Fix cdk template URL for nested stack.

fix_template_url.py

import json
import os
import sys

## read file args [asset_file, root_template_file, s3_object_prefix]
asset_file = sys.argv[1]
template_file = sys.argv[2]
object_prefix = sys.argv[3]
hash_map = {}

## read from asset file to build the asset_hash/s3_asset_path map
with open(asset_file,'r') as file:
  assets = json.loads(file.read())
  for asset_key in assets['files']:
    destinations = assets['files'][asset_key]['destinations']
    source = assets['files'][asset_key]['source']
    for dest in destinations:
      hash_map['/'+destinations[dest]['objectKey']] = object_prefix + source['path']

## rewrite the template file after setting TemplateURL to s3_asset_path
with open(template_file,'r+') as file:
  template_body = json.loads(file.read())
  for resource in template_body['Resources']:
    object_key = template_body['Resources'][resource]['Properties']['TemplateURL']['Fn::Join'][-1][-1]
    template_body['Resources'][resource]['Properties']['TemplateURL'] = hash_map[object_key]
  file.seek(0) 
  json.dump(template_body, file, indent=2)
  file.truncate()