extends SceneTree

# Headless gameplay test: run with
#   godot --headless -s res://tests/test_star_coverage.gd
# Verifies the shader-based starfield's uniforms actually track the camera:
# after moving/zooming the camera, camera_pos/camera_zoom fed to the
# starfield shader should match, at every zoom level (this replaces the old
# tile-symmetry check now that stars are a single procedural fragment
# shader pass with no CPU-side tiling to go asymmetric in the first place).

const TOLERANCE: float = 0.5

var main_scene: Node
var camera: Camera2D
var starfield: ColorRect


func _initialize() -> void:
	var packed: PackedScene = load("res://world/Main.tscn")
	main_scene = packed.instantiate()
	root.add_child(main_scene)
	camera = main_scene.get_node("Camera2D")
	starfield = main_scene.get_node("BackgroundLayer/Starfield")


func _process(_delta: float) -> bool:
	var all_ok: bool = true

	for zoom_level in [1.0, 3.0, 6.0]:
		camera.zoom = Vector2(zoom_level, zoom_level)
		camera.global_position = Vector2(zoom_level * 100.0, -zoom_level * 50.0)

		# Let the Starfield's own _process (which reads the camera and pushes
		# shader uniforms) run for this frame before checking.
		starfield._process(0.016)

		# The camera position is handed to the shader pre-split into a cell
		# index plus a fraction within that cell (so the shader never handles
		# a large absolute world coordinate - see Starfield.gd). Verify the
		# two parts reconstruct the real camera position exactly, and that
		# the fraction really is a fraction: if it ever left [0,1) the split
		# would be wrong and the shader would sample the wrong cell.
		var cell: Vector2 = starfield.material.get_shader_parameter("camera_cell")
		var frac: Vector2 = starfield.material.get_shader_parameter("camera_frac")
		var cell_size: float = starfield.material.get_shader_parameter("cell_size")
		var uniform_zoom: float = starfield.material.get_shader_parameter("camera_zoom")

		var reconstructed: Vector2 = (cell + frac) * cell_size
		var pos_ok: bool = reconstructed.distance_to(camera.global_position) <= TOLERANCE
		var frac_ok: bool = frac.x >= 0.0 and frac.x < 1.0 and frac.y >= 0.0 and frac.y < 1.0
		var zoom_ok: bool = abs(uniform_zoom - (1.0 / camera.zoom.x)) <= 0.01
		var ok: bool = pos_ok and frac_ok and zoom_ok
		all_ok = all_ok and ok

		print("zoom=%.1f camera_pos=%s reconstructed=%s frac=%s zoom=%.2f/%.2f %s" % [
			zoom_level, camera.global_position, reconstructed, frac,
			camera.zoom.x, uniform_zoom, "OK" if ok else "FAIL"
		])

	if all_ok:
		print("TEST_STAR_COVERAGE: PASS")
		quit(0)
	else:
		print("TEST_STAR_COVERAGE: FAIL")
		quit(1)
	return true