class_name TerrainHeightField
extends RefCounted

const SonarMaterial = preload("res://game/domain/sonar/sonar_material.gd")
const SiteTerrainData = preload("res://game/domain/sites/site_terrain_data.gd")

var _data: SiteTerrainData
var _minimum_elevation_m := 0.0
var _maximum_elevation_m := 0.0


static func from_data(data: SiteTerrainData) -> TerrainHeightField:
	if data == null or not data.validation_error().is_empty():
		return null
	var field := TerrainHeightField.new()
	field._data = data
	field._minimum_elevation_m = data.elevations_m[0]
	field._maximum_elevation_m = data.elevations_m[0]
	for elevation: float in data.elevations_m:
		field._minimum_elevation_m = minf(field._minimum_elevation_m, elevation)
		field._maximum_elevation_m = maxf(field._maximum_elevation_m, elevation)
	return field


func columns() -> int:
	return _data.columns


func rows() -> int:
	return _data.rows


func cell_size_m() -> float:
	return _data.cell_size_m


func origin_m() -> Vector2:
	return Vector2(_data.origin_x_m, _data.origin_z_m)


func bounds_m() -> Rect2:
	return Rect2(
		_data.origin_x_m,
		_data.origin_z_m,
		float(_data.columns - 1) * _data.cell_size_m,
		float(_data.rows - 1) * _data.cell_size_m
	)


func contains(x_m: float, z_m: float) -> bool:
	return bounds_m().has_point(Vector2(x_m, z_m))


func minimum_elevation_m() -> float:
	return _minimum_elevation_m


func maximum_elevation_m() -> float:
	return _maximum_elevation_m


func elevation_at_cell(column: int, row: int) -> float:
	return _data.elevations_m[_data.index_of(_clamp_column(column), _clamp_row(row))]


func material_at_cell(column: int, row: int) -> int:
	return _data.materials[_data.index_of(_clamp_column(column), _clamp_row(row))]


func cell_world_position(column: int, row: int) -> Vector3:
	return Vector3(
		_data.origin_x_m + float(column) * _data.cell_size_m,
		elevation_at_cell(column, row),
		_data.origin_z_m + float(row) * _data.cell_size_m
	)


func normal_at_cell(column: int, row: int) -> Vector3:
	var left := elevation_at_cell(column - 1, row)
	var right := elevation_at_cell(column + 1, row)
	var north := elevation_at_cell(column, row - 1)
	var south := elevation_at_cell(column, row + 1)
	var span_x := float(_clamp_column(column + 1) - _clamp_column(column - 1)) * _data.cell_size_m
	var span_z := float(_clamp_row(row + 1) - _clamp_row(row - 1)) * _data.cell_size_m
	var slope_x := (right - left) / span_x
	var slope_z := (south - north) / span_z
	return Vector3(-slope_x, 1.0, -slope_z).normalized()


func elevation_at(x_m: float, z_m: float) -> float:
	var column_f := clampf(
		(x_m - _data.origin_x_m) / _data.cell_size_m,
		0.0,
		float(_data.columns - 1)
	)
	var row_f := clampf(
		(z_m - _data.origin_z_m) / _data.cell_size_m,
		0.0,
		float(_data.rows - 1)
	)
	var column := mini(int(floorf(column_f)), _data.columns - 2)
	var row := mini(int(floorf(row_f)), _data.rows - 2)
	var tx := column_f - float(column)
	var tz := row_f - float(row)
	var top := lerpf(elevation_at_cell(column, row), elevation_at_cell(column + 1, row), tx)
	var bottom := lerpf(
		elevation_at_cell(column, row + 1),
		elevation_at_cell(column + 1, row + 1),
		tx
	)
	return lerpf(top, bottom, tz)


func material_at(x_m: float, z_m: float) -> int:
	var column := int(roundf((x_m - _data.origin_x_m) / _data.cell_size_m))
	var row := int(roundf((z_m - _data.origin_z_m) / _data.cell_size_m))
	return material_at_cell(column, row)


func reflectivity_for(material: int) -> float:
	match material:
		SonarMaterial.Value.SAND:
			return _data.sand_reflectivity
		_:
			return _data.rock_reflectivity


func _clamp_column(column: int) -> int:
	return clampi(column, 0, _data.columns - 1)


func _clamp_row(row: int) -> int:
	return clampi(row, 0, _data.rows - 1)