#! /usr/bin/python3
# -*- coding: utf-8 -*-

import sys
import os.path
import json
import jsonpatch
import tempfile
import argparse


parser = argparse.ArgumentParser(
    description='Apply a JSON patch on a JSON file')
parser.add_argument('ORIGINAL', type=argparse.FileType('r'),
                    help='Original file')
parser.add_argument('PATCH', type=argparse.FileType('r'),
                    nargs='?', default=sys.stdin,
                    help='Patch file (read from stdin if omitted)')
parser.add_argument('--indent', type=int, default=None,
                    help='Indent output by n spaces')
parser.add_argument('-b', '--backup', action='store_true',
                    help='Back up ORIGINAL if modifying in-place')
parser.add_argument('-i', '--in-place', action='store_true',
                    help='Modify ORIGINAL in-place instead of to stdout')
parser.add_argument('-v', '--version', action='version',
                    version='%(prog)s ' + jsonpatch.__version__)


def main():
    try:
        patch_files()
    except KeyboardInterrupt:
        sys.exit(1)


def patch_files():
    """ Diffs two JSON files and prints a patch """
    args = parser.parse_args()
    doc = json.load(args.ORIGINAL)
    patch = json.load(args.PATCH)
    result = jsonpatch.apply_patch(doc, patch)

    if args.in_place:
        dirname = os.path.abspath(os.path.dirname(args.ORIGINAL.name))

        try:
            # Attempt to replace the file atomically.  We do this by
            # creating a temporary file in the same directory as the
            # original file so we can atomically move the new file over
            # the original later.  (This is done in the same directory
	    # because atomic renames do not work across mount points.)

            fd, pathname = tempfile.mkstemp(dir=dirname)
            fp = os.fdopen(fd, 'w')
            atomic = True

        except OSError:
            # We failed to create the temporary file for an atomic
            # replace, so fall back to non-atomic mode by backing up
            # the original (if desired) and writing a new file.

            if args.backup:
                os.rename(args.ORIGINAL.name, args.ORIGINAL.name + '.orig')
            fp = open(args.ORIGINAL.name, 'w')
            atomic = False

    else:
        # Since we're not replacing the original file in-place, write
        # the modified JSON to stdout instead.

        fp = sys.stdout

    # By this point we have some sort of file object we can write the 
    # modified JSON to.

    json.dump(result, fp, indent=args.indent)
    fp.write('\n')

    if args.in_place:
        # Close the new file.  If we aren't replacing atomically, this
        # is our last step, since everything else is already in place.

        fp.close()

        if atomic:
            try:
                # Complete the atomic replace by linking the original
                # to a backup (if desired), fixing up the permissions
                # on the temporary file, and moving it into place.

                if args.backup:
                    os.link(args.ORIGINAL.name, args.ORIGINAL.name + '.orig')
                os.chmod(pathname, os.stat(args.ORIGINAL.name).st_mode)
                os.rename(pathname, args.ORIGINAL.name)

            except OSError:
                # In the event we could not actually do the atomic
                # replace, unlink the original to move it out of the
                # way and finally move the temporary file into place.
                
                os.unlink(args.ORIGINAL.name)
                os.rename(pathname, args.ORIGINAL.name)


if __name__ == "__main__":
    main()
