using System.Collections.Generic;
using System.Text;
using LibMMD.Model;
using UnityEngine;

namespace LibMMD.Motion
{
    /// <summary>Retargets standard VMD translations to the target model's measured leg length.</summary>
    internal sealed class MmdMotionTranslationScaler
    {
        // Median leg length of the normal-proportion reference models listed in
        // docs/MOTION_IK_SCALE_MODELS.txt. VMD does not contain its authoring skeleton.
        internal const float ReferenceLegLength = 9.7337f;

        private readonly Dictionary<int, float> _scales = new Dictionary<int, float>();

        internal MmdMotionTranslationScaler(MmdModel model)
        {
            BuildScales(model);
        }

        internal BonePose Apply(int boneIndex, BonePose pose)
        {
            if (_scales.TryGetValue(boneIndex, out var scale)) pose.Translation *= scale;
            return pose;
        }

        private void BuildScales(MmdModel model)
        {
            var sideScales = new float[2];
            for (var i = 0; i < model.Bones.Length; ++i)
            {
                var bone = model.Bones[i];
                if (!bone.HasIk || bone.IkInfoVal == null || bone.IkInfoVal.IkLinks == null ||
                    bone.IkInfoVal.IkLinks.Length < 2) continue;

                var side = GetSide(bone.Name, bone.NameEn);
                var knee = bone.IkInfoVal.IkLinks[0].LinkIndex;
                var thigh = bone.IkInfoVal.IkLinks[1].LinkIndex;
                var ankle = bone.IkInfoVal.IkTargetIndex;
                if (side < 0 || !IsValidBone(model, knee) || !IsValidBone(model, thigh) ||
                    !IsValidBone(model, ankle) || !IsLegChain(model, thigh, knee, ankle)) continue;

                var length = Vector3.Distance(model.Bones[thigh].Position, model.Bones[knee].Position) +
                             Vector3.Distance(model.Bones[knee].Position, model.Bones[ankle].Position);
                if (length > 1e-5f) sideScales[side] = length / ReferenceLegLength;
            }

            for (var i = 0; i < model.Bones.Length; ++i)
            {
                var bone = model.Bones[i];
                var side = GetSide(bone.Name, bone.NameEn);
                if (side >= 0 && sideScales[side] > 0f && IsFootOrToeIk(bone))
                    _scales[i] = sideScales[side];
            }

            var rootScale = 0f;
            var validSideCount = 0;
            foreach (var scale in sideScales)
            {
                if (scale <= 0f) continue;
                rootScale += scale;
                validSideCount++;
            }
            if (validSideCount == 0) return;
            rootScale /= validSideCount;
            for (var i = 0; i < model.Bones.Length; ++i)
                if (IsMotionRoot(model.Bones[i])) _scales[i] = rootScale;
        }

        private static bool IsMotionRoot(Bone bone)
        {
            var name = NormalizeBoneName(bone.Name);
            var nameEn = NormalizeBoneName(bone.NameEn);
            return name == "全ての親" || name == "センター" || name == "グルーブ" ||
                   nameEn == "master" || nameEn == "root" || nameEn == "center" || nameEn == "groove";
        }

        private static bool IsFootOrToeIk(Bone bone)
        {
            if (!bone.HasIk) return false;
            var name = NormalizeBoneName(bone.Name);
            var nameEn = NormalizeBoneName(bone.NameEn);
            return name.Contains("足ik") || name.Contains("つま先ik") ||
                   nameEn.Contains("legik") || nameEn.Contains("footik") || nameEn.Contains("toeik");
        }

        private static bool IsLegChain(MmdModel model, int thigh, int knee, int ankle) =>
            HasAnyName(model.Bones[thigh], "足", "leg", "thigh") &&
            HasAnyName(model.Bones[knee], "ひざ", "膝", "knee") &&
            HasAnyName(model.Bones[ankle], "足首", "ankle");

        private static bool HasAnyName(Bone bone, params string[] candidates)
        {
            var name = NormalizeBoneName(bone.Name);
            var nameEn = NormalizeBoneName(bone.NameEn);
            foreach (var candidate in candidates)
                if (name.Contains(candidate) || nameEn.Contains(candidate)) return true;
            return false;
        }

        private static int GetSide(string name, string nameEn)
        {
            var normalized = NormalizeBoneName(name);
            var normalizedEn = NormalizeBoneName(nameEn);
            if (normalized.StartsWith("左") || normalizedEn.StartsWith("left")) return 0;
            if (normalized.StartsWith("右") || normalizedEn.StartsWith("right")) return 1;
            return -1;
        }

        private static string NormalizeBoneName(string name) =>
            string.IsNullOrWhiteSpace(name)
                ? string.Empty
                : name.Normalize(NormalizationForm.FormKC).Replace(" ", string.Empty).ToLowerInvariant();

        private static bool IsValidBone(MmdModel model, int index) =>
            index >= 0 && index < model.Bones.Length;
    }
}