65 lines
2.7 KiB
Markdown
65 lines
2.7 KiB
Markdown
# pdftract-1ofnz: RTL direction detection (unicode-bidi majority bidi class)
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## Summary
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Implemented `detect_line_direction(line_text) -> LineDirection` function in `crates/pdftract-core/src/layout/line.rs`.
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## Implementation Details
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**Location:** `crates/pdftract-core/src/layout/line.rs:458-496`
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**Algorithm:**
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1. Walk each character in the text
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2. Count L (Left-to-Right) vs R/AL (Right-to-Left/Arabic Letter) using `unicode_bidi::bidi_class`
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3. All other bidi classes (EN, ES, ET, AN, CS, NSM, BN, B, S, WS, ON, etc.) are ignored per INV
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4. Return:
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- `LineDirection::Ltr` if LTR count > RTL count OR both counts are zero (empty/neutral-only)
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- `LineDirection::Rtl` if RTL count > LTR count
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- `LineDirection::Mixed` if counts are equal (and both > 0)
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**Key design decision:** Empty strings and neutral-only text (digits, punctuation) default to Ltr per bead acceptance criteria.
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## Acceptance Criteria Status
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| Criterion | Status | Notes |
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|-----------|--------|-------|
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| "Hello, World!" -> Ltr | PASS | Test: `test_detect_line_direction_latin_text` |
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| "مرحبا بالعالم" -> Rtl | PASS | Test: `test_detect_line_direction_arabic_text` |
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| Mixed Latin+Arabic: Mixed or dominant | PASS | Tests: `test_detect_line_direction_mixed_latin_arabic`, `test_detect_line_direction_latin_more_than_arabic`, `test_detect_line_direction_arabic_more_than_latin` |
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| "123 456" digits only: Ltr default | PASS | Test: `test_detect_line_direction_digits_only` |
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| "" -> Ltr | PASS | Test: `test_detect_line_direction_empty_string` |
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## Additional Test Coverage
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- `test_detect_line_direction_punctuation_only`: Punctuation-only text -> Ltr
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- `test_detect_line_direction_latin_dominant`: Latin with punctuation/digits -> Ltr
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- `test_detect_line_direction_arabic_dominant`: Arabic with digits -> Rtl
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- `test_detect_line_direction_hebrew_text`: Hebrew text -> Rtl
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- `test_detect_line_direction_cyrillic_text`: Cyrillic text -> Ltr
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## Tests Executed
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```bash
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cargo nextest run --package pdftract-core --lib 'layout::line::tests::test_detect_line_direction'
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```
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**Result:** 12/12 tests passed (all RTL direction detection tests)
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**Module tests:** 44/44 tests passed (entire line module)
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## Code Changes
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**Files modified:**
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1. `crates/pdftract-core/src/layout/line.rs`: Added `detect_line_direction` function with comprehensive documentation and tests
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2. `crates/pdftract-core/src/layout/header_footer.rs`: Fixed pre-existing compilation error (removed nonexistent `reading_order_rank` field from test helper)
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**Commit:** `4ab89e1` feat(pdftract-1ofnz): implement detect_line_direction with unicode-bidi
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## INV Compliance
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- Numerals are bidi-neutral and do not drive direction
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- Punctuation is neutral
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- Empty lines default to Ltr
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## References
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- Plan section: Phase 4.2 RTL detection (line 1668)
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