class_name BathymetricTerrainActor
extends StaticBody3D

const TerrainHeightField = preload("res://game/domain/sites/terrain_height_field.gd")
const TERRAIN_SHADER = preload("res://game/world/sites/seabed_terrain.gdshader")

const TILE_CELLS := 64
const VISIBILITY_RANGE_END_M := 260.0
const VISIBILITY_RANGE_MARGIN_M := 40.0

var _field: TerrainHeightField
var _material: ShaderMaterial
var _tiles_root: Node3D
var _collision: CollisionShape3D


func configure(field: TerrainHeightField) -> String:
	if field == null:
		return "terrain field is missing"
	_clear()
	_field = field
	_material = ShaderMaterial.new()
	_material.shader = TERRAIN_SHADER
	_build_tiles()
	_build_collision()
	return ""


func height_field() -> TerrainHeightField:
	return _field


func tile_count() -> int:
	return 0 if _tiles_root == null else _tiles_root.get_child_count()


func sonar_material_at(world_position: Vector3) -> int:
	return _field.material_at(world_position.x, world_position.z)


func sonar_reflectivity_at(world_position: Vector3) -> float:
	return _field.reflectivity_for(sonar_material_at(world_position))


func _clear() -> void:
	if _tiles_root != null:
		remove_child(_tiles_root)
		_tiles_root.free()
		_tiles_root = null
	if _collision != null:
		remove_child(_collision)
		_collision.free()
		_collision = null


func _build_tiles() -> void:
	_tiles_root = Node3D.new()
	_tiles_root.name = "Tiles"
	add_child(_tiles_root)
	var last_column := _field.columns() - 1
	var last_row := _field.rows() - 1
	var start_row := 0
	while start_row < last_row:
		var end_row := mini(start_row + TILE_CELLS, last_row)
		var start_column := 0
		while start_column < last_column:
			var end_column := mini(start_column + TILE_CELLS, last_column)
			_tiles_root.add_child(_build_tile(start_column, end_column, start_row, end_row))
			start_column = end_column
		start_row = end_row


func _build_tile(start_column: int, end_column: int, start_row: int, end_row: int) -> MeshInstance3D:
	var corner_min := _field.cell_world_position(start_column, start_row)
	var corner_max := _field.cell_world_position(end_column, end_row)
	var centre := Vector3(
		(corner_min.x + corner_max.x) * 0.5,
		0.0,
		(corner_min.z + corner_max.z) * 0.5
	)
	var vertices := PackedVector3Array()
	var normals := PackedVector3Array()
	var indices := PackedInt32Array()
	var columns_in_tile := end_column - start_column + 1
	for row in range(start_row, end_row + 1):
		for column in range(start_column, end_column + 1):
			vertices.append(_field.cell_world_position(column, row) - centre)
			normals.append(_field.normal_at_cell(column, row))
	for row in range(end_row - start_row):
		for column in range(end_column - start_column):
			var top_left := row * columns_in_tile + column
			var top_right := top_left + 1
			var bottom_left := top_left + columns_in_tile
			var bottom_right := bottom_left + 1
			indices.append_array([top_left, top_right, bottom_left])
			indices.append_array([top_right, bottom_right, bottom_left])
	var arrays: Array = []
	arrays.resize(Mesh.ARRAY_MAX)
	arrays[Mesh.ARRAY_VERTEX] = vertices
	arrays[Mesh.ARRAY_NORMAL] = normals
	arrays[Mesh.ARRAY_INDEX] = indices
	var mesh := ArrayMesh.new()
	mesh.add_surface_from_arrays(Mesh.PRIMITIVE_TRIANGLES, arrays)
	var instance := MeshInstance3D.new()
	instance.name = "Tile_%d_%d" % [start_column / TILE_CELLS, start_row / TILE_CELLS]
	instance.mesh = mesh
	instance.material_override = _material
	instance.position = centre
	instance.visibility_range_end = VISIBILITY_RANGE_END_M
	instance.visibility_range_end_margin = VISIBILITY_RANGE_MARGIN_M
	instance.visibility_range_fade_mode = GeometryInstance3D.VISIBILITY_RANGE_FADE_SELF
	return instance


func _build_collision() -> void:
	var shape := HeightMapShape3D.new()
	shape.map_width = _field.columns()
	shape.map_depth = _field.rows()
	var heights := PackedFloat32Array()
	heights.resize(_field.columns() * _field.rows())
	for row in _field.rows():
		for column in _field.columns():
			heights[row * _field.columns() + column] = _field.elevation_at_cell(column, row)
	shape.map_data = heights
	_collision = CollisionShape3D.new()
	_collision.name = "Collision"
	_collision.shape = shape
	var bounds := _field.bounds_m()
	_collision.position = Vector3(
		bounds.position.x + bounds.size.x * 0.5,
		0.0,
		bounds.position.y + bounds.size.y * 0.5
	)
	_collision.scale = Vector3(_field.cell_size_m(), 1.0, _field.cell_size_m())
	add_child(_collision)