extends Node
#warning-ignore-all:return_value_discarded
const STRUCT := preload('res://scripts/struct.gd')
const SLOT_IN_USE := 0xE41B
var struct_types := STRUCT.get_base_structarraytypes()

# FFV SRAM is 4 slots of 0x700byte save files
# $0000-$06FF - Save Slot 1
# $0700-$0DFF - Save Slot 2
# $0E00-$14FF - Save Slot 3
# $1500-$1BFF - Save Slot 4
# $1C00-$1FEF - Empty
# $1FF0-$1FF7 - Checksum (2 bytes per slot)
# $1FF8-$1FFF - use table - contains $E41B if a slot is in use (deleting a save will just change this)
# Checksum just sums up every 16bit word from 0x000-0x600 of the save slot, using the carry flag.
# The carry flag means that it is not strictly modulo arithmetic, but you have to add 1 every time you pass 0xFFFF

# Offsets within save slot
# $000:600 = $500:B00 in WRAM (0x7E0500:0x7E0B00)  only values that don't match are things like game frame timer which increments immediately after load
#
# $000-$04F - Character Slot 1
# $050=$09F - Character Slot 2
# $0A0=$0EF - Character Slot 3
# $0F0=$13F - Character Slot 4
# $447-$449 - Current Gil
#
# $5D8 - Current Map X position
# $5D9 - Current Map Y position
#
# $600-$6FF - Appears to be unused and zeroed out, not used for checksum. Maybe we can use it for cool metadata? :)

func get_slot_checksum(slot: StreamPeerBuffer) -> int:
	slot.seek(0)
	var checksum := 0
	for i in 0x600:  # Last 0x100 bytes aren't checksummed
		checksum += slot.get_u16()
		if checksum > 0xFFFF:  # Addition of shorts can only overflow
			checksum &= 0xFFFF
			if i < 0x5FF:
				checksum += 1  # TODO: confirm this carry flag edge case is correct!
	return checksum

func get_struct(buffer: StreamPeer, struct_name: String) -> Dictionary:
	# Does not seek to the start of the buffer.
	# Make sure it is set to where you want to start reading.
	if not (struct_name in struct_types):
		print_debug('Attempted to get undeclared struct: "%s"' % struct_name)
		return {}
	return struct_types[struct_name].get_value(buffer, [0, 0])

func put_struct(buffer: StreamPeer, struct_name: String, data: Dictionary):
	if not (struct_name in struct_types):
		print_debug('Attempted to put undeclared struct: "%s"' % struct_name)
		return
	struct_types[struct_name].put_value(buffer, data, [0, 0])

func deserialize_save_slot(buffer: StreamPeerBuffer) -> Dictionary:
	return struct_types['Save_slot'].get_value(buffer, [0, 0])

func load_save_slot(buffer: StreamPeerBuffer) -> Dictionary:
	# Like deserialize_save_slot, but also decodes strings and maybe other postprocessing later
	var data = deserialize_save_slot(buffer)
	data.character_names_decoded = StringLoader.decode_array(data.character_names, 'RPGe_small')
	for c in data.characters:
		c.equipped_abilities = [c.ability_1, c.ability_2, c.ability_3, c.ability_4]
	return data

func serialize_save_slot(data: Dictionary) -> StreamPeerBuffer:
	var buffer := StreamPeerBuffer.new()
	struct_types['Save_slot'].put_value(buffer, data, [0, 0])
	var padding := PoolByteArray()
	padding.resize(0x100)
	padding.fill(0)
	buffer.put_data(padding)
	return buffer

func make_snes_save_file(slot_dicts: Array) -> PoolByteArray:
	# Pass a length 4 array of dictionaries.
	# Falsey entries will be zeroed out slots, with the active flag at the end also zeroed.
	assert(len(slot_dicts) == 4)
	var buffer := StreamPeerBuffer.new()
	var zeroes := PoolByteArray()
	zeroes.resize(0x700)
	zeroes.fill(0)
	var checksums := []
	for dict in slot_dicts:
		if dict:
			var slot := serialize_save_slot(dict)
			var checksum := get_slot_checksum(slot)
			buffer.put_data(slot.data_array)
			if slot.data_array == zeroes:
				checksums.append(-1)
			else:
				checksums.append(checksum)
		else:
			buffer.put_data(zeroes)
			checksums.append(-1)
	# Pad from $1C00 == 7168 to $1FF0 == 8160
	buffer.put_data(zeroes.subarray(0, 991))  # BEWARE: SUBARRAY IS INCLUSIVE
	# Mystery byte TODO: INVESTIGATE LATER
	buffer.put_8(1)
	# Pad from $1FE1 == 8161 to $1FF0 == 8176
	buffer.put_data(zeroes.subarray(0, 14))  # BEWARE: SUBARRAY IS INCLUSIVE
	# Checksums
	for c in checksums:
		if c > -1:
			buffer.put_u16(c)
		else:
			buffer.put_u16(0)
	# Active flag
	for c in checksums:
		if c > -1:
			buffer.put_u16(SLOT_IN_USE)
		else:
			buffer.put_u16(0)
	return buffer.data_array

func get_save_slot(sram: File, slot_id: int) -> StreamPeerBuffer:
	var buffer := StreamPeerBuffer.new()
	sram.seek(0x700 * slot_id)
	buffer.set_data_array(sram.get_buffer(0x700))
	return buffer

func save_slot(sram: File, slot_id: int, slot: StreamPeerBuffer):
	sram.seek(0x700 * slot_id)
	sram.store_buffer(slot.data_array)
	sram.seek(0x1FF0 + (slot_id*2))
	sram.store_16(get_slot_checksum(slot))
	sram.seek(0x1FF8 + (slot_id*2))
	sram.store_16(SLOT_IN_USE)

func delete_save_slot(sram: File, slot_id: int):
	sram.seek(0x1FF8 + (slot_id*2))
	sram.store_16(0)

func _ready():
	STRUCT.parse_struct_definitions_from_tsv_filename('res://data/SNES_save.tsv', struct_types)