from flask import Response
import functools
import os

# 4MiB chunks
CHUNK_SIZE = 4_194_304

# Specification de l'entête du fichier
# Numéro Nom      Début   Taille   Description
#      1 name         0      100   Nom du fichier
#      2 mode       100        8   Permissions
#      3 uid        108        8   Propriétaire (inutilisé si format étendu)
#      4 gid        116        8   Groupe (inutilisé si format étendu)
#      5 size       124       12   Taille du fichier en octets.
#      6 mtime      136       12   Dernière modification en temps Unix.
#      7 chksum     148        8   Somme de contrôle de l'en-tête où ce champ est considéré comme rempli d'espaces (32)
#      8 type flag  156        1   Type de fichier
#      9 linkname   157      100   Nom du fichier pointé par ce lien symbolique (Si le type indique un lien symbolique)


def header_chunk(filename: str, filepath: str) -> bytes:
    stat = os.stat(filepath)
    buffer = bytearray()

    # Field 1: filename on 100 bytes
    buffer += filename.encode('ascii')
    buffer += b'\x00' * (100 - len(filename))

    # Field 2: mode, on 8 bytes
    # TODO we put 777 for test
    buffer += '0000777'.encode('ascii') + b'\x00'

    # Field 3: owner, we put 1000, default user
    buffer += '0001000'.encode('ascii') + b'\x00'

    # Field 4: group, we put 1000
    buffer += '0001000'.encode('ascii') + b'\x00'

    # Field 5: file size in bytes in ascii
    buffer += str(stat.st_size).rjust(11, '0').encode('ascii') + b'\x00'

    # Field 6: last modified, zeros for now
    # buffer += '00000000000'.encode('ascii') + b'\x00'
    buffer += '1721728914'.rjust(11, '0').encode('ascii') + b'\x00'

    # Field 7: checksum, we put spaces and we will edit it at the end
    buffer += '        '.encode('ascii')

    # Field 8: type flag, 0 because we only have regular files
    buffer += b'0'

    # Field 9: linkname, \x00s because we only have regular files
    buffer += b'\x00' * 100

    # POSIX 1003.1-1990: 255 empty bytes
    buffer += b'\x00' * 255

    # Compute the checksum
    checksum = str(functools.reduce(lambda x, y: x + y, buffer)).rjust(6, '0').encode('ascii') + b'\x00 '
    buffer[148:156] = checksum

    return bytes(buffer)


class TarSender:
    def __init__(self):
        self.files: dict[str, str] = {}

    def add_file(self, filename: str, filepath: str):
        self.files[filename] = filepath

    def response(self):
        def generate():
            for name, file in self.files.items():
                yield header_chunk(name, file)

                bytes_sent = 0

                with open(file, 'rb') as f:
                    while True:
                        bytes = f.read(CHUNK_SIZE)

                        if len(bytes) == 0:
                            break

                        bytes_sent += len(bytes)
                        yield bytes

                    # Because tar use records of 512 bytes, we need to pad the
                    # file with zeroes to fill the last chunk
                    yield b'\x00' * (512 - bytes_sent % 512)

        return Response(
            generate(),
            mimetype='application/x-tar',
            headers={'Content-Disposition': 'attachment; filename="archive.tar"'}
        )