using System.Collections.Generic;
using UnityEngine;
using UnityEngine.Animations;
using UnityEngine.Playables;
#if ENABLE_INPUT_SYSTEM
using UnityEngine.InputSystem;
#endif

/// <summary>
/// Sits next to the <see cref="PlayerCharacterController"/> and holds a list of <see cref="PlayerPose"/>s
/// plus the active index. The pose system owns all character animation — the Animator is left empty —
/// so it drives locomotion itself: standing still (or airborne / on a wall / on the ceiling) holds the
/// active pose's idle clip, walking on the ground plays that pose's optional walk clip, and sprinting
/// on the ground plays its optional run clip. Either locomotion clip is optional; when a pose leaves
/// one null, the idle pose is simply held in that state.
///
/// One key cycles to the next pose (wrapping), and sprinting in any state (ground, air, wall, ceiling)
/// snaps the selection back to the default pose. The selection is held continuously, so cycling or the
/// sprint reset shows up immediately instead of only once the player comes to a stop.
///
/// Clips are played through a tiny <see cref="PlayableGraph"/> (a two-input
/// <see cref="AnimationMixerPlayable"/> on an <see cref="AnimationPlayableOutput"/>) that drives the
/// Animator directly. Switching clip — between poses, or between idle/walk/run within a pose —
/// crossfades the outgoing and incoming clips over <see cref="poseBlendDuration"/> instead of snapping.
/// The per-pose ceiling y-offset is eased toward its target and routed through the controller (the
/// single writer of the model-offset transform) so it composes with the wall-lean instead of fighting it.
/// </summary>
[RequireComponent(typeof(PlayerCharacterController))]
[DisallowMultipleComponent]
// Run after PlayerCharacterController (default order 0) so the ceiling / sprint state polled below is
// this frame's, and the ceiling offset resolves without a one-frame seam.
[DefaultExecutionOrder(100)]
public partial class PlayerPoseController : MonoBehaviour
{
    [Header("Poses")]
    [Tooltip("Selectable poses. Index 0 is the default pose that sprinting resets to.")]
    [SerializeField] private List<PlayerPose> poses = new();

    [Tooltip("Index the selection resets to while sprinting in any state (the default/standard pose).")]
    [Min(0)]
    [SerializeField] private int defaultPoseIndex = 0;

    [Header("Input")]
#if ENABLE_INPUT_SYSTEM
    [Tooltip("Key that cycles to the next pose (wraps at the end of the list).")]
    [SerializeField] private Key cycleKey = Key.C;
#else
    [Tooltip("Key that cycles to the next pose (wraps at the end of the list).")]
    [SerializeField] private KeyCode cycleKey = KeyCode.C;
#endif

    [Header("Transitions")]
    [Tooltip("Seconds to crossfade from the previous pose to a newly selected one. 0 = instant snap.")]
    [Min(0f)]
    [SerializeField] private float poseBlendDuration = 0.2f;

    [Tooltip("Approach speed (local units/sec) for easing the ceiling y-offset toward its target. 0 = instant.")]
    [Min(0f)]
    [SerializeField] private float ceilingOffsetSpeed = 4f;

    [Tooltip("Apply Mecanim foot IK to the played humanoid clips. Off (default) plays each pose exactly as " +
             "authored. On bends the knees to plant the feet on the IK goal, which makes a straight-knee idle " +
             "render visibly bent even when the clip's Lower Leg Stretch muscle is fully straight.")]
    [SerializeField] private bool applyFootIK = false;

    private PlayerCharacterController _player;
    private Animator _animator;
    private string _graphName; // cached so building the graph allocates no string from the Update path

    private int _currentIndex;

    // Playables: a 2-input AnimationMixerPlayable that overrides the Animator Controller. Input 1 holds
    // the current ("to") pose; input 0 holds the outgoing ("from") pose during a crossfade and is empty
    // once the blend completes. Blending both inputs over a per-frame rest baseline (see below) makes
    // poses interpolate instead of snapping; an empty/partial "to" clip still resolves to rest.
    private PlayableGraph _graph;
    private AnimationPlayableOutput _output;
    private AnimationMixerPlayable _mixer;
    private AnimationClipPlayable _fromPlayable;
    private AnimationClipPlayable _toPlayable;
    private AnimationClip _toClip;        // the clip currently targeted (held on input 1)
    private bool _posePlaying;
    private float _blend;                 // 0..1 weight of the "to" input; 1 = fully on the target pose
    private bool _blending;

    private float _ceilingOffset;         // eased local-up offset currently fed to the controller

    // Rest pose snapshot of the whole Animator subtree, taken in Awake before the Animator first
    // evaluates. An AnimationClipPlayable only writes the bones its curves cover, so a clip that
    // doesn't key a bone (an empty clip like the T-pose, or a partial one) would otherwise leave that
    // bone frozen on the previous animation. Restoring this before each pose start makes every pose
    // define the full body. meshOffsetTarget is an ancestor of the Animator, so it is never in this
    // set and the controller's lean/ceiling offset stays untouched.
    private Transform[] _restBones;
    private Vector3[] _restPos;
    private Quaternion[] _restRot;
    private Vector3[] _restScale;

    /// <summary>Index of the currently selected pose.</summary>
    public int CurrentIndex => _currentIndex;

    void Awake()
    {
        _player = GetComponent<PlayerCharacterController>();
        _animator = _player ? _player.GetComponentInChildren<Animator>() : null;
        _graphName = $"{name}-Pose";
        if (_animator)
            CaptureRestPose();
        else
            Debug.LogWarning("[PlayerPoseController] No Animator on the PlayerCharacterController; poses cannot play.", this);
    }

    void Update()
    {
        if (CycleKeyPressed())
            NextPose();

        // Sprinting in any state (ground, air, wall, ceiling) snaps the selection back to the default
        // pose. Held continuously below, so the reset shows up immediately, not only once back on the floor.
        if (_player.IsSprinting)
            _currentIndex = WrapIndex(defaultPoseIndex);

        PlayerPose pose = ActivePose();

        // Pick the clip for the current locomotion state. Standing still, airborne, on a wall or on the
        // ceiling holds the idle pose; moving on the ground plays the run clip while sprinting or the
        // walk clip otherwise. Both locomotion clips are optional — a null one falls back to the idle
        // pose, so an unset walk clip keeps the held-pose behaviour. PlayPose crossfades on any change
        // and hands the rig back only when there is no clip at all (empty list / null idle clip).
        AnimationClip clip = pose ? pose.Clip : null;
        float speed = pose ? pose.ClipSpeed : 1f;
        if (pose && _player.IsMovingOnGround)
        {
            AnimationClip locomotion = _player.IsSprinting ? pose.RunClip : pose.WalkClip;
            if (locomotion)
            {
                clip = locomotion;
                speed = _player.IsSprinting ? pose.RunClipSpeed : pose.WalkClipSpeed;
            }
        }
        PlayPose(clip, speed);

        // Ceiling y-offset: only while stuck to the ceiling. Ease toward the target instead of
        // snapping, so entering and leaving the ceiling (and switching ceiling poses) glides. Routed
        // through the controller so it shares the wall-lean's single write of the model transform.
        float ceilingTarget = (pose && _player.IsOnCeiling) ? pose.CeilingYOffset : 0f;
        _ceilingOffset = ceilingOffsetSpeed > 0f
            ? Mathf.MoveTowards(_ceilingOffset, ceilingTarget, ceilingOffsetSpeed * Time.deltaTime)
            : ceilingTarget;
        _player.SetPoseLocalYOffset(_ceilingOffset);
    }

    void OnDisable()
    {
        // Hand the rig back to the Animator Controller and never leak a graph; rebuilt lazily on the
        // next idle frame. Also clear any ceiling offset we were holding.
        ReleasePose();
        _ceilingOffset = 0f;
        if (_player)
        {
            _player.SetPoseLocalYOffset(0f);
        }
    }

    /// <summary>Advances to the next pose, wrapping at the end of the list.</summary>
    public void NextPose() => SetPoseIndex(_currentIndex + 1);

    /// <summary>Steps back to the previous pose, wrapping at the start of the list.</summary>
    public void PreviousPose() => SetPoseIndex(_currentIndex - 1);

    /// <summary>Selects a pose by index, wrapping into range so cycling never goes out of bounds.</summary>
    public void SetPoseIndex(int index) => _currentIndex = WrapIndex(index);

    private int WrapIndex(int index)
    {
        int count = poses.Count;
        if (count == 0) return 0;
        return ((index % count) + count) % count;
    }

    private PlayerPose ActivePose()
    {
        if (poses.Count == 0) return null;
        return poses[Mathf.Clamp(_currentIndex, 0, poses.Count - 1)];
    }

    private bool CycleKeyPressed()
    {
#if ENABLE_INPUT_SYSTEM
        var keyboard = Keyboard.current;
        return keyboard != null && keyboard[cycleKey].wasPressedThisFrame;
#else
        return Input.GetKeyDown(cycleKey);
#endif
    }

    /// <summary>
    /// Plays and holds the given clip, overriding the Animator Controller. Switching to a different
    /// clip crossfades from the current pose over <see cref="poseBlendDuration"/> (the first pose, or a
    /// zero duration, appears instantly). Called every frame: it starts a transition on a clip change,
    /// advances any in-flight blend, applies <paramref name="speed"/> to the target playback, and
    /// re-snaps un-keyed bones to rest before the graph evaluates. A null clip (or no animator) releases
    /// back to the controller.
    /// </summary>
    private void PlayPose(AnimationClip clip, float speed)
    {
        if (!clip || !_animator)
        {
            ReleasePose();
            return;
        }

        EnsureGraph();

        if (!(_posePlaying && _toClip == clip))
            BeginTransition(clip);

        AdvanceBlend(Time.deltaTime);

        // Set every frame (not just on clip change) so tuning a pose's speed slider live in the inspector
        // takes effect immediately and re-selecting the same clip keeps its speed. The outgoing pose on
        // input 0 keeps the speed it carried, so a crossfade fades it out at its own pace.
        if (_toPlayable.IsValid())
            PlayableExtensions.SetSpeed(_toPlayable, speed);

        // Snap un-keyed bones to rest every frame, so each mixer input blends relative to rest: a
        // partial or empty clip (e.g. the T-pose) defines the whole body, and a crossfade interpolates
        // both poses against the same baseline. The graph overrides the keyed bones, weighted, when it
        // evaluates later this frame.
        ResetToRestPose();

        if (!_graph.IsPlaying())
            _graph.Play();

        _posePlaying = true;
    }

    /// <summary>Builds the graph (a 2-input mixer feeding the Animator output) lazily if it isn't alive yet.</summary>
    private void EnsureGraph()
    {
        if (_graph.IsValid())
            return;
        _graph = PlayableGraph.Create(_graphName);
        _graph.SetTimeUpdateMode(DirectorUpdateMode.GameTime);
        _mixer = AnimationMixerPlayable.Create(_graph, 2);
        _output = AnimationPlayableOutput.Create(_graph, "Pose", _animator);
        _output.SetSourcePlayable(_mixer);
    }

    /// <summary>
    /// Starts a crossfade to <paramref name="clip"/>: the in-flight target becomes the outgoing pose on
    /// input 0 (carrying its playback time), the new clip goes on input 1, and the blend ramps up from
    /// 0. The first pose (or a zero duration) snaps in at full weight with no fade-from-nothing.
    /// </summary>
    private void BeginTransition(AnimationClip clip)
    {
        bool hadPose = _posePlaying && _toPlayable.IsValid();

        // Drop the previous outgoing pose (already faded out, or none) before reusing input 0.
        if (_fromPlayable.IsValid())
        {
            _mixer.DisconnectInput(0);
            _graph.DestroyPlayable(_fromPlayable);
            _fromPlayable = default;
        }

        if (hadPose)
        {
            // Move the current target from input 1 to input 0 so it becomes the outgoing pose without a
            // recreate (its animation time carries over, no jump).
            _mixer.DisconnectInput(1);
            _fromPlayable = _toPlayable;
            _mixer.ConnectInput(0, _fromPlayable, 0);
        }

        _toPlayable = AnimationClipPlayable.Create(_graph, clip);
        // Off by default: foot IK plants the foot on its goal and bends the knee to reach it, so a straight-knee
        // pose renders bent (SampleAnimation, which the authoring tools check against, never applies it). The
        // outgoing pose on input 0 is a former _toPlayable, so it already carries this setting.
        _toPlayable.SetApplyFootIK(applyFootIK);
        _mixer.ConnectInput(1, _toPlayable, 0);
        _toClip = clip;

        _blend = (hadPose && poseBlendDuration > 0f) ? 0f : 1f;
        _blending = _blend < 1f;
        ApplyBlendWeights();
    }

    /// <summary>Advances an in-flight crossfade and drops the outgoing pose once it has fully faded.</summary>
    private void AdvanceBlend(float dt)
    {
        if (!_blending)
            return;
        _blend = poseBlendDuration > 0f ? Mathf.MoveTowards(_blend, 1f, dt / poseBlendDuration) : 1f;
        if (_blend >= 1f)
        {
            _blend = 1f;
            _blending = false;
            if (_fromPlayable.IsValid())
            {
                _mixer.DisconnectInput(0);
                _graph.DestroyPlayable(_fromPlayable);
                _fromPlayable = default;
            }
        }
        ApplyBlendWeights();
    }

    /// <summary>Pushes the current blend onto the mixer inputs (smoothstepped while a "from" pose exists).</summary>
    private void ApplyBlendWeights()
    {
        if (!_mixer.IsValid())
            return;
        bool hasFrom = _fromPlayable.IsValid();
        float w = hasFrom ? Mathf.SmoothStep(0f, 1f, _blend) : 1f;
        _mixer.SetInputWeight(0, hasFrom ? 1f - w : 0f);
        _mixer.SetInputWeight(1, _toPlayable.IsValid() ? w : 0f);
    }

    /// <summary>
    /// Snapshots every transform a pose clip can address (the Animator's whole subtree) in its
    /// authored rest pose. Taken in Awake before the Animator first evaluates, so it captures the rig
    /// at rest (the paintman rig's rest pose is its T-pose).
    /// </summary>
    private void CaptureRestPose()
    {
        _restBones = _animator.transform.GetComponentsInChildren<Transform>(true);
        int n = _restBones.Length;
        _restPos = new Vector3[n];
        _restRot = new Quaternion[n];
        _restScale = new Vector3[n];
        for (int i = 0; i < n; i++)
        {
            Transform t = _restBones[i];
            _restPos[i] = t.localPosition;
            _restRot[i] = t.localRotation;
            _restScale[i] = t.localScale;
        }
    }

    /// <summary>Restores the captured rest pose so an empty or partial pose clip fully defines the body.</summary>
    private void ResetToRestPose()
    {
        if (_restBones == null)
            return;
        for (int i = 0; i < _restBones.Length; i++)
        {
            Transform t = _restBones[i];
            if (!t)
                continue;
            t.localPosition = _restPos[i];
            t.localRotation = _restRot[i];
            t.localScale = _restScale[i];
        }
    }

    /// <summary>Destroys the graph so the Animator Controller (run/idle) drives the rig again.</summary>
    private void ReleasePose()
    {
        if (!_posePlaying)
            return;
        if (_graph.IsValid())
            _graph.Destroy();
        _graph = default;
        _output = default;
        _mixer = default;
        _fromPlayable = default;
        _toPlayable = default;
        _toClip = null;
        _blend = 0f;
        _blending = false;
        _posePlaying = false;
    }
}