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

namespace LibMMD.Unity3D.Animation
{
    /// <summary>Handles generated by the MMD Animation Rigging setup.</summary>
    public sealed class MmdRuntimeRig
    {
        internal MmdRuntimeRig(Transform rigRoot, Transform controlsRoot,
            IDictionary<string, Transform> targets,
            IDictionary<string, MmdIkControl> constraints)
        {
            RigRoot = rigRoot;
            ControlsRoot = controlsRoot;
            Targets = targets;
            Constraints = constraints;
        }

        public Transform RigRoot { get; }
        public float Weight { get; set; } = 1f;
        public Transform ControlsRoot { get; }
        public IDictionary<string, Transform> Targets { get; }
        public IDictionary<string, MmdIkControl> Constraints { get; }

        public bool SetWeight(string controlName, float weight)
        {
            if (!Constraints.TryGetValue(controlName, out var constraint)) return false;
            constraint.Weight = Mathf.Clamp01(weight);
            return true;
        }
    }

    /// <summary>Builds two-bone IK controls from standard MMD bone names at runtime.</summary>
    public static class MmdRuntimeRigBuilder
    {
        public const string LeftLeg = "LeftLeg";
        public const string RightLeg = "RightLeg";
        public const string LeftArm = "LeftArm";
        public const string RightArm = "RightArm";

        public static MmdRuntimeRig Build(GameObject animatorRoot, MmdModel model, GameObject[] bones)
        {
            if (animatorRoot == null) throw new ArgumentNullException(nameof(animatorRoot));
            if (model == null) throw new ArgumentNullException(nameof(model));
            if (bones == null || bones.Length != model.Bones.Length)
                throw new ArgumentException("Bone objects must match the MMD model.", nameof(bones));

            var rigObject = new GameObject("MmdIkConstraints");
            rigObject.transform.SetParent(animatorRoot.transform, false);
            // Controls must live outside the Animator hierarchy. If they are children of the
            // Animator, its animation stream restores them to bind/default values and scene or
            // script movement appears to have no effect on the IK job.
            var controls = new GameObject("MmdRigControls");
            var controlsParent = animatorRoot.transform.parent;
            controls.transform.SetParent(controlsParent, false);

            var lookup = BuildLookup(model, bones);
            var targets = new Dictionary<string, Transform>();
            var constraints = new Dictionary<string, MmdIkControl>();

            BuildChain(LeftLeg, rigObject.transform, controls.transform, lookup,
                // Solve the physical/source chain. Models with *D deform bones already copy
                // this chain through append transforms; solving *D and then copying its local
                // rotations back to differently-parented source bones is not equivalent.
                new[] { "左足", "leftleg", "左足D", "leftlegD" },
                new[] { "左ひざ", "左膝", "leftknee", "左ひざD", "左膝D", "leftkneeD" },
                new[] { "左足首", "leftankle", "左足首D", "leftankleD" },
                new[] { "左足ik", "leftlegik" },
                targets, constraints);
            BuildChain(RightLeg, rigObject.transform, controls.transform, lookup,
                new[] { "右足", "rightleg", "右足D", "rightlegD" },
                new[] { "右ひざ", "右膝", "rightknee", "右ひざD", "右膝D", "rightkneeD" },
                new[] { "右足首", "rightankle", "右足首D", "rightankleD" },
                new[] { "右足ik", "rightlegik" },
                targets, constraints);
            BuildChain(LeftArm, rigObject.transform, controls.transform, lookup,
                new[] { "左腕", "leftarm" }, new[] { "左ひじ", "左肘", "leftelbow" },
                new[] { "左手首", "leftwrist" }, null,
                targets, constraints);
            BuildChain(RightArm, rigObject.transform, controls.transform, lookup,
                new[] { "右腕", "rightarm" }, new[] { "右ひじ", "右肘", "rightelbow" },
                new[] { "右手首", "rightwrist" }, null,
                targets, constraints);

            return new MmdRuntimeRig(rigObject.transform, controls.transform, targets, constraints);
        }

        private static Dictionary<string, Transform> BuildLookup(MmdModel model, GameObject[] bones)
        {
            var result = new Dictionary<string, Transform>();
            for (var i = 0; i < bones.Length; i++)
            {
                AddName(result, model.Bones[i].Name, bones[i].transform);
                AddName(result, model.Bones[i].NameEn, bones[i].transform);
            }
            return result;
        }

        private static void AddName(IDictionary<string, Transform> lookup, string name, Transform bone)
        {
            var key = Normalize(name);
            if (key.Length > 0 && !lookup.ContainsKey(key)) lookup.Add(key, bone);
        }

        private static Transform Find(IDictionary<string, Transform> lookup, string[] names)
        {
            if (names == null) return null;
            foreach (var name in names)
                if (lookup.TryGetValue(Normalize(name), out var bone)) return bone;
            return null;
        }

        private static string Normalize(string name)
        {
            if (string.IsNullOrWhiteSpace(name)) return string.Empty;
            return name.Normalize(NormalizationForm.FormKC)
                .Replace(" ", string.Empty).Replace("_", string.Empty).ToLowerInvariant();
        }

        private static void BuildChain(string controlName, Transform rigRoot, Transform controlsRoot,
            IDictionary<string, Transform> lookup, string[] rootNames, string[] midNames,
            string[] tipNames, string[] targetNames,
            IDictionary<string, Transform> targets,
            IDictionary<string, MmdIkControl> constraints)
        {
            var root = Find(lookup, rootNames);
            var mid = Find(lookup, midNames);
            var tip = Find(lookup, tipNames);
            if (root == null || mid == null || tip == null) return;

            // Never use an animated MMD bone directly as a control: MmdAnimationDriver writes
            // it every frame, which makes Inspector/script movement appear to do nothing.
            // An IK bone is still useful as the initial target pose when the model provides one.
            var targetSource = Find(lookup, targetNames) ?? tip;
            var target = CreateControl(controlName + "Target", controlsRoot,
                targetSource.position, targetSource.rotation);

            var chainDirection = tip.position - root.position;
            var bendDirection = mid.position - Vector3.Lerp(root.position, tip.position, 0.5f);
            if (bendDirection.sqrMagnitude < 0.000001f)
                bendDirection = Vector3.forward * Mathf.Max(chainDirection.magnitude * 0.25f, 0.05f);
            var hint = CreateControl(controlName + "Hint", controlsRoot,
                mid.position + bendDirection.normalized * Mathf.Max(chainDirection.magnitude * 0.5f, 0.1f),
                Quaternion.identity);

            var constraintObject = new GameObject(controlName + "IK");
            constraintObject.transform.SetParent(rigRoot, false);
            var constraint = constraintObject.AddComponent<MmdIkControl>();
            constraint.Root = root;
            constraint.Mid = mid;
            constraint.Tip = tip;
            constraint.Target = target;
            constraint.Hint = hint;
            if (!tip.IsChildOf(mid) || !mid.IsChildOf(root))
            {
                Debug.LogError($"[MMD Rig] Invalid {controlName} chain: " +
                    $"root='{root.name}', mid='{mid.name}', tip='{tip.name}', " +
                    $"midUnderRoot={mid.IsChildOf(root)}, tipUnderMid={tip.IsChildOf(mid)}");
                UnityEngine.Object.Destroy(constraintObject);
                return;
            }
            // VMD owns the limb until the caller explicitly enables this control.
            constraint.Weight = 0f;
            targets[controlName] = target;
            constraints[controlName] = constraint;
        }

        private static Transform CreateControl(string name, Transform parent, Vector3 position, Quaternion rotation)
        {
            var control = new GameObject(name).transform;
            control.SetParent(parent, false);
            control.SetPositionAndRotation(position, rotation);
            return control;
        }
    }
}