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


## Row-major elevations (index = row * columns + column), the HeightMapShape3D layout.
func elevations_m() -> PackedFloat32Array:
	return _data.elevations_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:
	return _normal_at(_data.elevations_m, _clamp_column(column), _clamp_row(row))


## World positions of the cells [start_column..end_column] x [start_row..end_row]
## (bounds included, clamped to the grid), row-major. Same values as cell_world_position.
func cell_block_positions(start_column: int, end_column: int, start_row: int, end_row: int) -> PackedVector3Array:
	var first_column := _clamp_column(start_column)
	var last_column := _clamp_column(end_column)
	var first_row := _clamp_row(start_row)
	var last_row := _clamp_row(end_row)
	var elevations := _data.elevations_m
	var columns := _data.columns
	var cell_size := _data.cell_size_m
	var positions := PackedVector3Array()
	positions.resize((last_column - first_column + 1) * (last_row - first_row + 1))
	var index := 0
	for row in range(first_row, last_row + 1):
		var z := _data.origin_z_m + float(row) * cell_size
		var row_start := row * columns
		for column in range(first_column, last_column + 1):
			positions[index] = Vector3(
				_data.origin_x_m + float(column) * cell_size,
				elevations[row_start + column],
				z
			)
			index += 1
	return positions


## Normals of the same cell block, row-major. Same values as normal_at_cell.
func cell_block_normals(start_column: int, end_column: int, start_row: int, end_row: int) -> PackedVector3Array:
	var first_column := _clamp_column(start_column)
	var last_column := _clamp_column(end_column)
	var first_row := _clamp_row(start_row)
	var last_row := _clamp_row(end_row)
	var elevations := _data.elevations_m
	var normals := PackedVector3Array()
	normals.resize((last_column - first_column + 1) * (last_row - first_row + 1))
	var index := 0
	for row in range(first_row, last_row + 1):
		for column in range(first_column, last_column + 1):
			normals[index] = _normal_at(elevations, column, row)
			index += 1
	return normals


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


## Central differences, one-sided on the grid edges. column and row must be in range.
func _normal_at(elevations: PackedFloat32Array, column: int, row: int) -> Vector3:
	var columns := _data.columns
	var left := maxi(column - 1, 0)
	var right := mini(column + 1, columns - 1)
	var north := maxi(row - 1, 0)
	var south := mini(row + 1, _data.rows - 1)
	var slope_x := (
		(elevations[row * columns + right] - elevations[row * columns + left])
		/ (float(right - left) * _data.cell_size_m)
	)
	var slope_z := (
		(elevations[south * columns + column] - elevations[north * columns + column])
		/ (float(south - north) * _data.cell_size_m)
	)
	return Vector3(-slope_x, 1.0, -slope_z).normalized()


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)