using System;
using System.Collections.Generic;
using System.Globalization;
using System.Text.RegularExpressions;

namespace Paca.Core;

/// <summary>
/// Detected interval of silence in an audio/video stream.
/// </summary>
public sealed record SilenceSpan(double StartSec, double DurationSec, double EndSec);

/// <summary>
/// Effective playback and export window skipping unwanted intro and outro sections.
/// </summary>
public sealed record TrimWindow(double StartSec, double EndSec, double DurationSec);

/// <summary>
/// Intelligent video trimmer parsing silencedetect logs and producing lossless cuts for intros/outros.
/// </summary>
public static class VideoIntroOutroTrimmer
{
    private static readonly Regex SilenceStartRegex = new(@"silence_start:\s*([0-9.]+)", RegexOptions.Compiled);
    private static readonly Regex SilenceEndRegex = new(@"silence_end:\s*([0-9.]+)\s*\|\s*silence_duration:\s*([0-9.]+)", RegexOptions.Compiled);

    /// <summary>
    /// Parses ffmpeg silencedetect stderr output lines into structured silence spans.
    /// </summary>
    public static List<SilenceSpan> ParseSilenceSpans(string ffmpegOutput)
    {
        var spans = new List<SilenceSpan>();
        if (string.IsNullOrWhiteSpace(ffmpegOutput))
            return spans;

        var startMatches = SilenceStartRegex.Matches(ffmpegOutput);
        var endMatches = SilenceEndRegex.Matches(ffmpegOutput);

        var count = Math.Min(startMatches.Count, endMatches.Count);
        for (var i = 0; i < count; i++)
        {
            if (double.TryParse(startMatches[i].Groups[1].Value, NumberStyles.Float, CultureInfo.InvariantCulture, out var start) &&
                double.TryParse(endMatches[i].Groups[1].Value, NumberStyles.Float, CultureInfo.InvariantCulture, out var end) &&
                double.TryParse(endMatches[i].Groups[2].Value, NumberStyles.Float, CultureInfo.InvariantCulture, out var dur))
            {
                spans.Add(new SilenceSpan(start, dur, end));
            }
        }

        return spans;
    }

    /// <summary>
    /// Calculates safe playback trim window, guaranteeing at least 1 second duration.
    /// </summary>
    public static TrimWindow CalculateTrimWindow(double totalDurationSec, double skipIntroSec, double skipOutroSec)
    {
        if (totalDurationSec <= 0)
            return new TrimWindow(0, 1.0, 1.0);

        var start = Math.Max(0, skipIntroSec);
        var end = Math.Max(0, totalDurationSec - skipOutroSec);

        if (start >= end || (end - start) < 1.0)
        {
            start = 0;
            end = Math.Max(1.0, totalDurationSec);
        }

        var duration = end - start;
        return new TrimWindow(start, end, duration);
    }

    /// <summary>
    /// Builds ffmpeg CLI argument string for ultra-fast lossless video trimming.
    /// </summary>
    public static string BuildLosslessTrimCommandLine(
        string inputPath,
        string outputPath,
        double startSec,
        double durationSec)
    {
        if (string.IsNullOrWhiteSpace(inputPath)) throw new ArgumentException("Input path cannot be null or whitespace.", nameof(inputPath));
        if (string.IsNullOrWhiteSpace(outputPath)) throw new ArgumentException("Output path cannot be null or whitespace.", nameof(outputPath));

        var cleanIn = inputPath.Trim().Replace("\"", "");
        var cleanOut = outputPath.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.");

        startSec = Math.Max(0.0, startSec);
        durationSec = Math.Max(0.1, durationSec);

        var s = startSec.ToString("F2", CultureInfo.InvariantCulture);
        var d = durationSec.ToString("F2", CultureInfo.InvariantCulture);

        return $"-ss {s} -i \"{cleanIn}\" -t {d} -c copy \"{cleanOut}\" -y";
    }
}