package compositor

import "testing"

func TestGridRectsCoverExactly(t *testing.T) {
	cases := []struct {
		w, h, cols, rows int
	}{
		{1920, 1080, 2, 2},
		{1920, 1080, 3, 3},
		{1920, 1080, 1, 1},
		{1366, 768, 3, 2}, // odd dimensions to exercise remainder handling
	}
	for _, tc := range cases {
		rects := GridRects(tc.w, tc.h, tc.cols, tc.rows)
		if len(rects) != tc.cols*tc.rows {
			t.Fatalf("%dx%d grid %dx%d: got %d rects", tc.w, tc.h, tc.cols, tc.rows, len(rects))
		}
		// Sum of areas must equal the whole output with no gaps or overlap on
		// the axis boundaries: verify the last column reaches the right edge
		// and the last row reaches the bottom edge.
		last := rects[len(rects)-1]
		if last.X+last.W != tc.w {
			t.Errorf("%dx%d grid %dx%d: last cell right edge %d != %d", tc.w, tc.h, tc.cols, tc.rows, last.X+last.W, tc.w)
		}
		if last.Y+last.H != tc.h {
			t.Errorf("%dx%d grid %dx%d: last cell bottom edge %d != %d", tc.w, tc.h, tc.cols, tc.rows, last.Y+last.H, tc.h)
		}
		for i, r := range rects {
			if r.W <= 0 || r.H <= 0 {
				t.Errorf("cell %d has non-positive size %+v", i, r)
			}
		}
	}
}