import sys
import argparse


def reduce_file_size(filename, new_filename, n_packages, header_size=0, packet_size=32):
    """
    Create a smaller version of a binary file containing a defined number of data packages

    The file structure has to consist of a header (header_size) and multiple data packages of
    size packet_size. This preserves the header and only reduces the number of data packages.

    Parameters
    ----------
    filename:
        The source filename to load from.
    new_filename:
        The target filename to save to. Will be overwritten if it exists.
    n_packages:
        The number of packages to preserve in the file
    header_size:
        The size of the file header in byte. Default 0
    packet_size:
        The size of a single data package in byte. Default 32
    Returns
    -------

    """
    with open(filename, 'rb') as f:
        data = f.read(header_size + n_packages * packet_size)
    with open(new_filename, 'wb') as f:
        f.write(data)


param_help = """
tdt-tev': {'header_size': 0, 'packet_size': 8},  # uint8
'tdt-tsq': {'header_size': 0, 'packet_size': 40*8},
'tdt-sev': {'header_size': 0, 'packet_size': 8},  # uint8
'edf': {'header_size': 256 (number_of_signals + 1),  # 256 byte per channel and header
        'packet_size': number_of_signals * samples_in_datarecord * 2}}  # int16
"""

if __name__ == '__main__':
    parser = argparse.ArgumentParser(description='Bit-based file manipulation')
    subparsers = parser.add_subparsers(help='cut file', dest='subparser_name')

    # create the parser for the "cut" command
    parser_cut = subparsers.add_parser('cut', help='shorten file to limited bits')
    parser_cut.add_argument('filename', type=str, help='name of the file to load')
    parser_cut.add_argument('new_filename', type=str, help='name of the file to save')
    parser_cut.add_argument('n_packages', type=int, help='number of packages to preserve')
    parser_cut.add_argument('--header_size', metavar='header_size', type=int, nargs=1,
                            help='the size of the file header in bits')
    parser_cut.add_argument('--packet_size', metavar='packet_size', type=int, nargs=1,
                            help='the size of the data packets in bits')

    # add parser for printing help options for parameters
    parser.add_argument('--parameter_help', help='show suggested parameters', action='store_true')

    args = parser.parse_args()

    if args.parameter_help:
        print(param_help)
    elif args.subparser_name == 'cut':
        kwargs = {k: getattr(args, k)[0] for k in ['header_size', 'packet_size'] if k in args}
        reduce_file_size(filename=args.filename, new_filename=args.new_filename,
                         n_packages=args.n_packages, **kwargs)