using System.Collections.Generic;
using UnityEngine;
using Unheimlich.Features.Player;

namespace Unheimlich.World.Environment
{
    /// <summary>
    /// Infinite parallax staircase — tower approach.
    ///
    /// When the player enters the trigger zone from below:
    ///   - A full tower of (_maxIterations + 1) segments is spawned instantly above ground.
    ///   - The tower scrolls at a speed proportional to how far the player's Y deviates
    ///     from the trigger center — keeping the player locked near that height.
    ///     If the player stops moving, scroll speed drops to zero.
    ///   - When the topmost segment reaches ground level the stock is exhausted: the tower
    ///     decelerates, extras are destroyed, and the system resets.
    ///
    /// Entering from above mirrors the logic (tower ascends, stock is below ground).
    /// Re-triggerable indefinitely.
    ///
    /// Setup:
    ///   1. Add this component to the InfinityStair root.
    ///   2. Add <see cref="StaircaseTriggerZone"/> to the Trigger child.
    ///   3. Assign <see cref="_stairPrefab"/>.
    /// </summary>
    public class InfiniteStaircaseController : MonoBehaviour
    {
        // ─── Prefab ──────────────────────────────────────────────────────────

        [Header("Stair Prefab")]
        [Tooltip("One staircase segment prefab used to build the tower.")]
        [SerializeField] private GameObject _stairPrefab;

        [Tooltip("If true, the first child with renderers is reused as slot 0 rather than instantiated from the prefab.")]
        [SerializeField] private bool _useExistingChildAsBase = true;

        // ─── Iterations ──────────────────────────────────────────────────────

        [Header("Iterations")]
        [Tooltip("Number of full segment heights the player can traverse. Tower = (maxIterations + 1) segments.")]
        [SerializeField] private int _maxIterations = 4;

        // ─── Segment Bounds ──────────────────────────────────────────────────

        [Header("Segment Bounds — Auto-Detection")]
        [Tooltip("Renderer of the central column mesh in the stair asset. When assigned, segment height is read from its world bounds.")]
        [SerializeField] private Renderer _centralColumnRenderer;

        [Tooltip("Fallback segment height (m) used when no central column renderer is assigned.")]
        [SerializeField] private float _segmentHeight = 4.82f;

        [Tooltip("Y offset added to the segment height for fine-tuning snapping.")]
        [SerializeField] private float _segmentHeightOffset = 0f;

        // ─── Scroll Control ───────────────────────────────────────────────────

        [Header("Scroll Speed Control")]
        [Tooltip("Proportional gain: scroll speed (m/s) per metre of player deviation from the trigger center.")]
        [SerializeField] private float _correctionGain = 4f;

        [Tooltip("Maximum tower scroll speed in m/s.")]
        [SerializeField] private float _maxScrollSpeed = 8f;

        [Tooltip("SmoothDamp time for scroll speed transitions — prevents sudden jolts.")]
        [SerializeField] private float _scrollSmoothTime = 0.1f;

        // ─── Rotation Offset ─────────────────────────────────────────────────

        [Header("Rotation Offset")]
        [Tooltip("Y rotation applied to every spawned segment around its geometric bounds center (not its pivot).")]
        [SerializeField] private float _segmentRotationOffsetY = 0f;

        // ─── Debug ───────────────────────────────────────────────────────────

        [Header("Debug")]
        [SerializeField] private bool _drawGizmos = true;

        // ─── State ───────────────────────────────────────────────────────────

        private enum StairState { Idle, Active, Stopping, Done }
        private StairState _currentState = StairState.Idle;

        private Transform _playerTransform;

        /// <summary>Single parent moved to scroll the entire tower at once.</summary>
        private Transform _towerRoot;

        /// <summary>World Y of the trigger collider center, cached in Awake.</summary>
        private float _triggerCenterWorldY;

        /// <summary>True when the player entered from below (going up).</summary>
        private bool _enteredFromBelow;

        /// <summary>
        /// towerRoot.localPosition.y threshold signalling stock exhaustion.
        /// Negative when going up, positive when going down.
        /// </summary>
        private float _limitLocalY;

        /// <summary>Current scroll speed (signed). Positive means the tower moves down.</summary>
        private float _scrollSpeed;
        private float _scrollSpeedVelocity;

        private readonly Dictionary<int, GameObject> _segmentsBySlot = new();

        // ─── Properties ──────────────────────────────────────────────────────

        private float EffectiveSegmentHeight => _segmentHeight + _segmentHeightOffset;
        private float MaxTowerDisplacement   => _maxIterations * EffectiveSegmentHeight;

        // ─── Lifecycle ───────────────────────────────────────────────────────

        private void Awake()
        {
            AutoDetectBoundsFromColumn();
            CacheTriggerCenterY();
        }

        private void Update()
        {
            EnsurePlayerCached();

            switch (_currentState)
            {
                case StairState.Active:
                    UpdateScrollSpeed();
                    ApplyScrollToTower();
                    CheckLimitReached();
                    break;

                case StairState.Stopping:
                    DecelerateAndFinish();
                    break;
            }
        }

        // ─── Trigger Events ───────────────────────────────────────────────────

        /// <summary>
        /// Called by <see cref="StaircaseTriggerZone"/> when the player enters the collider.
        /// Detects entry direction, builds the tower, and starts the effect.
        /// </summary>
        public void OnPlayerEnteredTrigger()
        {
            if (_currentState != StairState.Idle && _currentState != StairState.Done) return;

            EnsurePlayerCached();
            if (_playerTransform == null) return;

            _enteredFromBelow    = _playerTransform.position.y < _triggerCenterWorldY;
            _scrollSpeed         = 0f;
            _scrollSpeedVelocity = 0f;

            BuildTower();
            _currentState = StairState.Active;
        }

        /// <summary>Called by <see cref="StaircaseTriggerZone"/> when the player exits. No action needed — the limit check drives the stop.</summary>
        public void OnPlayerExitedTrigger() { }

        // ─── Tower Construction ───────────────────────────────────────────────

        /// <summary>
        /// Spawns the full tower under a single _towerRoot Transform.
        /// UP:   slots 0..+N above ground. Limit = -N*h (descend to exhaust stock).
        /// DOWN: slots 0..-N below ground. Limit = +N*h (ascend to exhaust stock).
        /// </summary>
        private void BuildTower()
        {
            DestroyTower();

            _towerRoot = new GameObject("_TowerRoot").transform;
            _towerRoot.SetParent(transform, false);
            _towerRoot.localPosition = Vector3.zero;
            _towerRoot.localRotation = Quaternion.identity;
            _towerRoot.localScale    = Vector3.one;

            if (_enteredFromBelow)
            {
                for (int i = 0; i <= _maxIterations; i++)
                    SpawnSegmentAtSlot(i);
                _limitLocalY = -MaxTowerDisplacement;
            }
            else
            {
                for (int i = 0; i >= -_maxIterations; i--)
                    SpawnSegmentAtSlot(i);
                _limitLocalY = MaxTowerDisplacement;
            }
        }

        private void DestroyTower()
        {
            if (_towerRoot != null)
            {
                Destroy(_towerRoot.gameObject);
                _towerRoot = null;
            }
            _segmentsBySlot.Clear();
        }

        private void SpawnSegmentAtSlot(int slotIndex)
        {
            if (_segmentsBySlot.ContainsKey(slotIndex)) return;

            float localY = slotIndex * EffectiveSegmentHeight;
            GameObject segment;

            // Slot 0: try to reuse the existing scene child to avoid a visible pop.
            if (slotIndex == 0 && _useExistingChildAsBase)
            {
                Transform existing = FindExistingStairChild();
                if (existing != null)
                {
                    segment = existing.gameObject;
                    segment.transform.SetParent(_towerRoot, false);
                    segment.transform.localPosition = new Vector3(0f, localY, 0f);
                    segment.transform.localRotation = Quaternion.identity;
                    ApplyRotationOffsetFromCenter(segment);
                    _segmentsBySlot[slotIndex] = segment;
                    return;
                }
            }

            if (_stairPrefab == null) return;

            segment = Instantiate(_stairPrefab, _towerRoot);
            segment.transform.localPosition = new Vector3(0f, localY, 0f);
            segment.transform.localRotation = Quaternion.identity;
            ApplyRotationOffsetFromCenter(segment);
            _segmentsBySlot[slotIndex] = segment;
        }

        // ─── Scroll ───────────────────────────────────────────────────────────

        /// <summary>
        /// Proportional controller: error = player.y - triggerCenter.y.
        /// Positive error (player above center) → tower moves down → positive speed.
        /// Zero error (player at center) → speed converges to zero → tower stops.
        /// Speed is clamped so it can only push the tower in the intended direction,
        /// preventing the initial negative error from making the tower snap upward.
        /// </summary>
        private void UpdateScrollSpeed()
        {
            if (_playerTransform == null) return;

            float error     = _playerTransform.position.y - _triggerCenterWorldY;
            float rawTarget = Mathf.Clamp(error * _correctionGain, -_maxScrollSpeed, _maxScrollSpeed);

            bool towerHasMoved = _enteredFromBelow
                ? _towerRoot != null && _towerRoot.localPosition.y < -0.05f
                : _towerRoot != null && _towerRoot.localPosition.y >  0.05f;

            float targetSpeed = towerHasMoved
                ? rawTarget
                : (_enteredFromBelow ? Mathf.Max(rawTarget, 0f) : Mathf.Min(rawTarget, 0f));

            _scrollSpeed = Mathf.SmoothDamp(_scrollSpeed, targetSpeed, ref _scrollSpeedVelocity, _scrollSmoothTime);
        }

        private void ApplyScrollToTower()
        {
            if (_towerRoot == null) return;

            Vector3 pos = _towerRoot.localPosition;
            pos.y -= _scrollSpeed * Time.deltaTime;

            // Clamp to the stock limit — never overshoot the last segment.
            pos.y = _enteredFromBelow
                ? Mathf.Max(pos.y, _limitLocalY)
                : Mathf.Min(pos.y, _limitLocalY);

            _towerRoot.localPosition = pos;
        }

        private void CheckLimitReached()
        {
            if (_towerRoot == null) return;

            bool reached = _enteredFromBelow
                ? _towerRoot.localPosition.y <= _limitLocalY   // going up, tower descended enough
                : _towerRoot.localPosition.y >= _limitLocalY;  // going down, tower ascended enough

            if (reached)
                _currentState = StairState.Stopping;           
        }

        /// <summary>
        /// Smoothly brings the tower to rest before triggering cleanup.
        /// </summary>
        private void DecelerateAndFinish()
        {
            _scrollSpeed = Mathf.SmoothDamp(_scrollSpeed, 0f, ref _scrollSpeedVelocity, _scrollSmoothTime);
            ApplyScrollToTower();

            if (Mathf.Abs(_scrollSpeed) < 0.02f)
                FinishAndCleanup();
        }

        // ─── Cleanup ─────────────────────────────────────────────────────────

        /// <summary>
        /// Extracts the segment now at ground level, destroys the rest, and resets state.
        /// </summary>
        private void FinishAndCleanup()
        {
            _currentState = StairState.Done;
            if (_towerRoot == null) return;

            int keepSlot = _enteredFromBelow ? _maxIterations : -_maxIterations;
            _segmentsBySlot.TryGetValue(keepSlot, out GameObject keepSegment);

            if (keepSegment != null)
            {
                keepSegment.transform.SetParent(transform, true);
                keepSegment.transform.position = transform.position;
            }

            DestroyTower();

            if (keepSegment != null)
                _segmentsBySlot[0] = keepSegment;

            _scrollSpeed         = 0f;
            _scrollSpeedVelocity = 0f;
            _playerTransform     = null;

        }

        // ─── Helpers ─────────────────────────────────────────────────────────

        private void AutoDetectBoundsFromColumn()
        {
            if (_centralColumnRenderer == null) return;
            _segmentHeight = _centralColumnRenderer.bounds.size.y;
        }

        private void CacheTriggerCenterY()
        {
            StaircaseTriggerZone zone = GetComponentInChildren<StaircaseTriggerZone>();
            if (zone == null)
            {
                Debug.LogWarning("[InfiniteStaircase] No StaircaseTriggerZone found in children.", this);
                return;
            }

            Collider col = zone.GetComponent<Collider>();
            if (col != null)
                _triggerCenterWorldY = col.bounds.center.y;
            
        }

        private void EnsurePlayerCached()
        {
            if (_playerTransform != null) return;
            if (PlayerController.Instance != null)
                _playerTransform = PlayerController.Instance.transform;
        }

        /// <summary>
        /// Returns the first direct child of InfinityStair (excluding _towerRoot) that has renderers.
        /// </summary>
        private Transform FindExistingStairChild()
        {
            foreach (Transform child in transform)
            {
                if (child == _towerRoot) continue;
                if (child.GetComponentInChildren<MeshRenderer>() != null)
                    return child;
            }
            return null;
        }

        private void ApplyRotationOffsetFromCenter(GameObject segment)
        {
            if (Mathf.Approximately(_segmentRotationOffsetY, 0f)) return;
            segment.transform.RotateAround(ComputeWorldBoundsCenter(segment), Vector3.up, _segmentRotationOffsetY);
        }

        private Vector3 ComputeWorldBoundsCenter(GameObject segment)
        {
            Renderer[] renderers = segment.GetComponentsInChildren<Renderer>();
            if (renderers.Length == 0)
                return segment.transform.position + Vector3.up * (EffectiveSegmentHeight * 0.5f);

            Bounds combined = renderers[0].bounds;
            for (int i = 1; i < renderers.Length; i++)
                combined.Encapsulate(renderers[i].bounds);

            return combined.center;
        }

        // ─── Gizmos ──────────────────────────────────────────────────────────

        private void OnDrawGizmosSelected()
        {
            if (!_drawGizmos) return;

            float h = EffectiveSegmentHeight;
            Vector3 o = transform.position;

            Gizmos.color = new Color(0f, 1f, 0.5f, 0.35f);
            for (int i = 1; i <= _maxIterations; i++)
                Gizmos.DrawWireCube(new Vector3(o.x, o.y + i * h + h * 0.5f, o.z), new Vector3(1.8f, h * 0.95f, 1.8f));

            Gizmos.color = new Color(1f, 0.6f, 0f, 0.25f);
            for (int i = 1; i <= _maxIterations; i++)
                Gizmos.DrawWireCube(new Vector3(o.x, o.y - i * h + h * 0.5f, o.z), new Vector3(1.8f, h * 0.95f, 1.8f));

            Gizmos.color = Color.cyan;
            Gizmos.DrawLine(new Vector3(o.x - 2f, _triggerCenterWorldY, o.z), new Vector3(o.x + 2f, _triggerCenterWorldY, o.z));
        }
    }
}