"""German spell-check post-processing for OCR output."""

import logging
import os

from spellchecker import SpellChecker

from confidence import CORRECTION_MARKER, ILLEGIBLE_MARKER, collapse_adjacent_markers

logger = logging.getLogger(__name__)

_MIN_SPELL_CHECK_LEN = 4

_spell: SpellChecker | None = None


def load_spell_checker() -> None:
    """Load German spell checker with supplementary historical wordlist.

    Safe to call multiple times — no-op if already loaded.
    """
    global _spell
    if _spell is not None:
        return

    logger.info("Loading German spell checker...")
    _spell = SpellChecker(language="de")

    historical_path = os.path.join(os.path.dirname(__file__), "dictionaries", "de_historical.txt")
    if os.path.exists(historical_path):
        with open(historical_path, encoding="utf-8") as f:
            words = [
                line.strip()
                for line in f
                if line.strip() and not line.startswith("#")
            ]
        _spell.word_frequency.load_words(words)
        logger.info("Loaded %d historical German words", len(words))
    else:
        logger.warning("Historical German wordlist not found at %s", historical_path)

    logger.info("German spell checker ready")


def _strip_punctuation(token: str) -> tuple[str, str, str]:
    """Split token into (leading_punct, word, trailing_punct).

    'Word' characters are letters (including German umlauts) and digits.
    Everything else is treated as punctuation.
    """
    start = 0
    while start < len(token) and not (token[start].isalpha() or token[start].isdigit()):
        start += 1

    end = len(token)
    while end > start and not (token[end - 1].isalpha() or token[end - 1].isdigit()):
        end -= 1

    return token[:start], token[start:end], token[end:]


def _is_numeric(word: str) -> bool:
    return any(c.isdigit() for c in word)


def correct_text(text: str) -> str:
    """Spell-check OCR text, correcting errors and marking gibberish as [unleserlich].

    Already-present [unleserlich] tokens are preserved unchanged.
    Words of fewer than 4 characters are exempt (particles, abbreviations).
    Tokens containing digits pass through unchanged.
    Adjacent [unleserlich] markers are collapsed into one.
    Corrected tokens are marked with [?] (e.g. "Hauus" → "Haus[?]").

    Args:
        text: OCR output, possibly already containing [unleserlich] from confidence filtering.

    Returns:
        Corrected text with unresolvable words replaced by [unleserlich].
    """
    if _spell is None:
        raise RuntimeError("Spell checker not loaded — call load_spell_checker() first")

    if not text.strip():
        return text

    tokens = text.split()
    checked: list[str] = []

    for token in tokens:
        if token == ILLEGIBLE_MARKER:
            checked.append(token)
            continue

        leading, word, trailing = _strip_punctuation(token)

        if len(word) < _MIN_SPELL_CHECK_LEN:
            checked.append(token)
            continue

        if _is_numeric(word):
            checked.append(token)
            continue

        if _spell.known([word]):
            checked.append(token)
            continue

        correction = _spell.correction(word)
        if correction and _spell.word_frequency[correction] > 50:
            if word[0].isupper() and not correction[0].isupper():
                correction = correction.capitalize()
            checked.append(leading + correction + CORRECTION_MARKER + trailing)
        else:
            checked.append(ILLEGIBLE_MARKER)

    return " ".join(collapse_adjacent_markers(checked))