package sim

import "testing"

func TestRNGIsDeterministic(t *testing.T) {
	var seed [32]byte
	copy(seed[:], "quantum-arcade-test-seed")
	a, b := NewRNG(seed), NewRNG(seed)
	for i := 0; i < 1000; i++ {
		if x, y := a.Uint64(), b.Uint64(); x != y {
			t.Fatalf("iteration %d: %d != %d", i, x, y)
		}
	}
}

func TestDifferentSeedsDiverge(t *testing.T) {
	var s1, s2 [32]byte
	copy(s1[:], "seed-one")
	copy(s2[:], "seed-two")
	a, b := NewRNG(s1), NewRNG(s2)
	same := 0
	for i := 0; i < 100; i++ {
		if a.Uint64() == b.Uint64() {
			same++
		}
	}
	if same > 1 {
		t.Fatalf("streams collided %d times in 100 draws", same)
	}
}

func TestZeroSeedDoesNotDegenerate(t *testing.T) {
	var seed [32]byte // all zeros
	r := NewRNG(seed)
	first := r.Uint64()
	if first == 0 && r.Uint64() == 0 {
		t.Fatal("zero seed produced a degenerate all-zero stream")
	}
}

func TestUnitInRange(t *testing.T) {
	var seed [32]byte
	seed[0] = 9
	r := NewRNG(seed)
	for i := 0; i < 10000; i++ {
		u := r.Unit()
		if u < 0 || u >= 1<<32 {
			t.Fatalf("Unit() = %v out of [0,1)", u)
		}
	}
}