using System.Text;

namespace EmbyToolbox.Services;

public sealed class ChapterBuilderService
{
    public string BuildFfmetadata(IReadOnlyList<string> chapterTitles, IReadOnlyList<double> durationsSeconds)
    {
        if (chapterTitles.Count != durationsSeconds.Count)
        {
            throw new ArgumentException("Количество глав не совпадает с количеством длительностей.");
        }

        var sb = new StringBuilder();
        sb.AppendLine(";FFMETADATA1");
        long currentStartMs = 0;
        for (var i = 0; i < chapterTitles.Count; i++)
        {
            var durationMs = Math.Max(1L, (long)Math.Round(Math.Max(0.001, durationsSeconds[i]) * 1000.0, MidpointRounding.AwayFromZero));
            var endMs = currentStartMs + durationMs - 1;
            var title = string.IsNullOrWhiteSpace(chapterTitles[i]) ? $"Часть {i + 1}" : chapterTitles[i].Trim();
            sb.AppendLine("[CHAPTER]");
            sb.AppendLine("TIMEBASE=1/1000");
            sb.AppendLine($"START={currentStartMs}");
            sb.AppendLine($"END={endMs}");
            sb.AppendLine($"title={EscapeMetadataValue(title)}");
            currentStartMs += durationMs;
        }

        return sb.ToString();
    }

    private static string EscapeMetadataValue(string value) =>
        value
            .Replace("\\", "\\\\", StringComparison.Ordinal)
            .Replace("=", "\\=", StringComparison.Ordinal)
            .Replace(";", "\\;", StringComparison.Ordinal)
            .Replace("#", "\\#", StringComparison.Ordinal)
            .Replace(Environment.NewLine, " ", StringComparison.Ordinal)
            .Replace("\n", " ", StringComparison.Ordinal)
            .Replace("\r", " ", StringComparison.Ordinal);
}