breakpilot-lehrer/klausur-service/backend/ocr/layout/classify.py

"""
Column type classification for OCR layout analysis.

Entry point: classify_column_types() with 4-level fallback chain.
Also provides positional_column_regions() and _build_margin_regions().
Position-based classifiers (Level 2+3) in cv_layout_classify_position.py.
"""

import logging
from typing import Dict, List, Optional

import numpy as np

from cv_vocab_types import ColumnGeometry, PageRegion

from cv_layout_scoring import (
    _score_language,
    _score_role,
    _score_dictionary_signals,
    _classify_dictionary_columns,
)

from cv_layout_classify_position import (
    _classify_by_position_enhanced,
    _classify_by_position_fallback,
)

logger = logging.getLogger(__name__)


# ---------------------------------------------------------------------------
# Margin Region Building
# ---------------------------------------------------------------------------

def _build_margin_regions(
    all_regions: List[PageRegion],
    left_x: int,
    right_x: int,
    img_w: int,
    top_y: int,
    content_h: int,
) -> List[PageRegion]:
    """Create margin_left / margin_right PageRegions from content bounds.

    Margins represent the space between the image edge and the first/last
    content column.  They are used downstream for faithful page
    reconstruction but are skipped during OCR.
    """
    margins: List[PageRegion] = []
    # Minimum gap (px) to create a margin region
    _min_gap = 5

    if left_x > _min_gap:
        margins.append(PageRegion(
            type='margin_left', x=0, y=top_y,
            width=left_x, height=content_h,
            classification_confidence=1.0,
            classification_method='content_bounds',
        ))

    # Right margin: from end of last content column to image edge
    non_margin = [r for r in all_regions
                  if r.type not in ('margin_left', 'margin_right', 'header', 'footer',
                                    'margin_top', 'margin_bottom')]
    if non_margin:
        last_col_end = max(r.x + r.width for r in non_margin)
    else:
        last_col_end = right_x
    if img_w - last_col_end > _min_gap:
        margins.append(PageRegion(
            type='margin_right', x=last_col_end, y=top_y,
            width=img_w - last_col_end, height=content_h,
            classification_confidence=1.0,
            classification_method='content_bounds',
        ))

    if margins:
        logger.info(f"Margins: {[(m.type, m.x, m.width) for m in margins]} "
                     f"(left_x={left_x}, right_x={right_x}, img_w={img_w})")

    return margins


# ---------------------------------------------------------------------------
# Positional Column Regions
# ---------------------------------------------------------------------------

def positional_column_regions(
    geometries: List[ColumnGeometry],
    content_w: int,
    content_h: int,
    left_x: int,
) -> List[PageRegion]:
    """Classify columns by position only (no language scoring).

    Structural columns (page_ref, column_marker) are identified by geometry.
    Remaining content columns are labelled left->right as column_en, column_de,
    column_example.  The names are purely positional -- no language analysis.
    """
    structural: List[PageRegion] = []
    content_cols: List[ColumnGeometry] = []

    for g in geometries:
        rel_x = g.x - left_x
        # page_ref: narrow column in the leftmost 20% region
        if g.width_ratio < 0.12 and (rel_x / content_w if content_w else 0) < 0.20:
            structural.append(PageRegion(
                type='page_ref', x=g.x, y=g.y,
                width=g.width, height=content_h,
                classification_confidence=0.95,
                classification_method='positional',
            ))
        # column_marker: very narrow, few words
        elif g.width_ratio < 0.06 and g.word_count <= 15:
            structural.append(PageRegion(
                type='column_marker', x=g.x, y=g.y,
                width=g.width, height=content_h,
                classification_confidence=0.95,
                classification_method='positional',
            ))
        # empty or near-empty narrow column -> treat as margin/structural
        elif g.word_count <= 2 and g.width_ratio < 0.15:
            structural.append(PageRegion(
                type='column_marker', x=g.x, y=g.y,
                width=g.width, height=content_h,
                classification_confidence=0.85,
                classification_method='positional',
            ))
        else:
            content_cols.append(g)

    # Single content column -> plain text page
    if len(content_cols) == 1:
        g = content_cols[0]
        return structural + [PageRegion(
            type='column_text', x=g.x, y=g.y,
            width=g.width, height=content_h,
            classification_confidence=0.9,
            classification_method='positional',
        )]

    # No content columns
    if not content_cols:
        return structural

    # Sort content columns left->right and assign positional labels
    content_cols.sort(key=lambda g: g.x)

    # With exactly 2 content columns: if the left one is very wide (>35%),
    # it likely contains EN+DE combined, so the right one is examples.
    if (len(content_cols) == 2
            and content_cols[0].width_ratio > 0.35
            and content_cols[1].width_ratio > 0.20):
        labels = ['column_en', 'column_example']
    else:
        labels = ['column_en', 'column_de', 'column_example']

    regions = list(structural)
    for i, g in enumerate(content_cols):
        label = labels[i] if i < len(labels) else 'column_example'
        regions.append(PageRegion(
            type=label, x=g.x, y=g.y,
            width=g.width, height=content_h,
            classification_confidence=0.95,
            classification_method='positional',
        ))

    logger.info(f"PositionalColumns: {len(structural)} structural, "
                f"{len(content_cols)} content -> "
                f"{[r.type for r in regions]}")
    return regions


# ---------------------------------------------------------------------------
# Main Classification Entry Point
# ---------------------------------------------------------------------------

def classify_column_types(geometries: List[ColumnGeometry],
                          content_w: int,
                          top_y: int,
                          img_w: int,
                          img_h: int,
                          bottom_y: int,
                          left_x: int = 0,
                          right_x: int = 0,
                          inv: Optional[np.ndarray] = None,
                          document_category: Optional[str] = None,
                          margin_strip_detected: bool = False) -> List[PageRegion]:
    """Classify column types using a 3-level fallback chain.

    Level 0: Dictionary detection (if signals are strong enough)
    Level 1: Content-based (language + role scoring)
    Level 2: Position + language (old rules enhanced with language detection)
    Level 3: Pure position (exact old code, no regression)

    Args:
        geometries: List of ColumnGeometry from Phase A.
        content_w: Total content width.
        top_y: Top Y of content area.
        img_w: Full image width.
        img_h: Full image height.
        bottom_y: Bottom Y of content area.
        left_x: Left content bound (from _find_content_bounds).
        right_x: Right content bound (from _find_content_bounds).
        document_category: User-selected category (e.g. 'woerterbuch').
        margin_strip_detected: Whether a decorative A-Z margin strip was found.

    Returns:
        List of PageRegion with types, confidence, and method.
    """
    # _add_header_footer lives in cv_layout (avoids circular import at module
    # level).  Lazy-import here so the module can be tested independently when
    # cv_layout hasn't been modified yet.
    from cv_layout_detection import _add_header_footer  # noqa: E402

    content_h = bottom_y - top_y

    def _with_margins(result: List[PageRegion]) -> List[PageRegion]:
        """Append margin_left / margin_right regions to *result*."""
        margins = _build_margin_regions(result, left_x, right_x, img_w, top_y, content_h)
        return result + margins

    # Special case: single column -> plain text page
    if len(geometries) == 1:
        geom = geometries[0]
        return _with_margins([PageRegion(
            type='column_text', x=geom.x, y=geom.y,
            width=geom.width, height=geom.height,
            classification_confidence=0.9,
            classification_method='content',
        )])

    # --- Pre-filter: first/last columns with very few words -> column_ignore ---
    # Sub-columns from _detect_sub_columns() are exempt: they intentionally
    # have few words (page refs, markers) and should not be discarded.
    ignore_regions = []
    active_geometries = []
    for idx, g in enumerate(geometries):
        if (idx == 0 or idx == len(geometries) - 1) and g.word_count < 8 and not g.is_sub_column:
            ignore_regions.append(PageRegion(
                type='column_ignore', x=g.x, y=g.y,
                width=g.width, height=content_h,
                classification_confidence=0.95,
                classification_method='content',
            ))
            logger.info(f"ClassifyColumns: column {idx} (x={g.x}, words={g.word_count}) -> column_ignore (edge, few words)")
        else:
            active_geometries.append(g)

    # Re-index active geometries for classification
    for new_idx, g in enumerate(active_geometries):
        g.index = new_idx
    geometries = active_geometries

    # Handle edge case: all columns ignored or only 1 left
    if len(geometries) == 0:
        return _with_margins(ignore_regions)
    if len(geometries) == 1:
        geom = geometries[0]
        ignore_regions.append(PageRegion(
            type='column_text', x=geom.x, y=geom.y,
            width=geom.width, height=geom.height,
            classification_confidence=0.9,
            classification_method='content',
        ))
        return _with_margins(ignore_regions)

    # --- Score all columns ---
    lang_scores = [_score_language(g.words) for g in geometries]
    role_scores = [_score_role(g) for g in geometries]

    logger.info(f"ClassifyColumns: language scores: "
                f"{[(g.index, ls) for g, ls in zip(geometries, lang_scores)]}")
    logger.info(f"ClassifyColumns: role scores: "
                f"{[(g.index, rs) for g, rs in zip(geometries, role_scores)]}")

    # --- Level 0: Dictionary detection ---
    dict_signals = _score_dictionary_signals(
        geometries,
        document_category=document_category,
        margin_strip_detected=margin_strip_detected,
    )
    if dict_signals["is_dictionary"]:
        regions = _classify_dictionary_columns(
            geometries, dict_signals, lang_scores, content_h,
        )
        if regions is not None:
            logger.info("ClassifyColumns: Level 0 (dictionary) succeeded, confidence=%.3f",
                        dict_signals["confidence"])
            _add_header_footer(regions, top_y, bottom_y, img_w, img_h, inv=inv)
            return _with_margins(ignore_regions + regions)

    # --- Level 1: Content-based classification ---
    regions = _classify_by_content(geometries, lang_scores, role_scores, content_w, content_h)
    if regions is not None:
        logger.info("ClassifyColumns: Level 1 (content-based) succeeded")
        _add_header_footer(regions, top_y, bottom_y, img_w, img_h, inv=inv)
        return _with_margins(ignore_regions + regions)

    # --- Level 2: Position + language enhanced ---
    regions = _classify_by_position_enhanced(geometries, lang_scores, content_w, content_h)
    if regions is not None:
        logger.info("ClassifyColumns: Level 2 (position+language) succeeded")
        _add_header_footer(regions, top_y, bottom_y, img_w, img_h, inv=inv)
        return _with_margins(ignore_regions + regions)

    # --- Level 3: Pure position fallback (old code, no regression) ---
    logger.info("ClassifyColumns: Level 3 (position fallback)")
    regions = _classify_by_position_fallback(geometries, content_w, content_h)
    _add_header_footer(regions, top_y, bottom_y, img_w, img_h, inv=inv)
    return _with_margins(ignore_regions + regions)


# ---------------------------------------------------------------------------
# Level 1: Content-Based Classification
# ---------------------------------------------------------------------------

def _classify_by_content(geometries: List[ColumnGeometry],
                         lang_scores: List[Dict[str, float]],
                         role_scores: List[Dict[str, float]],
                         content_w: int,
                         content_h: int) -> Optional[List[PageRegion]]:
    """Level 1: Classify columns purely by content analysis.

    Requires clear language signals to distinguish EN/DE columns.
    Returns None if language signals are too weak.
    """
    regions = []
    assigned = set()

    # Step 1: Assign structural roles first (reference, marker)
    # left_20_threshold: only the leftmost ~20% of content area qualifies for page_ref
    left_20_threshold = geometries[0].x + content_w * 0.20 if geometries else 0

    for i, (geom, rs, ls) in enumerate(zip(geometries, role_scores, lang_scores)):
        is_left_side = geom.x < left_20_threshold
        has_strong_language = ls['eng'] > 0.3 or ls['deu'] > 0.3
        if rs['reference'] >= 0.5 and geom.width_ratio < 0.12 and is_left_side and not has_strong_language:
            regions.append(PageRegion(
                type='page_ref', x=geom.x, y=geom.y,
                width=geom.width, height=content_h,
                classification_confidence=rs['reference'],
                classification_method='content',
            ))
            assigned.add(i)
        elif rs['marker'] >= 0.7 and geom.width_ratio < 0.06:
            regions.append(PageRegion(
                type='column_marker', x=geom.x, y=geom.y,
                width=geom.width, height=content_h,
                classification_confidence=rs['marker'],
                classification_method='content',
            ))
            assigned.add(i)
        elif geom.width_ratio < 0.05 and not is_left_side:
            # Narrow column on the right side -> marker, not page_ref
            regions.append(PageRegion(
                type='column_marker', x=geom.x, y=geom.y,
                width=geom.width, height=content_h,
                classification_confidence=0.8,
                classification_method='content',
            ))
            assigned.add(i)

    # Step 2: Among remaining columns, find EN and DE by language scores
    remaining = [(i, geometries[i], lang_scores[i], role_scores[i])
                 for i in range(len(geometries)) if i not in assigned]

    if len(remaining) < 2:
        # Not enough columns for EN/DE pair
        if len(remaining) == 1:
            i, geom, ls, rs = remaining[0]
            regions.append(PageRegion(
                type='column_text', x=geom.x, y=geom.y,
                width=geom.width, height=content_h,
                classification_confidence=0.6,
                classification_method='content',
            ))
        regions.sort(key=lambda r: r.x)
        return regions

    # Check if we have enough language signal
    en_candidates = [(i, g, ls) for i, g, ls, rs in remaining if ls['eng'] > ls['deu'] and ls['eng'] > 0.05]
    de_candidates = [(i, g, ls) for i, g, ls, rs in remaining if ls['deu'] > ls['eng'] and ls['deu'] > 0.05]

    # Position tiebreaker: when language signals are weak, use left=EN, right=DE
    if (not en_candidates or not de_candidates) and len(remaining) >= 2:
        max_eng = max(ls['eng'] for _, _, ls, _ in remaining)
        max_deu = max(ls['deu'] for _, _, ls, _ in remaining)
        if max_eng < 0.15 and max_deu < 0.15:
            # Both signals weak -- fall back to positional: left=EN, right=DE
            sorted_remaining = sorted(remaining, key=lambda x: x[1].x)
            best_en = (sorted_remaining[0][0], sorted_remaining[0][1], sorted_remaining[0][2])
            best_de = (sorted_remaining[1][0], sorted_remaining[1][1], sorted_remaining[1][2])
            logger.info("ClassifyColumns: Level 1 using position tiebreaker (weak signals) - left=EN, right=DE")
            en_conf = 0.4
            de_conf = 0.4

            regions.append(PageRegion(
                type='column_en', x=best_en[1].x, y=best_en[1].y,
                width=best_en[1].width, height=content_h,
                classification_confidence=en_conf,
                classification_method='content',
            ))
            assigned.add(best_en[0])

            regions.append(PageRegion(
                type='column_de', x=best_de[1].x, y=best_de[1].y,
                width=best_de[1].width, height=content_h,
                classification_confidence=de_conf,
                classification_method='content',
            ))
            assigned.add(best_de[0])

            # Assign remaining as example
            for i, geom, ls, rs in remaining:
                if i not in assigned:
                    regions.append(PageRegion(
                        type='column_example', x=geom.x, y=geom.y,
                        width=geom.width, height=content_h,
                        classification_confidence=0.4,
                        classification_method='content',
                    ))
            regions.sort(key=lambda r: r.x)
            return regions

    if not en_candidates or not de_candidates:
        # Language signals too weak for content-based classification
        logger.info("ClassifyColumns: Level 1 failed - no clear EN/DE language split")
        return None

    # Pick the best EN and DE candidates
    best_en = max(en_candidates, key=lambda x: x[2]['eng'])
    best_de = max(de_candidates, key=lambda x: x[2]['deu'])

    # Position-aware EN selection: in typical textbooks the layout is EN | DE | Example.
    # Example sentences contain English function words ("the", "a", "is") which inflate
    # the eng score of the Example column.  When the best EN candidate sits to the RIGHT
    # of the DE column and there is another EN candidate to the LEFT, prefer the left one
    # -- it is almost certainly the real vocabulary column.
    if best_de[2]['deu'] > 0.5 and best_en[1].x > best_de[1].x and len(en_candidates) > 1:
        left_of_de = [c for c in en_candidates if c[1].x < best_de[1].x]
        if left_of_de:
            alt_en = max(left_of_de, key=lambda x: x[2]['eng'])
            logger.info(
                f"ClassifyColumns: Level 1 position fix -- best EN col {best_en[0]} "
                f"(eng={best_en[2]['eng']:.3f}) is right of DE col {best_de[0]}; "
                f"preferring left col {alt_en[0]} (eng={alt_en[2]['eng']:.3f})")
            best_en = alt_en

    if best_en[0] == best_de[0]:
        # Same column scored highest for both -- ambiguous
        logger.info("ClassifyColumns: Level 1 failed - same column highest for EN and DE")
        return None

    en_conf = best_en[2]['eng']
    de_conf = best_de[2]['deu']

    regions.append(PageRegion(
        type='column_en', x=best_en[1].x, y=best_en[1].y,
        width=best_en[1].width, height=content_h,
        classification_confidence=round(en_conf, 2),
        classification_method='content',
    ))
    assigned.add(best_en[0])

    regions.append(PageRegion(
        type='column_de', x=best_de[1].x, y=best_de[1].y,
        width=best_de[1].width, height=content_h,
        classification_confidence=round(de_conf, 2),
        classification_method='content',
    ))
    assigned.add(best_de[0])

    # Step 3: Remaining columns -> example or text based on role scores
    for i, geom, ls, rs in remaining:
        if i in assigned:
            continue
        if rs['sentence'] > 0.4:
            regions.append(PageRegion(
                type='column_example', x=geom.x, y=geom.y,
                width=geom.width, height=content_h,
                classification_confidence=round(rs['sentence'], 2),
                classification_method='content',
            ))
        else:
            regions.append(PageRegion(
                type='column_example', x=geom.x, y=geom.y,
                width=geom.width, height=content_h,
                classification_confidence=0.5,
                classification_method='content',
            ))

    regions.sort(key=lambda r: r.x)
    return regions