// commons-codec version compatibility level: 1.9
using Lucene.Net.Support;
using System;
using System.Collections.Generic;
using System.IO;
using System.Reflection;
using System.Text;
using System.Text.RegularExpressions;

namespace Lucene.Net.Analysis.Phonetic.Language.Bm
{
    /*
     * Licensed to the Apache Software Foundation (ASF) under one or more
     * contributor license agreements.  See the NOTICE file distributed with
     * this work for additional information regarding copyright ownership.
     * The ASF licenses this file to You under the Apache License, Version 2.0
     * (the "License"); you may not use this file except in compliance with
     * the License.  You may obtain a copy of the License at
     *
     *     http://www.apache.org/licenses/LICENSE-2.0
     *
     * Unless required by applicable law or agreed to in writing, software
     * distributed under the License is distributed on an "AS IS" BASIS,
     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     * See the License for the specific language governing permissions and
     * limitations under the License.
     */

    /// <summary>
    /// A phoneme rule.
    /// </summary>
    /// <remarks>
    /// Rules have a pattern, left context, right context, output phoneme, set of languages for which they apply
    /// and a logical flag indicating if all languages must be in play. A rule matches if:
    /// <list type="bullet">
    ///     <item><description>the pattern matches at the current position</description></item>
    ///     <item><description>the string up until the beginning of the pattern matches the left context</description></item>
    ///     <item><description>the string from the end of the pattern matches the right context</description></item>
    ///     <item><description>logical is ALL and all languages are in scope; or</description></item>
    ///     <item><description>logical is any other value and at least one language is in scope</description></item>
    /// </list>
    /// <para/>
    /// Rules are typically generated by parsing rules resources. In normal use, there will be no need for the user
    /// to explicitly construct their own.
    /// <para/>
    /// Rules are immutable and thread-safe.
    /// <para/>
    /// <b>Rules resources</b>
    /// <para/>
    /// Rules are typically loaded from resource files. These are UTF-8 encoded text files. They are systematically
    /// named following the pattern:
    /// <c>Lucene.Net.Analysis.Phonetic.Language.Bm.<see cref="NameType"/>_<see cref="RuleType"/>_[language].txt</c>
    /// <para/>
    /// The format of these resources is the following:
    /// <list type="table">
    ///     <item>
    ///         <term>Rules:</term>
    ///         <description>
    ///             whitespace separated, double-quoted strings. There should be 4 columns to each row, and these
    ///             will be interpreted as:
    ///             <list type="number">
    ///                 <item><description>pattern</description></item>
    ///                 <item><description>left context</description></item>
    ///                 <item><description>right context</description></item>
    ///                 <item><description>phoneme</description></item>
    ///             </list>
    ///         </description>
    ///     </item>
    ///     <item>
    ///         <term>End-of-line comments:</term>
    ///         <description>Any occurrence of '//' will cause all text following on that line to be discarded as a comment.</description>
    ///     </item>
    ///     <item>
    ///         <term>Multi-line comments:</term>
    ///         <description>Any line starting with '/*' will start multi-line commenting mode. This will skip all content until a line ending in '*' and '/' is found.</description>
    ///     </item>
    ///     <item>
    ///         <term>Blank lines:</term>
    ///         <description>All blank lines will be skipped.</description>
    ///     </item>
    /// </list>
    /// <para/>
    /// since 1.6
    /// </remarks>
    public class Rule
    {
        private static Regex PIPE = new Regex("[|]", RegexOptions.Compiled);
        private static Regex WHITESPACE = new Regex("\\s+", RegexOptions.Compiled);
        private static Regex PLUS = new Regex("[+]", RegexOptions.Compiled);

        private class AllStringsRMatcher : IRPattern
        {
            public bool IsMatch(StringBuilder input)
            {
                return true;
            }

            public bool IsMatch(string input)
            {
                return true;
            }

            public bool IsMatch(ICharSequence input)
            {
                return true;
            }
        }

        public static readonly IRPattern ALL_STRINGS_RMATCHER = new AllStringsRMatcher();


        public static readonly string ALL = "ALL";

        private static readonly string DOUBLE_QUOTE = "\"";

        private static readonly string HASH_INCLUDE = "#include";

        private static readonly IDictionary<NameType, IDictionary<RuleType, IDictionary<string, IDictionary<string, IList<Rule>>>>> RULES = LoadRules();

        private static IDictionary<NameType, IDictionary<RuleType, IDictionary<string, IDictionary<string, IList<Rule>>>>> LoadRules() // LUCENENET: Avoid static constructors (see https://github.com/apache/lucenenet/pull/224#issuecomment-469284006)
        {
            var rules = new Dictionary<NameType, IDictionary<RuleType, IDictionary<string, IDictionary<string, IList<Rule>>>>>();
            foreach (NameType s in Enum.GetValues(typeof(NameType)))
            {
                IDictionary<RuleType, IDictionary<string, IDictionary<string, IList<Rule>>>> rts =
                        new Dictionary<RuleType, IDictionary<string, IDictionary<string, IList<Rule>>>>();

                foreach (RuleType rt in Enum.GetValues(typeof(RuleType)))
                {
                    IDictionary<string, IDictionary<string, IList<Rule>>> rs = new Dictionary<string, IDictionary<string, IList<Rule>>>();

                    Languages ls = Languages.GetInstance(s);
                    foreach (string l in ls.GetLanguages())
                    {
                        try
                        {
                            rs[l] = ParseRules(CreateScanner(s, rt, l), CreateResourceName(s, rt, l));
                        }
                        catch (InvalidOperationException e)
                        {
                            throw new InvalidOperationException("Problem processing " + CreateResourceName(s, rt, l), e);
                        }
                    }
                    if (!rt.Equals(RuleType.RULES))
                    {
                        rs["common"] = ParseRules(CreateScanner(s, rt, "common"), CreateResourceName(s, rt, "common"));
                    }

                    rts[rt] = Collections.UnmodifiableMap(rs);
                }

                rules[s] = Collections.UnmodifiableMap(rts);
            }
            return rules;
        }

        private static bool Contains(ICharSequence chars, char input)
        {
            for (int i = 0; i < chars.Length; i++)
            {
                if (chars[i] == input)
                {
                    return true;
                }
            }
            return false;
        }
        private static bool Contains(string chars, char input)
        {
            for (int i = 0; i < chars.Length; i++)
            {
                if (chars[i] == input)
                {
                    return true;
                }
            }
            return false;
        }
        private static bool Contains(StringBuilder chars, char input)
        {
            for (int i = 0; i < chars.Length; i++)
            {
                if (chars[i] == input)
                {
                    return true;
                }
            }
            return false;
        }

        private static string CreateResourceName(NameType nameType, RuleType rt, string lang)
        {
            return string.Format("{0}_{1}_{2}.txt",
                                 nameType.GetName(), rt.GetName(), lang);
        }

        private static TextReader CreateScanner(NameType nameType, RuleType rt, string lang)
        {
            string resName = CreateResourceName(nameType, rt, lang);
            Stream rulesIS = typeof(Languages).GetTypeInfo().Assembly.FindAndGetManifestResourceStream(typeof(Languages), resName);

            if (rulesIS == null)
            {
                throw new ArgumentException("Unable to load resource: " + resName);
            }

            return new StreamReader(rulesIS, ResourceConstants.ENCODING);
        }

        private static TextReader CreateScanner(string lang)
        {
            string resName = string.Format("{0}.txt", lang); 
            Stream rulesIS = typeof(Languages).GetTypeInfo().Assembly.FindAndGetManifestResourceStream(typeof(Languages), resName);

            if (rulesIS == null)
            {
                throw new ArgumentException("Unable to load resource: " + resName);
            }

            return new StreamReader(rulesIS, ResourceConstants.ENCODING);
        }

        private static bool EndsWith(ICharSequence input, string suffix)
        {
            if (suffix.Length > input.Length)
            {
                return false;
            }
            for (int i = input.Length - 1, j = suffix.Length - 1; j >= 0; i--, j--)
            {
                if (input[i] != suffix[j])
                {
                    return false;
                }
            }
            return true;
        }

        private static bool EndsWith(string input, string suffix)
        {
            if (suffix.Length > input.Length)
            {
                return false;
            }
            for (int i = input.Length - 1, j = suffix.Length - 1; j >= 0; i--, j--)
            {
                if (input[i] != suffix[j])
                {
                    return false;
                }
            }
            return true;
        }

        private static bool EndsWith(StringBuilder input, string suffix)
        {
            if (suffix.Length > input.Length)
            {
                return false;
            }
            for (int i = input.Length - 1, j = suffix.Length - 1; j >= 0; i--, j--)
            {
                if (input[i] != suffix[j])
                {
                    return false;
                }
            }
            return true;
        }

        /// <summary>
        /// Gets rules for a combination of name type, rule type and languages.
        /// </summary>
        /// <param name="nameType">The <see cref="NameType"/> to consider.</param>
        /// <param name="rt">The <see cref="RuleType"/> to consider.</param>
        /// <param name="langs">The set of languages to consider.</param>
        /// <returns>A list of <see cref="Rule"/>s that apply.</returns>
        public static IList<Rule> GetInstance(NameType nameType, RuleType rt,
                                     LanguageSet langs)
        {
            IDictionary<string, IList<Rule>> ruleMap = GetInstanceMap(nameType, rt, langs);
            IList<Rule> allRules = new List<Rule>();
            foreach (IList<Rule> rules in ruleMap.Values)
            {
                allRules.AddRange(rules);
            }
            return allRules;
        }

        /// <summary>
        /// Gets rules for a combination of name type, rule type and a single language.
        /// </summary>
        /// <param name="nameType">The <see cref="NameType"/> to consider.</param>
        /// <param name="rt">The <see cref="RuleType"/> to consider.</param>
        /// <param name="lang">The language to consider.</param>
        /// <returns>A list of <see cref="Rule"/>s that apply.</returns>
        public static IList<Rule> GetInstance(NameType nameType, RuleType rt, string lang)
        {
            return GetInstance(nameType, rt, LanguageSet.From(new HashSet<string>() { lang }));
        }

        /// <summary>
        /// Gets rules for a combination of name type, rule type and languages.
        /// <para/>
        /// since 1.9
        /// </summary>
        /// <param name="nameType">The <see cref="NameType"/> to consider.</param>
        /// <param name="rt">The <see cref="RuleType"/> to consider.</param>
        /// <param name="langs">The set of languages to consider.</param>
        /// <returns>A map containing all <see cref="Rule"/>s that apply, grouped by the first character of the rule pattern.</returns>
        public static IDictionary<string, IList<Rule>> GetInstanceMap(NameType nameType, RuleType rt,
                                                             LanguageSet langs)
        {
            return langs.IsSingleton ? GetInstanceMap(nameType, rt, langs.GetAny()) :
                                         GetInstanceMap(nameType, rt, Languages.ANY);
        }

        /// <summary>
        /// Gets rules for a combination of name type, rule type and a single language.
        /// <para/>
        /// since 1.9
        /// </summary>
        /// <param name="nameType">The <see cref="NameType"/> to consider.</param>
        /// <param name="rt">The <see cref="RuleType"/> to consider.</param>
        /// <param name="lang">The language to consider.</param>
        /// <returns>A map containing all <see cref="Rule"/>s that apply, grouped by the first character of the rule pattern.</returns>
        public static IDictionary<string, IList<Rule>> GetInstanceMap(NameType nameType, RuleType rt,
                                                             string lang)
        {
            IDictionary<RuleType, IDictionary<string, IDictionary<string, IList<Rule>>>> nameTypes;
            IDictionary<string, IDictionary<string, IList<Rule>>> ruleTypes;
            IDictionary<string, IList<Rule>> rules = null;

            if (RULES.TryGetValue(nameType, out nameTypes) && nameTypes != null &&
                nameTypes.TryGetValue(rt, out ruleTypes) && ruleTypes != null &&
                ruleTypes.TryGetValue(lang, out rules) && rules != null)
            {
            }
            else
            {
                throw new ArgumentException(string.Format("No rules found for {0}, {1}, {2}.",
                                                   nameType.GetName(), rt.GetName(), lang));
            }

            return rules;
        }

        private static Phoneme ParsePhoneme(string ph)
        {
            int open = ph.IndexOf('[');
            if (open >= 0)
            {
                if (!ph.EndsWith("]", StringComparison.Ordinal))
                {
                    throw new ArgumentException("Phoneme expression contains a '[' but does not end in ']'");
                }
                string before = ph.Substring(0, open - 0);
                string input = ph.Substring(open + 1, (ph.Length - 1) - (open + 1));
                ISet<string> langs = new HashSet<string>(PLUS.Split(input).TrimEnd());

                return new Phoneme(before, LanguageSet.From(langs));
            }
            else
            {
                return new Phoneme(ph, Languages.ANY_LANGUAGE);
            }
        }

        private static IPhonemeExpr ParsePhonemeExpr(string ph)
        {
            if (ph.StartsWith("(", StringComparison.Ordinal))
            { // we have a bracketed list of options
                if (!ph.EndsWith(")", StringComparison.Ordinal))
                {
                    throw new ArgumentException("Phoneme starts with '(' so must end with ')'");
                }

                IList<Phoneme> phs = new List<Phoneme>();
                string body = ph.Substring(1, (ph.Length - 1) - 1);
                foreach (string part in PIPE.Split(body).TrimEnd())
                {
                    phs.Add(ParsePhoneme(part));
                }
                if (body.StartsWith("|", StringComparison.Ordinal) || body.EndsWith("|", StringComparison.Ordinal))
                {
                    phs.Add(new Phoneme("", Languages.ANY_LANGUAGE));
                }

                return new PhonemeList(phs);
            }
            else
            {
                return ParsePhoneme(ph);
            }
        }

        private class RuleAnonymousHelper : Rule
        {
            private readonly int myLine;
            private readonly string loc;

            public RuleAnonymousHelper(string pat, string lCon, string rCon, IPhonemeExpr ph, int cLine, string location)
                : base(pat, lCon, rCon, ph)
            {
                this.myLine = cLine;
                this.loc = location;
            }

            public override string ToString()
            {
                StringBuilder sb = new StringBuilder();
                sb.Append("Rule");
                sb.Append("{line=").Append(myLine);
                sb.Append(", loc='").Append(loc).Append('\'');
                sb.Append('}');
                return sb.ToString();
            }
        }

        private static IDictionary<string, IList<Rule>> ParseRules(TextReader reader, string location)
        {
            IDictionary<string, IList<Rule>> lines = new HashMap<string, IList<Rule>>();
            int currentLine = 0;

            bool inMultilineComment = false;
            string rawLine;
            try
            {
                while ((rawLine = reader.ReadLine()) != null)
                {
                    currentLine++;
                    string line = rawLine;

                    if (inMultilineComment)
                    {
                        if (line.EndsWith(ResourceConstants.EXT_CMT_END, StringComparison.Ordinal))
                        {
                            inMultilineComment = false;
                        }
                    }
                    else
                    {
                        if (line.StartsWith(ResourceConstants.EXT_CMT_START, StringComparison.Ordinal))
                        {
                            inMultilineComment = true;
                        }
                        else
                        {
                            // discard comments
                            int cmtI = line.IndexOf(ResourceConstants.CMT, StringComparison.Ordinal);
                            if (cmtI >= 0)
                            {
                                line = line.Substring(0, cmtI);
                            }

                            // trim leading-trailing whitespace
                            line = line.Trim();

                            if (line.Length == 0)
                            {
                                continue; // empty lines can be safely skipped
                            }

                            if (line.StartsWith(HASH_INCLUDE, StringComparison.Ordinal))
                            {
                                // include statement
                                string incl = line.Substring(HASH_INCLUDE.Length).Trim();
                                if (incl.Contains(" "))
                                {
                                    throw new ArgumentException("Malformed import statement '" + rawLine + "' in " +
                                                                       location);
                                }
                                else
                                {
                                    lines.PutAll(ParseRules(CreateScanner(incl), location + "->" + incl));
                                }
                            }
                            else
                            {
                                // rule
                                string[] parts = WHITESPACE.Split(line).TrimEnd();
                                if (parts.Length != 4)
                                {
                                    throw new ArgumentException("Malformed rule statement split into " + parts.Length +
                                                                       " parts: " + rawLine + " in " + location);
                                }
                                else
                                {
                                    try
                                    {
                                        string pat = StripQuotes(parts[0]);
                                        string lCon = StripQuotes(parts[1]);
                                        string rCon = StripQuotes(parts[2]);
                                        IPhonemeExpr ph = ParsePhonemeExpr(StripQuotes(parts[3]));
                                        int cLine = currentLine;
                                        Rule r = new RuleAnonymousHelper(pat, lCon, rCon, ph, cLine, location);

                                        string patternKey = r.pattern.Substring(0, 1 - 0);
                                        IList<Rule> rules;
                                        if (!lines.TryGetValue(patternKey, out rules) || rules == null)
                                        {
                                            rules = new List<Rule>();
                                            lines[patternKey] = rules;
                                        }
                                        rules.Add(r);
                                    }
                                    catch (ArgumentException e)
                                    {
                                        throw new InvalidOperationException("Problem parsing line '" + currentLine + "' in " +
                                                                        location, e);
                                    }
                                }
                            }
                        }
                    }
                }
            }
            finally
            {
                reader.Dispose();
            }

            return lines;
        }

        private class RPatternHelper : IRPattern
        {
            private readonly Func<StringBuilder, bool> isMatchSB;
            private readonly Func<string, bool> isMatchStr;
            private readonly Func<ICharSequence, bool> isMatchCS;

            public RPatternHelper(Func<StringBuilder, bool> isMatchSB, Func<string, bool> isMatchStr, Func<ICharSequence, bool> isMatchCS)
            {
                this.isMatchSB = isMatchSB;
                this.isMatchStr = isMatchStr;
                this.isMatchCS = isMatchCS;
            }

            public bool IsMatch(StringBuilder input)
            {
                return isMatchSB(input);
            }

            public bool IsMatch(string input)
            {
                return isMatchStr(input);
            }

            public bool IsMatch(ICharSequence input)
            {
                return isMatchCS(input);
            }
        }

        /// <summary>
        /// Attempts to compile the regex into direct string ops, falling back to <see cref="Regex"/> and <see cref="Match"/> in the worst case.
        /// </summary>
        /// <param name="regex">The regular expression to compile.</param>
        /// <returns>An RPattern that will match this regex.</returns>
        private static IRPattern GetPattern(string regex)
        {
            bool startsWith = regex.StartsWith("^", StringComparison.Ordinal);
            bool endsWith = regex.EndsWith("$", StringComparison.Ordinal);
            string content = regex.Substring(startsWith ? 1 : 0, (endsWith ? regex.Length - 1 : regex.Length) - (startsWith ? 1 : 0));
            bool boxes = content.Contains("[");

            if (!boxes)
            {
                if (startsWith && endsWith)
                {
                    // exact match
                    if (content.Length == 0)
                    {
                        // empty
                        return new RPatternHelper(isMatchSB: (input) =>
                        {
                            return input.Length == 0;
                        }, isMatchStr: (input) =>
                        {
                            return input.Length == 0;
                        }, isMatchCS: (input) =>
                        {
                            return input.Length == 0;
                        });
                    }
                    else
                    {

                        return new RPatternHelper(isMatchSB: (input) =>
                        {
                            return input.Equals(content);
                        }, isMatchStr: (input) =>
                        {
                            return input.Equals(content);
                        }, isMatchCS: (input) =>
                        {
                            return input.Equals(content);
                        });
                    }
                }
                else if ((startsWith || endsWith) && content.Length == 0)
                {
                    // matches every string
                    return ALL_STRINGS_RMATCHER;
                }
                else if (startsWith)
                {
                    // matches from start
                    return new RPatternHelper(isMatchSB: (input) =>
                    {
                        return StartsWith(input, content);
                    }, isMatchStr: (input) =>
                    {
                        return StartsWith(input, content);
                    }, isMatchCS: (input) =>
                    {
                        return StartsWith(input, content);
                    });

                }
                else if (endsWith)
                {
                    // matches from start
                    return new RPatternHelper(isMatchSB: (input) =>
                    {
                        return EndsWith(input, content);
                    }, isMatchStr: (input) =>
                    {
                        return EndsWith(input, content);
                    }, isMatchCS: (input) =>
                    {
                        return EndsWith(input, content);
                    });
                }
            }
            else
            {
                bool startsWithBox = content.StartsWith("[", StringComparison.Ordinal);
                bool endsWithBox = content.EndsWith("]", StringComparison.Ordinal);

                if (startsWithBox && endsWithBox)
                {
                    string boxContent = content.Substring(1, (content.Length - 1) - 1);
                    if (!boxContent.Contains("["))
                    {
                        // box containing alternatives
                        bool negate = boxContent.StartsWith("^", StringComparison.Ordinal);
                        if (negate)
                        {
                            boxContent = boxContent.Substring(1);
                        }
                        string bContent = boxContent;
                        bool shouldMatch = !negate;

                        if (startsWith && endsWith)
                        {
                            // exact match
                            return new RPatternHelper(isMatchSB: (input) =>
                            {
                                return input.Length == 1 && Contains(bContent, input[0]) == shouldMatch;
                            }, isMatchStr: (input) =>
                            {
                                return input.Length == 1 && Contains(bContent, input[0]) == shouldMatch;
                            }, isMatchCS: (input) =>
                            {
                                return input.Length == 1 && Contains(bContent, input[0]) == shouldMatch;
                            });
                        }
                        else if (startsWith)
                        {
                            // first char
                            return new RPatternHelper(isMatchSB: (input) =>
                            {
                                return input.Length > 0 && Contains(bContent, input[0]) == shouldMatch;
                            }, isMatchStr: (input) =>
                            {
                                return input.Length > 0 && Contains(bContent, input[0]) == shouldMatch;
                            }, isMatchCS: (input) =>
                            {
                                return input.Length > 0 && Contains(bContent, input[0]) == shouldMatch;
                            });
                        }
                        else if (endsWith)
                        {
                            // last char
                            return new RPatternHelper(isMatchSB: (input) =>
                            {
                                return input.Length > 0 && Contains(bContent, input[input.Length - 1]) == shouldMatch;
                            }, isMatchStr: (input) =>
                            {
                                return input.Length > 0 && Contains(bContent, input[input.Length - 1]) == shouldMatch;
                            }, isMatchCS: (input) =>
                            {
                                return input.Length > 0 && Contains(bContent, input[input.Length - 1]) == shouldMatch;
                            });
                        }
                    }
                }
            }
            Regex pattern = new Regex(regex, RegexOptions.Compiled);

            return new RPatternHelper(isMatchSB: (input) =>
            {
                Match matcher = pattern.Match(input.ToString());
                return matcher.Success;
            }, isMatchStr: (input) =>
            {
                Match matcher = pattern.Match(input);
                return matcher.Success;
            }, isMatchCS: (input) =>
            {
                Match matcher = pattern.Match(input.ToString());
                return matcher.Success;
            });
        }

        private static bool StartsWith(ICharSequence input, string prefix)
        {
            if (prefix.Length > input.Length)
            {
                return false;
            }
            for (int i = 0; i < prefix.Length; i++)
            {
                if (input[i] != prefix[i])
                {
                    return false;
                }
            }
            return true;
        }

        private static bool StartsWith(string input, string prefix)
        {
            if (prefix.Length > input.Length)
            {
                return false;
            }
            for (int i = 0; i < prefix.Length; i++)
            {
                if (input[i] != prefix[i])
                {
                    return false;
                }
            }
            return true;
        }

        private static bool StartsWith(StringBuilder input, string prefix)
        {
            if (prefix.Length > input.Length)
            {
                return false;
            }
            for (int i = 0; i < prefix.Length; i++)
            {
                if (input[i] != prefix[i])
                {
                    return false;
                }
            }
            return true;
        }

        private static string StripQuotes(string str)
        {
            if (str.StartsWith(DOUBLE_QUOTE, StringComparison.Ordinal))
            {
                str = str.Substring(1);
            }

            if (str.EndsWith(DOUBLE_QUOTE, StringComparison.Ordinal))
            {
                str = str.Substring(0, str.Length - 1);
            }

            return str;
        }

        private readonly IRPattern lContext;

        private readonly string pattern;

        private readonly IPhonemeExpr phoneme;

        private readonly IRPattern rContext;

        /// <summary>
        /// Creates a new rule.
        /// </summary>
        /// <param name="pattern">The pattern.</param>
        /// <param name="lContext">The left context.</param>
        /// <param name="rContext">The right context.</param>
        /// <param name="phoneme">The resulting phoneme.</param>
        public Rule(string pattern, string lContext, string rContext, IPhonemeExpr phoneme)
        {
            this.pattern = pattern;
            this.lContext = GetPattern(lContext + "$");
            this.rContext = GetPattern("^" + rContext);
            this.phoneme = phoneme;
        }

        /// <summary>
        /// Gets the left context pattern. This is a regular expression that must match to the left of the pattern.
        /// </summary>
        public virtual IRPattern LContext
        {
            get { return this.lContext; }
        }

        /// <summary>
        /// Gets the pattern. This is a string-literal that must exactly match.
        /// </summary>
        public virtual string Pattern
        {
            get { return this.pattern; }
        }

        /// <summary>
        /// Gets the phoneme. If the rule matches, this is the phoneme associated with the pattern match.
        /// </summary>
        public virtual IPhonemeExpr Phoneme
        {
            get { return this.phoneme; }
        }

        /// <summary>
        /// Gets the right context pattern. This is a regular expression that must match to the right of the pattern.
        /// </summary>
        public virtual IRPattern RContext
        {
            get { return this.rContext; }
        }

        /// <summary>
        /// Decides if the pattern and context match the input starting at a position. It is a match if the
        /// <see cref="LContext"/> matches <paramref name="input"/> up to <paramref name="i"/>, <see cref="Pattern"/> matches at <paramref name="i"/> and
        /// <see cref="RContext"/> matches from the end of the match of <see cref="Pattern"/> to the end of <paramref name="input"/>.
        /// </summary>
        /// <param name="input">The input <see cref="ICharSequence"/>.</param>
        /// <param name="i">The int position within the input.</param>
        /// <returns><c>true</c> if the pattern and left/right context match, <c>false</c> otherwise.</returns>
        public virtual bool PatternAndContextMatches(ICharSequence input, int i)
        {
            if (i < 0)
            {
                throw new ArgumentOutOfRangeException("Can not match pattern at negative indexes");
            }

            int patternLength = this.pattern.Length;
            int ipl = i + patternLength;

            if (ipl > input.Length)
            {
                // not enough room for the pattern to match
                return false;
            }

            // evaluate the pattern, left context and right context
            // fail early if any of the evaluations is not successful
            if (!input.SubSequence(i, ipl).Equals(this.pattern))
            {
                return false;
            }
            else if (!this.rContext.IsMatch(input.SubSequence(ipl, input.Length)))
            {
                return false;
            }
            return this.lContext.IsMatch(input.SubSequence(0, i));
        }

        /// <summary>
        /// Decides if the pattern and context match the input starting at a position. It is a match if the
        /// <see cref="LContext"/> matches <paramref name="input"/> up to <paramref name="i"/>, <see cref="Pattern"/> matches at <paramref name="i"/> and
        /// <see cref="RContext"/> matches from the end of the match of <see cref="Pattern"/> to the end of <paramref name="input"/>.
        /// </summary>
        /// <param name="input">The input <see cref="string"/>.</param>
        /// <param name="i">The int position within the input.</param>
        /// <returns><c>true</c> if the pattern and left/right context match, <c>false</c> otherwise.</returns>
        // LUCENENET specific
        public virtual bool PatternAndContextMatches(string input, int i) 
        {
            if (i < 0)
            {
                throw new ArgumentOutOfRangeException("Can not match pattern at negative indexes");
            }

            int patternLength = this.pattern.Length;
            int ipl = i + patternLength;

            if (ipl > input.Length)
            {
                // not enough room for the pattern to match
                return false;
            }

            // evaluate the pattern, left context and right context
            // fail early if any of the evaluations is not successful
            if (!input.Substring(i, (ipl - i)).Equals(this.pattern, StringComparison.Ordinal))
            {
                return false;
            }
            else if (!this.rContext.IsMatch(input.Substring(ipl, (input.Length - ipl))))
            {
                return false;
            }
            return this.lContext.IsMatch(input.Substring(0, (i - 0)));
        }

        /// <summary>
        /// Decides if the pattern and context match the input starting at a position. It is a match if the
        /// <see cref="LContext"/> matches <paramref name="input"/> up to <paramref name="i"/>, <see cref="Pattern"/> matches at <paramref name="i"/> and
        /// <see cref="RContext"/> matches from the end of the match of <see cref="Pattern"/> to the end of <paramref name="input"/>.
        /// </summary>
        /// <param name="input">The input <see cref="StringBuilder"/>.</param>
        /// <param name="i">The int position within the input.</param>
        /// <returns><c>true</c> if the pattern and left/right context match, <c>false</c> otherwise.</returns>
        // LUCENENET specific
        public virtual bool PatternAndContextMatches(StringBuilder input, int i)
        {
            if (i < 0)
            {
                throw new ArgumentOutOfRangeException("Can not match pattern at negative indexes");
            }

            int patternLength = this.pattern.Length;
            int ipl = i + patternLength;

            if (ipl > input.Length)
            {
                // not enough room for the pattern to match
                return false;
            }

            // evaluate the pattern, left context and right context
            // fail early if any of the evaluations is not successful
            if (!input.ToString(i, (ipl - i)).Equals(this.pattern, StringComparison.Ordinal))
            {
                return false;
            }
            else if (!this.rContext.IsMatch(input.ToString(ipl, (input.Length - ipl))))
            {
                return false;
            }
            return this.lContext.IsMatch(input.ToString(0, (i - 0)));
        }

    }

    public sealed class Phoneme : IPhonemeExpr
    {
        private class PhonemeComparer : IComparer<Phoneme>
        {
            public int Compare(Phoneme o1, Phoneme o2)
            {
                for (int i = 0; i < o1.phonemeText.Length; i++)
                {
                    if (i >= o2.phonemeText.Length)
                    {
                        return +1;
                    }
                    int c = o1.phonemeText[i] - o2.phonemeText[i];
                    if (c != 0)
                    {
                        return c;
                    }
                }

                if (o1.phonemeText.Length < o2.phonemeText.Length)
                {
                    return -1;
                }

                return 0;
            }
        }

        public static readonly IComparer<Phoneme> COMPARER = new PhonemeComparer();
        private readonly StringBuilder phonemeText;
        private readonly LanguageSet languages;

        public Phoneme(string phonemeText, LanguageSet languages)
        {
            this.phonemeText = new StringBuilder(phonemeText);
            this.languages = languages;
        }

        public Phoneme(StringBuilder phonemeText, LanguageSet languages)
        {
            this.phonemeText = new StringBuilder(phonemeText.ToString());
            this.languages = languages;
        }

        public Phoneme(ICharSequence phonemeText, LanguageSet languages)
        {
            this.phonemeText = new StringBuilder(phonemeText.ToString());
            this.languages = languages;
        }

        public Phoneme(Phoneme phonemeLeft, Phoneme phonemeRight)
            : this(phonemeLeft.phonemeText, phonemeLeft.languages)
        {
            this.phonemeText.Append(phonemeRight.phonemeText);
        }

        public Phoneme(Phoneme phonemeLeft, Phoneme phonemeRight, LanguageSet languages)
            : this(phonemeLeft.phonemeText, languages)
        {
            this.phonemeText.Append(phonemeRight.phonemeText);
        }

        public Phoneme Append(string str)
        {
            this.phonemeText.Append(str);
            return this;
        }

        public LanguageSet Languages
        {
            get { return this.languages; }
        }

        public IList<Phoneme> Phonemes
        {
            get { return new Phoneme[] { this }; }
        }

        public string GetPhonemeText()
        {
            return this.phonemeText.ToString();
        }

        [Obsolete("since 1.9")]
        public Phoneme Join(Phoneme right)
        {
            return new Phoneme(this.phonemeText.ToString() + right.phonemeText.ToString(),
                               this.languages.RestrictTo(right.Languages));
        }
    }

    public interface IPhonemeExpr
    {
        IList<Phoneme> Phonemes { get; }
    }

    public sealed class PhonemeList : IPhonemeExpr
    {
        private readonly IList<Phoneme> phonemes;

        public PhonemeList(IList<Phoneme> phonemes)
        {
            this.phonemes = phonemes;
        }

        public IList<Phoneme> Phonemes
        {
            get { return this.phonemes; }
        }
    }

    /// <summary>
    /// A minimal wrapper around the functionality of <see cref="Rule"/> Pattern that we use, to allow for alternate implementations.
    /// </summary>
    public interface IRPattern
    {
        bool IsMatch(ICharSequence input);
        bool IsMatch(string input);
        bool IsMatch(StringBuilder input);
    }
}
