package fluvial

import (
	"testing"

	"salty/terrain/internal/world"
)

// The whole point of the move from an index hash to a position hash: a planet is solved one landmass at a
// time, so the same physical cell turns up in grids of different widths at different offsets. If the jitter
// disagreed between them, every place two frames met would show a line.
func TestJitterFollowsThePositionNotTheIndex(t *testing.T) {
	p, err := world.New(512, 8, 100, 50, 2, 512)
	if err != nil {
		t.Fatal(err)
	}

	// Two frames of different widths, both covering planet column 5, row 7.
	a := Grid{W: 16, H: 16}
	a.SetSeed(11)
	a.SetFrame(world.Frame{P: p, X0: 0, Y0: 0, W: 16, H: 16})

	b := Grid{W: 9, H: 12}
	b.SetSeed(11)
	b.SetFrame(world.Frame{P: p, X0: 3, Y0: 4, W: 9, H: 12})

	for k := int32(0); k < 9; k++ {
		ja := hashXY(a.seed, a.worldX(5), a.worldY(7), k)
		jb := hashXY(b.seed, b.worldX(2), b.worldY(3), k)
		if ja != jb {
			t.Fatalf("k=%d: frame a gives %v, frame b gives %v for the same planet cell", k, ja, jb)
		}
	}

	// And it must still be a hash: the neighbouring cell gets an unrelated value.
	if hashXY(a.seed, a.worldX(5), a.worldY(7), 0) == hashXY(a.seed, a.worldX(6), a.worldY(7), 0) {
		t.Error("neighbouring cells hash the same")
	}
}

// A frame that straddles the seam sees the same positions as one that does not.
func TestJitterWrapsAtTheSeam(t *testing.T) {
	p, err := world.New(512, 8, 100, 50, 0, 512)
	if err != nil {
		t.Fatal(err)
	}
	at := Grid{W: 8, H: 8}
	at.SetSeed(3)
	at.SetFrame(world.Frame{P: p, X0: 60, Y0: 0, W: 8, H: 8})
	origin := Grid{W: 8, H: 8}
	origin.SetSeed(3)
	origin.SetFrame(world.Frame{P: p, X0: 0, Y0: 0, W: 8, H: 8})

	// The seam frame's column 4 is planet column 0, which is the origin frame's column 0.
	if got, want := at.worldX(4), origin.worldX(0); got != want {
		t.Fatalf("world column = %d, want %d", got, want)
	}
	if hashXY(at.seed, at.worldX(4), at.worldY(2), 0) != hashXY(origin.seed, origin.worldX(0), origin.worldY(2), 0) {
		t.Error("the same planet cell jitters differently on either side of the seam")
	}
}

// Without a frame a grid is its own world at the origin, which is what the square canvas is and what every
// existing test relies on.
func TestNoFrameMeansTheGridIsTheWorld(t *testing.T) {
	g := Grid{W: 8, H: 8}
	g.SetSeed(1)
	if got := g.worldX(7); got != 7 {
		t.Errorf("worldX(7) = %d, want 7", got)
	}
	if got := g.worldY(3); got != 3 {
		t.Errorf("worldY(3) = %d, want 3", got)
	}
}