#!/usr/bin/env fuchsia-vendored-python
# Copyright 2019 The Fuchsia Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

import difflib
import json
import sys


def usage():
    print(
        "Usage:\n"
        "  diff_json.py FILE1 FILE2 OUTPUT\n"
        "  Generates canonical json text for FILE1 and FILE2, then does a normal text comparison,\n"
        "  writing the diff output to OUTPUT."
    )


def main():
    if len(sys.argv) != 4:
        usage()
        exit(-1)
    try:
        with open(sys.argv[1], "r") as file1:
            with open(sys.argv[2], "r") as file2:
                with open(sys.argv[3], "w") as result:
                    json1 = json.load(file1)
                    json2 = json.load(file2)
                    canon1 = json.dumps(
                        json1, sort_keys=True, indent=2
                    ).splitlines()
                    canon2 = json.dumps(
                        json2, sort_keys=True, indent=2
                    ).splitlines()
                    diff = difflib.unified_diff(
                        canon1, canon2, sys.argv[1], sys.argv[2], lineterm=""
                    )
                    diffstr = "\n".join(diff)
                    result.write(diffstr)
                    if len(diffstr) != 0:
                        print(
                            f"Error: non-empty diff between canonical json representations:\n{diffstr}"
                        )
                        exit(-4)
    except IOError as e:
        print(f"Error accessing files: {e}")
        usage()
        exit(-2)
    except ValueError as e:
        print(f"Error decoding json: {e}")
        exit(-3)


if __name__ == "__main__":
    sys.exit(main())