// Copyright 2005-2015 Giacomo Stelluti Scala & Contributors. All rights reserved. See License.md in the project root for license information.

using System;
using System.Collections.Generic;
using System.Linq;
using CommandLine.Infrastructure;
using CSharpx;
using RailwaySharp.ErrorHandling;
using System.Text.RegularExpressions;

namespace CommandLine.Core
{
    static class Tokenizer
    {
        public static Result<IEnumerable<Token>, Error> Tokenize(
            IEnumerable<string> arguments,
            Func<string, NameLookupResult> nameLookup)
        {
            return Tokenizer.Tokenize(arguments, nameLookup, tokens => tokens);
        }

        public static Result<IEnumerable<Token>, Error> Tokenize(
            IEnumerable<string> arguments,
            Func<string, NameLookupResult> nameLookup,
            Func<IEnumerable<Token>, IEnumerable<Token>> normalize)
        {
            var errors = new List<Error>();
            Action<Error> onError = errors.Add;

            var tokens = (from arg in arguments
                          from token in !arg.StartsWith("-", StringComparison.Ordinal)
                               ? new[] { Token.Value(arg) }
                               : arg.StartsWith("--", StringComparison.Ordinal)
                                     ? TokenizeLongName(arg, onError)
                                     : TokenizeShortName(arg, nameLookup)
                          select token)
                            .Memoize();

            var normalized = normalize(tokens).Memoize();

            var unkTokens = (from t in normalized where t.IsName() && nameLookup(t.Text) == NameLookupResult.NoOptionFound select t).Memoize();

            return Result.Succeed(normalized.Where(x => !unkTokens.Contains(x)), errors.Concat(from t in unkTokens select new UnknownOptionError(t.Text)));
        }

        public static Result<IEnumerable<Token>, Error> PreprocessDashDash(
            IEnumerable<string> arguments,
            Func<IEnumerable<string>, Result<IEnumerable<Token>, Error>> tokenizer)
        {
            if (arguments.Any(arg => arg.EqualsOrdinal("--")))
            {
                var tokenizerResult = tokenizer(arguments.TakeWhile(arg => !arg.EqualsOrdinal("--")));
                var values = arguments.SkipWhile(arg => !arg.EqualsOrdinal("--")).Skip(1).Select(Token.ValueForced);
                return tokenizerResult.Map(tokens => tokens.Concat(values));
            }
            return tokenizer(arguments);
        }

        public static Result<IEnumerable<Token>, Error> ExplodeOptionList(
            Result<IEnumerable<Token>, Error> tokenizerResult,
            Func<string, Maybe<char>> optionSequenceWithSeparatorLookup)
        {
            var tokens = tokenizerResult.SucceededWith().Memoize();

            var exploded = new List<Token>(tokens is ICollection<Token> coll ? coll.Count : tokens.Count());
            var nothing = Maybe.Nothing<char>();  // Re-use same Nothing instance for efficiency
            var separator = nothing;
            foreach (var token in tokens) {
                if (token.IsName()) {
                    separator = optionSequenceWithSeparatorLookup(token.Text);
                    exploded.Add(token);
                } else {
                    // Forced values are never considered option values, so they should not be split
                    if (separator.MatchJust(out char sep) && sep != '\0' && !token.IsValueForced()) {
                        if (token.Text.Contains(sep)) {
                            exploded.AddRange(token.Text.Split(sep).Select(Token.ValueFromSeparator));
                        } else {
                            exploded.Add(token);
                        }
                    } else {
                        exploded.Add(token);
                    }
                    separator = nothing;  // Only first value after a separator can possibly be split
                }
            }
            return Result.Succeed(exploded as IEnumerable<Token>, tokenizerResult.SuccessMessages());
        }

        /// <summary>
        /// Normalizes the given <paramref name="tokens"/>.
        /// </summary>
        /// <returns>The given <paramref name="tokens"/> minus all names, and their value if one was present, that are not found using <paramref name="nameLookup"/>.</returns>
        public static IEnumerable<Token> Normalize(
            IEnumerable<Token> tokens, Func<string, bool> nameLookup)
        {
            var toExclude =
                from i in
                    tokens.Select(
                        (t, i) =>
                        {
                            if (t.IsName() == false
                                || nameLookup(t.Text))
                            {
                                return Maybe.Nothing<Tuple<Token, Token>>();
                            }

                            var next = tokens.ElementAtOrDefault(i + 1).ToMaybe();
                            var removeValue = next.MatchJust(out var nextValue)
                                              && next.MapValueOrDefault(p => p.IsValue() && ((Value)p).ExplicitlyAssigned, false);
                            return Maybe.Just(new Tuple<Token, Token>(t, removeValue ? nextValue : null));
                        }).Where(i => i.IsJust())
                select i.FromJustOrFail();

            var normalized = tokens.Where(t => toExclude.Any(e => ReferenceEquals(e.Item1, t) || ReferenceEquals(e.Item2, t)) == false);

            return normalized;
        }

        public static Func<
                    IEnumerable<string>,
                    IEnumerable<OptionSpecification>,
                    Result<IEnumerable<Token>, Error>>
            ConfigureTokenizer(
                    StringComparer nameComparer,
                    bool ignoreUnknownArguments,
                    bool enableDashDash)
        {
            return (arguments, optionSpecs) =>
                {
                    var normalize = ignoreUnknownArguments
                        ? toks => Tokenizer.Normalize(toks,
                            name => NameLookup.Contains(name, optionSpecs, nameComparer) != NameLookupResult.NoOptionFound)
                        : new Func<IEnumerable<Token>, IEnumerable<Token>>(toks => toks);

                    var tokens = enableDashDash
                        ? Tokenizer.PreprocessDashDash(
                                arguments,
                                args =>
                                    Tokenizer.Tokenize(args, name => NameLookup.Contains(name, optionSpecs, nameComparer), normalize))
                        : Tokenizer.Tokenize(arguments, name => NameLookup.Contains(name, optionSpecs, nameComparer), normalize);
                    var explodedTokens = Tokenizer.ExplodeOptionList(tokens, name => NameLookup.HavingSeparator(name, optionSpecs, nameComparer));
                    return explodedTokens;
                };
        }

        private static IEnumerable<Token> TokenizeShortName(
            string value,
            Func<string, NameLookupResult> nameLookup)
        {
            //Allow single dash as a value
            if (value.Length == 1 && value[0] == '-')
            {
                yield return Token.Value(value);
                yield break;
            }
            if (value.Length > 1 && value[0] == '-' && value[1] != '-')
            {
                var text = value.Substring(1);

                if (char.IsDigit(text[0]))
                {
                    yield return Token.Value(value);
                    yield break;
                }

                if (value.Length == 2)
                {
                    yield return Token.Name(text);
                    yield break;
                }

                var i = 0;
                foreach (var c in text)
                {
                    var n = new string(c, 1);
                    var r = nameLookup(n);
                    // Assume first char is an option
                    if (i > 0 && r == NameLookupResult.NoOptionFound) break;
                    i++;
                    yield return Token.Name(n);
                    // If option expects a value (other than a boolean), assume following chars are that value
                    if (r == NameLookupResult.OtherOptionFound) break;
                }

                if (i < text.Length)
                {
                    yield return Token.Value(text.Substring(i));
                }
            }
        }

        private static IEnumerable<Token> TokenizeLongName(
            string value,
            Action<Error> onError)
        {
            if (value.Length > 2 && value.StartsWith("--", StringComparison.Ordinal))
            {
                var text = value.Substring(2);
                var equalIndex = text.IndexOf('=');
                if (equalIndex <= 0)
                {
                    yield return Token.Name(text);
                    yield break;
                }
                if (equalIndex == 1) // "--="
                {
                    onError(new BadFormatTokenError(value));
                    yield break;
                }

                var tokenMatch = Regex.Match(text, "^([^=]+)=([^ ].*)$");

                if (tokenMatch.Success)
                {
                    yield return Token.Name(tokenMatch.Groups[1].Value);
                    yield return Token.Value(tokenMatch.Groups[2].Value, true);
                }
                else
                {
                    onError(new BadFormatTokenError(value));
                    yield break;
                }
            }
        }
    }
}