extends RefCounted

## Frozen v1 encoder from commit 627b200, kept only as the byte-compatibility
## oracle and unoptimized benchmark baseline. Do not update with production changes.
##
## Dictionary insertion order never affects the result. Type tags and byte
## lengths make the canonical form unambiguous, and Array order remains
## significant. Runtime Objects and other process-local values are rejected;
## callers must first export them to Dictionaries, Arrays and value types.

const FORMAT_VERSION := 1
const MAX_NESTING_DEPTH := 128


static func compute(value: Variant) -> String:
	var canonical := canonical_bytes(value)
	if canonical.is_empty():
		return ""
	var context := HashingContext.new()
	if context.start(HashingContext.HASH_SHA256) != OK:
		push_error("Could not initialize the simulation digest hash")
		return ""
	context.update(canonical)
	return context.finish().hex_encode()


static func canonical_bytes(value: Variant) -> PackedByteArray:
	var output := PackedByteArray()
	_append_ascii(output, "the-tree:simulation-digest:v%d;" % FORMAT_VERSION)
	if not _encode_value(value, output, 0):
		return PackedByteArray()
	return output


static func _encode_value(value: Variant, output: PackedByteArray, depth: int) -> bool:
	if depth > MAX_NESTING_DEPTH:
		push_error("SimulationDigest data exceeds the maximum nesting depth")
		return false

	match typeof(value):
		TYPE_NIL:
			_append_ascii(output, "n")
		TYPE_BOOL:
			_append_ascii(output, "b1" if bool(value) else "b0")
		TYPE_INT:
			_append_ascii(output, "i%d;" % int(value))
		TYPE_FLOAT:
			_append_ascii(output, "f")
			return _append_float64(output, float(value))
		TYPE_STRING:
			_append_sized_bytes(output, "s", String(value).to_utf8_buffer())
		TYPE_STRING_NAME:
			_append_sized_bytes(output, "q", String(value).to_utf8_buffer())
		TYPE_VECTOR2:
			var vector: Vector2 = value
			_append_ascii(output, "v2")
			return _append_float64(output, vector.x) and _append_float64(output, vector.y)
		TYPE_VECTOR2I:
			var vector: Vector2i = value
			_append_ascii(output, "w2")
			_append_ascii(output, "i%d;i%d;" % [vector.x, vector.y])
		TYPE_RECT2:
			var rect: Rect2 = value
			_append_ascii(output, "r2")
			return (
				_append_float64(output, rect.position.x)
				and _append_float64(output, rect.position.y)
				and _append_float64(output, rect.size.x)
				and _append_float64(output, rect.size.y)
			)
		TYPE_RECT2I:
			var rect: Rect2i = value
			_append_ascii(output, "x2")
			_append_ascii(output, "i%d;i%d;i%d;i%d;" % [rect.position.x, rect.position.y, rect.size.x, rect.size.y])
		TYPE_VECTOR3:
			var vector: Vector3 = value
			_append_ascii(output, "v3")
			return (
				_append_float64(output, vector.x)
				and _append_float64(output, vector.y)
				and _append_float64(output, vector.z)
			)
		TYPE_VECTOR3I:
			var vector: Vector3i = value
			_append_ascii(output, "w3")
			_append_ascii(output, "i%d;i%d;i%d;" % [vector.x, vector.y, vector.z])
		TYPE_VECTOR4:
			var vector: Vector4 = value
			_append_ascii(output, "v4")
			return (
				_append_float64(output, vector.x)
				and _append_float64(output, vector.y)
				and _append_float64(output, vector.z)
				and _append_float64(output, vector.w)
			)
		TYPE_VECTOR4I:
			var vector: Vector4i = value
			_append_ascii(output, "w4")
			_append_ascii(output, "i%d;i%d;i%d;i%d;" % [vector.x, vector.y, vector.z, vector.w])
		TYPE_COLOR:
			var color: Color = value
			_append_ascii(output, "c")
			return (
				_append_float64(output, color.r)
				and _append_float64(output, color.g)
				and _append_float64(output, color.b)
				and _append_float64(output, color.a)
			)
		TYPE_ARRAY:
			return _encode_array(value, output, depth)
		TYPE_DICTIONARY:
			return _encode_dictionary(value, output, depth)
		TYPE_PACKED_BYTE_ARRAY:
			_append_sized_bytes(output, "pb", value)
		TYPE_PACKED_INT32_ARRAY, TYPE_PACKED_INT64_ARRAY:
			return _encode_packed_int_array(value, output)
		TYPE_PACKED_FLOAT32_ARRAY, TYPE_PACKED_FLOAT64_ARRAY:
			return _encode_packed_float_array(value, output)
		TYPE_PACKED_STRING_ARRAY:
			return _encode_packed_string_array(value, output)
		TYPE_PACKED_VECTOR2_ARRAY:
			return _encode_packed_vector2_array(value, output)
		TYPE_PACKED_VECTOR3_ARRAY:
			return _encode_packed_vector3_array(value, output)
		TYPE_PACKED_COLOR_ARRAY:
			return _encode_packed_color_array(value, output)
		_:
			push_error("SimulationDigest does not support Variant type %s" % type_string(typeof(value)))
			return false
	return true


static func _encode_array(value: Array, output: PackedByteArray, depth: int) -> bool:
	_append_ascii(output, "a%d:" % value.size())
	for item in value:
		if not _encode_value(item, output, depth + 1):
			return false
	return true


static func _encode_dictionary(value: Dictionary, output: PackedByteArray, depth: int) -> bool:
	var entries: Array[Dictionary] = []
	for key in value:
		var encoded_key := PackedByteArray()
		if not _encode_value(key, encoded_key, depth + 1):
			return false
		entries.append({
			"sort_key": encoded_key.hex_encode(),
			"encoded_key": encoded_key,
			"value": value[key],
		})
	entries.sort_custom(func(left: Dictionary, right: Dictionary) -> bool:
		return String(left["sort_key"]) < String(right["sort_key"])
	)

	_append_ascii(output, "d%d:" % entries.size())
	for entry in entries:
		var encoded_key: PackedByteArray = entry["encoded_key"]
		output.append_array(encoded_key)
		if not _encode_value(entry["value"], output, depth + 1):
			return false
	return true


static func _encode_packed_int_array(value: Variant, output: PackedByteArray) -> bool:
	var tag := "pi32" if typeof(value) == TYPE_PACKED_INT32_ARRAY else "pi64"
	_append_ascii(output, "%s%d:" % [tag, value.size()])
	for item in value:
		_append_ascii(output, "i%d;" % int(item))
	return true


static func _encode_packed_float_array(value: Variant, output: PackedByteArray) -> bool:
	var tag := "pf32" if typeof(value) == TYPE_PACKED_FLOAT32_ARRAY else "pf64"
	_append_ascii(output, "%s%d:" % [tag, value.size()])
	for item in value:
		if not _append_float64(output, float(item)):
			return false
	return true


static func _encode_packed_string_array(value: PackedStringArray, output: PackedByteArray) -> bool:
	_append_ascii(output, "ps%d:" % value.size())
	for item in value:
		_append_sized_bytes(output, "s", item.to_utf8_buffer())
	return true


static func _encode_packed_vector2_array(value: PackedVector2Array, output: PackedByteArray) -> bool:
	_append_ascii(output, "pv2%d:" % value.size())
	for item in value:
		if not _append_float64(output, item.x) or not _append_float64(output, item.y):
			return false
	return true


static func _encode_packed_vector3_array(value: PackedVector3Array, output: PackedByteArray) -> bool:
	_append_ascii(output, "pv3%d:" % value.size())
	for item in value:
		if (
			not _append_float64(output, item.x)
			or not _append_float64(output, item.y)
			or not _append_float64(output, item.z)
		):
			return false
	return true


static func _encode_packed_color_array(value: PackedColorArray, output: PackedByteArray) -> bool:
	_append_ascii(output, "pc%d:" % value.size())
	for item in value:
		if (
			not _append_float64(output, item.r)
			or not _append_float64(output, item.g)
			or not _append_float64(output, item.b)
			or not _append_float64(output, item.a)
		):
			return false
	return true


static func _append_float64(output: PackedByteArray, value: float) -> bool:
	if is_nan(value) or is_inf(value):
		push_error("SimulationDigest rejects NaN and infinite float values")
		return false
	var normalized := 0.0 if value == 0.0 else value
	var encoded := PackedByteArray()
	encoded.resize(8)
	encoded.encode_double(0, normalized)
	output.append_array(encoded)
	return true


static func _append_sized_bytes(output: PackedByteArray, tag: String, value: PackedByteArray) -> void:
	_append_ascii(output, "%s%d:" % [tag, value.size()])
	output.append_array(value)


static func _append_ascii(output: PackedByteArray, value: String) -> void:
	output.append_array(value.to_utf8_buffer())