breakpilot-lehrer/klausur-service/backend/cv_syllable_detect.py

"""
Syllable divider insertion for dictionary pages.

For confirmed dictionary pages (is_dictionary=True), processes all content
column cells:
  1. Strips existing | dividers for clean normalization
  2. Merges pipe-gap spaces (where OCR split a word at a divider position)
  3. Applies pyphen syllabification to each word >= 3 alpha chars (DE then EN)
  4. Only modifies words that pyphen recognizes — garbled OCR stays as-is

No CV gate needed — the dictionary detection confidence is sufficient.
pyphen uses Hunspell/TeX hyphenation dictionaries and is very reliable.

Lizenz: Apache 2.0 (kommerziell nutzbar)
DATENSCHUTZ: Alle Verarbeitung erfolgt lokal.
"""

import logging
import re
from typing import Any, Dict, List, Optional, Tuple

import numpy as np

logger = logging.getLogger(__name__)

# IPA/phonetic characters — skip cells containing these
_IPA_RE = re.compile(r'[\[\]ˈˌːʃʒθðŋɑɒæɔəɛɜɪʊʌ]')

# Common German words that should NOT be merged with adjacent tokens.
# These are function words that appear as standalone words between
# headwords/definitions on dictionary pages.
_STOP_WORDS = frozenset([
    # Articles
    'der', 'die', 'das', 'dem', 'den', 'des',
    'ein', 'eine', 'einem', 'einen', 'einer',
    # Pronouns
    'er', 'es', 'sie', 'wir', 'ihr', 'ich', 'man', 'sich',
    # Prepositions
    'mit', 'von', 'zu', 'für', 'auf', 'in', 'an', 'um', 'am', 'im',
    'aus', 'bei', 'nach', 'vor', 'bis', 'durch', 'über', 'unter',
    'zwischen', 'ohne', 'gegen',
    # Conjunctions
    'und', 'oder', 'als', 'wie', 'wenn', 'dass', 'weil', 'aber',
    # Adverbs
    'auch', 'noch', 'nur', 'schon', 'sehr', 'nicht',
    # Verbs
    'ist', 'hat', 'wird', 'kann', 'soll', 'muss', 'darf',
    'sein', 'haben',
    # Other
    'kein', 'keine', 'keinem', 'keinen', 'keiner',
])

# Cached hyphenators
_hyph_de = None
_hyph_en = None


def _get_hyphenators():
    """Lazy-load pyphen hyphenators (cached across calls)."""
    global _hyph_de, _hyph_en
    if _hyph_de is not None:
        return _hyph_de, _hyph_en
    try:
        import pyphen
    except ImportError:
        return None, None
    _hyph_de = pyphen.Pyphen(lang='de_DE')
    _hyph_en = pyphen.Pyphen(lang='en_US')
    return _hyph_de, _hyph_en


def _hyphenate_word(word: str, hyph_de, hyph_en) -> Optional[str]:
    """Try to hyphenate a word using DE then EN dictionary.

    Returns word with | separators, or None if not recognized.
    """
    hyph = hyph_de.inserted(word, hyphen='|')
    if '|' in hyph:
        return hyph
    hyph = hyph_en.inserted(word, hyphen='|')
    if '|' in hyph:
        return hyph
    return None


def _try_merge_pipe_gaps(text: str, hyph_de) -> str:
    """Merge fragments separated by single spaces where OCR split at a pipe.

    Example: "Kaf fee" -> "Kaffee" (pyphen recognizes the merged word).
    Multi-step: "Ka bel jau" -> "Kabel jau" -> "Kabeljau".

    Guards against false merges:
    - The FIRST token must be pure alpha (word start — no attached punctuation)
    - The second token may have trailing punctuation (comma, period) which
      stays attached to the merged word: "Kä" + "fer," -> "Käfer,"
    - Common German function words (der, die, das, ...) are never merged
    - At least one fragment must be very short (<=3 alpha chars)
    """
    parts = text.split(' ')
    if len(parts) < 2:
        return text

    result = [parts[0]]
    i = 1
    while i < len(parts):
        prev = result[-1]
        curr = parts[i]

        # Extract alpha-only core for lookup
        prev_alpha = re.sub(r'[^a-zA-ZäöüÄÖÜßẞ]', '', prev)
        curr_alpha = re.sub(r'[^a-zA-ZäöüÄÖÜßẞ]', '', curr)

        # Guard 1: first token must be pure alpha (word-start fragment)
        #          second token may have trailing punctuation
        # Guard 2: neither alpha core can be a common German function word
        # Guard 3: the shorter fragment must be <= 3 chars (pipe-gap signal)
        # Guard 4: combined length must be >= 4
        should_try = (
            prev == prev_alpha  # first token: pure alpha (word start)
            and prev_alpha and curr_alpha
            and prev_alpha.lower() not in _STOP_WORDS
            and curr_alpha.lower() not in _STOP_WORDS
            and min(len(prev_alpha), len(curr_alpha)) <= 3
            and len(prev_alpha) + len(curr_alpha) >= 4
        )

        if should_try:
            merged_alpha = prev_alpha + curr_alpha
            hyph = hyph_de.inserted(merged_alpha, hyphen='-')
            if '-' in hyph:
                # pyphen recognizes merged word — collapse the space
                result[-1] = prev + curr
                i += 1
                continue

        result.append(curr)
        i += 1

    return ' '.join(result)


def _syllabify_text(text: str, hyph_de, hyph_en) -> str:
    """Syllabify all significant words in a text string.

    1. Strip existing | dividers
    2. Merge pipe-gap spaces where possible
    3. Apply pyphen to each word >= 3 alphabetic chars
    4. Words pyphen doesn't recognize stay as-is (no bad guesses)
    """
    if not text:
        return text

    # Skip cells that contain IPA transcription characters
    if _IPA_RE.search(text):
        return text

    # Phase 1: strip existing pipe dividers for clean normalization
    clean = text.replace('|', '')

    # Phase 2: merge pipe-gap spaces (OCR fragments from pipe splitting)
    clean = _try_merge_pipe_gaps(clean, hyph_de)

    # Phase 3: tokenize and syllabify each word
    # Split on whitespace and comma/semicolon sequences, keeping separators
    tokens = re.split(r'(\s+|[,;:]+\s*)', clean)

    result = []
    for tok in tokens:
        if not tok or re.match(r'^[\s,;:]+$', tok):
            result.append(tok)
            continue

        # Strip trailing/leading punctuation for pyphen lookup
        m = re.match(r'^([^a-zA-ZäöüÄÖÜßẞ]*)(.*?)([^a-zA-ZäöüÄÖÜßẞ]*)$', tok)
        if not m:
            result.append(tok)
            continue
        lead, word, trail = m.group(1), m.group(2), m.group(3)

        if len(word) < 3 or not re.search(r'[a-zA-ZäöüÄÖÜß]', word):
            result.append(tok)
            continue

        hyph = _hyphenate_word(word, hyph_de, hyph_en)
        if hyph:
            result.append(lead + hyph + trail)
        else:
            result.append(tok)

    return ''.join(result)


def insert_syllable_dividers(
    zones_data: List[Dict],
    img_bgr: np.ndarray,
    session_id: str,
) -> int:
    """Insert pipe syllable dividers into dictionary cells.

    For dictionary pages: process all content column cells, strip existing
    pipes, merge pipe-gap spaces, and re-syllabify using pyphen.

    Pre-check: at least 5% of content cells must already contain ``|`` from
    OCR.  This guards against false-positive dictionary detection on pages
    like synonym dictionaries or alphabetical word lists that have no actual
    syllable divider lines.

    Returns the number of cells modified.
    """
    hyph_de, hyph_en = _get_hyphenators()
    if hyph_de is None:
        logger.warning("pyphen not installed — skipping syllable insertion")
        return 0

    # Pre-check: count cells that already have | from OCR.
    # Real dictionary pages with printed syllable dividers will have OCR-
    # detected pipes in many cells.  Pages without syllable dividers will
    # have zero — skip those to avoid false syllabification.
    total_col_cells = 0
    cells_with_pipes = 0
    for z in zones_data:
        for cell in z.get("cells", []):
            if cell.get("col_type", "").startswith("column_"):
                total_col_cells += 1
                if "|" in cell.get("text", ""):
                    cells_with_pipes += 1

    if total_col_cells > 0:
        pipe_ratio = cells_with_pipes / total_col_cells
        if pipe_ratio < 0.05:
            logger.info(
                "build-grid session %s: skipping syllable insertion — "
                "only %.1f%% of cells have existing pipes (need >=5%%)",
                session_id, pipe_ratio * 100,
            )
            return 0

    insertions = 0
    for z in zones_data:
        for cell in z.get("cells", []):
            ct = cell.get("col_type", "")
            if not ct.startswith("column_"):
                continue
            text = cell.get("text", "")
            if not text:
                continue

            new_text = _syllabify_text(text, hyph_de, hyph_en)
            if new_text != text:
                cell["text"] = new_text
                insertions += 1

    if insertions:
        logger.info(
            "build-grid session %s: syllable dividers inserted/normalized "
            "in %d cells (pyphen)",
            session_id, insertions,
        )
    return insertions