Libation/Source/AaxDecrypter/AaxcDownloadMultiConverter.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using AAXClean;
using AAXClean.Codecs;
using Dinah.Core;
using Dinah.Core.StepRunner;
using FileManager;

namespace AaxDecrypter
{
	public class AaxcDownloadMultiConverter : AaxcDownloadConvertBase
	{
		protected override StepSequence Steps { get; }
		private static TimeSpan minChapterLength { get; } = TimeSpan.FromSeconds(3);
		private List<string> multiPartFilePaths { get; } = new List<string>();

		public AaxcDownloadMultiConverter(string outFileName, string cacheDirectory, IDownloadOptions dlOptions)
			: base(outFileName, cacheDirectory, dlOptions)
		{
			Steps = new StepSequence
			{
				Name = "Download and Convert Aaxc To " + DownloadOptions.OutputFormat,

				["Step 1: Get Aaxc Metadata"] = Step_GetMetadata,
				["Step 2: Download Decrypted Audiobook"] = Step_DownloadAudiobookAsMultipleFilesPerChapter,
				["Step 3: Cleanup"] = Step_Cleanup,
			};
		}

		/*
https://github.com/rmcrackan/Libation/pull/127#issuecomment-939088489

If the chapter truly is empty, that is, 0 audio frames in length, then yes it is ignored.
If the chapter is shorter than 3 seconds long but still has some audio frames, those frames are combined with the following chapter and not split into a new file.

I also implemented file naming by chapter title. When 2 or more consecutive chapters are combined, the first of the combined chapter's title is used in the file name. For example, given an audiobook with the following chapters:

00:00:00 - 00:00:02 | Part 1
00:00:02 - 00:35:00 | Chapter 1
00:35:02 - 01:02:00 | Chapter 2
01:02:00 - 01:02:02 | Part 2
01:02:02 - 01:41:00 | Chapter 3
01:41:00 - 02:05:00 | Chapter 4

The book will be split into the following files:

00:00:00 - 00:35:00 | Book - 01 - Part 1.m4b
00:35:00 - 01:02:00 | Book - 02 - Chapter 2.m4b
01:02:00 - 01:41:00 | Book - 03 - Part 2.m4b
01:41:00 - 02:05:00 | Book - 04 - Chapter 4.m4b

That naming may not be desirable for everyone, but it's an easy change to instead use the last of the combined chapter's title in the file name.
		 */
		private bool Step_DownloadAudiobookAsMultipleFilesPerChapter()
		{
			var zeroProgress = Step_DownloadAudiobook_Start();

			var chapters = DownloadOptions.ChapterInfo.Chapters;

			// Ensure split files are at least minChapterLength in duration.
			var splitChapters = new ChapterInfo(DownloadOptions.ChapterInfo.StartOffset);

			var runningTotal = TimeSpan.Zero;
			string title = "";

			for (int i = 0; i < chapters.Count; i++)
			{
				if (runningTotal == TimeSpan.Zero)
					title = chapters[i].Title;

				runningTotal += chapters[i].Duration;

				if (runningTotal >= minChapterLength)
				{
					splitChapters.AddChapter(title, runningTotal);
					runningTotal = TimeSpan.Zero;
				}
			}

			// reset, just in case
			multiPartFilePaths.Clear();

			ConversionResult result;

			AaxFile.ConversionProgressUpdate += AaxFile_ConversionProgressUpdate;
			if (DownloadOptions.OutputFormat == OutputFormat.M4b)
				result = ConvertToMultiMp4a(splitChapters);
			else
				result = ConvertToMultiMp3(splitChapters);
			AaxFile.ConversionProgressUpdate -= AaxFile_ConversionProgressUpdate;

			Step_DownloadAudiobook_End(zeroProgress);

			return result == ConversionResult.NoErrorsDetected;
		}

		private ConversionResult ConvertToMultiMp4a(ChapterInfo splitChapters)
		{
			var chapterCount = 0;
			return AaxFile.ConvertToMultiMp4a
				(
					splitChapters,
					newSplitCallback => Callback(++chapterCount, splitChapters, newSplitCallback),
					DownloadOptions.TrimOutputToChapterLength
				);
		}

		private ConversionResult ConvertToMultiMp3(ChapterInfo splitChapters)
		{
			var chapterCount = 0;
			return AaxFile.ConvertToMultiMp3
				(
					splitChapters,
					newSplitCallback => Callback(++chapterCount, splitChapters, newSplitCallback),
					DownloadOptions.LameConfig,
					DownloadOptions.TrimOutputToChapterLength
				);
		}


		private void Callback(int currentChapter, ChapterInfo splitChapters, NewMP3SplitCallback newSplitCallback)
			=> Callback(currentChapter, splitChapters, newSplitCallback);

		private void Callback(int currentChapter, ChapterInfo splitChapters, NewSplitCallback newSplitCallback)
		{
			MultiConvertFileProperties props = new()
			{
				OutputFileName = OutputFileName,
				PartsPosition = currentChapter,
				PartsTotal = splitChapters.Count,
				Title = newSplitCallback?.Chapter?.Title,
			};
			newSplitCallback.OutputFile = createOutputFileStream(props);
			newSplitCallback.TrackTitle = DownloadOptions.GetMultipartTitleName(props);
			newSplitCallback.TrackNumber = currentChapter;
			newSplitCallback.TrackCount = splitChapters.Count;
		}

		private FileStream createOutputFileStream(MultiConvertFileProperties multiConvertFileProperties)
		{
			var fileName = DownloadOptions.GetMultipartFileName(multiConvertFileProperties);
			fileName = FileUtility.GetValidFilename(fileName);

			multiPartFilePaths.Add(fileName);

			FileUtility.SaferDelete(fileName);

			var file = File.Open(fileName, FileMode.OpenOrCreate);
			OnFileCreated(fileName);
			return file;
		}
	}
}