using System.Drawing.Drawing2D;

namespace WinFormsApp3
{
    /// <summary>
    /// 本页视频下载列表：每个候选视频用 ffmpeg 抽 3 张间隔 5 秒的截图拼成预览条，
    /// 肉眼对比哪个是当前视频后勾选，选文件夹批量下载。
    /// 当前正在播放的那条默认勾上。
    /// </summary>
    public partial class VideoListForm : Form
    {
        private const int RowHeight = 124;
        private const int PreviewWidth = 496;
        private const int PreviewHeight = 100;

        private readonly Func<VideoCandidate, CancellationToken, Task<(Image? Image, string? Error)>> _previewFactory;
        private readonly List<VideoRow> _rows = new();
        private readonly CancellationTokenSource _loadCts = new();
        private int _generatedCount;
        private int _failedCount;

        /// <summary>点“下载选中”后带回的勾选候选（按列表顺序）。</summary>
        public List<VideoCandidate> SelectedCandidates { get; } = new();

        public VideoListForm(IReadOnlyList<VideoCandidate> candidates, IReadOnlyCollection<string> currentUrls,
            Func<VideoCandidate, CancellationToken, Task<(Image? Image, string? Error)>> previewFactory)
        {
            InitializeComponent();

            _previewFactory = previewFactory;
            BuildRows(candidates, currentUrls);
        }

        private void BuildRows(IReadOnlyList<VideoCandidate> candidates, IReadOnlyCollection<string> currentUrls)
        {
            int y = 8;
            foreach (VideoCandidate candidate in candidates)
            {
                bool isCurrent = currentUrls.Contains(candidate.Url);
                VideoRow row = new VideoRow(candidate, Describe(candidate, isCurrent), isCurrent)
                {
                    Location = new Point(8, y),
                    Width = Math.Max(620, pnlVideos.ClientSize.Width - 24),
                };
                row.CheckChanged += (_, _) => UpdateSelectionCount();
                _rows.Add(row);
                pnlVideos.Controls.Add(row);
                y += RowHeight + 6;
            }

            pnlVideos.Resize += (_, _) =>
            {
                foreach (VideoRow row in _rows)
                {
                    row.Width = Math.Max(620, pnlVideos.ClientSize.Width - 24);
                }
            };

            UpdateSelectionCount();
        }

        /// <summary>
        /// 截图预览在后台生成（三条并发），生成一条刷新一条；
        /// 失败时把原因直接写在预览条上，不让界面一直停在“生成中…”。
        /// </summary>
        protected override async void OnShown(EventArgs e)
        {
            base.OnShown(e);

            if (_rows.Count == 0)
            {
                lblHint.Text = "本页没有可下载的视频";
                return;
            }

            SemaphoreSlim semaphore = new SemaphoreSlim(3);
            Task[] tasks = _rows.Select(async row =>
            {
                await semaphore.WaitAsync(_loadCts.Token);
                try
                {
                    Image? preview = null;
                    string? error = null;
                    try
                    {
                        (preview, error) = await _previewFactory(row.Candidate, _loadCts.Token);
                    }
                    catch (OperationCanceledException)
                    {
                        PreviewLog.Write("预览任务被取消（列表已关闭）");
                        return;
                    }
                    catch (Exception ex)
                    {
                        // 抽帧失败按“无预览”处理，勾选与下载不受影响
                        error = ex.Message;
                    }

                    PreviewLog.Write($"预览回传 UI img={(preview != null ? "ok" : "null")} error={(error ?? "-")}");

                    if (_loadCts.IsCancellationRequested || !IsHandleCreated || IsDisposed)
                    {
                        preview?.Dispose();
                        return;
                    }

                    BeginInvoke(() =>
                    {
                        row.SetResult(preview, error);
                        if (preview == null) _failedCount++;
                        _generatedCount++;
                        // 最后一行刷新时直接切到完成文案，不依赖 WhenAll 后续代码的时序
                        lblHint.Text = _generatedCount < _rows.Count
                            ? $"截图生成中… {_generatedCount}/{_rows.Count}" +
                              (_failedCount > 0 ? $"（{_failedCount} 条失败，原因见预览条）" : string.Empty)
                            : (_failedCount == 0
                                ? "截图已生成，对比后勾选要下载的视频"
                                : $"截图生成完毕（{_failedCount} 条失败，原因见预览条；不影响勾选下载）");
                    });
                }
                finally
                {
                    semaphore.Release();
                }
            }).ToArray();

            await Task.WhenAll(tasks);

            if (!IsDisposed && !_loadCts.IsCancellationRequested)
            {
                lblHint.Text = _failedCount == 0
                    ? "截图已生成，对比后勾选要下载的视频"
                    : $"截图生成完毕（{_failedCount} 条失败，原因见预览条；不影响勾选下载）";
            }
        }

        protected override void OnFormClosed(FormClosedEventArgs e)
        {
            _loadCts.Cancel();
            _loadCts.Dispose();
            base.OnFormClosed(e);
        }

        private void UpdateSelectionCount()
        {
            btnDownload.Text = $"下载选中 ({_rows.Count(r => r.IsChecked)})";
        }

        private void btnDownload_Click(object sender, EventArgs e)
        {
            SelectedCandidates.Clear();
            SelectedCandidates.AddRange(_rows.Where(r => r.IsChecked).Select(r => r.Candidate));

            if (SelectedCandidates.Count == 0)
            {
                MessageBox.Show(this, "先勾选要下载的视频（看截图对比哪个是当前视频）。",
                    "下载列表", MessageBoxButtons.OK, MessageBoxIcon.Information);
                return;
            }

            DialogResult = DialogResult.OK;
        }

        private static string Describe(VideoCandidate candidate, bool isCurrent)
        {
            List<string> tags = new List<string>();
            if (isCurrent) tags.Add("当前播放");
            if (candidate.PlaylistText != null) tags.Add("内存播放列表");
            else if (VideoDownloader.IsHlsUrl(candidate.Url)) tags.Add("m3u8");
            if (!string.IsNullOrEmpty(candidate.AudioUrl)) tags.Add("音频轨已配对·自动合并");
            if (tags.Count == 0) tags.Add("直链");

            string hostLine;
            try
            {
                Uri u = new Uri(candidate.Url);
                string last = Path.GetFileName(u.AbsolutePath);
                hostLine = last.Length > 0 ? $"{u.Host} … {last}" : u.Host;
            }
            catch
            {
                hostLine = candidate.Url.Length > 90 ? candidate.Url[..90] + "…" : candidate.Url;
            }

            return $"【{string.Join("】【", tags)}】\n{hostLine}";
        }

        /// <summary>
        /// 把抽到的 JPEG 帧横向拼成一条预览图（约 3×160 宽），供列表行显示。
        /// </summary>
        public static Image? ComposeFrames(List<byte[]> frames)
        {
            if (frames == null || frames.Count == 0) return null;

            List<Image> source = new List<Image>();
            foreach (byte[] frame in frames)
            {
                try
                {
                    Image img = Image.FromStream(new MemoryStream(frame));
                    source.Add(img);
                }
                catch
                {
                    // 坏帧直接跳过
                }
            }
            if (source.Count == 0) return null;

            const int cellW = 160;
            const int gap = 8;
            int cellH = PreviewHeight - 4;

            var sizes = source.Select(img =>
            {
                int w = cellW;
                int h = Math.Max(1, (int)Math.Round((double)cellW * img.Height / img.Width));
                if (h > cellH)
                {
                    h = cellH;
                    w = Math.Max(1, (int)Math.Round((double)cellH * img.Width / img.Height));
                }
                return (w, h);
            }).ToList();

            int canvasW = source.Count * cellW + (source.Count - 1) * gap;
            int canvasH = sizes.Max(s => s.h);
            Bitmap strip = new Bitmap(canvasW, canvasH);

            using (Graphics g = Graphics.FromImage(strip))
            {
                g.Clear(Color.Black);
                g.InterpolationMode = InterpolationMode.HighQualityBicubic;
                for (int i = 0; i < source.Count; i++)
                {
                    int x = i * (cellW + gap) + (cellW - sizes[i].w) / 2;
                    int y = (canvasH - sizes[i].h) / 2;
                    g.DrawImage(source[i], new Rectangle(x, y, sizes[i].w, sizes[i].h));
                }
            }

            foreach (Image img in source) img.Dispose();
            return strip;
        }

        /// <summary>
        /// 一行候选：勾选框 + 截图预览条 + 说明文字。
        /// </summary>
        private sealed class VideoRow : UserControl
        {
            private readonly CheckBox _check = new();
            private readonly PictureBox _preview = new();
            private readonly ToolTip _tip = new();

            public VideoCandidate Candidate { get; }
            public bool IsChecked => _check.Checked;
            public event EventHandler? CheckChanged;

            public VideoRow(VideoCandidate candidate, string description, bool isChecked)
            {
                Candidate = candidate;
                Height = RowHeight;
                Margin = new Padding(0);

                TableLayoutPanel layout = new TableLayoutPanel
                {
                    Dock = DockStyle.Fill,
                    ColumnCount = 3,
                    RowCount = 1,
                };
                layout.ColumnStyles.Add(new ColumnStyle(SizeType.Absolute, 30F));
                layout.ColumnStyles.Add(new ColumnStyle(SizeType.Absolute, PreviewWidth + 8F));
                layout.ColumnStyles.Add(new ColumnStyle(SizeType.Percent, 100F));

                _check.Dock = DockStyle.None;
                _check.Anchor = AnchorStyles.Top;
                _check.Location = new Point(4, 6);
                _check.Checked = isChecked;
                _check.CheckedChanged += (_, _) => CheckChanged?.Invoke(this, EventArgs.Empty);

                _preview.Size = new Size(PreviewWidth, PreviewHeight);
                _preview.SizeMode = PictureBoxSizeMode.Zoom;
                _preview.BackColor = Color.FromArgb(28, 28, 28);
                _preview.Image = Placeholder();

                Label text = new Label
                {
                    Dock = DockStyle.Fill,
                    Padding = new Padding(8, 4, 4, 2),
                    Text = description,
                    TextAlign = ContentAlignment.TopLeft,
                };

                layout.Controls.Add(_check, 0, 0);
                layout.Controls.Add(_preview, 1, 0);
                layout.Controls.Add(text, 2, 0);
                Controls.Add(layout);
            }

            public void SetResult(Image? image, string? error)
            {
                _preview.Image?.Dispose();
                if (image != null)
                {
                    _preview.Image = image;
                    _tip.SetToolTip(_preview, string.Empty);
                }
                else
                {
                    // 把失败原因直接画在预览条上，一眼能看出是超时还是防盗链
                    string reason = string.IsNullOrWhiteSpace(error) ? "截图不可用" : error!;
                    _preview.Image = Placeholder(reason);
                    _tip.SetToolTip(_preview, reason);
                }
            }

            /// <summary>截图还没生成好（或生成失败）时行内显示的占位条。</summary>
            private static Image Placeholder(string? message = null)
            {
                Bitmap bmp = new Bitmap(PreviewWidth, PreviewHeight);
                using Graphics g = Graphics.FromImage(bmp);
                g.Clear(Color.FromArgb(28, 28, 28));
                using (var cellBrush = new SolidBrush(Color.FromArgb(56, 56, 56)))
                {
                    for (int i = 0; i < 3; i++)
                    {
                        g.FillRectangle(cellBrush, i * 168, 0, 160, PreviewHeight);
                    }
                }
                using Font font = new Font("Microsoft YaHei UI", 8F);
                string text = message ?? "截图生成中…";
                Color color = message == null ? Color.Gray : Color.FromArgb(230, 140, 90);
                // 失败原因可能较长，在预览条区域内自动换行
                var rect = new RectangleF(4, 4, PreviewWidth - 8, PreviewHeight - 8);
                using var format = new StringFormat { Trimming = StringTrimming.EllipsisCharacter, FormatFlags = StringFormatFlags.LineLimit };
                g.DrawString(text, font, new SolidBrush(color), rect, format);
                return bmp;
            }
        }
    }
}