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EpubToSplitTxt

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EpubToSplitTxt

.NET C# License

Epub eBook to Text Conversion and Chapter Splitting System

Convert .epub format eBooks to plain text and intelligently split into separate TXT files by chapter

English | 中文 | Русский | 한국어 | 日本語

✨ Features

  • ✅ Automatically parse Epub file structure and extract plain text
  • ✅ Intelligent chapter title recognition (supports Chinese and English formats)
  • ✅ Split by chapter into separate TXT files with sequence numbers to maintain reading order
  • ✅ Support for special chapters like preface, prologue, etc.
  • ✅ UTF-8 without BOM encoding output for compatibility
  • ✅ Stream processing for large files with low memory usage
  • ✅ Configurable chapter matching rules

🛠️ Tech Stack

Library Version Purpose
.NET 9.0 Runtime Environment
VersOne.Epub 3.3.0 Epub File Parsing
HtmlAgilityPack 1.11.59 HTML Content Cleaning
Microsoft.Extensions.Configuration - Configuration Management

🚀 Quick Start

1. Build Project

dotnet build

2. Prepare Epub Files

Place your .epub eBook files in the RawEpub directory:

EpubToSplitTxt/
├── RawEpub/
│   ├── Novel1.epub
│   └── Novel2.epub

3. Run Program

dotnet run

4. View Results

The program will automatically generate the following directory structure:

EpubToSplitTxt/
├── IntermediateTxt/          # Intermediate files (full text)
│   ├── Novel1_Full.txt
│   └── Novel2_Full.txt
├── SplitOutput/              # Chapter split output
│   ├── Novel1/
│   │   ├── 000_Prologue.txt
│   │   ├── 001_Chapter1_Rebirth.txt
│   │   ├── 002_Chapter2_Training.txt
│   │   └── ...
│   └── Novel2/
│       └── ...

⚙️ Configuration

Configuration file: appsettings.json

{
  "Splitter": {
    "ChapterRegex": "(^第[0-9一二三四五六七八九十百千]+[章节卷].*)|(^Chapter [0-9]+.*)|(^序章.*)|(^楔子.*)|(^引子.*)|(^后记.*)|(^尾声.*)",
    "MinChapterLength": 100
  },
  "Paths": {
    "RawEpubFolder": "./RawEpub",
    "IntermediateTxtFolder": "./IntermediateTxt",
    "SplitOutputFolder": "./SplitOutput"
  }
}

Configuration Options

Option Description Default
Splitter:ChapterRegex Regular expression for chapter title matching Supports Chinese/Arabic numerals, etc.
Splitter:MinChapterLength Minimum chapter character count (warns if below) 100
Paths:RawEpubFolder Raw Epub file directory ./RawEpub
Paths:IntermediateTxtFolder Full text intermediate file directory ./IntermediateTxt
Paths:SplitOutputFolder Chapter split output directory ./SplitOutput

📑 Supported Chapter Formats

Default supported chapter title formats:

  • ✅ Chinese numerals: 第一章, 第二十章, 第一百章
  • ✅ Arabic numerals: 第1章, 第001章
  • ✅ English format: Chapter 1, Chapter 2
  • ✅ Special chapters: 序章, 楔子, 引子, 后记, 尾声

To support other formats, modify the ChapterRegex in appsettings.json.

📊 Processing Flow

[Epub File]
    ↓
[EpubConverter] Parse Epub structure
    ↓
[Clean HTML] Remove tags, convert entities
    ↓
[Full Text] Merge into single TXT file
    ↓
[TextSplitter] Scan lines and match chapters
    ↓
[Chapter Files] Output as separate files with sequence numbers

📝 Log Description

  • [INFO]: Normal processing info (parsing progress, statistics)
  • [WARN]: Warning info (chapter too small, no chapters matched, etc.)
  • [ERROR]: Error info (corrupted file, I/O errors, etc.)

⚡ Performance Optimization

  • ✅ Pre-compiled regular expressions (RegexOptions.Compiled)
  • ✅ Stream reading for large text files (StreamReader)
  • ✅ Avoid loading entire text into memory at once
  • ✅ UTF-8 without BOM encoding to reduce file size

⚠️ Notes

  1. Encoding: All output files use UTF-8 without BOM encoding
  2. Filenames: Automatically clean illegal characters, replace with underscores
  3. Directory Structure: Create separate subfolder for each book to avoid confusion
  4. Regex Timeout: Chapter matching has 1-second timeout to prevent backtracking traps

🏗️ System Architecture

Core Components

  • EpubConverter: Responsible for parsing Epub files and extracting plain text
  • TextSplitter: Responsible for chapter recognition and text splitting
  • AppSettings: Configuration management model

Dependencies

Program.cs
   ├── EpubConverter (VersOne.Epub, HtmlAgilityPack)
   ├── TextSplitter (System.Text.RegularExpressions)
   └── AppSettings (Microsoft.Extensions.Configuration)

🔧 Extension Development

Custom Chapter Matching Rules

Modify the regular expression in appsettings.json:

{
  "Splitter": {
    "ChapterRegex": "Your custom regex pattern"
  }
}

Add New Output Formats

Modify the SplitTextAsync method in TextSplitter.cs to support other formats (e.g., Markdown).

📄 License

This project is for personal learning and research only. Please comply with relevant copyright laws.

🤝 Contributing

Issues and Pull Requests are welcome!

Made with ❤️ using .NET 9 and VersOne.Epub