merge-features.py

#!/usr/bin/env python3

import argparse
import json
import sys


def error(message):
    sys.stderr.write(message)
    sys.stderr.write("\n")
    sys.exit(1)


def invalid_file(features_file, message):
    error(f"Invalid features file '{features_file}': {message}")


def parse_args():
    parser = argparse.ArgumentParser(
        formatter_class=argparse.RawDescriptionHelpFormatter,
        description="""
        Merges the given feature files together into DEST (or stdout if DEST
        is not given). Each file FILE must be given a corresponding PREFIX to
        prefix the name of each entry in its features list, though these could
        be empty if no prefix is required.

        Note that the files and prefixes are treated as an ordered list, ie.
        the first FILE corresponds to the first PREFIX.
        """)

    parser.add_argument(
        "--file", "-f", action="append", dest="files",
        help="path of a file to merge"
    )
    parser.add_argument(
        "--prefix", "-p", action="append", dest="prefixes",
        help="prefix to prepend to the name of each feature"
    )
    parser.add_argument(
        "dest", nargs="?",
        help="path to store the merged file"
    )

    return parser.parse_known_args()


def read_features(from_file, add_prefix):
    with open(from_file, "r") as f:
        features_dict = json.load(f)

    if "features" not in features_dict:
        invalid_file(from_file, "missing 'features' key")

    features = []
    for feature in features_dict["features"]:
        if "name" not in feature:
            invalid_file(from_file, "missing name in features list")

        features.append({"name": add_prefix + feature["name"]})
    return features


def main():
    (args, _) = parse_args()

    if not args.files:
        error("No files to merge were provided")

    if len(args.files) != len(args.prefixes):
        error("Must supply the same number of files and prefixes")

    features = []
    for i, (f, prefix) in enumerate(zip(args.files, args.prefixes)):
        features.extend(read_features(f, prefix))

    data = {
        "features": features
    }

    if args.dest:
        with open(args.dest, "w") as f:
            json.dump(data, f, indent=2)
    else:
        sys.stdout.write(json.dumps(data, indent=2))


if __name__ == '__main__':
    main()