using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Runtime.CompilerServices;

namespace VideoDownloader.App.Browser.Features;

/// <summary>CoreWebView2DownloadOperation 의 최소 추상화(단위 테스트 fake 교체 가능).</summary>
public interface IDownloadOperation
{
    string Uri { get; }
    string FileName { get; }
    long BytesReceived { get; }
    long TotalBytesToReceive { get; }
    /// <summary>InProgress / Interrupted / Completed / Cancelled</summary>
    string State { get; }
    void Pause();
    void Resume();
    void Cancel();
    /// <summary>BytesReceived/State 변경 통지(구현은 호스트 스레드에서 발화).</summary>
    event Action? Changed;
}

/// <summary>다운로드 매니저 UI 항목(T1-5) — 진행률/속도/상태를 INPC 로 노출.</summary>
public sealed class PageDownloadItem : INotifyPropertyChanged
{
    public IDownloadOperation Op { get; }
    public string FileName { get; }
    public string Uri { get; }
    public long TotalBytes { get; }
    private long _received;
    private long _bps;
    private string _state;

    public PageDownloadItem(IDownloadOperation op, string fileName)
    {
        Op = op;
        FileName = fileName;
        Uri = op.Uri;
        TotalBytes = op.TotalBytesToReceive;
        _received = op.BytesReceived;
        _state = op.State;
        op.Changed += () =>
        {
            _received = op.BytesReceived;
            _state = op.State;
            OnPropertyChangedAll();
        };
    }

    public double Percent => TotalBytes > 0 ? Math.Clamp(_received * 100.0 / TotalBytes, 0, 100) : 0;
    public long BytesPerSecond => _bps;
    public string State => _state;
    public bool IsFinished => _state is "Completed" or "Interrupted" or "Cancelled";
    public bool CanControl => _state == "InProgress";

    public string SpeedText => _bps switch
    {
        <= 0 => "—",
        < 1024 => $"{(double)_bps:F1} B/s",
        < 1024 * 1024 => $"{_bps / 1024.0:F1} KB/s",
        _ => $"{_bps / 1024.0 / 1024.0:F1} MB/s",
    };

    private long? _lastSpeedReceived;

    /// <summary>속도 갱신: (현재까지 수신 바이트, 직전 호출로부터 경과).</summary>
    public void UpdateSpeed(long receivedNow, TimeSpan elapsed)
    {
        _received = receivedNow;
        if (elapsed.TotalSeconds > 0)
        {
            var delta = Math.Max(0, receivedNow - (_lastSpeedReceived ?? 0));
            _bps = (long)(delta / elapsed.TotalSeconds);
        }
        _lastSpeedReceived = receivedNow;
        OnPropertyChangedAll();
    }

    public event PropertyChangedEventHandler? PropertyChanged;
    private void OnPropertyChangedAll()
    {
        foreach (var n in new[] { nameof(Percent), nameof(BytesPerSecond), nameof(SpeedText), nameof(State), nameof(IsFinished), nameof(CanControl) })
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(n));
    }
}

/// <summary>페이지 다운로드 목록(T1-5) — 최신순, 일시정지/재개/취소, 완료 정리.</summary>
public sealed class PageDownloadTracker
{
    public ObservableCollection<PageDownloadItem> Items { get; } = new();

    public PageDownloadItem Add(IDownloadOperation op, string fileName)
    {
        var item = new PageDownloadItem(op, fileName);
        Items.Insert(0, item);
        return item;
    }

    public void Pause(PageDownloadItem item) => item.Op.Pause();
    public void Resume(PageDownloadItem item) => item.Op.Resume();
    public void Cancel(PageDownloadItem item) => item.Op.Cancel();

    public void ClearCompleted()
    {
        foreach (var done in Items.Where(i => i.IsFinished).ToList())
            Items.Remove(done);
    }
}