using System.Collections.Generic;
using TMPro;
using UnityEngine;
using UnityEngine.InputSystem;
using UnityEngine.UI;

namespace Jovian.PopupSystem.UI {
    /// <summary>
    /// MonoBehaviour reference holder for a popup view. Manages the grow-only element cache,
    /// screen positioning, and visibility. One instance per registered <see cref="PopupCategory"/>.
    /// </summary>
    public class PopupReference : MonoBehaviour {
        [SerializeField] RectTransform content;
        [SerializeField] CanvasGroup canvasGroup;
        [SerializeField] RectTransform background;

        [Header("Element Prefabs")]
        [SerializeField] TMP_Text headerPrefab;
        [SerializeField] TMP_Text textPrefab;
        [SerializeField] RectTransform statPrefab; // horizontal layout with label + value TMP_Text children
        [SerializeField] Image imagePrefab;
        [SerializeField] Image separatorPrefab;

        // Element caches (grow-only)
        readonly List<TMP_Text> headerCache = new();
        readonly List<TMP_Text> textCache = new();
        readonly List<StatEntry> statCache = new();
        readonly List<Image> imageCache = new();
        readonly List<Image> separatorCache = new();

        struct StatEntry {
            public RectTransform root;
            public TMP_Text label;
            public TMP_Text value;
        }

        int headerIndex;
        int textIndex;
        int statIndex;
        int imageIndex;
        int separatorIndex;

        // Positioning state
        PopupPositionMode positionMode;
        RectTransform anchorTarget;
        AnchorSide anchorSide;
        Vector2 followOffset;
        float screenEdgePadding;
        float maxWidth;
        bool isVisible;
        bool layoutDirty;
        Canvas rootCanvas;
        Camera canvasCamera;

        public CanvasGroup CanvasGroup => canvasGroup;
        public RectTransform Content => content;
        public bool IsVisible => isVisible;

        /// <summary>Constrains the popup's horizontal size to the given maximum width in pixels.</summary>
        public void SetMaxWidth(float maxPopupWidth) {
            maxWidth = maxPopupWidth;
            if(maxWidth > 0f) {
                var rt = (RectTransform)transform;
                var size = rt.sizeDelta;
                size.x = Mathf.Min(size.x, maxWidth);
                rt.sizeDelta = size;
            }
        }

        /// <summary>Shows or hides the popup GameObject. Resets alpha to 0 when hiding.</summary>
        public void SetVisible(bool visible) {
            isVisible = visible;
            gameObject.SetActive(visible);
            if(!visible) {
                canvasGroup.alpha = 0f;
            }
        }

        /// <summary>Deactivates all cached content elements and marks layout as dirty.</summary>
        public void ClearContent() {
            DeactivateRange(headerCache, ref headerIndex);
            DeactivateRange(textCache, ref textIndex);
            for(int i = 0; i < statIndex; i++) {
                statCache[i].root.gameObject.SetActive(false);
            }
            statIndex = 0;
            DeactivateRange(imageCache, ref imageIndex);
            DeactivateRange(separatorCache, ref separatorIndex);
            layoutDirty = true;
        }

        private static void DeactivateRange<T>(List<T> cache, ref int index) where T : Component {
            for(int i = 0; i < index; i++) {
                cache[i].gameObject.SetActive(false);
            }
            index = 0;
        }

        // --- Element access (grow-only) ---

        /// <summary>Returns the next available header element from the cache, or creates one.</summary>
        public TMP_Text GetHeader() {
            return GetOrCreate(headerCache, headerPrefab, ref headerIndex);
        }

        /// <summary>Returns the next available text element from the cache, or creates one.</summary>
        public TMP_Text GetText() {
            return GetOrCreate(textCache, textPrefab, ref textIndex);
        }

        /// <summary>Returns the next available stat row (label + value pair) from the cache, or creates one.</summary>
        public (TMP_Text label, TMP_Text value) GetStat() {
            if(statIndex < statCache.Count) {
                var existing = statCache[statIndex];
                existing.root.gameObject.SetActive(true);
                existing.root.SetAsLastSibling();
                statIndex++;
                return (existing.label, existing.value);
            }

            var created = Instantiate(statPrefab, content);
            created.gameObject.SetActive(true);
            created.SetAsLastSibling();
            var children = created.GetComponentsInChildren<TMP_Text>(true);
            var entry = new StatEntry { root = created, label = children[0], value = children[1] };
            statCache.Add(entry);
            statIndex++;
            return (entry.label, entry.value);
        }

        /// <summary>Returns the next available image element from the cache, or creates one.</summary>
        public Image GetImage() {
            return GetOrCreate(imageCache, imagePrefab, ref imageIndex);
        }

        /// <summary>Returns the next available separator element from the cache, or creates one.</summary>
        public Image GetSeparator() {
            return GetOrCreate(separatorCache, separatorPrefab, ref separatorIndex);
        }

        private T GetOrCreate<T>(List<T> cache, T prefab, ref int index) where T : Component {
            if(index < cache.Count) {
                var existing = cache[index];
                existing.gameObject.SetActive(true);
                existing.transform.SetAsLastSibling();
                index++;
                return existing;
            }

            var created = Instantiate(prefab, content);
            created.gameObject.SetActive(true);
            created.transform.SetAsLastSibling();
            cache.Add(created);
            index++;
            return created;
        }

        // --- Positioning ---

        /// <summary>Configures the popup to anchor to a target element on the specified side.</summary>
        public void SetAnchorMode(RectTransform target, AnchorSide side, float edgePadding) {
            positionMode = PopupPositionMode.AnchorToElement;
            anchorTarget = target;
            anchorSide = side;
            screenEdgePadding = edgePadding;
        }

        /// <summary>Configures the popup to follow the mouse cursor with the given offset.</summary>
        public void SetFollowMouseMode(Vector2 offset, float edgePadding) {
            positionMode = PopupPositionMode.FollowMouse;
            followOffset = offset;
            screenEdgePadding = edgePadding;
        }

        /// <summary>Positions the popup at a fixed screen coordinate with edge clamping.</summary>
        public void SetFixedPosition(Vector2 screenPos, float edgePadding) {
            positionMode = PopupPositionMode.AnchorToElement;
            anchorTarget = null;
            screenEdgePadding = edgePadding;
            PositionAtScreenPoint(screenPos);
        }

        /// <summary>Updates the popup position based on the current mode (follow mouse or anchored).</summary>
        public void UpdatePosition() {
            if(positionMode == PopupPositionMode.FollowMouse) {
                PositionAtScreenPoint(Mouse.current.position.ReadValue() + followOffset);
            }
            else if(anchorTarget != null) {
                PositionAnchoredTo(anchorTarget, anchorSide);
            }
        }

        private void CacheCanvas() {
            if(rootCanvas != null) {
                return;
            }
            rootCanvas = GetComponentInParent<Canvas>()?.rootCanvas;
            canvasCamera = rootCanvas != null && rootCanvas.renderMode != RenderMode.ScreenSpaceOverlay
                ? rootCanvas.worldCamera : null;
        }

        private void PositionAnchoredTo(RectTransform target, AnchorSide side) {
            CacheCanvas();
            var targetRect = GetScreenRect(target, canvasCamera);
            var popupRect = GetScreenRect((RectTransform)transform, canvasCamera);
            var popupSize = popupRect.size;

            var pos = side switch {
                AnchorSide.Below => new Vector2(targetRect.center.x - popupSize.x * 0.5f, targetRect.yMin - popupSize.y),
                AnchorSide.Above => new Vector2(targetRect.center.x - popupSize.x * 0.5f, targetRect.yMax),
                AnchorSide.Left => new Vector2(targetRect.xMin - popupSize.x, targetRect.center.y - popupSize.y * 0.5f),
                AnchorSide.Right => new Vector2(targetRect.xMax, targetRect.center.y - popupSize.y * 0.5f),
                _ => targetRect.center
            };

            PositionAtScreenPoint(pos);
        }

        private void PositionAtScreenPoint(Vector2 screenPos) {
            CacheCanvas();
            var rt = (RectTransform)transform;
            if(layoutDirty) {
                LayoutRebuilder.ForceRebuildLayoutImmediate(content);
                layoutDirty = false;
            }
            var popupSize = GetScreenRect(rt, canvasCamera).size;

            // Clamp to screen
            screenPos.x = Mathf.Clamp(screenPos.x, screenEdgePadding, Screen.width - popupSize.x - screenEdgePadding);
            screenPos.y = Mathf.Clamp(screenPos.y, screenEdgePadding, Screen.height - popupSize.y - screenEdgePadding);

            // Convert screen position to parent local space
            var parentRt = rt.parent as RectTransform;
            if(parentRt != null) {
                RectTransformUtility.ScreenPointToLocalPointInRectangle(parentRt, screenPos, canvasCamera, out var localPos);
                rt.localPosition = localPos;
            }
            else {
                rt.position = screenPos;
            }
        }

        private static readonly Vector3[] cornersBuffer = new Vector3[4];

        private static Rect GetScreenRect(RectTransform rt, Camera camera) {
            rt.GetWorldCorners(cornersBuffer);
            // Convert world corners to screen space
            var min = RectTransformUtility.WorldToScreenPoint(camera, cornersBuffer[0]);
            var max = RectTransformUtility.WorldToScreenPoint(camera, cornersBuffer[2]);
            return new Rect(min, max - min);
        }
    }
}