feat: implement application factory and Google OAuth integration

app/__init__.py

@@ -0,0 +1,45 @@
+from flask_dance.contrib.google import make_google_blueprint
+from flask_dance.consumer.storage.sqla import SQLAlchemyStorage
+from flask_sqlalchemy import SQLAlchemy
+from flask_login import LoginManager
+from flask_migrate import Migrate
+from flask import Flask
+
+db = SQLAlchemy()
+migrate = Migrate()
+login_manager = LoginManager()
+
+
+def create_app():
+    app = Flask(__name__)
+    app.config.from_object("config.Config")
+
+    db.init_app(app)
+    migrate.init_app(app, db)
+    login_manager.init_app(app)
+
+    @login_manager.user_loader
+    def load_user(user_id):
+        from .models import User
+
+        return User.query.get(int(user_id))
+
+    from .blueprints.main import main_bp
+
+    app.register_blueprint(main_bp)
+
+    from .models import OAuth
+
+    google_bp = make_google_blueprint(
+        client_id=app.config["GOOGLE_CLIENT_ID"],
+        client_secret=app.config["GOOGLE_CLIENT_SECRET"],
+        scope=[
+            "https://www.googleapis.com/auth/userinfo.profile",
+            "https://www.googleapis.com/auth/userinfo.email",
+            "openid",
+        ],
+        storage=SQLAlchemyStorage(OAuth, db.session),
+    )
+    app.register_blueprint(google_bp, url_prefix="/login")
+
+    return app