Streamlining the setup process.

- dependency version pinning
- automatic `secret_key` generation
- automatic config file generation
- installing `once` script
- setup instructions in README.md
- adding an architecture diagram

app.py

@@ -1,23 +1,74 @@
 #!/usr/bin/env python3
 
 import os
-from aws_cdk import (
-    core,
-    aws_route53 as route53)
+import base64
+import configparser
+from typing import Optional
 
+from aws_cdk import core
 from once.once_stack import OnceStack, CustomDomainStack
 
-SECRET_KEY = os.getenv('SECRET_KEY', 'ho/KbLqa65F4uKumCOl30SQwWh4hV7BqpuJVl7urq2XuxkvHmBk/QC9l53og0B3X3dSZun7zDYBH6MdOkjj6CQ==')
-DOMAIN_NAME = os.getenv('DOMAIN_NAME')
+
+ONCE_CONFIG_FILE = os.getenv('ONCE_CONFIG_FILE', os.path.expanduser('~/.once'))
+
+SECRET_KEY = os.getenv('SECRET_KEY')
+CUSTOM_DOMAIN = os.getenv('CUSTOM_DOMAIN')
 HOSTED_ZONE_NAME = os.getenv('HOSTED_ZONE_NAME')
 HOSTED_ZONE_ID = os.getenv('HOSTED_ZONE_ID')
 
 
-app = core.App()
-once = OnceStack(app, 'once',
-    secret_key=SECRET_KEY,
-    custom_domain=DOMAIN_NAME,
-    hosted_zone_id=HOSTED_ZONE_ID,
-    hosted_zone_name=HOSTED_ZONE_NAME)
+def generate_random_key() -> str:
+    return base64.b64encode(os.urandom(128)).decode('utf-8')
 
-app.synth()
+
+def generate_config(secret_key: Optional[str] = None,
+    custom_domain: str = None,
+    hosted_zone_name: str = None,
+    hosted_zone_id: str = None) -> configparser.ConfigParser:
+    config = configparser.ConfigParser()
+
+    config['once'] = {
+        'secret_key': secret_key or generate_random_key(),
+    }
+
+    config['deployment'] = {}
+    if all([custom_domain, hosted_zone_name, hosted_zone_id]):
+        config['once']['base_url'] = f'https://{custom_domain}'
+        config['deployment'] = {
+            'custom_domain': custom_domain,
+            'hosted_zone_name': hosted_zone_name,
+            'hosted_zone_id': hosted_zone_id
+        }
+    return config
+
+
+def get_config(config_gile: str = ONCE_CONFIG_FILE) -> configparser.ConfigParser:
+    if not os.path.exists(ONCE_CONFIG_FILE):
+        print(f'Generating configuration file at {ONCE_CONFIG_FILE}')
+        with open(ONCE_CONFIG_FILE, 'w') as config_file:
+            config = generate_config(
+                secret_key=SECRET_KEY,
+                custom_domain=CUSTOM_DOMAIN,
+                hosted_zone_name=HOSTED_ZONE_NAME,
+                hosted_zone_id=HOSTED_ZONE_ID)
+            config.write(config_file)
+    else:
+        config = configparser.ConfigParser()
+        config.read(ONCE_CONFIG_FILE)
+    return config
+
+
+def main():
+    config = get_config()
+
+    kwargs = {'secret_key': config['once']['secret_key']}
+    if config.has_section('deployment'):
+        kwargs.update(config['deployment'])
+
+    app = core.App()
+    once = OnceStack(app, 'once', **kwargs)
+    app.synth()
+
+
+if __name__ == '__main__':
+    main()