"""Image preprocessing pipeline for aged document OCR quality improvement."""

import logging
import os

import cv2
import numpy as np
from PIL import Image

logger = logging.getLogger(__name__)

CLAHE_CLIP_LIMIT = float(os.environ.get("OCR_CLAHE_CLIP_LIMIT", "2.0"))
CLAHE_TILE_SIZE = int(os.environ.get("OCR_CLAHE_TILE_SIZE", "8"))


def preprocess_page(image: Image.Image) -> Image.Image:
    """Apply CLAHE + grayscale + Gaussian blur to improve OCR quality on aged documents.

    Falls back silently to the original image if cv2, numpy, or memory errors occur.
    Unexpected exceptions (programming errors) are allowed to propagate.
    """
    try:
        img_array = np.array(image)
        lab = cv2.cvtColor(img_array, cv2.COLOR_RGB2LAB)
        del img_array

        l_channel = lab[:, :, 0].copy()
        del lab

        clahe = cv2.createCLAHE(
            clipLimit=CLAHE_CLIP_LIMIT,
            tileGridSize=(CLAHE_TILE_SIZE, CLAHE_TILE_SIZE),
        )
        l_clahe = clahe.apply(l_channel)
        del l_channel

        blurred = cv2.GaussianBlur(l_clahe, (3, 3), 0)
        del l_clahe

        result = Image.fromarray(blurred, mode="L")
        del blurred

        return result
    except (cv2.error, ValueError, MemoryError) as e:
        logger.warning(
            "preprocess_page failed (falling back to original): %s: %s",
            type(e).__name__,
            e,
        )
        return image