46c515e255
Implement FontKind enum and classify_font() function for Phase 2.1 font type detection. Includes strip_subset_prefix() for handling font subset names (e.g., ABCDEF+Times-Roman). FontKind variants: - Type1, Type1Std14 (Standard 14) - TrueType, OpenTypeCFF - Type0, CIDFontType0, CIDFontType2 - Type3 Classifier reads /Subtype, /BaseFont, and for Type0 fonts, descendant CIDFont subtype. OpenTypeCFF detected via /FontDescriptor /FontFile3 with /Subtype /OpenType. All 27 font tests pass. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
77 lines
3.3 KiB
Markdown
77 lines
3.3 KiB
Markdown
# pdftract-3uq: Font subtype classifier and BaseFont prefix stripper
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## Summary
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Implemented the font type classification module (`crates/pdftract-core/src/font/mod.rs`) with:
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1. **`FontKind` enum** - Represents all PDF font types:
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- `Type1` - Non-Standard-14 Type 1 fonts
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- `Type1Std14` - Standard 14 fonts (Times-Roman, Helvetica, Courier, Symbol, ZapfDingbats)
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- `TrueType` - TrueType fonts
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- `Type0` - Composite fonts with descendant CIDFonts
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- `CIDFontType0` - CFF-based CID fonts
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- `CIDFontType2` - TrueType-based CID fonts
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- `Type3` - Bitmap/content-stream defined fonts
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- `OpenTypeCFF` - OpenType fonts with CFF data
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2. **`strip_subset_prefix(name: &str) -> &str`** - Removes 6-uppercase-letter subset prefix
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- Exactly validates 6 ASCII uppercase letters + `+`
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- Returns unchanged for invalid patterns (too short, lowercase, no prefix)
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3. **`classify_font(font_dict: &PdfDict) -> FontKind`** - Classifies fonts by:
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- Reading `/Subtype` to get base font type
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- Checking Standard 14 font names (with or without subset prefix)
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- For Type0 fonts, reading descendant CIDFont's `/Subtype`
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- Checking `/FontDescriptor` for `/FontFile3` with `/Subtype /OpenType` to distinguish OpenTypeCFF
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## Acceptance Criteria Status
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| Criterion | Status | Notes |
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|-----------|--------|-------|
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| Unit tests for all 8 FontKind branches | PASS | 21 font-specific tests cover all branches |
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| `strip_subset_prefix("ABCDEF+Times-Roman") == "Times-Roman"` | PASS | Tested in `test_strip_subset_prefix_valid` |
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| `strip_subset_prefix("ABCD+Foo") == "ABCD+Foo"` | PASS | Tested in `test_strip_subset_prefix_too_short` |
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| `strip_subset_prefix("abcdef+Foo") == "abcdef+Foo"` | PASS | Tested in `test_strip_subset_prefix_lowercase` |
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| Std-14 detection ignores subset prefix | PASS | Tested in `test_is_standard_14_font` and `test_classify_font_type1_standard_with_subset` |
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## Implementation Details
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### FontKind enum methods
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- `is_standard_14()` - Returns true for Type1Std14
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- `is_cid_font()` - Returns true for Type0, CIDFontType0, CIDFontType2
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- `is_type3()` - Returns true for Type3 fonts
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### Standard 14 fonts
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The hardcoded list includes all 14 canonical names:
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- Times family: Times-Roman, Times-Bold, Times-Italic, Times-BoldItalic
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- Helvetica family: Helvetica, Helvetica-Bold, Helvetica-Oblique, Helvetica-BoldOblique
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- Courier family: Courier, Courier-Bold, Courier-Oblique, Courier-BoldOblique
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- Symbol, ZapfDingbats
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### Edge cases handled
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- `/Subtype` with or without leading slash
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- Missing `/Subtype` (defaults to Type1)
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- Empty or missing `/DescendantFonts` array for Type0 fonts
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- Indirect references to FontDescriptor or DescendantFonts (skipped, returns default)
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## Files Modified
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- `crates/pdftract-core/src/lib.rs` - Added `pub mod font;`
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- `crates/pdftract-core/src/font/mod.rs` - New module with FontKind enum and classifier functions
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## Testing
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All 27 font-related tests pass:
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- 21 tests in font::tests
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- 6 tests in other modules that reference font types
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Test coverage includes:
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- Subset prefix stripping (valid, invalid, edge cases)
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- Standard 14 font detection (with and without prefix)
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- All 8 FontKind variants
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- Type0 with CIDFont descendants
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- OpenTypeCFF detection via FontDescriptor
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## Commit
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`git commit` to follow with conventional commit message citing this bead.
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