using System;
using System.Collections.Generic;
using System.Globalization;
using System.Text;
using System.Web.Script.Serialization;

namespace Server.Custom.Bridge
{
    /// <summary>
    ///     Outbound JSON is written by hand into a StringBuilder. It runs on the Core thread for
    ///     every emitted event, and the measured budget in docs/PLAN.md assumes this cost, not a
    ///     reflection serializer's.
    ///
    ///     Inbound JSON is parsed with JavaScriptSerializer. Commands arrive at human rates, so
    ///     correctness beats speed there, and parsing happens on the reader thread anyway.
    /// </summary>
    public static class BridgeJson
    {
        private static readonly DateTime Epoch = new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc);

        [ThreadStatic]
        private static JavaScriptSerializer _parser;

        public static long NowMs()
        {
            return (long)(DateTime.UtcNow - Epoch).TotalMilliseconds;
        }

        // ---- outbound ----

        /// <summary>Opens an object and writes the `t` and `kind` fields.</summary>
        public static StringBuilder Begin(string kind)
        {
            var sb = new StringBuilder(256);
            sb.Append("{\"t\":").Append(NowMs());
            sb.Append(",\"kind\":\"").Append(kind).Append('"');
            return sb;
        }

        public static StringBuilder Str(this StringBuilder sb, string name, string value)
        {
            sb.Append(",\"").Append(name).Append("\":");

            if (value == null)
                sb.Append("null");
            else
                Escape(sb, value);

            return sb;
        }

        public static StringBuilder Num(this StringBuilder sb, string name, long value)
        {
            sb.Append(",\"").Append(name).Append("\":").Append(value);
            return sb;
        }

        public static StringBuilder Num(this StringBuilder sb, string name, double value)
        {
            sb.Append(",\"").Append(name).Append("\":")
              .Append(value.ToString("R", CultureInfo.InvariantCulture));
            return sb;
        }

        public static StringBuilder Bool(this StringBuilder sb, string name, bool value)
        {
            sb.Append(",\"").Append(name).Append("\":").Append(value ? "true" : "false");
            return sb;
        }

        /// <summary>Serial as the canonical "0x1A2B" string the sidecar keys on.</summary>
        public static StringBuilder Ser(this StringBuilder sb, string name, Serial serial)
        {
            sb.Append(",\"").Append(name).Append("\":\"0x")
              .Append(serial.Value.ToString("X")).Append('"');
            return sb;
        }

        /// <summary>Closes the object. The trailing newline is the frame delimiter.</summary>
        public static string End(this StringBuilder sb)
        {
            sb.Append('}');
            return sb.ToString();
        }

        public static void Escape(StringBuilder sb, string value)
        {
            sb.Append('"');

            for (int i = 0; i < value.Length; i++)
            {
                char c = value[i];

                switch (c)
                {
                    case '"': sb.Append("\\\""); break;
                    case '\\': sb.Append("\\\\"); break;
                    case '\n': sb.Append("\\n"); break;
                    case '\r': sb.Append("\\r"); break;
                    case '\t': sb.Append("\\t"); break;
                    case '\b': sb.Append("\\b"); break;
                    case '\f': sb.Append("\\f"); break;
                    default:
                        if (c < ' ')
                            sb.Append("\\u").Append(((int)c).ToString("x4"));
                        else
                            sb.Append(c);
                        break;
                }
            }

            sb.Append('"');
        }

        // ---- inbound ----

        /// <summary>
        ///     Parses one line into a dictionary. Returns null on malformed input rather than
        ///     throwing: a bad line from the sidecar must never reach a game code path.
        /// </summary>
        public static Dictionary<string, object> Parse(string line)
        {
            if (String.IsNullOrEmpty(line))
                return null;

            try
            {
                if (_parser == null)
                {
                    _parser = new JavaScriptSerializer();
                    _parser.MaxJsonLength = 1 << 20;
                }

                return _parser.Deserialize<Dictionary<string, object>>(line);
            }
            catch
            {
                return null;
            }
        }

        public static string GetString(Dictionary<string, object> o, string key)
        {
            object v;

            if (o == null || !o.TryGetValue(key, out v) || v == null)
                return null;

            return v as string ?? Convert.ToString(v, CultureInfo.InvariantCulture);
        }

        public static int GetInt(Dictionary<string, object> o, string key, int fallback)
        {
            object v;

            if (o == null || !o.TryGetValue(key, out v) || v == null)
                return fallback;

            try
            {
                return Convert.ToInt32(v, CultureInfo.InvariantCulture);
            }
            catch
            {
                return fallback;
            }
        }
    }
}