#!/usr/bin/env python3

import argparse
import os
import re
import sys

from subprocess import check_call

PROG_NAME = os.path.basename(sys.argv[0])

def die(msg):
    print('{}: error: {}'.format(PROG_NAME, msg), file=sys.stderr)
    sys.exit(1)

def parse_args():
    p = argparse.ArgumentParser()
    p.add_argument('--convert-tool', default='convert')
    p.add_argument('-d', '--debug', action='store_true')
    p.add_argument('src_filename')
    p.add_argument('dest_filename')
    return p.parse_args()

def main():
    args = parse_args()

    src_filename = args.src_filename
    dest_filename = args.dest_filename

    # The badly named "convert" tool is an ImageMagick tool.
    convert_args = [args.convert_tool, src_filename]

    if re.search('grayscale', dest_filename):
        convert_args += [
            '-set', 'colorspace', 'Gray',
            '-separate',
            '-average',
        ]

    match = re.search(r'(\d+)x(\d+)', dest_filename)
    if match is None:
        die('dest_filename {!r} contains no size'.format(dest_filename))

    width = match.groups(0)[0]
    height = match.groups(0)[1]

    convert_args += [
        '-adaptive-resize', '{}x{}'.format(width, height),
        dest_filename,
    ]

    if args.debug:
        print('run: ' + ' '.join(map(repr, convert_args)))

    check_call(convert_args)

if __name__ == '__main__':
    main()