class_name SonarReliefMeshBuilder
extends RefCounted

const SonarMaterial = preload("res://game/domain/sonar/sonar_material.gd")
const SonarSample = preload("res://game/domain/sonar/sonar_sample.gd")
const SonarScan = preload("res://game/domain/sonar/sonar_scan.gd")

const COLOR_DEEP := Color("173f91")
const COLOR_LOW := Color("168fc1")
const COLOR_MIDDLE := Color("36b979")
const COLOR_HIGH := Color("d7d93d")
const COLOR_PEAK := Color("ee5734")
const COLOR_METAL := Color("ff6b22")


static func build_full_mesh(
	scan: SonarScan,
	material: StandardMaterial3D
) -> ArrayMesh:
	var mesh := ArrayMesh.new()
	for row in range(1, scan.samples.rows):
		add_row_band(mesh, scan, row, material)
	return mesh


static func add_row_band(
	mesh: ArrayMesh,
	scan: SonarScan,
	row: int,
	material: StandardMaterial3D
) -> int:
	var vertices := PackedVector3Array()
	var normals := PackedVector3Array()
	var colors := PackedColorArray()
	for column in range(scan.samples.columns - 1):
		var top_left: SonarSample = scan.samples.sample_at(row - 1, column)
		var top_right: SonarSample = scan.samples.sample_at(row - 1, column + 1)
		var bottom_left: SonarSample = scan.samples.sample_at(row, column)
		var bottom_right: SonarSample = scan.samples.sample_at(row, column + 1)
		if not (
			top_left.observed
			and top_right.observed
			and bottom_left.observed
			and bottom_right.observed
		):
			continue
		_append_triangle(
			vertices, normals, colors, scan,
			top_left, bottom_left, top_right
		)
		_append_triangle(
			vertices, normals, colors, scan,
			top_right, bottom_left, bottom_right
		)
	if vertices.is_empty():
		return 0
	var arrays: Array = []
	arrays.resize(Mesh.ARRAY_MAX)
	arrays[Mesh.ARRAY_VERTEX] = vertices
	arrays[Mesh.ARRAY_NORMAL] = normals
	arrays[Mesh.ARRAY_COLOR] = colors
	mesh.add_surface_from_arrays(Mesh.PRIMITIVE_TRIANGLES, arrays)
	mesh.surface_set_material(mesh.get_surface_count() - 1, material)
	return vertices.size() / 3


static func add_grid_band(
	mesh: ArrayMesh,
	scan: SonarScan,
	row: int,
	material: StandardMaterial3D
) -> int:
	var vertices := PackedVector3Array()
	for column in scan.samples.columns:
		if column % 6 != 0 and column != scan.samples.columns - 1:
			continue
		_append_grid_segment(
			vertices,
			scan.samples.sample_at(row - 1, column),
			scan.samples.sample_at(row, column)
		)
	if row == 1 or row % 4 == 0 or row == scan.samples.rows - 1:
		for column in range(scan.samples.columns - 1):
			_append_grid_segment(
				vertices,
				scan.samples.sample_at(row, column),
				scan.samples.sample_at(row, column + 1)
			)
	if vertices.is_empty():
		return 0
	var arrays: Array = []
	arrays.resize(Mesh.ARRAY_MAX)
	arrays[Mesh.ARRAY_VERTEX] = vertices
	mesh.add_surface_from_arrays(Mesh.PRIMITIVE_LINES, arrays)
	mesh.surface_set_material(mesh.get_surface_count() - 1, material)
	return vertices.size() / 2


static func _append_grid_segment(
	vertices: PackedVector3Array,
	a: SonarSample,
	b: SonarSample
) -> void:
	if not a.observed or not b.observed:
		return
	vertices.append(a.position_m + a.normal * 0.08)
	vertices.append(b.position_m + b.normal * 0.08)


static func _append_triangle(
	vertices: PackedVector3Array,
	normals: PackedVector3Array,
	colors: PackedColorArray,
	scan: SonarScan,
	a: SonarSample,
	b: SonarSample,
	c: SonarSample
) -> void:
	for sample: SonarSample in [a, b, c]:
		vertices.append(sample.position_m)
		normals.append(sample.normal)
		colors.append(_sample_color(scan, sample))


static func _sample_color(scan: SonarScan, sample: SonarSample) -> Color:
	if sample.material == SonarMaterial.Value.METAL:
		return COLOR_METAL
	var height := inverse_lerp(
		scan.minimum_elevation_m,
		scan.maximum_elevation_m,
		sample.elevation_m
	)
	var color: Color
	if height <= 0.28:
		color = COLOR_DEEP.lerp(COLOR_LOW, height / 0.28)
	elif height <= 0.52:
		color = COLOR_LOW.lerp(COLOR_MIDDLE, (height - 0.28) / 0.24)
	elif height <= 0.76:
		color = COLOR_MIDDLE.lerp(COLOR_HIGH, (height - 0.52) / 0.24)
	else:
		color = COLOR_HIGH.lerp(COLOR_PEAK, (height - 0.76) / 0.24)
	var light_direction := Vector3(-0.35, 0.82, -0.45).normalized()
	var slope_light := clampf(sample.normal.dot(light_direction), 0.0, 1.0)
	var shade := lerpf(0.68, 1.0, slope_light)
	var lit_color := color.lerp(Color.WHITE, sample.intensity * 0.08)
	return Color(
		lit_color.r * shade,
		lit_color.g * shade,
		lit_color.b * shade,
		lit_color.a
	)