, empty fields are included in the result, and nested fields can be indicated.
        public string ToFormattedString(int[] indices = null, string separator = " ", string open = null, string close = null, bool includeEmpty = false) {
            StringBuilder sb = new StringBuilder();
            ToStringBuilderFormatted(sb,indices,separator,open,close,includeEmpty);
            return sb.ToString();
        }
 
        public override string ToString() {
            StringBuilder sb = new StringBuilder();
            ToStringBuilder(sb);
            return sb.ToString();
        }
 
        /// Appends the CompoundValue to the string builder.
        /// Uses recursion to write nested CompoundValues.
        public void ToStringBuilder(StringBuilder sb) {
            if (Parent != null) {
                sb.Append(CompoundOpen);
            }
            for (int i = 0; i < Count; i++) {
                object v = this[i];
                if (i > 0) {
                    sb.Append(ValueSeparator);
                }
                if (v is CompoundValue) {
                    ((CompoundValue)v).ToStringBuilder(sb);
                }
                else if (v != null) {
                    string s = v.ToString();
                    if (s.IndexOfAny(Delimiters) >= 0) {
                        // enclose this value with DoubleQuotes
                        sb.Append(DoubleQuote);
                        int start = sb.Length;
                        sb.Append(s);
                        // replace DoubleQuote with 2DoubleQuote
                        sb.Replace("\"","\"\"",start,s.Length);
                        sb.Append(DoubleQuote);
                    }
                    else {
                        sb.Append(s);
                    }
                }
            }
 
            if (Parent != null) {
                sb.Append(CompoundClose);
            }
        }
 
        /// Appends the CompoundValue to the string builder, using the specified fields and format delimiters.
        /// Uses recursion to write nested CompoundValues.
        /// @param sb the output string builder
        /// @param indices the field indices to include; these apply only to this level of values; null means all fields.
        /// @param separator the separator to use
        /// @param open the nested value(s) opening delimiter
        /// @param close the nested value(s) closing delimiter (ignored if 'open' is null)
        /// @param includeEmpty By default empty fields are not included, but if you want the delimiters can be written for empty fields as well.
        public void ToStringBuilderFormatted(StringBuilder sb, int[] indices = null, string separator = " ", string open = null, string close = null, bool includeEmpty = false) {
            int openPos = sb.Length;
            if (Parent != null) {
                sb.Append(open);
            }
            int startPos = sb.Length;
            for (int i = 0; (indices == null) ? i < Count : i < indices.Length; i++) {
                object v = this[(indices == null) ? i : indices[i]];
                int separatorPos = -1;
                if (sb.Length > startPos) {
                    separatorPos = sb.Length;
                    sb.Append(separator);
                }
                if (v is CompoundValue) {
                    ((CompoundValue)v).ToStringBuilderFormatted(sb,null,separator,open,close,includeEmpty);
                }
                else if (v != null) {
                    string s = v.ToString();
                    sb.Append(s);
                }
                if (!includeEmpty && (separatorPos >= 0) && (separator != null)) {
                    // determine if we should remove the separator
                    if (sb.Length == (separatorPos + separator.Length)) {
                        sb.Remove(separatorPos,separator.Length);
                    }
                }
            }
            if (Parent != null && (open != null)) {
                if (!includeEmpty) {
                    // determine if we should remove the opening delimiter
                    if (sb.Length == (openPos + open.Length)) {
                        sb.Remove(openPos,open.Length);
                    }
                }
                else {
                    sb.Append(close);
                }
            }
        }
    }
 
    /// Class of properties that can have multiple values.
    ///
    /// The values are typically contained in a CompoundValue container.
    /// Three subclasses can be distinghuished:
    /// - list properties: a list of multiple similar values
    /// - structured properties: a set of sub-properties, each with its own name
    /// - a combination of both, e.g. an ordered list of values
    ///
    public class CompoundProperty : Property {
 
        /// Get the value as CompoundValue
        /// @note may return null
        public CompoundValue CompoundValue {
            get { return Value as CompoundValue; }
            set { Value = value; }
        }
 
        /// Get the names of the compound fields (if any)
        public virtual string[] FieldNames { get; set; }
 
        /// Get the number of values (first order)
        public int ValueCount {
            get {
                if (Value == null) return 0;
                if (CompoundValue == null) return 1;
                return CompoundValue.Count;
            }
        }
 
        /// Default constructor
        public CompoundProperty() {
        }
 
        /// Initializing Constructor
        public CompoundProperty(string name, object value = null) : base(name,value) {
        }
 
        /// Add the value, optionally at the specified index.
        public void AddValue(object value, int? index = null) {
            // check if we have a compound value to hold the new value
            CompoundValue cv = base.Value as CompoundValue;
            if (cv == null) {
                cv = new CompoundValue();
                if (base.Value != null) {
                    // preserve the degenerate first value
                    cv.Add(base.Value);
                }
                base.Value = cv;
            }
            if (index == null) {
                // simply add the value to the Value list
                cv.Add(value);
            }
            else {
                // add the new value to the list at the specified index
                object atIndex = cv.GetValue((int)index);
                // do we have a CompoundValue there?
                CompoundValue svc = atIndex as CompoundValue;
                if (svc == null) {
                    // no, create one
                    svc = new CompoundValue(cv);
                    if (atIndex != null) {
                        // preserve the (degenerate) first value of the list
                        svc.Add(atIndex);
                    }
                    // set the CompoundValue at the index
                    cv.SetValue((int)index,svc);
                }
                // add the value to the list
                svc.Add(value);
            }
        }
 
        /// Get the name of the compound field at the specified index.
        public string GetFieldName(int index) {
            if (FieldNames == null) {
                throw new Exception("FieldNames not initialized");
            }
            return FieldNames[(index < FieldNames.Length ? index : FieldNames.Length - 1)];
        }
 
        /// Get the value, optionally at the specified indices.
        public object GetValue(int? index = null, int? subIndex = null) {
            object value = base.Value;
            if (index == null) {
                return value;
            }
            if (value is CompoundValue) {
                value = ((CompoundValue)value).GetValue((int)index);
                if (subIndex == null) {
                    return value;
                }
                if (value is CompoundValue) {
                    return ((CompoundValue)value).GetValue((int)subIndex);
                }
                else if (subIndex == 0) {
                    return value;
                }
                return null;
            }
            else if ((index == 0) && (subIndex == null || subIndex == 0)) {
                return value;
            }
            return null;
        }
 
        /// Get the values as string, optionally at the specified field index.
        public string[] GetValuesAsString(int? index = null) {
            object value = base.Value;
            if ((index != null) && (value is CompoundValue)) {
                // get the string values of the specified field
                value = ((CompoundValue)value).GetValue((int)index);
            }
            string[] result = null;
            if (value is CompoundValue) {
                CompoundValue cv = (CompoundValue)value;
                result = new string[cv.Count];
                for (int i = 0; i < cv.Count; i++) {
                    if (cv[i] != null) {
                        result[i] = cv[i].ToString();
                    }
                }
            }
            else if (value != null) {
                result = new string[1];
                result[0] = value.ToString();
            }
            return result;
        }
 
        /// Set the value, optionally at the specified indices.
        public void SetValue(object value, int index = 0, int subIndex = 0) {
            // check if we have a compound value to hold the new value
            CompoundValue cv = base.Value as CompoundValue;
            if (cv == null) {
                if ((index == 0) && (subIndex == 0)) {
                    // degenerate case: store the value directly
                    base.Value = value;
                    return;
                }
                // we need a CompoundValue, so create one to hold the value
                cv = new CompoundValue();
                if (base.Value != null) {
                    // preserve the degenerate first value
                    cv.Add(base.Value);
                }
                base.Value = cv;
            }
            // check if we have a CompoundValue to hold the value
            object atIndex = cv.GetValue(index);
            CompoundValue scv = atIndex as CompoundValue;
            if (scv == null) {
                if (subIndex == 0) {
                    // degenerate case: store the value directly
                    cv.SetValue(index,value);
                    return;
                }
                scv = new CompoundValue(cv);
                if (atIndex != null) {
                    // preserve the degenerate first value
                    scv.Add(atIndex);
                }
                cv.SetValue(index,scv);
            }
            scv.SetValue(subIndex, value);
        }
 
        /// Set the values, optionally at the specified index.
        /// @note other values (at the index) are removed
        public void SetValuesAsString(string[] values, int? index = null) {
            if (values == null) {
                throw new ArgumentNullException("values");
            }
            CompoundValue cv = base.Value as CompoundValue;
            if (cv == null) {
                // we need a CompoundValue, so create one to hold the values
                cv = new CompoundValue();
                base.Value = cv;
            }
            if (index == null) {
                // replace existing fields with the values
                cv.Clear();
                cv.AddRange(values);
            }
            else {
                // replace values of field 'index'
                // check if we have a CompoundValue to hold the value
                CompoundValue scv = cv.GetValue((int)index) as CompoundValue;
                if (scv == null) {
                    scv = new CompoundValue(cv);
                    cv.SetValue((int)index,scv);
                }
                // replace existing subfields with the values
                scv.Clear();
                scv.AddRange(values);
            }
        }
    }
 
    /// Extension methods on standard .NET classes
    public static class Extensions {
         
        /// Return the substring after the specified search string.
        ///
        /// - If the value of `value` or `search` is the empty sequence, it is interpreted as the zero-length string.
        /// - If the value of `search` is the zero-length string, then the function returns the value of `value`.
        /// - If the value of `value` does not contain a string that is equal to the value of `search`, then the function returns the zero-length string.
        /// - The function returns the substring of the value of `value` that follows in the value of `value` the first occurrence of `search`.
        /// @param value the string to get a substring of
        /// @param search the string to search as prefix of the part to return
        /// @see https://www.w3.org/TR/xpath-functions-31/#func-substring-after
        public static string SubstringAfter(this string value, string search) {
            if (!string.IsNullOrEmpty(value) && !string.IsNullOrEmpty(search)) {
                int position = value.IndexOf(search);
                return (position < 0) ? string.Empty : value.Substring(position + search.Length);
            }
            return value;
        }
    }
 
    ///
    /// A keyed collection of ItemObjects.
    ///
    /// The ItemList has an internal dictionary for a fast lookup of items, based on their Identifier.
    /// Since the Identifier of an ItemObject is mutable, the update of the ItemObject.Identifier results in an update of the
    /// associated ItemList as well; the ItemObject holds a reference to the Dictionary for this.
    /// An ItemObject can only be in one ItemList.
    /// @see https://docs.microsoft.com/en-us/dotnet/api/system.collections.objectmodel.keyedcollection-2?view=netframework-4.5.2
    ///
    public class ItemList : System.Collections.ObjectModel.KeyedCollection<string,ItemObject> {
 
        /// The default constructor.
        /// The specified dictionary threshold 0 means that the internal Dictionary
        /// is created the first time an object is added.
        public ItemList() : base(null, 0) {
        }
 
        /// Create a new ItemObject and add it to the Dictionary.
        /// @param name the (display) name of the ItemObject
        /// @param id a unique identifier URI; by default a new UUID URI is generated
        public ItemObject NewItem(string name = null, nl.nlsw.Identifiers.Uri id = null) {
            ItemObject result = new ItemObject(name,id);
            Add(result);
            return result;
        }
 
        /// Get the key of the ItemObject object.
        protected override string GetKeyForItem(ItemObject item) {
            // The Identifier is the key.
            return item.Identifier.ToString();
        }
 
        protected override void InsertItem(int index, ItemObject newItem) {
            if (newItem.ItemList != null) {
                throw new ArgumentException("The item is already registered in a list.",newItem.Name);
            }
 
            base.InsertItem(index, newItem);
            newItem.ItemList = this;
        }
 
        /// Move the items from the other ItemList into this one.
        /// @post other will be empty
        /// @exception one of the imported items has a key that already exists
        public void MoveFrom(ItemList other) {
            for (int i = other.Count - 1; i >= 0; i--) {
                ItemObject p = other[i];
                other.RemoveItem(i);
                Add(p);
            }
        }
 
        protected override void SetItem(int index, ItemObject newItem) {
            ItemObject replaced = Items[index];
 
            if (newItem.ItemList != null) {
                throw new ArgumentException("The item is already registered in a list.",newItem.Name);
            }
 
            base.SetItem(index, newItem);
            newItem.ItemList = this;
            replaced.ItemList = null;
        }
 
        protected override void RemoveItem(int index) {
            ItemObject removedItem = Items[index];
 
            base.RemoveItem(index);
            removedItem.ItemList = null;
        }
 
        protected override void ClearItems() {
            foreach (ItemObject item in Items) {
                item.ItemList = null;
            }
            base.ClearItems();
        }
 
        /// To be called from ItemObject.Identifier.set
        internal void ChangeKey(ItemObject item, string newKey) {
            base.ChangeItemKey(item, newKey);
        }
    }
 
    ///
    /// The ItemObject class represents a named item with a unique identifier,
    /// that is collected in an ItemList.
    ///
    /// An ItemObject may have properties. Each ItemObject is registered in a single ItemList.
    ///
    /// @note The name Item cannot be used if you want the class to have an indexer property.
    /// The .NET runtime uses the name "Item" for these properties, and this results
    /// in the compiler error "Item" member names cannot be the same as their
    /// enclosing type.
    /// @note The use of the name 'Thing' for this class is rejected, because we don't want
    /// the condition "Person is Thing" to be true.
    /// @see https://schema.org/Thing
    ///
    public class ItemObject {
        /// The ItemList (keyed collection of items) that this ItemObject belongs to.
        private ItemList _ItemList = null;
        /// Unique identifier of the item, e.g. a urn:uuid
        private nl.nlsw.Identifiers.Uri _Identifier = null;
        /// Properties of the item
        private Properties _Properties = null;
 
        /// Get a property or the properties by case insensitive name
        [System.Xml.Serialization.XmlIgnore()]
        public object this[string name] {
            get {
                if (_Properties != null) {
                    return _Properties[name];
                }
                return null;
            }
        }
 
        /// The ItemList that this ItemObject belongs to.
        [System.Xml.Serialization.XmlIgnore()]
        public ItemList ItemList {
            get { return this._ItemList; }
            internal set {
                this._ItemList = value;
            }
        }
 
        public bool HasProperties {
            get { return (_Properties != null) && (_Properties.Count > 0); }
        }
 
        ///
        /// The unique identifier of the ItemObject.
        /// The value should be a normalized Uri, such that a string
        /// comparison can be used for equality check.
        /// The Uri.Equals is not suited since e.q. a comparison of a mailto-uri (i.e. an
        /// e-mail address) will fail since UserInfo is not included in the Uri.Equals.
        /// A UUID is preferred as identifier.
        ///
        /// The (string value) Identifier is used as key in the associated ItemList.
        /// If the Identifier is changed, the ItemList is automatically updated.
        /// In that case, an ArgumentException is thrown if the new value is null or an existing key.
        ///
        [System.Xml.Serialization.XmlIgnore()]
        public nl.nlsw.Identifiers.Uri Identifier {
            get { return this._Identifier; }
            set {
                if (ItemList != null) {
                    // @todo change Identifier comparison from string to the Identifier object itself
                    ItemList.ChangeKey(this, value == null ? null : value.ToString());
                }
                this._Identifier = value;
            }
        }
 
        /// Get an icon character representing the (type of) ItemObject.
        /// @note to represent any Unicode char, you need a string in C#,
        /// since a char is only 16-bit
        [System.Xml.Serialization.XmlIgnore()]
        public virtual string IconChar {
            get { return "\u2022"; } // BULLET
        }
 
        [System.Xml.Serialization.XmlIgnore()]
        public string Name { get; set; }
 
        [System.Xml.Serialization.XmlIgnore()]
        public Properties Properties {
            get {
                if (_Properties == null) {
                    _Properties = new Properties();
                }
                return _Properties;
            }
        }
 
 
        /// Default and initializing constructor
        /// @param name the (display) name of the ItemObject
        /// @param id a unique identifier URI; by default a new UUID URI is generated
        public ItemObject(string name = null, nl.nlsw.Identifiers.Uri id = null) {
            if (id == null) {
                // create a new UUID URI
                id = nl.nlsw.Identifiers.UrnUri.NewUuidUrnUri();
            }
            this.Identifier = id;
            this.Name = name;
        }
 
        /// Get the replacement value of the specified macro for this object.
        /// @param macro the macro to get the value of
        /// @return the macro value, or null if not available
        public virtual string GetMacroValue(string macro) {
            if (string.Equals("name",macro,StringComparison.OrdinalIgnoreCase)) {
                return this.Name;
            }
            else if (string.Equals("id",macro,StringComparison.OrdinalIgnoreCase)) {
                return (this.Identifier == null) ? null : this.Identifier.ToString();
            }
            else if (string.Equals("uuid",macro,StringComparison.OrdinalIgnoreCase)) {
                return nl.nlsw.Identifiers.UrnUri.GetUUIDString(this.Identifier);
            }
            return null;
        }
 
        /// Get properties by name, and (optionally) attribute name and value.
        public Properties GetProperties(string name, string attrName = null, string attrValue = null) {
            if (_Properties != null) {
                return _Properties.Get(name,attrName,attrValue);
            }
            return null;
        }
 
        /// Get the first property by name, and (optionally) attribute name and value.
        public Property GetProperty(string name, string attrName = null, string attrValue = null) {
            if (_Properties != null) {
                return _Properties.GetProperty(name,attrName,attrValue);
            }
            return null;
        }
 
        public override string ToString() {
            return (string.IsNullOrEmpty(Name) ? (Identifier == null ? null : Identifier.ToString()) : Name);
        }
    }
 
    /// A stack of ItemObjects, typically used when processing nested sets of ItemObjects.
    public class ItemStack : System.Collections.Generic.Stack<ItemObject> {
    }
 
    /// A Property of an ItemObject.
    ///
    /// Class of attributed Name=Value objects, holding a property of an ItemObject.
    /// The value of the property can be formatted in different ways based on a IFormatProvider.
    ///
    public class Property : IFormattable {
        private Attributes _attrs = null;
        private object _Value;
        /// the name of the attribute that holds the group name of the property
        public static readonly string GroupNameAttribute = ".group";
 
        /// The name of the group that the property belongs to.
        public string GroupName {
            get { return GetAttribute(GroupNameAttribute); }
            set { SetAttribute(GroupNameAttribute, value); }
        }
 
        /// The attributes of the property
        public Attributes Attributes {
            get {
                if (_attrs == null) {
                    _attrs = new Attributes();
                }
                return _attrs;
            }
        }
 
        /// Get or set an attribute of the property.
        public string this[string name] {
            get { return GetAttribute(name); }
            set { SetAttribute(name, value); }
        }
 
        /// Get an icon character representing the (type of) Property.
        /// @note to represent any Unicode char, you need a string in C#,
        /// since a char is only 16-bit
        public virtual string IconChar {
            // U+214A PROPERTY LINE
            // (think of the symbol as indicating the start of another property)
            get { return "\u214A"; }
        }
 
        /// The name of the property
        public string Name { get; set; }
 
        /// The value of the property
        public virtual object Value {
            get { return _Value; }
            set { _Value = value; }
        }
 
        /// The type of the value
        public virtual string ValueType {
            get { return "text"; }
        }
 
        public bool HasAttributes {
            get { return (_attrs != null) && (_attrs.Count > 0); }
        }
 
        /// Class constructor
        static Property() {
        }
 
        /// Default constructor
        public Property() {
        }
 
        /// Initializing Constructor
        public Property(string name, object value = null) {
            this.Name = name;
            this.Value = value;
        }
 
        /// Get the value of the specified attribute. If not present, the default value is returned.
        /// If the attribute has multiple values, they are returned as a comma-separated list, without proper enquoting.
        public string GetAttribute(string name, string defaultValue = null) {
            if (_attrs != null) {
                return _attrs.Get(name) ?? defaultValue;
            }
            return defaultValue;
        }
 
        /// Test whether the property has an attribute with the specified name and (optionally) value combination.
        /// Name comparison is case-insensitive, value comparison is case-sensitive.
        public bool HasAttribute(string name, string value = null) {
            if (_attrs != null) {
                string[] values = _attrs.GetValues(name);
                if (values != null) {
                    return (value == null) || (System.Array.IndexOf(values,value) >= 0);
                }
            }
            return false;
        }
 
        /// Check if this property has the specified name.
        /// Performs a case-insensitive compare.
        public bool HasName(string name) {
            return (String.Compare(Name,name,StringComparison.OrdinalIgnoreCase) == 0);
        }
 
        /// Test whether the attribute name represents an internal, hidden attribute.
        /// A name represents a hidden attribute if:
        /// - the name is null or empty, indicating no attribute, which is hidden by its nature
        /// - it starts with a FULL STOP, indicating an internal attribute
        public virtual bool IsHiddenAttribute(string name) {
            return string.IsNullOrEmpty(name) || name.StartsWith(".",StringComparison.Ordinal);
        }
 
        /// Set the value of the specified attribute.
        public void SetAttribute(string name, string value) {
            Attributes.Set(name,value);
        }
 
        /// Object.ToString()
        /// To be used for general display of the property
        /// By default, return Value.ToString()
        public override string ToString() {
            return Value == null ? null : Value.ToString();
        }
 
        /// IFormattable.ToString()
        /// To be used for (formatted) output of the property value.
        /// By default, returns Value.ToString()
        public virtual string ToString(string format, IFormatProvider formatProvider) {
            return Value == null ? null : Value.ToString();
        }
    }
 
    /// A list of properties
    /// The list may contain multiple properties with the same name.
    public class Properties : List<Property> {
 
        /// Get a property or the properties by case insensitive name
        public object this[string name] {
            get {
                Property first = null;
                Properties list = null;
                foreach (Property prop in this) {
                    if (prop.HasName(name)) {
                        if (first == null) {
                            first = prop;
                        }
                        else {
                            if (list == null) {
                                list = new Properties();
                                list.Add(first);
                            }
                            list.Add(prop);
                        }
                    }
                }
                return (list == null ? (object)first : (object)list);
            }
        }
 
        /// Add a property
        /// @deprecated use a factory method API for type specific properties
        public Property AddProperty(string name, object value) {
            Property prop = new Property(name,value);
            Add(prop);
            return prop;
        }
 
        /// Get the properties by (optionally) case insensitive name,
        /// and (optionally) case insensitive attribute name,
        /// and (optionally) case sensitive attribute value.
        /// E.g. get all properties with a specific attribute (value) by setting name to null.
        public Properties Get(string name, string attrName = null, string attrValue = null) {
            Properties result = null;
            foreach (Property prop in this) {
                if (((name == null) || prop.HasName(name))
                && ((attrName == null) || prop.HasAttribute(attrName,attrValue))) {
                    if (result == null) {
                        result = new Properties();
                    }
                    result.Add(prop);
                }
            }
            return result;
        }
 
        /// Get the first property by (optionally) case insensitive name,
        /// and (optionally) case insensitive attribute name,
        /// and (optionally) case sensitive attribute value.
        public Property GetProperty(string name, string attrName = null, string attrValue = null) {
            foreach (Property prop in this) {
                if (((name == null) || prop.HasName(name))
                && ((attrName == null) || prop.HasAttribute(attrName,attrValue))) {
                    return prop;
                }
            }
            return null;
        }
 
        /// Remove all properties with the specified name
        public void RemoveProperty(string name) {
            for (int i = Count-1; i >= 0; i--) {
                if (this[i].HasName(name)) {
                    Remove(this[i]);
                }
            }
        }
    }
 
    /// Base class for reading ItemObjects from a stream
    public class Reader : System.IDisposable {
        /// declare the stack used during parsing (nested) items
        private ItemStack _ItemStack = new nl.nlsw.Items.ItemStack();
        /// the default encoding of the source text
        private System.Text.Encoding _DefaultEncoding;
        /// the buffer for unfolding content lines
        private System.Text.StringBuilder _ContentLine = new System.Text.StringBuilder();
        /// the buffer for lines to process when no format is known yet
        private List<string> _LineCache;
        /// Track whether Dispose has been called.
        private bool _Disposed = false;
 
        /// Buffer for unfolding the current content line
        public System.Text.StringBuilder ContentLine {
            get { return _ContentLine; }
        }
 
        /// The current source encoding
        public System.Text.Encoding CurrentEncoding {
            get {
                System.IO.StreamReader sr = this.TextReader as System.IO.StreamReader;
                if (sr != null) {
                    // the StreamReader may have detected another encoding than the default
                    return sr.CurrentEncoding;
                }
                return _DefaultEncoding;
            }
        }
 
        /// The current ItemObject
        public ItemObject CurrentItem {
            get { return (_ItemStack.Count == 0) ? null : _ItemStack.Peek(); }
        }
 
        /// The target ItemList for read ItemObjects
        public ItemList CurrentItemList { get; set; }
 
        /// The default Encoding to use
        public System.Text.Encoding DefaultEncoding {
            get { return _DefaultEncoding; }
        }
 
        /// The number of files read
        public int FileCount { get; set; }
 
        /// The current file being read
        public System.IO.FileInfo FileInfo { get; set; }
 
        /// The name of the file or other source being read
        public string FileName {
            get {
                if (FileInfo != null) {
                    return FileInfo.FullName;
                }
                if (TextReader != null) {
                    System.IO.StreamReader sr = TextReader as System.IO.StreamReader;
                    if (sr != null) {
                        if (sr.BaseStream is System.IO.FileStream) {
                            return ((System.IO.FileStream)sr.BaseStream).Name;
                        }
                        if (sr.BaseStream is System.Net.Sockets.NetworkStream) {
                            // no more info retrievable
                            return "<networkstream>";
                        }
                    }
                    return "<stream>";
                }
                return "<pipe>";
            }
        }
 
        /// Check if the reader has cached lines
        public bool HasCachedLines {
            get { return _LineCache != null && _LineCache.Count > 0; }
        }
 
        /// Check if the reader has a content line read
        public bool HasContentLine {
            get { return _ContentLine.Length > 0; }
        }
 
        /// The buffer for lines to process when no format is known yet
        public List<string> LineCache {
            get {
                if (_LineCache == null) {
                    _LineCache = new List<string>();
                }
                return _LineCache;
            }
        }
 
        /// The number of ItemObjects read
        public int ItemCount { get; set; }
 
        /// Next line must be joined with the previous one,
        /// as part of QuotedPrintable encoded data
        public bool QuotedPrintableFolding { get; set; }
 
        /// To keep track of the ItemObject nesting
        public ItemStack Stack {
            get { return _ItemStack; }
        }
 
        /// The TextReader to use for reading
        public System.IO.TextReader TextReader { get; set; }
 
        /// Default constructor
        public Reader() {
            _DefaultEncoding = System.Text.Encoding.UTF8;
        }
 
        /// Initializing constructor
        public Reader(System.Text.Encoding defaultEncoding = null) {
            _DefaultEncoding = defaultEncoding ?? System.Text.Encoding.UTF8;
        }
 
        /// Implementation of IDisposable
        public void Dispose() {
            Dispose(true);
            // This object will be cleaned up by the Dispose method.
            // Therefore, you should call GC.SuppressFinalize to
            // take this object off the finalization queue
            // and prevent finalization code for this object
            // from executing a second time.
            GC.SuppressFinalize(this);
        }
 
        /// Dispose(bool disposing) executes in two distinct scenarios.
        /// If disposing equals true, the method has been called directly
        /// or indirectly by a user's code. Managed and unmanaged resources
        /// can be disposed.
        /// If disposing equals false, the method has been called by the
        /// runtime from inside the finalizer and you should not reference
        /// other objects. Only unmanaged resources can be disposed.
        protected virtual void Dispose(bool disposing) {
            if (!this._Disposed) {
                if (disposing) {
                    // clean up managed resources
                    if (TextReader != null) {
                        TextReader.Dispose();
                        TextReader = null;
                    }
                    FileInfo = null;
                }
                this._Disposed = true;
            }
        }
 
        ///
        /// Decode a string containing a compound value, i.e. delimited fields, optionally with nested sub-fields.
        /// In addition, or alternatively, escaped characters can be unescaped.
        /// Escaped delimiters are unescaped in the returned result automatically.
        ///
        /// Example use cases:
        /// - the data string does not contain any of the delimiters: the input string is returned
        ///
        /// - the data string only contains escaped delimiters or other escape sequences: the unescaped string is returned
        /// @example "simple text string\, that may contain a delimiter like \\" => "simple text string, that may contain a delimiter like \"
        ///
        /// - a string containing delimited list members (a List<String> is returned with the members; actually a CompundValue, since that is also a List)
        /// @example "member 1,member\, with path \\,member 3" => ( "member 1", "member, with path \", "member 3" )
        ///
        /// - a string containing delimited fields with simple string content or a list of members (a List<Object> is returned with the fields, either a String or a List<String>)
        /// @example "field 1;field2\, member 1, field2\, member 2;field 3" => ( "field 1", ( "field 2, member1", "field 2, member 2"), "field 3" )
        ///
        /// Example application is decoding the vCard property value.
        ///
        /// @param data the input data string
        /// @param delimiters the first character in the array must be the escape character; subsequent characters are the ordered delimiters of the nested fields
        /// @param replacements the additional escape sequences that need to be decoded; the delimiters are replaced automatically; a non-specified escape sequence
        /// is left as-is.
        /// @return a System.String or a nl.nlsw.Items.CompoundValue
        ///
        public static object DecodeCompoundValue(string data, char[] delimiters, Dictionary<char,string> replacements = null) {
            int position = (delimiters != null) ? data.IndexOfAny(delimiters) : -1;
            if (position == -1) {
                // no delimiters specified or present, return the input string
                return data;
            }
            System.Text.StringBuilder sb = new System.Text.StringBuilder();
            CompoundValue cv = null;
            string replacement;
            int start = 0;
 
            for (; (position = data.IndexOfAny(delimiters, position)) != -1; start = position) {
                sb.Append(data,start, position - start);
                start = position;
                char delim = data[position++];
                int delindex = Array.IndexOf<char>(delimiters,delim);
                if (delindex < 0) {
                    throw new InvalidOperationException("found compound value delimiter must be in the array of delimiters");
                }
                else if (delindex == 0) {
                    // the EscapeCharacter found
                    if (position < data.Length) {
                        if (Array.IndexOf<char>(delimiters,data[position]) != -1) {
                            // copy the escaped delimiter
                            sb.Append(data[position]);
                        }
                        else if ((replacements != null) && replacements.TryGetValue(data[position],out replacement)) {
                            // it is one of the replacements
                            sb.Append(replacement);
                        }
                        else {
                            // other character: copy both (keep original text) and continue
                            sb.Append(data,start,2);
                        }
                        position++;
                    }
                    else {
                        // EscapeChar at end of data: copy and finish
                        sb.Append(delim);
                    }
                }
                else {
                    // delimiter is one of the compound field delimiters
                    if (cv == null) {
                        // start a compound value for this delimiter
                        cv = new CompoundValue();
                    }
                    int depth = delindex - 1;
                    if (depth == cv.Depth) {
                        // sibling field parsed
                        cv.Add(sb.ToString());
                        sb.Clear();
                    }
                    else if (depth > cv.Depth) {
                        while (depth > cv.Depth) {
                            // increase level
                            CompoundValue child = new CompoundValue(cv);
                            cv.Add(child);
                            cv = child;
                        }
                        cv.Add(sb.ToString());
                        sb.Clear();
                    }
                    else {
                        cv.Add(sb.ToString());
                        sb.Clear();
                        while (depth < cv.Depth) {
                            if (cv.Parent == null) {
                                throw new FormatException("stack underflow during compound value parsing");
                            }
                            cv = cv.Parent;
                        }
                    }
                }
            }
            if (start < data.Length) {
                sb.Append(data,start, data.Length - start);
            }
            if (cv != null) {
                if (sb.Length > 0) {
                    cv.Add(sb.ToString());
                    sb.Clear();
                }
                while (cv.Parent != null) {
                    cv = cv.Parent;
                }
                return cv;
            }
            // simply return the unescaped string, no compound value present
            return sb.ToString();
        }
 
        /// Decode Base64 encoded text
        /// @see https://en.wikipedia.org/wiki/Base64
        public static string DecodeBase64Text(string data, System.Text.Encoding encoding) {
            // convert base64 text to array
            byte[] bytes = System.Convert.FromBase64String(data);
            // convert bytes to text
            return encoding.GetString(bytes);
        }
 
        ///
        /// Decode Base64 encoded text recursively in a list
        ///
        public static System.Collections.IList DecodeBase64Text(System.Collections.IList data, System.Text.Encoding encoding) {
            for (int i = 0; i < data.Count; i++) {
                if (data[i] is string) {
                    data[i] = DecodeBase64Text((string)(data[i]), encoding);
                }
                else if (data[i] is System.Collections.IList) {
                    data[i] = DecodeBase64Text((System.Collections.IList)(data[i]), encoding);
                }
            }
            return data;
        }
 
        /// Decode Quoted-Printable text
        ///
        /// @see https://en.wikipedia.org/wiki/Quoted-printable
        /// @see https://stackoverflow.com/questions/2226554/c-class-for-decoding-quoted-printable-encoding
        public static string DecodeQuotedPrintable(string data, System.Text.Encoding encoding) {
            int position = data.IndexOf('=');
            if (position == -1) {
                // no fields, members, or escaped chars present, return the input string
                return data;
            }
            System.Text.StringBuilder result = new System.Text.StringBuilder(data.Length);
            System.Collections.Generic.List<byte> bytes = new System.Collections.Generic.List<byte>();
            int start = 0;
            for (start = 0; ((position = data.IndexOf('=', position)) != -1) && (position + 2 < data.Length); start = position) {
                result.Append(data, start, position - start);
 
                do {
                    position++;
                    if ((data[position] == '\r') && (data[position + 1] == '\n')) {
                        // unfold soft line breaks: remove "=\r\n" from data
                        position += 2;
                    }
                    else {
                        try {
                            // hex-convert a byte
                            bytes.Add(System.Convert.ToByte(data.Substring(position, 2), 16));
                        }
                        catch (Exception ex) {
                            throw new Exception(data.Substring(position, 2),ex);
                        }
                        position += 2;
                    }
                } while ((position < data.Length) && (data[position] == '='));
                if (bytes.Count > 0) {
                    // convert bytes to text
                    string equivalent = encoding.GetString(bytes.ToArray());
                    result.Append(equivalent);
                    bytes.Clear();
                }
            }
            if (start < data.Length) {
                result.Append(data, start, data.Length - start);
            }
            return result.ToString();
        }
 
        /// Decode Quoted-Printable text recursively in a list
        ///
        public static System.Collections.IList DecodeQuotedPrintable(System.Collections.IList data, System.Text.Encoding encoding) {
            for (int i = 0; i < data.Count; i++) {
                if (data[i] is string) {
                    data[i] = DecodeQuotedPrintable((string)(data[i]), encoding);
                }
                else if (data[i] is System.Collections.IList) {
                    data[i] = DecodeQuotedPrintable((System.Collections.IList)(data[i]), encoding);
                }
            }
            return data;
        }
    }
 
    ///
    /// Base class for writing ItemObjects.
    /// Writing to string is supported via the StringWriter base class.
    /// Creating an XmlDocument is also supported.
    /// @todo specialize into TextWriter and XmlWriter ?
    public class Writer : System.IO.StringWriter, System.IFormatProvider, System.ICustomFormatter {
        /// The ItemObject being written
        private ItemObject _CurrentItem;
        /// The current node to add content to
        private System.Xml.XmlNode _CurrentNode;
        /// The current XmlDocument being written
        private System.Xml.XmlDocument _Document;
        /// The XML namespace manager associated with the current document
        private System.Xml.XmlNamespaceManager _NamespaceManager;
        /// Hashtable of XML namespaces
        private System.Collections.Hashtable _Namespaces;
        /// Write the XmlDocument with non-significant line breaks and hierarchical indenting
        /// for easy human reading.
        private bool _Indent = false;
 
        /// The culture to use during writing.
        /// @todo distinguish from the iFormatProvider of the StringWriter
        public System.Globalization.CultureInfo CultureInfo {
            get; set;
        }
 
        /// The current XmlNode to write to.
        /// By default of a specific node set the DocumentElement of the Document is returned.
        public System.Xml.XmlNode CurrentNode {
            get {
                if (_CurrentNode == null && Document != null) {
                    return Document.DocumentElement;
                }
                return _CurrentNode;
            }
            set { _CurrentNode = value; }
        }
 
        /// The ItemObject being written
        public ItemObject CurrentItem {
            get { return _CurrentItem; }
            set {
                if (value != _CurrentItem) {
                    if (_CurrentItem != null) {
                        // auto-increment ItemCount
                        ItemCount++;
                    }
                }
                _CurrentItem = value;
            }
        }
 
        /// The XmlDocument to write to.
        public System.Xml.XmlDocument Document {
            get { return _Document; }
            set {
                if (_Document != value) {
                    _Document = value;
                    // refresh the associated namespacemanager on next get
                    _NamespaceManager = null;
                }
            }
        }
 
        public override System.Text.Encoding Encoding {
            get { return System.Text.Encoding.UTF8; }
        }
 
        /// The current property (value) requires Base64 encoding,
        /// e.g. because of non-ASCII characters present
        public bool EncodeBase64 { get; set; }
 
        /// Write the XmlDocument with non-significant line breaks
        /// and hierarchical indenting for easy human reading.
        public bool Indent {
            get { return _Indent; }
            set { _Indent = value; }
        }
 
        /// The XmlNamespaceManager needed for SelectNodes() and SelectSingleNode().
        public System.Xml.XmlNamespaceManager NamespaceManager {
            get {
                if ((_NamespaceManager == null) && (_Document != null)) {
                    // create the manager
                    _NamespaceManager = new XmlNamespaceManager(_Document.NameTable);
                    if (_Namespaces != null) {
                        // fill with the registered namespaces
                        foreach (DictionaryEntry entry in _Namespaces) {
                            _NamespaceManager.AddNamespace(entry.Key.ToString(), entry.Value.ToString());
                        }
                    }
                }
                return _NamespaceManager;
            }
        }
 
        /// The XML namespaces needed for SelectNodes() and SelectSingleNode().
        public System.Collections.Hashtable Namespaces {
            get { return _Namespaces; }
            set {
                if (_Namespaces != value) {
                    _Namespaces = value;
                    // clear the NamespaceManager to force an update on next get
                    _NamespaceManager = null;
                }
            }
        }
 
        /// Keep track of the number of ItemObjects written
        public int ItemCount { get; set; }
 
        /// Get the Position in the underlying StringBuilder
        public int Position {
            get { return GetStringBuilder().Length; }
        }
 
        /// Default constructor
        /// Uses the invariant culture, for persistent storage.
        public Writer() : base(System.Globalization.CultureInfo.InvariantCulture) {
        }
 
        /// Initializing constructor
        /// Uses the invariant culture, for persistent storage.
        public Writer(IFormatProvider provider) : base(provider) {
        }
 
        /// Encode text as Base64 encoded text
        /// @see https://en.wikipedia.org/wiki/Base64
        public static string EncodeBase64Text(string data, System.Text.Encoding encoding) {
            // get the byte representation of the text data, for the given encoding
            byte[] bytes = encoding.GetBytes(data);
            // convert binary data to base64 text string
            return System.Convert.ToBase64String(bytes);
        }
 
        ///
        /// Flushes the contents of the internal string builder to the specified file,
        /// and clears the string builder.
        /// The file is written in UTF-8 wihout BOM.
        ///
        public void FlushToFile(string filename) {
            System.Text.StringBuilder sb = GetStringBuilder();
            // write UTF8 text without BOM
            System.IO.File.WriteAllText(filename, sb.ToString());
            // clear the buffer
            sb.Clear();
        }
 
        ///
        /// Flushes the contents of the internal string builder to a string,
        /// and clears the string builder.
        /// @return the content string
        ///
        public string FlushToString() {
            System.Text.StringBuilder sb = GetStringBuilder();
            string result = sb.ToString();
            // clear the buffer
            sb.Clear();
            return result;
        }
 
        /// Format a Property (value)
        /// ICustomFormatter.Format()
        public virtual string Format(string format, object arg, IFormatProvider formatProvider) {
            return null;
        }
 
        /// IFormatProvider.GetFormat()
        public virtual object GetFormat(Type formatType) {
            return this;
        }
 
        ///
        /// Perform line folding on the (possibly long) line in the string buffer (starting at startIndex),
        /// by inserting a LineBreak after each section of the line of which the byte representation of the
        /// encoding counts OctetsPerLine bytes or less.
        /// The string buffer is supposed to contain a single line, i.e. any newline characters already present
        /// are handled as normal characters.
        /// @param LineBreakLineChars the number of characters of the LineBreak to include in the next line
        ///
        public void OctetBasedLineFolding(int startIndex = 0,
                int OctetsPerLine = 75, string LineBreak = "\r\n ", int LineBreakLineChars = 1) {
            System.Text.StringBuilder sb = GetStringBuilder();
            int maxBytesPerChar = Encoding.GetMaxByteCount(1);
            if ((startIndex < 0) || (startIndex >= sb.Length)) {
                throw new ArgumentOutOfRangeException("startIndex","startIndex must be in the string buffer range");
            }
            if (OctetsPerLine < maxBytesPerChar) {
                throw new ArgumentOutOfRangeException("OctetsPerLine","OctetsPerLine seems rather small");
            }
            // check if line folding may be necessary
            if ((maxBytesPerChar * (sb.Length - startIndex)) > OctetsPerLine) {
                // determine the chunk size: we take as muchs chars as possible, assume 1 byte per char
                int lineChunkOctets = OctetsPerLine;
                // copy the string buffer contents in a consecutive array
                char[] chars = new char [sb.Length - startIndex];
                sb.CopyTo(startIndex,chars,0,sb.Length - startIndex);
                for (int start = 0, linestart = startIndex; start < chars.Length; ) {
                    // determine the actual chunk size (limit to remaining number of chars)
                    int count = Math.Min(lineChunkOctets,chars.Length - start);
                    // count the bytes of the chunk of the line
                    int numBytes = Encoding.GetByteCount(chars, start, count);
                    // reduce the chunk while still too many bytes needed
                    while ((count > 0) && (numBytes > lineChunkOctets)) {
                        // reduce number of characters until number of bytes fit
                        numBytes = Encoding.GetByteCount(chars, start, --count);
                    }
                    // do we need to insert a LineBreak?
                    if ((chars.Length > (start + count)) && (count > 0)) {
                        // yes
                        sb.Insert(linestart + count,LineBreak);
                        // account the LineBreak in the line position
                        linestart += LineBreak.Length;
                        // the next line is already started with some chars from the line break (those chars have 1 byte per char).
                        lineChunkOctets = OctetsPerLine - LineBreakLineChars;
                    }
                    else {
                        // we are done
                        break;
                    }
                    start += count; linestart += count;
                }
            }
        }
 
        /// Write the specified field values of the specified entry as CSV line to the stringbuffer of the writer.
        /// @param fields the column (field) identifiers
        /// @param entry the hashtable with the entry values; if null the field identifiers are written (header line)
        public void WriteCSVLine(string[] fields, System.Collections.IDictionary entry = null) {
            // use our own encoder in CompoundValue
            nl.nlsw.Items.CompoundValue cv = new nl.nlsw.Items.CompoundValue();
            if (entry != null) {
                foreach (string field in fields) {
                    cv.Add(entry[field]);
                }
            }
            else {
                foreach (string field in fields) {
                    cv.Add(field);
                }
            }
            // write the CSV line entry to the string buffer
            WriteLine(cv.ToString());
        }
    }
}