"""Tests for the image preprocessing pipeline."""

import numpy as np
import pytest
from PIL import Image
from unittest.mock import patch


def _make_yellowed_image(width=100, height=100):
    """Dark, faded yellowed page: L values in a narrow low range with spatial noise.

    Very dark (R≈30, G≈20, B≈10) → L_cv ≈ 80-100 in OpenCV uint8 LAB space.
    The per-pixel noise gives each CLAHE tile a non-trivial histogram to equalize,
    which stretches the narrow dark range toward [0-255] and reliably increases mean L.
    """
    rng = np.random.default_rng(42)
    arr = np.zeros((height, width, 3), dtype=np.uint8)
    arr[:, :, 0] = np.clip(30 + rng.integers(-8, 9, (height, width)), 0, 255)
    arr[:, :, 1] = np.clip(20 + rng.integers(-5, 6, (height, width)), 0, 255)
    arr[:, :, 2] = np.clip(10 + rng.integers(-3, 4, (height, width)), 0, 255)
    return Image.fromarray(arr.astype(np.uint8), mode="RGB")


class TestPreprocessPage:
    def test_output_has_same_dimensions_as_input(self):
        from preprocessing import preprocess_page

        img = Image.new("RGB", (150, 200))
        result = preprocess_page(img)

        assert result.size == img.size

    def test_l_channel_mean_increases_on_yellowed_image(self):
        """CLAHE equalizes the dark narrow-range histogram toward [0-255], raising mean L."""
        from preprocessing import preprocess_page
        import cv2

        img = _make_yellowed_image()

        arr_before = np.array(img)
        lab_before = cv2.cvtColor(arr_before, cv2.COLOR_RGB2LAB)
        l_mean_before = float(lab_before[:, :, 0].mean())

        result = preprocess_page(img)

        # Output is grayscale (mode "L"); its values ARE the CLAHE-enhanced L channel
        l_mean_after = float(np.array(result).mean())

        assert l_mean_after > l_mean_before

    def test_does_not_crash_on_sub_tile_size_image(self):
        """A 1×1 image is smaller than the CLAHE tile (8×8) in both axes.
        preprocess_page must not raise — it either succeeds or falls back silently."""
        from preprocessing import preprocess_page

        img = Image.new("RGB", (1, 1), color=(128, 100, 80))
        result = preprocess_page(img)

        assert isinstance(result, Image.Image)

    def test_falls_back_to_pixel_identical_original_on_cv2_error(self):
        """When cv2 raises a known error, preprocess_page returns the unmodified original image."""
        from preprocessing import preprocess_page

        img = Image.new("RGB", (80, 60), color=(123, 45, 67))
        original_pixels = list(img.getdata())

        with patch("preprocessing.cv2.cvtColor", side_effect=ValueError("bad input")):
            result = preprocess_page(img)

        result_pixels = list(result.getdata())
        assert result_pixels == original_pixels

    def test_unexpected_exception_propagates(self):
        """A RuntimeError (programming error) must propagate — not be swallowed by the cv2 fallback."""
        from preprocessing import preprocess_page

        img = Image.new("RGB", (80, 60))

        with patch("preprocessing.cv2.cvtColor", side_effect=RuntimeError("unexpected")):
            with pytest.raises(RuntimeError, match="unexpected"):
                preprocess_page(img)