# CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

## Build & Test Commands

```bash
# Build everything
gradle build

# Run all tests
gradle test

# Run tests for a specific module
gradle :parser:test
gradle :layout:test
gradle :renderer-pdf:test
gradle :app:test

# Run a single test class
gradle :parser:test --tests ChordProParserTest

# Run a single test method
gradle :parser:test --tests "ChordProParserTest.parse complete song"

# Build and run CLI
gradle :cli:run --args="build -d /path/to/project"
gradle :cli:run --args="validate -d /path/to/project"

# Launch GUI
gradle :gui:run
```

Requires Java 21 (configured in `gradle.properties`). Kotlin 2.1.10, Gradle 9.3.1.

## Architecture

**Pipeline:** Parse → Measure → Paginate → Render

`SongbookPipeline` (in `app`) orchestrates the full flow:
1. `ConfigParser` reads `songbook.yaml` → `BookConfig`
2. `ChordProParser` reads `.chopro` files → `Song` objects
3. `Validator` checks config and songs
4. `MeasurementEngine` calculates each song's height in mm using `FontMetrics`
5. `TocGenerator` estimates TOC page count and creates entries
6. `PaginationEngine` arranges songs into pages (greedy spread packing)
7. `PdfBookRenderer` generates the PDF via OpenPDF

**Module dependency graph:**
```
model ← parser
model ← layout
model ← renderer-pdf
parser, layout, renderer-pdf ← app
app ← cli (Clikt)
app, parser ← gui (Compose Desktop)
```

`model` is the foundation with no dependencies — all data classes, the `FontMetrics` interface, and the `BookRenderer` interface live here. The `FontMetrics` abstraction decouples layout from rendering: `PdfFontMetrics` is the real implementation (in renderer-pdf), `StubFontMetrics` is used in layout tests.

**Pagination constraint:** Songs spanning 2 pages must start on a left (even) page. The `PaginationEngine` inserts filler images or blank pages to enforce this.

## Key Types

- `Song` → sections → `SongLine` → `LineSegment(chord?, text)` — chord is placed above the text segment
- `PageContent` — sealed class: `SongPage`, `FillerImage`, `BlankPage`
- `SectionType` — enum: `VERSE`, `CHORUS`, `BRIDGE`, `REPEAT`
- `BuildResult` — returned by `SongbookPipeline.build()` with success/errors/counts

## Song Format

ChordPro-compatible `.chopro` files: directives in `{braces}`, chords in `[brackets]` inline with lyrics, comments with `#`. See `songs/` for examples.

## Test Patterns

Tests use `kotlin.test` annotations with Kotest assertions (`shouldBe`, `shouldHaveSize`, etc.) on JUnit 5. Layout tests use `StubFontMetrics` to avoid PDF font dependencies. App integration tests create temp directories with song files and config.

## Package

All code under `de.pfadfinder.songbook.*` — subpackages match module names (`.model`, `.parser`, `.layout`, `.renderer.pdf`, `.app`, `.cli`, `.gui`).