jedarden 46c515e255 feat(pdftract-3uq): add font type classifier and subset prefix stripper

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>

2026-05-23 13:42:57 -04:00

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pdftract-3uq: Font subtype classifier and BaseFont prefix stripper

Summary

Implemented the font type classification module (crates/pdftract-core/src/font/mod.rs) with:

FontKind enum - Represents all PDF font types:
- Type1 - Non-Standard-14 Type 1 fonts
- Type1Std14 - Standard 14 fonts (Times-Roman, Helvetica, Courier, Symbol, ZapfDingbats)
- TrueType - TrueType fonts
- Type0 - Composite fonts with descendant CIDFonts
- CIDFontType0 - CFF-based CID fonts
- CIDFontType2 - TrueType-based CID fonts
- Type3 - Bitmap/content-stream defined fonts
- OpenTypeCFF - OpenType fonts with CFF data
strip_subset_prefix(name: &str) -> &str - Removes 6-uppercase-letter subset prefix
- Exactly validates 6 ASCII uppercase letters + +
- Returns unchanged for invalid patterns (too short, lowercase, no prefix)
classify_font(font_dict: &PdfDict) -> FontKind - Classifies fonts by:
- Reading /Subtype to get base font type
- Checking Standard 14 font names (with or without subset prefix)
- For Type0 fonts, reading descendant CIDFont's /Subtype
- Checking /FontDescriptor for /FontFile3 with /Subtype /OpenType to distinguish OpenTypeCFF

Acceptance Criteria Status

Criterion	Status	Notes
Unit tests for all 8 FontKind branches	PASS	21 font-specific tests cover all branches
`strip_subset_prefix("ABCDEF+Times-Roman") == "Times-Roman"`	PASS	Tested in `test_strip_subset_prefix_valid`
`strip_subset_prefix("ABCD+Foo") == "ABCD+Foo"`	PASS	Tested in `test_strip_subset_prefix_too_short`
`strip_subset_prefix("abcdef+Foo") == "abcdef+Foo"`	PASS	Tested in `test_strip_subset_prefix_lowercase`
Std-14 detection ignores subset prefix	PASS	Tested in `test_is_standard_14_font` and `test_classify_font_type1_standard_with_subset`

Implementation Details

FontKind enum methods

is_standard_14() - Returns true for Type1Std14
is_cid_font() - Returns true for Type0, CIDFontType0, CIDFontType2
is_type3() - Returns true for Type3 fonts

Standard 14 fonts

The hardcoded list includes all 14 canonical names:

Times family: Times-Roman, Times-Bold, Times-Italic, Times-BoldItalic
Helvetica family: Helvetica, Helvetica-Bold, Helvetica-Oblique, Helvetica-BoldOblique
Courier family: Courier, Courier-Bold, Courier-Oblique, Courier-BoldOblique
Symbol, ZapfDingbats

Edge cases handled

/Subtype with or without leading slash
Missing /Subtype (defaults to Type1)
Empty or missing /DescendantFonts array for Type0 fonts
Indirect references to FontDescriptor or DescendantFonts (skipped, returns default)

Files Modified

crates/pdftract-core/src/lib.rs - Added pub mod font;
crates/pdftract-core/src/font/mod.rs - New module with FontKind enum and classifier functions

Testing

All 27 font-related tests pass:

21 tests in font::tests
6 tests in other modules that reference font types

Test coverage includes:

Subset prefix stripping (valid, invalid, edge cases)
Standard 14 font detection (with and without prefix)
All 8 FontKind variants
Type0 with CIDFont descendants
OpenTypeCFF detection via FontDescriptor

Commit

git commit to follow with conventional commit message citing this bead.

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