Proof-of-concept OpenTimelineIO schema downgrader

schema_downgrader.py

#!/usr/bin/env python
#
# SPDX-License-Identifier: Apache-2.0
# Copyright Contributors to the OpenTimelineIO project
#
# This file is for discussion regarding this OpenTimelineIO issue:
# https://github.com/PixarAnimationStudios/OpenTimelineIO/issues/1295

"""Experimental tool to downgrade an OTIO file.
"""

import argparse
import json
import sys
import os
from urllib.parse import urlparse


def parse_args():
    """parse arguments out of sys.argv"""
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument("-i", "--input", type=str, required=True, help="File to read.")
    parser.add_argument("-o", "--output", type=str, help="File to write.")
    parser.add_argument(
        "-d",
        "--dryrun",
        action="store_true",
        default=False,
        help="Print changes without saving anything.",
    )

    args = parser.parse_args()

    if not (args.output or args.dryrun):
        print("ERROR: You must specify either --output or --dryrun")
        sys.exit(1)

    return args


def downgrade_Example_7(example):
    """Downgrade an Example.7 to Example.6"""
    example['OTIO_SCHEMA'] = 'Example.6'
    example['old_field'] = example.get('modern_field', 'default value')
    del example['modern_field']

    # Chain to the next downgrader, if needed
    return downgrade_Example_6(example)


def downgrade_Clip_2(clip):
    """Downgrade a Clip.2 to Clip.1 by retaining only the active media reference."""
    key = clip.get('active_media_reference_key', 'DEFAULT_MEDIA')
    media_ref = clip.get('media_references', {}).get(key)

    # Should we stash the lost media references into metadata?
    clip['metadata']['otio-schema-downgrader'] = {
        'downgraded_from': clip['OTIO_SCHEMA'],
        'lost_values': {
            'active_media_reference_key': key,
            'media_references': clip.get('media_references')
        }
    }

    # Modify the clip
    clip['OTIO_SCHEMA'] = 'Clip.1'
    clip['media_reference'] = media_ref
    del clip['media_references']
    del clip['active_media_reference_key']

    # NOTE: We can leave 'enabled' as-is. That was added after Clip.1,
    # but didn't warrant an upgrade to Clip.2 because it was purely additive.
    # del clip['enabled']

    return clip


def downgrade(data):
    if isinstance(data, dict):
        schema = data.get('OTIO_SCHEMA')
        if schema:
            # This is an OTIO schema object.
            # Check it's version
            schema_name, version = schema.split('.')

            # Is there a downgrade function for this?
            downgrader_name = 'downgrade_{}_{}'.format(schema_name, version)
            downgrader_fn = globals().get(downgrader_name)
            if downgrader_fn:
                # Call the downgrade function
                data = downgrader_fn(data)

        # TODO: Should this happen before or after the downgrade?
        for key, val in data.items():
            data[key] = downgrade(val)

    elif isinstance(data, list):
        for i, val in enumerate(data):
            data[i] = downgrade(val)

    return data


def main():
    args = parse_args()

    input_text = open(args.input).read()
    input_data = json.loads(input_text)
    output_data = downgrade(input_data)
    output_text = json.dumps(
        output_data,
        indent = 4,
        # sort_keys = True
    )
    if args.dryrun:
        print(output_text)
    else:
        open(args.output, "w").write(output_text)

if __name__ == "__main__":
    main()