using System;
using System.Collections.Generic;
using UnityEditor;
using UnityEngine;

namespace Chameleon.Editor.WebAssets
{
    /// <summary>
    /// Reusable catalog browser for importer windows: search field + responsive
    /// thumbnail grid with lazy, throttled thumbnail loading. The host window owns
    /// the catalog data and reacts to cell clicks via the onSelect callback.
    /// </summary>
    public sealed class AssetBrowserGrid
    {
        public sealed class Entry
        {
            public string Key;          // slug / asset id
            public string Name;         // display name (cell label)
            public string ThumbnailUrl;
            public string Search;       // pre-lowered haystack for filtering
        }

        private const int MaxResults = 150;
        private const int MaxThumbInFlight = 6;

        private readonly Action _repaint;

        private List<Entry> _catalog;
        private readonly List<Entry> _filtered = new List<Entry>();
        private string _searchQuery = "";
        private Vector2 _gridScroll;

        private readonly Dictionary<string, Texture2D> _thumbs = new Dictionary<string, Texture2D>();
        private readonly HashSet<string> _thumbRequested = new HashSet<string>();
        private int _thumbsInFlight;

        public AssetBrowserGrid(Action repaint)
        {
            _repaint = repaint;
        }

        public bool HasCatalog => _catalog != null;

        public void SetCatalog(List<Entry> catalog)
        {
            _catalog = catalog;
            ApplyFilter();
        }

        /// <summary>Draws search field, match count and the grid. Call only when HasCatalog.</summary>
        public void Draw(Action<Entry> onSelect, Action reloadCatalog, string itemNoun, float gridHeight = 320f)
        {
            using (new EditorGUILayout.HorizontalScope())
            {
                EditorGUI.BeginChangeCheck();
                _searchQuery = EditorGUILayout.TextField("Search", _searchQuery);
                if (EditorGUI.EndChangeCheck())
                    ApplyFilter();
                if (reloadCatalog != null && GUILayout.Button("↻", GUILayout.Width(26)))
                    reloadCatalog();
            }

            int shown = Mathf.Min(_filtered.Count, MaxResults);
            string cap = _filtered.Count > MaxResults ? $", showing first {MaxResults}" : "";
            EditorGUILayout.LabelField(
                $"{_filtered.Count} match(es){cap} of {_catalog.Count} {itemNoun}.",
                EditorStyles.miniLabel);

            DrawGrid(shown, onSelect, gridHeight);
        }

        private void DrawGrid(int count, Action<Entry> onSelect, float gridHeight)
        {
            const float cell = 104f;
            const float pad = 6f;
            float viewW = EditorGUIUtility.currentViewWidth - 24f;
            int cols = Mathf.Max(1, Mathf.FloorToInt((viewW + pad) / (cell + pad)));

            _gridScroll = EditorGUILayout.BeginScrollView(_gridScroll, GUILayout.Height(gridHeight));

            int rows = Mathf.CeilToInt(count / (float)cols);
            for (int row = 0; row < rows; row++)
            {
                using (new EditorGUILayout.HorizontalScope())
                {
                    for (int c = 0; c < cols; c++)
                    {
                        int i = row * cols + c;
                        if (i >= count)
                        {
                            GUILayout.FlexibleSpace();
                            break;
                        }
                        DrawCell(_filtered[i], cell, onSelect);
                    }
                }
            }

            EditorGUILayout.EndScrollView();
        }

        private void DrawCell(Entry a, float size, Action<Entry> onSelect)
        {
            using (new EditorGUILayout.VerticalScope(GUILayout.Width(size)))
            {
                var thumbRect = GUILayoutUtility.GetRect(size, size - 22f,
                    GUILayout.Width(size), GUILayout.Height(size - 22f));

                var tex = GetThumb(a);
                if (tex)
                    GUI.DrawTexture(thumbRect, tex, ScaleMode.ScaleToFit);
                else
                    EditorGUI.DrawRect(thumbRect, new Color(0f, 0f, 0f, 0.15f));

                // Transparent hit target over the thumbnail.
                if (GUI.Button(thumbRect, new GUIContent("", a.Name), GUIStyle.none))
                    onSelect?.Invoke(a);

                EditorGUILayout.LabelField(new GUIContent(a.Name, a.Name),
                    EditorStyles.miniLabel, GUILayout.Width(size));
            }
        }

        /// <summary>Lazy, throttled thumbnail loader — only visible cells request, capped in-flight.</summary>
        private Texture2D GetThumb(Entry a)
        {
            if (_thumbs.TryGetValue(a.Key, out var tex))
            {
                if (tex)
                    return tex;
                // Cached texture was destroyed (e.g. play-mode cleanup) — purge and re-request.
                _thumbs.Remove(a.Key);
                _thumbRequested.Remove(a.Key);
            }

            // Don't add to _thumbRequested until a slot is free, so it retries next repaint.
            if (!_thumbRequested.Contains(a.Key) && _thumbsInFlight < MaxThumbInFlight)
            {
                _thumbRequested.Add(a.Key);
                _thumbsInFlight++;
                EditorWebRequest.GetTexture(a.ThumbnailUrl,
                    t => { _thumbs[a.Key] = t; _thumbsInFlight--; _repaint?.Invoke(); },
                    _ => { _thumbsInFlight--; _repaint?.Invoke(); }); // no retry-spam on error
            }
            return null;
        }

        private void ApplyFilter()
        {
            _filtered.Clear();
            if (_catalog == null)
                return;

            var q = _searchQuery?.Trim().ToLowerInvariant();
            if (string.IsNullOrEmpty(q))
            {
                _filtered.AddRange(_catalog);
                return;
            }

            var terms = q.Split((char[])null, StringSplitOptions.RemoveEmptyEntries);
            foreach (var a in _catalog)
            {
                bool all = true;
                foreach (var t in terms)
                    if (a.Search.IndexOf(t, StringComparison.Ordinal) < 0) { all = false; break; }
                if (all)
                    _filtered.Add(a);
            }
        }
    }
}