using FluidExplorer.Services.Icons;
using FluidExplorer.Services.Operations;
using Microsoft.UI.Xaml.Media;

namespace FluidExplorer.Services;

/// <summary>
/// 降级占位实现：当真实现（外壳图标服务 / 文件操作引擎）在构造阶段抛异常时兜底，
/// 保证主界面还能打开浏览（图标为空、操作给出明确失败提示），而不是整个程序起不来。
/// </summary>
internal sealed class PlaceholderIconService : IIconService
{
    public Task<ImageSource?> GetIconAsync(string path, bool isDirectory, int size, CancellationToken cancellationToken)
        => Task.FromResult<ImageSource?>(null);

    public Task<ImageSource?> GetThumbnailAsync(string path, int size, CancellationToken cancellationToken)
        => Task.FromResult<ImageSource?>(null);

    public Task<ImageSource?> GetExtensionIconAsync(string extension, int size, CancellationToken cancellationToken)
        => Task.FromResult<ImageSource?>(null);

    public ImageSource? GetSpecialFolderIcon(string parsingName, int size) => null;

    public void ClearCache() { }
}

internal sealed class PlaceholderOperationService : IFileOperationService
{
    private readonly List<FileOperationJob> _jobs = [];

    public IReadOnlyList<FileOperationJob> Jobs => _jobs;
    public event EventHandler? JobsChanged;

    // 占位实现永远不会产生撤销记录，事件显式忽略订阅以避免空事件告警
    public event EventHandler? UndoStackChanged
    {
        add { }
        remove { }
    }

    public Func<ConflictInfo, Task<ConflictResolution>>? ConflictResolver { get; set; }
    public bool CanUndo => false;
    public string? UndoDescription => null;

    private FileOperationJob Fail(FileOperationKind kind, IReadOnlyList<string> sources, string destination)
    {
        var job = new FileOperationJob
        {
            Kind = kind,
            Title = "文件操作服务不可用",
            Sources = sources,
            Destination = destination,
            State = JobState.Failed,
            Error = "文件操作引擎尚未接入。"
        };
        _jobs.Add(job);
        JobsChanged?.Invoke(this, EventArgs.Empty);
        return job;
    }

    public FileOperationJob EnqueueCopy(IReadOnlyList<string> sources, string destination, ConflictPolicy policy = ConflictPolicy.Ask)
        => Fail(FileOperationKind.Copy, sources, destination);

    public FileOperationJob EnqueueMove(IReadOnlyList<string> sources, string destination, ConflictPolicy policy = ConflictPolicy.Ask)
        => Fail(FileOperationKind.Move, sources, destination);

    public FileOperationJob EnqueueDelete(IReadOnlyList<string> paths, bool permanent = false)
        => Fail(FileOperationKind.Delete, paths, string.Empty);

    public FileOperationJob EnqueueRename(string path, string newName) => Fail(FileOperationKind.Rename, [path], newName);

    public FileOperationJob EnqueueNewFolder(string parentDirectory, string name) => Fail(FileOperationKind.NewFolder, [parentDirectory], name);

    public void Pause(Guid jobId) { }
    public void Resume(Guid jobId) { }
    public void Cancel(Guid jobId) { }
    public void ClearFinished() { }
    public Task<OperationResult> UndoAsync(CancellationToken cancellationToken = default)
        => Task.FromResult(new OperationResult(false, 0, 0, 0, "没有可撤销的操作。"));

    public Task<(long Bytes, int Items)> MeasureAsync(IReadOnlyList<string> paths, CancellationToken cancellationToken)
        => Task.FromResult((0L, 0));
}