Epub Book Pipeline

EPUB Book Pipeline

Provides the EPUB-specific mechanical operations for extracting, chunking, rebuilding, and validating EPUB files. It handles the structural EPUB work so you can focus on whatever content transformation you need to apply in between.

Pipeline Overview

origin.epub → [Step 1: Extract] → source.md + toc_original.yaml + terminology_candidates.md
              → [Step 2: Chunk] → chunk-*.md files (for parallel processing)
              → [** your content modifications here **]
              → [Step 3: Rebuild] → modified.epub
              → [Step 4: Validate]

Execution Rule

Run the requested pipeline step directly without pre-checking dependencies, environment variables, or configuration. If something is wrong, the scripts will fail with clear errors — check and fix only then.

Requirements

pip install ebooklib beautifulsoup4 lxml

Scripts at {baseDir}/scripts/.

Step 1: Extract EPUB → Structured Markdown

python {baseDir}/scripts/extract_epub.py --epub <input.epub> --output-dir <output_dir>

What it does:

• Parses EPUB structure (OPF, NCX, CSS, spine)
• Extracts text-bearing XHTML into a single merged markdown file
• Adds structural markers: <!-- FILE: ... -->, <!-- CHAPTER-HEADING-IMAGE: ... -->, <!-- IMAGE: ... -->
• Extracts NCX navLabel entries into toc_original.yaml (for later TOC rebuilding)
• Scans katakana sequences into terminology_candidates.md (proper noun candidates for review)

Output:

Critical: <!-- FILE: ... --> markers map each section to its original XHTML file. Never remove or modify them — the rebuild step relies on them to place modified content back into the correct XHTML files.

Step 2: Chunk source.md for Parallel Processing

When an EPUB is large, chunking lets you process sections independently (e.g., in parallel subagents, or one section at a time):

python {baseDir}/scripts/chunk_source.py \
  --source <output_dir>/source.md \
  --output-dir <output_dir>/chunks/ \
  --max-chars 12000

--max-chars controls target chars per chunk (default 6000). All internal thresholds (flush threshold, merge floor, merge cap) scale proportionally.

Chunking rules:

• <!-- FILE: ... --> markers are atomic — never split across chunks
• Oversize FILE sections split at blank-line-separated paragraph boundaries (never mid-paragraph)
• --- scene separators are standalone paragraph blocks
• If a chunk would end with an h1 heading, the h1 is moved to the next chunk
• Small trailing fragments (< max_chars/3) merge back into the previous chunk
• Tiny FILE sections (image-only pages, short sections) accumulate into adjacent chunks rather than creating standalone tiny blocks

Output: chunk-NN.md files + chunk_index.json mapping chunk numbers to <!-- FILE: ... --> ranges.

After you've modified the chunk content, concatenate them back into a single markdown file (in order) for the rebuild step:

cat chunks/chunk-*.md > ../modified.md

Or if processing sequentially, you can edit source.md directly and skip Step 2 entirely.

Step 3: Rebuild EPUB

After modifying the markdown content, rebuild it into a valid EPUB:

python {baseDir}/scripts/rebuild_epub.py \
  --epub <origin.epub> \
  --translation <modified.md> \
  --output <final.epub> \
  [--toc <toc_original.yaml>]

Arguments:

• --epub: Original EPUB file (used as structural template)
• --translation: Modified markdown with content changes
• --output: Output EPUB path
• --toc: YAML file for TOC label customization (auto-detects next to --translation if omitted)
• --from-lang / --to-lang: Source/target language codes (defaults: ja → zh-CN); only needed if the script's built-in language-specific transformations (ruby removal, writing mode, typography CSS) apply to your use case

What it does:

• Copies original EPUB as base, replaces text per <!-- FILE: ... --> mapped sections
• Rebuilds NCX/EPUB3 TOC from toc_original.yaml (if provided)
• Preserves all non-text assets (images, fonts, stylesheets) from the original
• Handles both EPUB2 and EPUB3 formats
• Handles SVG-wrapper pages (cover, color plates) — preserved as-is

TOC customization: Create a YAML file (based on toc_original.yaml) to customize TOC labels when rebuilding:

book_title: The Original Title
toc:
  - play_order: 1
    label: "Custom Chapter Title"
    src: "Text/p-006.xhtml#toc-001"

Fields not specified fall back to the original EPUB's values.

Step 4: Validate

Verify the rebuilt EPUB is structurally sound:

python {baseDir}/scripts/validate_epub.py \
  --epub <final.epub> \
  --source-md <output_dir>/source.md \
  --translation-md <output_dir>/modified.md

Checks: ZIP structure, OPF metadata integrity, all text-bearing XHTML files present and well-formed, image integrity, TOC consistency across NCX and nav.xhtml, structural marker alignment between source and modified content.

Output format:

• Each XHTML file is scanned individually; issues reported as [WARN] per file
• Summary line: XHTML files checked: N (OK: M, no Chinese: ..., ruby: ..., lang: ...)
• Overall result: Summary: X/Y checks passed (Z%) — exits 0 unless a critical structural error prevents verification

Optional:

• --sample: XHTML filename to sample for content validation (default: p-007.xhtml)
• --verbose: Show all checks including passing ones

Full Pipeline Example

BASE=book-work

# 1. Extract
python scripts/extract_epub.py --epub book.epub --output-dir $BASE/

# 2. (Optional) Chunk for parallel processing
python scripts/chunk_source.py --source $BASE/source.md --output-dir $BASE/chunks/ --max-chars 12000

# 3. Apply your content modifications to chunk-*.md or source.md
#    (this is where you edit text, replace content, reformat, etc.)

# 4. Rebuild
python scripts/rebuild_epub.py --epub book.epub --translation $BASE/modified.md --output $BASE/final.epub

# 5. Validate
python scripts/validate_epub.py --epub $BASE/final.epub --source-md $BASE/source.md --translation-md $BASE/modified.md

Edge Cases

• SVG-wrapper pages (cover, color plates): Preserved as-is
• Chapter heading images (<h1><img>): Image kept, additional text can be inserted via the markdown
• Scene breaks: ○/● → --- in markdown, restored during rebuild — --- alignment must match original one-to-one; mismatches shift subsequent paragraphs
• Empty paragraphs (<p><br/>): Preserved structurally
• EPUB2 vs EPUB3: Both handled (NCX and nav.xhtml)
• Embedded fonts: Preserved automatically
• Right-to-left / vertical writing mode CSS: Removed during rebuild (controlled by --from-lang/--to-lang); skipped if the generated CSS doesn't apply to your direction

Scripts Reference