import argparse
import datetime
import logging
import os
import shutil
import re

# https://en.wikipedia.org/wiki/Template:Quantities_of_bytes
DATA_SIZE_UNIT_BYTE_CONVERSION_FACTOR = {
    'B': 1,
    'kB': 10**3,
    'KB': 10**3,
    'MB': 10**6,
    'GB': 10**9,
    'TB': 10**12,
    'KiB': 2**10,
    'MiB': 2**20,
    'GiB': 2**30,
    'TiB': 2**40,
}


def data_size_to_bytes(size_with_unit: str) -> int:
    match = re.match(r'^([\d\.]+)\s*([A-Za-z]+)?$', size_with_unit)
    if not match:
        raise ValueError('Unable to parse data size {!r}'.format(size_with_unit))
    unit_symbol = match.group(2)
    if unit_symbol:
        try:
            byte_conversion_factor = DATA_SIZE_UNIT_BYTE_CONVERSION_FACTOR[unit_symbol]
        except KeyError:
            raise ValueError('Unknown data size unit symbol {!r}'.format(unit_symbol))
    else:
        byte_conversion_factor = 1
    byte_size = float(match.group(1)) * byte_conversion_factor
    return int(round(byte_size, 0))


def main():
    argparser = argparse.ArgumentParser(
        description='Delete files with earliest modification date'
                    ' until a minimum of --free-bytes are available on the respective disk')
    argparser.add_argument('-d', '--debug', action='store_true')
    argparser.add_argument('--free-bytes', type=data_size_to_bytes, required=True,
                           help='examples: 1024, 1024B, 4KiB, 4KB, 2TB')
    argparser.add_argument('root_dir_path', metavar='ROOT_DIR')
    args = argparser.parse_args()
    logging.basicConfig(level=logging.DEBUG if args.debug else logging.INFO,
                        format='%(asctime)s:%(levelname)s:%(message)s',
                        datefmt='%Y-%m-%dT%H:%M:%S%z')
    logging.debug('Required free bytes: %d', args.free_bytes)
    disk_usage = shutil.disk_usage(args.root_dir_path)
    logging.debug(disk_usage)
    if disk_usage.free >= args.free_bytes:
        logging.debug('Requirement already fulfilled')
        return
    file_paths = [os.path.join(dirpath, filename)
                  for dirpath, _, filenames in os.walk(args.root_dir_path)
                  for filename in filenames]
    file_mtime_paths = [(os.stat(p).st_mtime, p) for p in file_paths]
    file_mtime_paths.sort()
    removed_files_counter = 0
    last_mtime = None
    for file_mtime, file_path in file_mtime_paths:
        if shutil.disk_usage(args.root_dir_path).free >= args.free_bytes:
            break
        os.remove(file_path)
        logging.debug('Removed file %s', file_path)
        removed_files_counter += 1
        last_mtime = file_mtime
    if removed_files_counter == 0:
        logging.warning('No files to remove')
    else:
        logging.info('Removed %d file(s) with modification date <= %s', removed_files_counter,
                     datetime.datetime.utcfromtimestamp(last_mtime).isoformat('T'))


if __name__ == '__main__':
    main()