"""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 any step fails.
    """
    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 Exception as e:
        logger.warning(
            "preprocess_page failed (falling back to original): %s: %s",
            type(e).__name__,
            e,
        )
        return image