using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;

namespace axXez.TS3.Protocol
{
    /// <summary>
    /// Encodes, decodes, builds, and parses the TeamSpeak text protocol format
    /// shared by both the ServerQuery (TCP) and UDP voice transports.
    /// </summary>
    public static class TsEncoding
    {
        private static readonly Dictionary<char, string> _escapeMap = new()
        {
            ['\\'] = "\\\\",
            ['/'] = "\\/",
            [' '] = "\\s",
            ['|'] = "\\p",
            ['\f'] = "\\f",
            ['\n'] = "\\n",
            ['\r'] = "\\r",
            ['\t'] = "\\t",
            ['\v'] = "\\v",
        };

        private static readonly Dictionary<char, char> _unescapeMap = new()
        {
            ['\\'] = '\\',
            ['/'] = '/',
            ['s'] = ' ',
            ['p'] = '|',
            ['f'] = '\f',
            ['n'] = '\n',
            ['r'] = '\r',
            ['t'] = '\t',
            ['v'] = '\v',
        };

        private static readonly Regex _bbcodeEscape = new(@"(\[\/?(?!B|I|U|COLOR|URL|LEFT|CENTER|RIGHT|SIZE|IMG|LIST)=?[\w\d]*?\]|!)\[\/?(?=B|I|U|COLOR|URL|LEFT|CENTER|RIGHT|SIZE|IMG|LIST)", RegexOptions.IgnoreCase | RegexOptions.Compiled);

        /// <summary>Escapes a string to TeamSpeak text protocol format.</summary>
        public static string Escape(string str)
        {
            var sb = new StringBuilder(str.Length * 2);
            foreach (char ch in str)
            {
                if (_escapeMap.TryGetValue(ch, out var esc))
                    sb.Append(esc);
                else
                    sb.Append(ch);
            }
            return sb.ToString();
        }

        /// <summary>Unescapes a TeamSpeak text protocol formatted string.</summary>
        public static string Unescape(string str)
        {
            var sb = new StringBuilder(str.Length);
            for (int i = 0; i < str.Length; i++)
            {
                if (str[i] == '\\')
                {
                    if (++i >= str.Length) throw new FormatException("Invalid escape sequence.");
                    if (!_unescapeMap.TryGetValue(str[i], out char mapped))
                        throw new FormatException($"Unknown escape: \\{str[i]}");
                    sb.Append(mapped);
                }
                else
                {
                    sb.Append(str[i]);
                }
            }
            return sb.ToString();
        }

        /// <summary>Builds a TeamSpeak parameter string without a command name.</summary>
        public static string Build(Dictionary<string, object> parameters)
            => parameters is null ? "" : Build(parameters.ToDictionary(
                kv => kv.Key,
                kv => kv.Value is bool b ? (b ? "1" : "0") : kv.Value?.ToString()));

        /// <summary>Builds a TeamSpeak parameter string without a command name.</summary>
        public static string Build(Dictionary<string, string> parameters)
        {
            if (parameters is null) return "";
            var sb = new StringBuilder();
            foreach (var kv in parameters)
            {
                if (kv.Value == null) continue;
                if (sb.Length > 0) sb.Append(' ');
                sb.Append(kv.Key);
                sb.Append('=');
                sb.Append(Escape(kv.Value));
            }
            return sb.ToString();
        }

        /// <summary>Builds a TeamSpeak command string from a name and parameters.</summary>
        public static string Build(string name, Dictionary<string, object> parameters)
            => $"{name} {Build(parameters)}";

        /// <summary>Builds a TeamSpeak command string from a name and string parameters.</summary>
        public static string Build(string name, Dictionary<string, string> parameters)
            => $"{name} {Build(parameters)}";

        /// <summary>Parses a TeamSpeak command string into a <see cref="TsMessage"/>.</summary>
        public static TsMessage Parse(string raw)
            => TsMessage.Parse(raw);

        /// <summary>Fixes TS6 BBCode rendering bugs caused by unknown tags or '!' immediately before a valid BBCode tag.</summary>
        public static string FixTs6BBCode(string str)
            => _bbcodeEscape.Replace(str, @"\${1}[/");

        /// <inheritdoc cref="Escape(string)"/>
        public static string ToTsFormat(this string str)
            => Escape(str);

        /// <inheritdoc cref="Unescape(string)"/>
        public static string FromTsFormat(this string str)
            => Unescape(str);

        /// <summary>Applies BBCode fixes then escapes to TeamSpeak ServerQuery format. Use this for outgoing text messages.</summary>
        public static string ToTsMessageFormat(this string str)
            => Escape(FixTs6BBCode(str));
    }
}