package planet

import (
	"math"
	"testing"
)

// boxDown is what the two overview heightmaps are made with, and a planet's two sides rarely share an
// integer factor, so it has to be right at a ratio that does not divide.
func TestBoxDownAveragesAndKeepsTheMean(t *testing.T) {
	const w, h = 12, 7
	src := make([]float32, w*h)
	sum := 0.0
	for i := range src {
		src[i] = float32(i%5) + float32(i/w)
		sum += float64(src[i])
	}
	want := sum / float64(len(src))

	for _, d := range [][2]int{{6, 7}, {4, 3}, {5, 3}, {12, 7}, {1, 1}} {
		out := boxDown(src, w, h, d[0], d[1])
		if len(out) != d[0]*d[1] {
			t.Fatalf("%dx%d: got %d values", d[0], d[1], len(out))
		}
		got := 0.0
		for _, v := range out {
			got += float64(v)
		}
		got /= float64(len(out))
		// Buckets do not all hold the same number of cells at a ratio that does not divide, so the mean of
		// the means drifts a little; what must not happen is a bucket left empty or a value invented.
		if math.Abs(got-want) > 0.35 {
			t.Errorf("%dx%d: mean %.3f, source mean %.3f", d[0], d[1], got, want)
		}
		lo, hi := math.Inf(1), math.Inf(-1)
		for _, v := range out {
			lo = math.Min(lo, float64(v))
			hi = math.Max(hi, float64(v))
		}
		if lo < 0 || hi > 11 {
			t.Errorf("%dx%d: range %.2f..%.2f is outside the source's 0..10", d[0], d[1], lo, hi)
		}
	}
}

func TestBoxDownIsIdentityAtTheSameSize(t *testing.T) {
	src := []float32{1, 2, 3, 4, 5, 6}
	out := boxDown(src, 3, 2, 3, 2)
	for i := range src {
		if out[i] != src[i] {
			t.Fatalf("cell %d: %v, want %v", i, out[i], src[i])
		}
	}
}