## see https://ragnarokresearchlab.github.io/file-formats/grf
class_name GRF


var header: Header

class Header:
	const BYTE_LENGTH := 46
	
	## Byte Length: 15
	## Master of Magic
	var signature: String
	
	## Byte Length: 15
	var encryption: PackedByteArray
	
	## Byte Type: u32
	## Byte Length: 4
	var file_table_offset: int
	
	## Byte Type: u32
	## Byte Length: 4
	var scrambling_seed: int
	
	## Byte Type: u32
	## Byte Length: 4
	var scrambled_file_count: int
	
	## Byte Type: u32
	## Byte Length: 4
	var version: int
	
	
	func get_file_count() -> int:
		return scrambled_file_count - scrambling_seed - 7
	
	
	static func from_bytes(bytes: PackedByteArray):
		var header = Header.new()
		
		header.signature = bytes.slice(0, 15).get_string_from_utf8()
		header.encryption = bytes.slice(15, 15 + 15)
		header.file_table_offset = bytes.decode_u32(30)
		header.scrambling_seed = bytes.decode_u32(34)
		header.scrambled_file_count = bytes.decode_u32(38)
		header.version = bytes.decode_u32(42)
		
		return header


var file_table: FileTable

class FileTable:
	const BYTE_LENGTH := 8
	
	## Byte Type: u32
	## Byte Length: 4
	var compressed_size: int
	
	## Byte Type: u32
	## Byte Length: 4
	var decompressed_size: int
	
	var compressed_record_headers: PackedByteArray
	var decompressed_record_headers: PackedByteArray
	
	
	func generate_compressed_record_headers(grf_file: FileAccess):
		compressed_record_headers = grf_file.get_buffer(compressed_size)
	
	
	func decompress():
		decompressed_record_headers = compressed_record_headers.decompress(
			decompressed_size,
			FileAccess.CompressionMode.COMPRESSION_DEFLATE
		)
	
	
	static func from_bytes(bytes: PackedByteArray):
		var file_table = FileTable.new()
		
		file_table.compressed_size = bytes.decode_u32(0)
		file_table.decompressed_size = bytes.decode_u32(4)
		
		return file_table


var file_entries: Array[FileEntry]

class FileEntry:
	const BYTE_LENGTH := 17
	
	var file_name: String
	
	## Byte Type: u32
	## Byte Length: 4
	var compressed_size: int
	
	## Byte Type: u32
	## Byte Length: 4
	var byte_aligned_size: int
	
	## Byte Type: u32
	## Byte Length: 4
	var decompressed_size: int
	
	## Byte Type: u8
	## Byte Length: 1
	var file_type: int
	
	## Byte Type: u32
	## Byte Length: 4
	var offset: int
	
	
	func get_byte_length() -> int:
		return BYTE_LENGTH #+ file_name.to_ascii_buffer().size()
	
	
	func get_file_path() -> String:
		var parts = file_name.split("\\")
		
		return "/".join(parts)
	
	
	func get_contents(grf_file: FileAccess):
		var previous_position = grf_file.get_position()
		
		grf_file.seek(Header.BYTE_LENGTH + offset)
		var buffer = grf_file.get_buffer(byte_aligned_size)
		var contents = buffer.decompress(
			decompressed_size,
			FileAccess.CompressionMode.COMPRESSION_DEFLATE
		)
		
		grf_file.seek(previous_position)
		
		return contents
	
	
	static func from_bytes_with_filename(bytes: PackedByteArray, file_name: String):
		var file_entry = FileEntry.new()
		
		file_entry.file_name = file_name
		file_entry.compressed_size = bytes.decode_u32(0)
		file_entry.byte_aligned_size = bytes.decode_u32(4)
		file_entry.decompressed_size = bytes.decode_u32(8)
		file_entry.file_type = bytes.decode_u8(12)
		file_entry.offset = bytes.decode_u32(13)
		
		return file_entry


var file_access: FileAccess


static func open(path: String):
	var grf = GRF.new()
	
	grf.file_access = FileAccess.open(path, FileAccess.ModeFlags.READ)
	
	grf.header = GRF.Header.from_bytes(grf.file_access.get_buffer(Header.BYTE_LENGTH))
	
	grf.file_access.seek(Header.BYTE_LENGTH + grf.header.file_table_offset)
	grf.file_table = FileTable.from_bytes(grf.file_access.get_buffer(8))
	
	grf.file_table.generate_compressed_record_headers(grf.file_access)
	grf.file_table.decompress()
	
	grf.file_entries = [] as Array[FileEntry]
	var file_entry_offset = 0
	while file_entry_offset < grf.file_table.decompressed_record_headers.size():
		var file_name_size = grf.file_table.decompressed_record_headers.find(0, file_entry_offset) + 1 - file_entry_offset
		var file_entry = FileEntry.from_bytes_with_filename(
			grf.file_table.decompressed_record_headers.slice(
				file_entry_offset + file_name_size,
				file_entry_offset + file_name_size + FileEntry.BYTE_LENGTH
			),
			grf.file_table.decompressed_record_headers.slice(
				file_entry_offset,
				file_entry_offset + file_name_size
			).get_string_from_ascii()
		)
		
		grf.file_entries.append(file_entry)
		file_entry_offset += file_entry.get_byte_length() + file_name_size
	
	return grf


func write():
	for file_entry in file_entries:
		var file_path: String = file_entry.get_file_path()
		
		var base_directory = DirAccess.open("res://data")
		base_directory.make_dir_recursive("extracted/" + file_path.get_base_dir())
		
		var file = FileAccess.open("res://data/extracted/%s" % [file_path], FileAccess.WRITE_READ)
		file.store_buffer(file_entry.get_contents(file_access))