using System.Collections.ObjectModel;
using System.Windows.Input;
using Avalonia.Media.Imaging;
using Avalonia.Threading;
using Microsoft.VisualBasic.FileIO;

namespace CVRManager.ViewModels;

public class GalleryItemVM : ObservableObject
{
    Bitmap? thumb;

    public GalleryItemVM(GalleryViewModel owner, string path)
    {
        Path = path;
        Name = System.IO.Path.GetFileName(path);
        DateText = File.GetLastWriteTime(path).ToString("yyyy-MM-dd  HH:mm");
        CopyCommand = new RelayCommand(() => owner.CopyAsync(this));
        DeleteCommand = new RelayCommand(() => owner.DeleteAsync(this));
        OpenCommand = new RelayCommand(() => owner.Open(this));
        ShowCommand = new RelayCommand(() => owner.Show(this));
    }

    public string Path { get; }
    public string Name { get; }
    public string DateText { get; }
    public Bitmap? Thumb { get => thumb; set => Set(ref thumb, value); }
    public ICommand CopyCommand { get; }
    public ICommand DeleteCommand { get; }
    public ICommand OpenCommand { get; }
    public ICommand ShowCommand { get; }
}

public class GalleryViewModel : ObservableObject
{
    const int PageSize = 48;
    readonly MainViewModel main;
    List<string> all = new();
    int shown;
    string status = "";
    bool loading;

    public GalleryViewModel(MainViewModel main)
    {
        this.main = main;
        RefreshCommand = new RelayCommand(RefreshAsync);
        MoreCommand = new RelayCommand(LoadMore);
        OpenFolderCommand = new RelayCommand(() =>
        {
            Directory.CreateDirectory(Root);
            System.Diagnostics.Process.Start(new System.Diagnostics.ProcessStartInfo("explorer.exe", $"\"{Root}\"") { UseShellExecute = true });
        });
    }

    public static string Root => System.IO.Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.MyPictures), "ChilloutVR");

    public ObservableCollection<GalleryItemVM> Items { get; } = new();
    public ICommand RefreshCommand { get; }
    public ICommand MoreCommand { get; }
    public ICommand OpenFolderCommand { get; }
    public string Status { get => status; private set => Set(ref status, value); }
    public bool HasMore => shown < all.Count;
    public bool IsEmpty => !loading && all.Count == 0;
    public string FolderText => Root;

    public async Task RefreshAsync()
    {
        loading = true;
        Status = "Looking for screenshots...";
        var found = await Task.Run(() =>
        {
            if (!Directory.Exists(Root)) return new List<string>();
            return Directory.EnumerateFiles(Root, "*.png", System.IO.SearchOption.AllDirectories)
                .Select(f => (f, t: File.GetLastWriteTimeUtc(f)))
                .OrderByDescending(x => x.t)
                .Select(x => x.f)
                .ToList();
        });
        loading = false;
        all = found;
        shown = 0;
        Items.Clear();
        LoadMore();
        Raise(nameof(IsEmpty));
    }

    void LoadMore()
    {
        var batch = all.Skip(shown).Take(PageSize).ToList();
        shown += batch.Count;
        foreach (var path in batch)
        {
            var item = new GalleryItemVM(this, path);
            Items.Add(item);
            _ = LoadThumbAsync(item);
        }
        Status = all.Count == 0 ? "No screenshots yet." : $"Showing {shown} of {all.Count} screenshots";
        Raise(nameof(HasMore));
    }

    static readonly SemaphoreSlim DecodeGate = new(3);

    static async Task LoadThumbAsync(GalleryItemVM item)
    {
        await DecodeGate.WaitAsync();
        try
        {
            var bmp = await Task.Run(() =>
            {
                try
                {
                    using var fs = File.OpenRead(item.Path);
                    return Bitmap.DecodeToWidth(fs, 360);
                }
                catch { return null; }
            });
            if (bmp != null) Dispatcher.UIThread.Post(() => item.Thumb = bmp);
        }
        finally { DecodeGate.Release(); }
    }

    public async Task CopyAsync(GalleryItemVM item)
    {
        if (main.CopyImage == null) return;
        try
        {
            await main.CopyImage(item.Path);
            main.ReportStatus($"Copied {item.Name} to the clipboard.");
        }
        catch (Exception e) { main.ReportStatus($"Could not copy the image: {e.Message}"); }
    }

    public async Task DeleteAsync(GalleryItemVM item)
    {
        if (main.Confirm != null && !await main.Confirm($"Delete {item.Name}?\nIt is moved to the Recycle Bin.")) return;
        try
        {
            await Task.Run(() => FileSystem.DeleteFile(item.Path, UIOption.OnlyErrorDialogs, RecycleOption.SendToRecycleBin));
            Items.Remove(item);
            all.Remove(item.Path);
            shown = Math.Max(0, shown - 1);
            Status = $"Showing {shown} of {all.Count} screenshots";
            Raise(nameof(HasMore));
            Raise(nameof(IsEmpty));
        }
        catch (Exception e) { main.ReportStatus($"Could not delete the image: {e.Message}"); }
    }

    public void Open(GalleryItemVM item) =>
        System.Diagnostics.Process.Start(new System.Diagnostics.ProcessStartInfo(item.Path) { UseShellExecute = true });

    public void Show(GalleryItemVM item) =>
        System.Diagnostics.Process.Start(new System.Diagnostics.ProcessStartInfo("explorer.exe", $"/select,\"{item.Path}\"") { UseShellExecute = true });
}