"""
# cloud_task_delete_old_appengine_versions.py

This is a python file designed to operate as a Cloud Function.
On trigger, it will delete all but the number of non-active 
versions equal to `RETAIN_LAST_N_VERSIONS` below (default 5).

Note: failure to delete will not raise an exception. If you're
running into bugs, see the commented line below to help debug
if the delete call is throwing errors

- entrypoint: cloud_build_complete
- recommended trigger: Cloud Pub/Sub cloud builds topic
- runtime: Python 3.7

## requirements.txt
requests>=2.23.0

"""

import base64
import requests
import json

RETAIN_LAST_N_VERSIONS = 5


def list_versions(access_token):
    url = 'https://appengine.googleapis.com/v1/apps/trophy-gg/services/default/versions'
    headers = {
        'Authorization': 'Bearer {}'.format(access_token)
    }

    r = requests.get(url, headers=headers)
    r.raise_for_status()

    return r.json()['versions']


def version_delete(name, access_token):
    url = 'https://appengine.googleapis.com/v1/{}'
    headers = {
        'Authorization': 'Bearer {}'.format(access_token)
    }

    r = requests.delete(url.format(name), headers=headers)
    # Uncomment below if debugging
    # r.raise_for_status()
    return r.json()

def cloud_build_complete(event, context):
     """Triggered from a message on a Cloud Pub/Sub topic.
     Args:
     event (dict): Event payload.
     context (google.cloud.functions.Context): Metadata for the event.
     """
     pubsub_message = base64.b64decode(event['data']).decode('utf-8')
     
     data = {}
     if isinstance(pubsub_message, str):
          try:
               data = json.loads(pubsub_message)
          except json.JSONDecodeError:
               return
     
     if data.get('status') != 'SUCCESS' or data.get('buildTriggerId') != '9683f557-71da-4daf-a00a-85924bb34afb':
          return
     
     print('Deleting old backend versions...')
     
     scope = 'https://www.googleapis.com/auth/appengine.admin,https://www.googleapis.com/auth/cloud-platform'
     r = requests.get("http://metadata.google.internal/computeMetadata/v1/instance/service-accounts/default/token",
          params={
               'scopes': scope
          },
          headers={
               'Metadata-Flavor': 'Google'
          })
     r.raise_for_status()
     access_token = r.json()['access_token']
     versions = list_versions(access_token)

     if len(versions) <= RETAIN_LAST_N_VERSIONS+1:
          return

     for version in versions[RETAIN_LAST_N_VERSIONS+1:]:
          version_delete(version['name'], access_token)