using System;
using System.Collections.Generic;
using System.Globalization;
using System.Text;

namespace Luneraria.Core.Tests
{
    /// <summary>
    /// Minimal JSON reader for the golden files, without package dependencies (the same code
    /// runs in Unity and in the .NET harness). Objects keep their key order; numbers without
    /// fraction or exponent become long, all others double.
    /// </summary>
    public static class MiniJson
    {
        public static object Parse(string text)
        {
            int at = 0;
            object value = ReadValue(text, ref at);
            SkipSpace(text, ref at);
            if (at != text.Length)
                throw new FormatException("trailing characters at " + at);
            return value;
        }

        static void SkipSpace(string text, ref int at)
        {
            while (at < text.Length && char.IsWhiteSpace(text[at]))
                at++;
        }

        static object ReadValue(string text, ref int at)
        {
            SkipSpace(text, ref at);
            char c = text[at];
            if (c == '{')
                return ReadObject(text, ref at);
            if (c == '[')
                return ReadArray(text, ref at);
            if (c == '"')
                return ReadString(text, ref at);
            if (text.Length - at >= 4 && string.CompareOrdinal(text, at, "true", 0, 4) == 0)
            {
                at += 4;
                return true;
            }
            if (text.Length - at >= 5 && string.CompareOrdinal(text, at, "false", 0, 5) == 0)
            {
                at += 5;
                return false;
            }
            if (text.Length - at >= 4 && string.CompareOrdinal(text, at, "null", 0, 4) == 0)
            {
                at += 4;
                return null;
            }
            return ReadNumber(text, ref at);
        }

        static OrderedMap<string, object> ReadObject(string text, ref int at)
        {
            var result = new OrderedMap<string, object>();
            at++;
            SkipSpace(text, ref at);
            if (text[at] == '}')
            {
                at++;
                return result;
            }
            while (true)
            {
                SkipSpace(text, ref at);
                string key = ReadString(text, ref at);
                SkipSpace(text, ref at);
                if (text[at] != ':')
                    throw new FormatException("expected ':' at " + at);
                at++;
                result[key] = ReadValue(text, ref at);
                SkipSpace(text, ref at);
                if (text[at] == ',')
                {
                    at++;
                    continue;
                }
                if (text[at] == '}')
                {
                    at++;
                    return result;
                }
                throw new FormatException("expected ',' or '}' at " + at);
            }
        }

        static List<object> ReadArray(string text, ref int at)
        {
            var result = new List<object>();
            at++;
            SkipSpace(text, ref at);
            if (text[at] == ']')
            {
                at++;
                return result;
            }
            while (true)
            {
                result.Add(ReadValue(text, ref at));
                SkipSpace(text, ref at);
                if (text[at] == ',')
                {
                    at++;
                    continue;
                }
                if (text[at] == ']')
                {
                    at++;
                    return result;
                }
                throw new FormatException("expected ',' or ']' at " + at);
            }
        }

        static string ReadString(string text, ref int at)
        {
            if (text[at] != '"')
                throw new FormatException("expected string at " + at);
            at++;
            var builder = new StringBuilder();
            while (true)
            {
                char c = text[at++];
                if (c == '"')
                    return builder.ToString();
                if (c != '\\')
                {
                    builder.Append(c);
                    continue;
                }
                char escape = text[at++];
                switch (escape)
                {
                    case '"': builder.Append('"'); break;
                    case '\\': builder.Append('\\'); break;
                    case '/': builder.Append('/'); break;
                    case 'b': builder.Append('\b'); break;
                    case 'f': builder.Append('\f'); break;
                    case 'n': builder.Append('\n'); break;
                    case 'r': builder.Append('\r'); break;
                    case 't': builder.Append('\t'); break;
                    case 'u':
                        builder.Append((char)int.Parse(text.Substring(at, 4), NumberStyles.HexNumber, CultureInfo.InvariantCulture));
                        at += 4;
                        break;
                    default: throw new FormatException("bad escape at " + at);
                }
            }
        }

        static object ReadNumber(string text, ref int at)
        {
            int start = at;
            bool fraction = false;
            while (at < text.Length && "+-0123456789.eE".IndexOf(text[at]) >= 0)
            {
                if (text[at] == '.' || text[at] == 'e' || text[at] == 'E')
                    fraction = true;
                at++;
            }
            string token = text.Substring(start, at - start);
            if (!fraction)
            {
                long whole;
                if (long.TryParse(token, NumberStyles.Integer, CultureInfo.InvariantCulture, out whole))
                    return whole;
            }
            return double.Parse(token, NumberStyles.Float, CultureInfo.InvariantCulture);
        }

        // ---------------------------------------------------------------- access helpers
        public static OrderedMap<string, object> Obj(object value) { return (OrderedMap<string, object>)value; }

        public static List<object> Arr(object value) { return (List<object>)value; }

        public static double Num(object value) { return value is long l ? l : (double)value; }

        public static int Int(object value) { return value is long l ? (int)l : (int)(double)value; }

        public static string Str(object value) { return value == null ? "" : value.ToString(); }

        public static object Get(OrderedMap<string, object> map, string key)
        {
            object value;
            return map.TryGetValue(key, out value) ? value : null;
        }
    }
}