using FluidExplorer.Models;
using FluidExplorer.Services.Icons;
using FluidExplorer.ViewModels;
using Microsoft.UI.Dispatching;

namespace FluidExplorer.Services.ItemVisuals;

/// <summary>
/// 列表里每一行的图标/缩略图按需加载：只为真正可见的行发请求，
/// 内置并发上限与去重，滚动再快也不会把外壳图标接口打爆。
/// </summary>
public sealed class ItemVisualService(IIconService icons, DispatcherQueue ui)
{
    /// <summary>诊断开关：FLUID_DISABLE_ICONS=1 时完全跳过外壳取图（用于隔离图标路径引发的问题）。</summary>
    private static readonly bool IconsDisabled = Environment.GetEnvironmentVariable("FLUID_DISABLE_ICONS") == "1";

    private static readonly HashSet<string> ThumbnailExtensions = new(StringComparer.OrdinalIgnoreCase)
    {
        "jpg", "jpeg", "png", "gif", "bmp", "webp", "tif", "tiff", "heic", "heif", "avif", "ico", "svg",
        "mp4", "mkv", "avi", "mov", "wmv", "m4v", "webm", "mpg", "mpeg", "ts",
        "pdf"
    };

    private readonly SemaphoreSlim _iconGate = new(6, 6);
    private readonly SemaphoreSlim _thumbGate = new(3, 3);
    private readonly HashSet<string> _inFlight = new(StringComparer.OrdinalIgnoreCase);
    private readonly object _sync = new();

    public bool IsThumbnailCandidate(string extension) => ThumbnailExtensions.Contains(extension);

    /// <summary>为一行请求小图标（列表/详情视图）。</summary>
    public void RequestIcon(ExplorerItem item, int size = 32)
    {
        if (IconsDisabled) return;
        var key = "i|" + item.FullPath + "|" + size;
        if (!TryBegin(key)) return;

        _ = Task.Run(async () =>
        {
            try
            {
                var source = await icons.GetIconAsync(item.FullPath, item.IsDirectory, size, CancellationToken.None).ConfigureAwait(false);
                if (source is null && !item.IsDirectory)
                    source = await icons.GetExtensionIconAsync(item.Extension, size, CancellationToken.None).ConfigureAwait(false);
                if (source is null) return;
                ui.TryEnqueue(() => { try { item.Icon = source; } catch (Exception ex) { App.Log($"设置图标失败: {ex.Message}"); } });
            }
            catch
            {
                // 图标失败不影响使用
            }
            finally
            {
                _iconGate.Release();
            }
        });
    }

    /// <summary>为一行请求缩略图（网格视图）；失败则保留图标。</summary>
    public void RequestThumbnail(ExplorerItem item, int size)
    {
        if (IconsDisabled) return;
        if (item.IsDirectory || !IsThumbnailCandidate(item.Extension))
        {
            RequestIcon(item, Math.Min(size, 96));
            return;
        }

        var key = "t|" + item.FullPath + "|" + size;
        if (!TryBeginThumb(key)) return;

        _ = Task.Run(async () =>
        {
            try
            {
                var source = await icons.GetThumbnailAsync(item.FullPath, size, CancellationToken.None).ConfigureAwait(false);
                if (source is null)
                {
                    source = await icons.GetIconAsync(item.FullPath, false, Math.Min(size, 96), CancellationToken.None).ConfigureAwait(false);
                    if (source is null) return;
                    ui.TryEnqueue(() => { try { item.Icon = source; } catch (Exception ex) { App.Log($"设置图标失败: {ex.Message}"); } });
                    return;
                }
                ui.TryEnqueue(() =>
                {
                    try
                    {
                        item.HasThumbnail = true;
                        item.Icon = source;
                    }
                    catch (Exception ex)
                    {
                        App.Log($"设置缩略图失败: {ex.Message}");
                    }
                });
            }
            catch
            {
                // 忽略
            }
            finally
            {
                _thumbGate.Release();
            }
        });
    }

    public void RequestIcon(SearchResultItem item, int size = 32)
    {
        if (IconsDisabled) return;
        var key = "si|" + item.FullPath + "|" + size;
        if (!TryBegin(key)) return;

        _ = Task.Run(async () =>
        {
            try
            {
                var source = await icons.GetIconAsync(item.FullPath, item.IsDirectory, size, CancellationToken.None).ConfigureAwait(false);
                if (source is null && !item.IsDirectory)
                    source = await icons.GetExtensionIconAsync(item.Hit.Extension, size, CancellationToken.None).ConfigureAwait(false);
                if (source is null) return;
                ui.TryEnqueue(() => { try { item.Icon = source; } catch (Exception ex) { App.Log($"设置图标失败: {ex.Message}"); } });
            }
            catch
            {
                // 忽略
            }
            finally
            {
                _iconGate.Release();
            }
        });
    }

    /// <summary>导航离开时清掉去重表（已缓存的位图仍在图标服务里）。</summary>
    public void ResetPending()
    {
        lock (_sync) _inFlight.Clear();
    }

    private bool TryBegin(string key)
    {
        lock (_sync)
        {
            if (!_inFlight.Add(key)) return false;
        }
        if (!_iconGate.Wait(0))
        {
            lock (_sync) _inFlight.Remove(key);
            // 让给其它行，稍后由可见性变化再次触发
            return false;
        }
        return true;
    }

    private bool TryBeginThumb(string key)
    {
        lock (_sync)
        {
            if (!_inFlight.Add(key)) return false;
        }
        if (!_thumbGate.Wait(0))
        {
            lock (_sync) _inFlight.Remove(key);
            return false;
        }
        return true;
    }
}