evaluation_kit/evaluation/text_metrics.py

"""Text accuracy metrics: edit distance, CER, bucket summaries."""

from __future__ import annotations

import sys
from pathlib import Path

_BOX_GROUPING = str(Path(__file__).resolve().parent.parent / "box_grouping")
if _BOX_GROUPING not in sys.path:
    sys.path.insert(0, _BOX_GROUPING)

import unicodedata
from typing import Any, Sequence

from spatial import normalize_whitespace


CER_BUCKET_KEYS = (
    "lt_0_1",
    "0_1_to_0_3",
    "0_3_to_0_6",
    "0_6_to_1",
    "gt_1",
)
HIGH_IMPACT_REGION_EXAMPLE_COUNT = 3


def safe_rate(count: int, total: int) -> float:
    if total == 0:
        return 0.0
    return round(count / total, 6)


def safe_mean(values: list[float]) -> float:
    if not values:
        return 0.0
    return round(sum(values) / len(values), 6)


def safe_error_rate(edit_distance_value: int, gt_length: int) -> float:
    if gt_length == 0:
        return 0.0 if edit_distance_value == 0 else 1.0
    return round(edit_distance_value / gt_length, 6)


def cer_bucket_key(cer: float) -> str:
    if cer < 0.1:
        return "lt_0_1"
    if cer < 0.3:
        return "0_1_to_0_3"
    if cer < 0.6:
        return "0_3_to_0_6"
    if cer <= 1.0:
        return "0_6_to_1"
    return "gt_1"


def build_cer_bucket_summary(
    cers: list[float],
) -> dict[str, dict[str, int | float]]:
    counts = {bucket_key: 0 for bucket_key in CER_BUCKET_KEYS}
    for cer in cers:
        counts[cer_bucket_key(cer)] += 1
    total = len(cers)
    return {
        bucket_key: {
            "count": count,
            "rate": safe_rate(count, total),
        }
        for bucket_key, count in counts.items()
    }


def normalize_punctuation_chars(text: str) -> str:
    """Normalize visually similar or OCR-confused characters to canonical form.

    Applied to both gt and predicted text before CER so that encoding
    differences do not count as errors.  Rules are explicit char-to-char (or
    string-to-string) mappings — extend CHAR_MAP or SEQUENCE_MAP as needed.
    """
    CHAR_LAST = ":"
    CHAR_MAP: dict[str, str] = {
        "֊":  "-",
         "—":  "-",
        "́": "՛",  # COMBINING ACUTE ACCENT ́       → ՛ ARMENIAN EMPHASIS MARK
        "`": "`",  # GRAVE ACCENT ` — canonical form (paired with ՝ → ` below)
        "՝": "`",  # ՝ ARMENIAN COMMA → ` GRAVE ACCENT
        "․": ".",  # ONE DOT LEADER ․               → . FULL STOP
        "…": "...",     # HORIZONTAL ELLIPSIS …           → ...
        "№": "N",  # U+2116 NUMERO SIGN              → N
        "։": CHAR_LAST,
        ":":  CHAR_LAST,  # U+003A  COLON
        "˸":  CHAR_LAST,  # U+02F8  MODIFIER LETTER RAISED COLON
        "︓":  CHAR_LAST,  # U+FE13  PRESENTATION FORM FOR VERTICAL COLON
        "︰":  CHAR_LAST,  # U+FE30  PRESENTATION FORM FOR VERTICAL TWO DOT LEADER
        "：": CHAR_LAST,  # U+FF1A  FULLWIDTH COLON
        "∶":  CHAR_LAST,  # U+2236  RATIO
        "꞉":  CHAR_LAST,  # U+A789  MODIFIER LETTER COLON
    }

    # Multi-character substitutions — applied BEFORE single-char replacements
    SEQUENCE_MAP: list[tuple[str, str]] = [
        ("--", "—"),    # double hyphen --               → — EM DASH
        ("եւ", "և"),   # old Armenian yev spelling      → և ligature
    ]

    for wrong, correct in SEQUENCE_MAP:
        text = text.replace(wrong, correct)

    return "".join(CHAR_MAP.get(ch, ch) for ch in text)


def edit_distance(left: Sequence[Any] | str, right: Sequence[Any] | str) -> int:
    left_items = list(left)
    right_items = list(right)

    if left_items == right_items:
        return 0
    if not left_items:
        return len(right_items)
    if not right_items:
        return len(left_items)

    if len(left_items) < len(right_items):
        left_items, right_items = right_items, left_items

    previous = list(range(len(right_items) + 1))
    for left_index, left_item in enumerate(left_items, start=1):
        current = [left_index]
        for right_index, right_item in enumerate(right_items, start=1):
            insertion = current[right_index - 1] + 1
            deletion = previous[right_index] + 1
            substitution = previous[right_index - 1] + (left_item != right_item)
            current.append(min(insertion, deletion, substitution))
        previous = current
    return previous[-1]


_ARMENIAN_SCHWA = "ը"


def _schwa_free_char_positions(
    text: str, join_word_indices: frozenset[int]
) -> frozenset[int]:
    """Return char positions in *text* that belong to hyphen-joined words."""
    if not join_word_indices:
        return frozenset()
    positions: set[int] = set()
    char_offset = 0
    for idx, word in enumerate(text.split()):
        if idx in join_word_indices:
            for i in range(len(word)):
                positions.add(char_offset + i)
        char_offset += len(word) + 1
    return frozenset(positions)


def edit_distance_schwa_forgiving(
    left: str, right: str, right_schwa_free: frozenset[int]
) -> int:
    """Edit distance where inserting ը at positions in right_schwa_free costs 0."""
    if not right_schwa_free:
        return edit_distance(left, right)

    left_items = list(left)
    right_items = list(right)

    if left_items == right_items:
        return 0
    if not left_items:
        return sum(
            0 if (j in right_schwa_free and ch == _ARMENIAN_SCHWA) else 1
            for j, ch in enumerate(right_items)
        )
    if not right_items:
        return len(left_items)

    # Initialise first row (all insertions from right)
    previous = [0]
    for j, ch in enumerate(right_items):
        ins_cost = 0 if (j in right_schwa_free and ch == _ARMENIAN_SCHWA) else 1
        previous.append(previous[-1] + ins_cost)

    for left_index, left_item in enumerate(left_items, start=1):
        current = [left_index]
        for right_index, right_item in enumerate(right_items, start=1):
            j = right_index - 1
            ins_cost = 0 if (j in right_schwa_free and right_item == _ARMENIAN_SCHWA) else 1
            insertion = current[right_index - 1] + ins_cost
            deletion = previous[right_index] + 1
            substitution = previous[right_index - 1] + (left_item != right_item)
            current.append(min(insertion, deletion, substitution))
        previous = current
    return previous[-1]


def compute_text_metrics(
    gt_text: str,
    predicted_text: str,
    *,
    predicted_hyphen_join_word_indices: frozenset[int] = frozenset(),
) -> dict[str, Any]:
    gt_normalized = unicodedata.normalize(
        "NFC", normalize_whitespace(gt_text)
    )
    predicted_normalized = unicodedata.normalize(
        "NFC", normalize_whitespace(predicted_text)
    )
    gt_normalized = normalize_punctuation_chars(normalize_whitespace(gt_normalized))
    predicted_normalized = normalize_punctuation_chars(
        normalize_whitespace(predicted_normalized)
    )
    schwa_free = _schwa_free_char_positions(
        predicted_normalized, predicted_hyphen_join_word_indices
    )
    char_distance = edit_distance_schwa_forgiving(gt_normalized, predicted_normalized, schwa_free)
    char_distance_lower = edit_distance_schwa_forgiving(
        gt_normalized.lower(), predicted_normalized.lower(), schwa_free
    )

    return {
        "gt_normalized_text": gt_normalized,
        "pr_normalized_text": predicted_normalized,
        "gt_char_count": len(gt_normalized),
        "predicted_char_count": len(predicted_normalized),
        "char_edit_distance": char_distance,
        "cer": safe_error_rate(char_distance, len(gt_normalized)),
        "char_edit_distance_lowercase": char_distance_lower,
        "cer_lowercase": safe_error_rate(char_distance_lower, len(gt_normalized)),
    }


def summarize_region_example(
    region: dict[str, Any],
    *,
    include_error_stats: bool = False,
) -> dict[str, Any]:
    text_metrics = region["text_metrics"]
    summary = {
        "gt_normalized_text": text_metrics["gt_normalized_text"],
        "pr_normalized_text": text_metrics["pr_normalized_text"],
    }
    for field_name in ("region_id", "box_ids", "gt_box_details"):
        if field_name in region:
            summary[field_name] = region[field_name]
    if include_error_stats:
        summary.update(
            {
                "gt_char_count": text_metrics["gt_char_count"],
                "char_edit_distance": text_metrics["char_edit_distance"],
                "cer": text_metrics["cer"],
            }
        )
    for field_name in ("page_name", "predictions_csv", "annotations_json"):
        if field_name in region:
            summary[field_name] = region[field_name]
    return summary