using System;
using System.Text;

namespace Paca.Core;

/// <summary>
/// Configuration for tiled thumbnail sprite sheet generation.
/// </summary>
public sealed record SpriteSheetConfig(
    int Columns,
    int Rows,
    int ThumbWidth,
    int ThumbHeight,
    int IntervalSec)
{
    public int TotalTilesPerSheet => Columns * Rows;
    public int SheetWidth => Columns * ThumbWidth;
    public int SheetHeight => Rows * ThumbHeight;
}

/// <summary>
/// Generates ffmpeg tile filter pipelines and WebVTT sprite coordinate mappings for scrubbing preview.
/// </summary>
public static class VideoSpriteSheetGenerator
{
    /// <summary>
    /// Builds ffmpeg CLI command line for rendering tiled thumbnail sprite sheet JPEG.
    /// </summary>
    public static string BuildFfmpegSpriteCommandLine(
        string inputVideoPath,
        string outputJpgPath,
        SpriteSheetConfig config)
    {
        if (string.IsNullOrWhiteSpace(inputVideoPath)) throw new ArgumentException("Input video path cannot be null or whitespace.", nameof(inputVideoPath));
        if (string.IsNullOrWhiteSpace(outputJpgPath)) throw new ArgumentException("Output JPG path cannot be null or whitespace.", nameof(outputJpgPath));

        var cleanIn = inputVideoPath.Trim().Replace("\"", "");
        var cleanOut = outputJpgPath.Trim().Replace("\"", "");

        if (string.Equals(System.IO.Path.GetFullPath(cleanIn), System.IO.Path.GetFullPath(cleanOut), StringComparison.OrdinalIgnoreCase))
            throw new InvalidOperationException("입력 파일과 출력 파일 경로가 동일할 수 없습니다.");

        if (config.IntervalSec <= 0) throw new ArgumentOutOfRangeException(nameof(config.IntervalSec), "Interval must be positive.");
        if (config.Columns <= 0 || config.Rows <= 0) throw new ArgumentOutOfRangeException(nameof(config), "Columns and Rows must be positive.");

        return $"-i \"{cleanIn}\" -vf \"fps=1/{config.IntervalSec},scale={config.ThumbWidth}:{config.ThumbHeight},tile={config.Columns}x{config.Rows}\" -frames:v 1 \"{cleanOut}\" -y";
    }

    /// <summary>
    /// Generates standard WebVTT subtitle/scrubber specification with #xywh coordinates.
    /// </summary>
    public static string GenerateVttMapping(
        string spriteFileName,
        double totalDurationSec,
        SpriteSheetConfig config)
    {
        if (config.IntervalSec <= 0) throw new ArgumentOutOfRangeException(nameof(config.IntervalSec), "Interval must be positive.");
        if (config.Columns <= 0 || config.Rows <= 0) throw new ArgumentOutOfRangeException(nameof(config), "Columns and Rows must be positive.");

        var sb = new StringBuilder();
        sb.AppendLine("WEBVTT");
        sb.AppendLine();

        var tileIndex = 0;
        for (double start = 0; start < totalDurationSec; start += config.IntervalSec)
        {
            var end = Math.Min(start + config.IntervalSec, totalDurationSec);
            var startTimeStr = FormatVttTime(start);
            var endTimeStr = FormatVttTime(end);

            var col = tileIndex % config.Columns;
            var row = (tileIndex / config.Columns) % config.Rows;
            var x = col * config.ThumbWidth;
            var y = row * config.ThumbHeight;

            sb.AppendLine($"{startTimeStr} --> {endTimeStr}");
            sb.AppendLine($"{spriteFileName}#xywh={x},{y},{config.ThumbWidth},{config.ThumbHeight}");
            sb.AppendLine();

            tileIndex++;
        }

        return sb.ToString();
    }

    private static string FormatVttTime(double seconds)
    {
        var ts = TimeSpan.FromSeconds(seconds);
        return $"{(int)ts.TotalHours:D2}:{ts.Minutes:D2}:{ts.Seconds:D2}.{ts.Milliseconds:D3}";
    }
}