package helper

import (
	"fmt"
	"math"
	"testing"
)

func TestLinearize(t *testing.T) {
	tests := []struct {
		value uint32
		want  float64
	}{
		// the minimum and maximum legal values should map to 0 and 1, respectively.
		{0x0000, 0.0},
		{0xffff, 1.0},

		// check what would be 0x01 in 8-bit sRGB.
		// this is below the point where it the function switches from linear to exponential.
		{0x0101, 0x1.3e312a36f1977p-12},

		// check the midpoint of the gamma curve.
		{0x7fff, 0x1.b6577fc57aa37p-03},

		// We do support values beyond the maximum legal value, although you probably shouldn't depend on it
		// as the converse function will map these to the maximum legal value, creating an asymmetry.
		{0x10000, 0x1.000246626b604p+00},
		{math.MaxUint32, 0x1.2912a0c535107p+38},
	}
	for _, tt := range tests {
		t.Run(fmt.Sprintf("0x%04x", tt.value), func(t *testing.T) {
			if got := Linearize(tt.value); !EqFloat64Fuzzy(got, tt.want) {
				t.Errorf("Linearize(0x%04x) = %x: want %x", tt.value, got, tt.want)
			}
		})
	}

	t.Run("monotonically increasing", func(t *testing.T) {
		for i, prev := uint32(1), Linearize(0); i < 0x10000; i++ {
			got := Linearize(i)
			if got <= prev {
				t.Errorf("Linearize(0x%04x) = %x; want > %x", i, got, prev)
			}
			prev = got
		}
	})
}

func TestDelinearize(t *testing.T) {
	tests := []struct {
		value float64
		want  uint32
	}{
		// make sure clamping to legal values is happening.
		{-1, 0x0000},
		{2, 0xffff},

		// again with the next values below 0 and above 1.
		{math.Nextafter(0, math.Inf(-1)), 0},
		{math.Nextafter(1, math.Inf(1)), 0xffff},

		// and lastly, the non-finites.
		{math.Inf(-1), 0x0000},
		{math.Inf(1), 0xffff},
		{math.NaN(), 0x0000},
	}
	for _, tt := range tests {
		t.Run(fmt.Sprintf("%x", tt.value), func(t *testing.T) {
			if got := Delinearize(tt.value); got != tt.want {
				t.Errorf("Delinearize(%x) = 0x%04x: want 0x%04x", tt.value, got, tt.want)
			}
		})
	}

	t.Run("lossless conversion of legal values", func(t *testing.T) {
		for c := uint32(0); c < 0x10000; c++ {
			got := Delinearize(Linearize(c))
			if got != c {
				t.Errorf("Delinearize(Linearize(0x%04x)) != 0x%04x", c, got)
				return
			}
		}
	})
}