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

namespace Luneraria.Core.Tests
{
    /// <summary>
    /// Float diagnosis for a runtime (docs/port/U1.5-UNITY.md): evaluates the core's own Vec2 and
    /// GdMath operations on the inputs of tools/godot-golden/float_probe.gd and compares the raw
    /// bits with Godot's results (Golden/float_probe.json). A second part classifies how the
    /// runtime evaluates float32 expressions: strictly per operation, with double-precision
    /// intermediates (allowed by ECMA-335 I.12.1.3) or with fused multiply-add.
    /// </summary>
    public static class FloatProbe
    {
        public sealed class Result
        {
            public int Rows;
            public readonly OrderedMap<string, int> Identical = new OrderedMap<string, int>();
            public readonly OrderedMap<string, double> WorstUlps = new OrderedMap<string, double>();
            public readonly OrderedMap<string, int> Evaluation = new OrderedMap<string, int>();
            public int EvaluationSamples;

            public int Mismatches
            {
                get
                {
                    int total = 0;
                    foreach (KeyValuePair<string, int> pair in Identical)
                        total += Rows - pair.Value;
                    return total;
                }
            }

            public string ToJson(string runtime, string label)
            {
                var text = new StringBuilder();
                text.Append("{\n");
                text.AppendFormat("  \"runtime\": \"{0}\",\n  \"label\": \"{1}\",\n  \"rows\": {2},\n", runtime, label, Rows);
                text.Append("  \"identical_to_godot\": {");
                bool first = true;
                foreach (KeyValuePair<string, int> pair in Identical)
                {
                    text.AppendFormat(CultureInfo.InvariantCulture, "{0}\n    \"{1}\": {2}", first ? "" : ",", pair.Key, pair.Value);
                    first = false;
                }
                text.Append("\n  },\n  \"worst_ulps\": {");
                first = true;
                foreach (KeyValuePair<string, double> pair in WorstUlps)
                {
                    text.AppendFormat(CultureInfo.InvariantCulture, "{0}\n    \"{1}\": {2}", first ? "" : ",", pair.Key, pair.Value);
                    first = false;
                }
                text.AppendFormat("\n  }},\n  \"evaluation_samples\": {0},\n  \"evaluation_matches\": {{", EvaluationSamples);
                first = true;
                foreach (KeyValuePair<string, int> pair in Evaluation)
                {
                    text.AppendFormat(CultureInfo.InvariantCulture, "{0}\n    \"{1}\": {2}", first ? "" : ",", pair.Key, pair.Value);
                    first = false;
                }
                text.Append("\n  }\n}\n");
                return text.ToString();
            }
        }

        public static Result Run(string goldenDirectory)
        {
            var result = new Result();
            var probe = MiniJson.Obj(MiniJson.Parse(File.ReadAllText(Path.Combine(goldenDirectory, "float_probe.json"))));
            foreach (object item in MiniJson.Arr(probe["rows"]))
            {
                List<object> row = MiniJson.Arr(item);
                float[] f = Floats(MiniJson.Str(row[0]));
                double[] d = Doubles(MiniJson.Str(row[1]));
                var a = new Vec2(f[0], f[1]);
                var b = new Vec2(f[2], f[3]);
                float w = f[4];
                float s = f[5];
                result.Rows++;
                Compare(result, "length", a.Length(), f[6]);
                Compare(result, "length_squared", a.LengthSquared(), f[7]);
                Compare(result, "distance_to", a.DistanceTo(b), f[8]);
                Compare(result, "distance_squared_to", a.DistanceSquaredTo(b), f[9]);
                Compare(result, "dot", a.Dot(b), f[10]);
                Vec2 n = a.Normalized();
                Compare(result, "normalized", n.X, f[11], n.Y, f[12]);
                Vec2 l = a.Lerp(b, w);
                Compare(result, "lerp", l.X, f[13], l.Y, f[14]);
                Vec2 c = a.LimitLength(0.9f);
                Compare(result, "limit_length", c.X, f[15], c.Y, f[16]);
                Compare(result, "multiply", (a * s).X, f[17]);
                Compare(result, "divide", (a / s).Y, f[18]);
                Compare(result, "sub_normalized", (a - b).Normalized().X, f[19]);
                double angle = GdMath.Atan2(a.X, a.Y);
                if (!result.Identical.ContainsKey("atan2"))
                    result.Identical["atan2"] = 0;
                if (BitConverter.DoubleToInt64Bits(angle) == BitConverter.DoubleToInt64Bits(d[0]))
                    result.Identical["atan2"] += 1;
                Classify(result, f);
            }
            return result;
        }

        static void Compare(Result result, string name, float actual, float expected)
        {
            Compare(result, name, actual, expected, 0f, 0f);
        }

        static void Compare(Result result, string name, float actualX, float expectedX, float actualY, float expectedY)
        {
            if (!result.Identical.ContainsKey(name))
            {
                result.Identical[name] = 0;
                result.WorstUlps[name] = 0.0;
            }
            double ulps = Math.Max(Ulps(actualX, expectedX), Ulps(actualY, expectedY));
            if (ulps == 0.0)
                result.Identical[name] += 1;
            if (ulps > result.WorstUlps[name])
                result.WorstUlps[name] = ulps;
        }

        /// <summary>Distance in units of the last place (float32).</summary>
        public static double Ulps(float a, float b)
        {
            if (BitConverter.ToInt32(BitConverter.GetBytes(a), 0) == BitConverter.ToInt32(BitConverter.GetBytes(b), 0))
                return 0.0;
            if (float.IsNaN(a) || float.IsNaN(b))
                return double.PositiveInfinity;
            long ia = Ordered(a);
            long ib = Ordered(b);
            return Math.Abs(ia - ib);
        }

        static long Ordered(float value)
        {
            int bits = BitConverter.ToInt32(BitConverter.GetBytes(value), 0);
            return bits < 0 ? (long)int.MinValue - bits : bits;
        }

        /// <summary>
        /// How does this runtime evaluate `x*x + y*y` and `a + (b - a) * w` with float32 operands?
        /// The candidates are computed with explicit conversions, which ECMA-335 guarantees to
        /// narrow: per-operation float32, double intermediates rounded once, fused multiply-add.
        /// </summary>
        static void Classify(Result result, float[] f)
        {
            float x = f[0];
            float y = f[1];
            float a = f[0];
            float b = f[2];
            float w = f[4];
            float natural = SumOfSquares(x, y);
            float strict = (float)((float)(x * x) + (float)(y * y));
            float wide = (float)((double)x * x + (double)y * y);
            float fused = (float)((double)x * x + (double)(float)(y * y));
            float naturalLerp = LerpNatural(a, b, w);
            float strictLerp = (float)(a + (float)((float)(b - a) * w));
            float wideLerp = (float)(a + ((double)b - a) * w);
            result.EvaluationSamples++;
            Count(result, "sum_of_squares_strict_float32", natural == strict);
            Count(result, "sum_of_squares_double_intermediate", natural == wide);
            Count(result, "sum_of_squares_fused", natural == fused);
            Count(result, "sum_of_squares_candidates_differ", strict != wide);
            Count(result, "lerp_strict_float32", naturalLerp == strictLerp);
            Count(result, "lerp_double_intermediate", naturalLerp == wideLerp);
            Count(result, "lerp_candidates_differ", strictLerp != wideLerp);
        }

        static void Count(Result result, string key, bool hit)
        {
            if (!result.Evaluation.ContainsKey(key))
                result.Evaluation[key] = 0;
            if (hit)
                result.Evaluation[key] += 1;
        }

        // Kept out of line so the expressions are compiled the way the core's own code is.
        [System.Runtime.CompilerServices.MethodImpl(System.Runtime.CompilerServices.MethodImplOptions.NoInlining)]
        static float SumOfSquares(float x, float y) { return x * x + y * y; }

        [System.Runtime.CompilerServices.MethodImpl(System.Runtime.CompilerServices.MethodImplOptions.NoInlining)]
        static float LerpNatural(float a, float b, float w) { return a + (b - a) * w; }

        static float[] Floats(string hex)
        {
            byte[] bytes = Bytes(hex);
            var values = new float[bytes.Length / 4];
            for (int i = 0; i < values.Length; i++)
                values[i] = BitConverter.ToSingle(bytes, i * 4);
            return values;
        }

        static double[] Doubles(string hex)
        {
            byte[] bytes = Bytes(hex);
            var values = new double[bytes.Length / 8];
            for (int i = 0; i < values.Length; i++)
                values[i] = BitConverter.ToDouble(bytes, i * 8);
            return values;
        }

        static byte[] Bytes(string hex)
        {
            var bytes = new byte[hex.Length / 2];
            for (int i = 0; i < bytes.Length; i++)
                bytes[i] = byte.Parse(hex.Substring(i * 2, 2), NumberStyles.HexNumber, CultureInfo.InvariantCulture);
            return bytes;
        }
    }
}