docs(20-01): complete OGG Vorbis tag writer implementation plan

- SUMMARY.md with implementation details and decisions - STATE.md updated with position, metrics, and key decisions - ROADMAP.md updated with Phase 20 progress (1/2 plans) - REQUIREMENTS.md: OGG-01 through OGG-05 marked complete
2026-03-19 13:55:39 -04:00
parent 5e98c03634
commit d289390396
4 changed files with 137 additions and 26 deletions
@@ -0,0 +1,107 @@
+---
+phase: 20-ogg-vorbis-tag-writer
+plan: 01
+subsystem: tagwriter
+tags: [ogg, vorbis, crc32, metadata, cover-art, vorbis-comment, metadata-block-picture]
+
+# Dependency graph
+requires:
+  - phase: 19-wav-tag-writer
+    provides: AtomicWrite pattern, TagChanges interface, pipeline dispatch pattern
+provides:
+  - OGG Vorbis tag writing (text fields + cover art)
+  - Custom OGG page parser/writer with MSB-first CRC32
+  - Vorbis Comment packet parse/serialize with raw byte preservation
+  - METADATA_BLOCK_PICTURE base64 encoding for OGG cover art
+  - FormatOGG constant and pipeline integration
+affects: [21-ogg-vorbis-tag-writer-tests, metadata, tagwriter]
+
+# Tech tracking
+tech-stack:
+  added: []
+  patterns: [OGG page parser/writer, MSB-first CRC32 lookup table, Vorbis Comment raw byte preservation, base64 METADATA_BLOCK_PICTURE encoding]
+
+key-files:
+  created:
+    - backend/tagwriter/ogg.go
+    - backend/tagwriter/ogg_vorbis.go
+  modified:
+    - backend/tagwriter/tagwriter.go
+    - backend/tagwriter/pipeline.go
+
+key-decisions:
+  - "Custom OGG CRC32 with precomputed 256-entry lookup table (Go's hash/crc32 uses incompatible reflected bit ordering)"
+  - "Raw byte preservation for non-edited Vorbis Comment entries to avoid corrupting non-UTF-8 tags"
+  - "Combined comment+setup header pages per Vorbis spec with 255-segment-per-page splitting"
+
+patterns-established:
+  - "OGG page parser: lenient-read (warn on CRC mismatch) / strict-write (always correct CRC)"
+  - "Vorbis Comment raw byte entries: [][]byte instead of []string for non-UTF-8 safety"
+  - "METADATA_BLOCK_PICTURE + legacy COVERART/COVERARTMIME stripping on all cover art operations"
+
+requirements-completed: [OGG-01, OGG-02, OGG-03, OGG-04, OGG-05]
+
+# Metrics
+duration: 3min
+completed: 2026-03-19
+---
+
+# Phase 20 Plan 01: OGG Vorbis Tag Writer Implementation Summary
+
+**Custom OGG page parser/writer with MSB-first CRC32, Vorbis Comment packet serializer with METADATA_BLOCK_PICTURE cover art, and pipeline integration for .ogg files**
+
+## Performance
+
+- **Duration:** 3 min
+- **Started:** 2026-03-19T17:50:03Z
+- **Completed:** 2026-03-19T17:53:47Z
+- **Tasks:** 1
+- **Files modified:** 4
+
+## Accomplishments
+- Custom OGG page parser with lenient CRC and strict validation (single-stream Vorbis only)
+- MSB-first CRC32 lookup table matching libogg reference implementation
+- Vorbis Comment parse/serialize with raw byte preservation for non-edited fields
+- METADATA_BLOCK_PICTURE base64 cover art encoding with legacy field stripping
+- Full pipeline integration: FormatOGG constant, .ogg detection, writeOggTags dispatch
+
+## Task Commits
+
+Each task was committed atomically:
+
+1. **Task 1: Create OGG page parser/writer with CRC32 and writeOggTags entry point** - `5e98c03` (feat)
+
+## Files Created/Modified
+- `backend/tagwriter/ogg.go` - OGG page parser/writer, CRC32 lookup table, writeOggTags entry point, packet extraction/splitting, page building
+- `backend/tagwriter/ogg_vorbis.go` - Vorbis Comment packet parse/serialize, field manipulation, METADATA_BLOCK_PICTURE encoding, text/cover art change application
+- `backend/tagwriter/tagwriter.go` - Added FormatOGG constant and .ogg case in DetectFormat
+- `backend/tagwriter/pipeline.go` - Added case FormatOGG dispatch to writeOggTags
+
+## Decisions Made
+- Used custom MSB-first CRC32 implementation (Go's hash/crc32 uses reflected bit ordering — incompatible with OGG spec)
+- Raw byte entries ([][]byte) for Vorbis Comment fields instead of strings — preserves non-UTF-8 tags from other tools
+- Comment and setup header packets share pages per Vorbis spec; page splitting at 255-segment boundaries handles large cover art
+- Page sequence numbers renumbered from 0 after header page count changes
+
+## Deviations from Plan
+
+None - plan executed exactly as written.
+
+## Issues Encountered
+None
+
+## User Setup Required
+None - no external service configuration required.
+
+## Next Phase Readiness
+- OGG tag writer implementation complete, ready for round-trip tests (Plan 02)
+- All existing MP3/FLAC/WAV tests pass (no regressions verified)
+- `go build` and `go vet` pass clean
+
+## Self-Check: PASSED
+
+All files verified on disk, all commits found in git log.
+
+---
+*Phase: 20-ogg-vorbis-tag-writer*
+*Completed: 2026-03-19*