import numpy as np
import pytest

from bookmark.image_processing import crop_to_book


def make_reference(size=100, color=200):
    return np.full((size, size, 3), color, dtype=np.uint8)


def make_book_frame(size=100, ref_color=200, book_color=50, box=(30, 30, 20, 20)):
    frame = np.full((size, size, 3), ref_color, dtype=np.uint8)
    x, y, w, h = box
    frame[y:y + h, x:x + w] = book_color
    return frame


def test_crop_raises_when_no_difference_from_reference():
    reference = make_reference()
    with pytest.raises(ValueError):
        crop_to_book(reference.copy(), reference)


def test_crop_returns_region_around_book_with_margin():
    reference = make_reference()
    frame = make_book_frame(box=(30, 30, 20, 20))

    cropped = crop_to_book(frame, reference, margin=10)

    # book occupies x:[30,50) y:[30,50), with margin=10 expected crop is
    # roughly x:[20,60) y:[20,60) -> 40x40
    assert cropped.shape[0] == pytest.approx(40, abs=2)
    assert cropped.shape[1] == pytest.approx(40, abs=2)


def test_crop_clamps_margin_to_frame_bounds():
    reference = make_reference()
    frame = make_book_frame(box=(0, 0, 20, 20))

    cropped = crop_to_book(frame, reference, margin=10)

    # book touches top-left corner, margin should clamp instead of going negative
    assert cropped.shape[0] <= 30
    assert cropped.shape[1] <= 30