writer.py

import os, struct, zlib

def get_padding_amount(offset):
    return ((24 - (offset % 16)) % 16)

def intToBytes(number):
    return int(number).to_bytes(4, byteorder="little", signed=False)


nus3file = open(r'D:\Modding\Super Smash Bros. Ultimate\Audio\new_test.nus3audio', "r+b")

info = {
    "HEADER": {},
    "AUDIINDX": {},
    "TNID": {},
    "NMOF": {},
    "ADOF": {},
    "TNNM": {},
    "JUNK": {},
    "PACK": {},
}

#region Header
info["HEADER"]["magic"] = nus3file.read(4).decode()
info["HEADER"]["filesize"] = struct.unpack("<I", nus3file.read(4))[0]
#endregion

#region Audiindx
info["AUDIINDX"]["magic"] = nus3file.read(8).decode()
info["AUDIINDX"]["size"] = struct.unpack("<I", nus3file.read(4))[0]
info["AUDIINDX"]["count"] = struct.unpack("<I", nus3file.read(4))[0]
#endregion

#region Tone ID
info["TNID"]["magic"] = nus3file.read(4).decode()
info["TNID"]["size"] = struct.unpack("<I", nus3file.read(4))[0]

if info["TNID"]["size"] >= info["AUDIINDX"]["count"] * 4:
    info["TNID"]["tracknumbers"] = []
    for x in range(info["AUDIINDX"]["count"]):
        info["TNID"]["tracknumbers"].append(struct.unpack("<I", nus3file.read(4))[0])
else:
    info["TNID"]["data"] = []
    for x in range(info["TNID"]["size"]):
        info["TNID"]["data"].append(nus3file.read(1))
#endregion

#region NMOF
info["NMOF"]["magic"] = nus3file.read(4).decode()
info["NMOF"]["size"] = struct.unpack("<I", nus3file.read(4))[0]

if info["NMOF"]["size"] >= info["AUDIINDX"]["count"] * 4:
    info["NMOF"]["names"] = []
    for x in range(info["AUDIINDX"]["count"]):
        info["NMOF"]["names"].append(struct.unpack("<I", nus3file.read(4))[0])
else:
    info["NMOF"]["data"] = []
    for x in range(info["NMOF"]["size"]):
        info["NMOF"]["data"].append(nus3file.read(1))
#endregion

#region ADOF
info["ADOF"]["magic"] = nus3file.read(4).decode()
info["ADOF"]["size"] = struct.unpack("<I", nus3file.read(4))[0]

if info["ADOF"]["size"] >= info["AUDIINDX"]["count"] * 8:
    info["ADOF"]["file_entry"] = []
    for x in range(info["AUDIINDX"]["count"]):
        file_entry = {
            "fileOffset": struct.unpack("<I", nus3file.read(4))[0],
            "fileSize": struct.unpack("<I", nus3file.read(4))[0]
        }
        info["ADOF"]["file_entry"].append(file_entry)
else:
    info["ADOF"]["data"] = []
    for x in range(info["ADOF"]["size"]):
        info["ADOF"]["data"].append(nus3file.read(1))
#endregion

#region TNNM
info["TNNM"]["magic"] = nus3file.read(4).decode()
info["TNNM"]["size"] = struct.unpack("<I", nus3file.read(4))[0]
info["TNNM"]["name_entries"] = []

nus3string = ""
for x in range(info["TNNM"]["size"]):
    res = nus3file.read(1)
    if res != b'\x00':
        nus3string = "%s%s" % (nus3string, res.decode())
    else:
        info["TNNM"]["name_entries"].append(nus3string)
        nus3string = ""
#endregion

#region JUNK
info["JUNK"]["magic"] = nus3file.read(4).decode()
info["JUNK"]["size"] = struct.unpack("<I", nus3file.read(4))[0]

for x in range(info["JUNK"]["size"]):
    res = nus3file.read(1)
#endregion

#region PACK
info["PACK"]["magic"] = nus3file.read(4).decode()
info["PACK"]["size"] = struct.unpack("<I", nus3file.read(4))[0]
#endregion

#region Link file data with fileData entry
for x in range(len(info["ADOF"]["file_entry"])):
    nus3file.seek(info["ADOF"]["file_entry"][x]["fileOffset"])
    info["ADOF"]["file_entry"][x]["fileData"] = nus3file.read(info["ADOF"]["file_entry"][x]["fileSize"])
#endregion

# Close original nus3file
nus3file.close()

#region Open and Save test.lopus to one of the entries
custom_lopus = open("test.lopus", "r+b")

info["ADOF"]["file_entry"][0]["fileData"] = custom_lopus.read()

custom_lopus.close()
#endregion
    
string_offsets = []
file_offsets = []

nus3_size = len("NUS3") + 4
audi_size = len("AUDIINDX") + (4 * 2)
tnid_size = len("TNID") + 4 + (4 * len(info["ADOF"]["file_entry"]))
nmof_size = tnid_size
adof_size = len("ADOF") + 4 + (4 * len(info["ADOF"]["file_entry"]) * 2)

string_section_start = nus3_size + audi_size + tnid_size + nmof_size + adof_size + len("TNNM") + 4

string_section_size = 0

for x in range(len(info["TNNM"]["name_entries"])):
    string_offsets.append(string_section_start + string_section_size)
    string_section_size += len(info["TNNM"]["name_entries"][x]) + 1

junk_pad = get_padding_amount(string_section_start + string_section_size + len("JUNK") + 4)
junk_size = len("JUNK") + 4 + junk_pad

pack_section_start = string_section_start + string_section_size + junk_size + len("PACK") + 4

pack_section_size_no_pad = 0
pack_section_size = 0
existing_files = {}
files_to_pack = []

for x in range(len(info["ADOF"]["file_entry"])):
    data_hash = zlib.crc32(info["ADOF"]["file_entry"][x]["fileData"])
    
    offset_pair = {}

    if data_hash not in existing_files:
        pair = {
            "fileOffset": pack_section_start + pack_section_size,
            'fileSize': len(info["ADOF"]["file_entry"][x]["fileData"])
        }
        existing_files[data_hash] = pair
        files_to_pack.append(info["ADOF"]["file_entry"][x])
        pack_section_size_no_pad = pack_section_size + len(info["ADOF"]["file_entry"][x]["fileData"])
        pack_section_size += int(((len(info["ADOF"]["file_entry"][x]["fileData"]) + 15) / 16)) * 16

        offset_pair = pair
    else:
        offset_pair = existing_files[data_hash]

    file_offsets.append(offset_pair)

if len(info["ADOF"]["file_entry"]) == 1:
    pack_section_size = pack_section_size_no_pad

filesize = pack_section_start + pack_section_size

try:
    os.remove("output.nus3audio")
except:
    pass

nus3output = open("output.nus3audio", "x+b")

nus3output.write(b'NUS3')
nus3output.write(intToBytes(filesize - nus3_size))

nus3output.write(b'AUDIINDX')
nus3output.write(intToBytes(4))
nus3output.write(intToBytes(len(info["ADOF"]["file_entry"])))

nus3output.write(b'TNID')
nus3output.write(intToBytes(len(info["ADOF"]["file_entry"]) * 4))
for x in range(len(info["ADOF"]["file_entry"])):
    nus3output.write(intToBytes(x))

nus3output.write(b'NMOF')
nus3output.write(intToBytes(len(info["ADOF"]["file_entry"]) * 4))
for x in string_offsets:
    nus3output.write(intToBytes(x))

nus3output.write(b'ADOF')
nus3output.write(intToBytes(len(info["ADOF"]["file_entry"] * 8)))
for x in file_offsets:
    nus3output.write(intToBytes(x["fileOffset"]))
    nus3output.write(intToBytes(x["fileSize"]))

nus3output.write(b'TNNM')
nus3output.write(intToBytes(string_section_size))
for x in range(len(info["TNNM"]["name_entries"])):
    nus3output.write(info["TNNM"]["name_entries"][x].encode() + b'\x00')

nus3output.write(b'JUNK')
nus3output.write(intToBytes(junk_pad))
for x in range(junk_pad):
    nus3output.write(int(0).to_bytes(1, byteorder="little", signed=False))

nus3output.write(b'PACK')
nus3output.write(intToBytes(pack_section_size))

for x in files_to_pack:
    nus3output.write(x["fileData"])
    fill = nus3output.tell() % 16
    for i in range(fill):
        nus3output.write(int(0).to_bytes(1, byteorder="little", signed=False))