template-fastapi/{{project_slug}}/fastapi_init.py.jinja

"""FastAPI application initialization is performed here."""

import os
from contextlib import asynccontextmanager

from fastapi import FastAPI
from fastapi.middleware.cors import CORSMiddleware
from fastapi.middleware.gzip import GZipMiddleware
from fastapi.openapi.docs import get_swagger_ui_html
from fastapi.responses import JSONResponse

from {{project_slug}}.config import {{ProjectName}}Config
from {{project_slug}}.db.connection.manager import PostgresConnectionManager
from {{project_slug}}.dependencies import connection_manager_dep, logger_dep, metrics_dep
from {{project_slug}}.exceptions.mapper import ExceptionMapper
from {{project_slug}}.handlers.debug import DebugException, DebugExceptionWithParams
from {{project_slug}}.middlewares.exception_handler import ExceptionHandlerMiddleware
from {{project_slug}}.middlewares.observability import ObservabilityMiddleware
from {{project_slug}}.observability.metrics import init_metrics
from {{project_slug}}.observability.otel_agent import OpenTelemetryAgent
from {{project_slug}}.utils.observability import URLsMapper, configure_logging

from .handlers import list_of_routers
from .version import LAST_UPDATE, VERSION


def _get_exception_mapper(debug: bool) -> ExceptionMapper:
    mapper = ExceptionMapper()
    if debug:
        mapper.register_simple(DebugException, 506, "That's how a debug exception look like")
        mapper.register_func(
            DebugExceptionWithParams,
            lambda exc: JSONResponse(
                {"error": "That's how a debug exception with params look like", "message": exc.message},
                status_code=exc.status_code,
            ),
        )
    return mapper


def bind_routes(application: FastAPI, prefix: str, debug: bool) -> None:
    """Bind all routes to application."""
    for router in list_of_routers:
        if not debug:
            to_remove = []
            for i, route in enumerate(router.routes):
                if "debug" in route.path:
                    to_remove.append(i)
            for i in to_remove[::-1]:
                del router.routes[i]
        if len(router.routes) > 0:
            application.include_router(router, prefix=(prefix if "/" not in {r.path for r in router.routes} else ""))


def get_app(prefix: str = "/api") -> FastAPI:
    """Create application and all dependable objects."""

    if "CONFIG_PATH" not in os.environ:
        raise ValueError("CONFIG_PATH environment variable is not set")
    app_config: {{ProjectName}}Config = {{ProjectName}}Config.from_file(os.getenv("CONFIG_PATH"))

    description = "{{project_description}}"

    application = FastAPI(
        title="{{project_name}}",
        description=description,
        docs_url=None,
        openapi_url=f"{prefix}/openapi",
        version=f"{VERSION} ({LAST_UPDATE})",
        terms_of_service="http://swagger.io/terms/",
        contact={"email": "idu@itmo.ru"},
        license_info={"name": "Apache 2.0", "url": "http://www.apache.org/licenses/LICENSE-2.0.html"},
        lifespan=lifespan,
    )
    bind_routes(application, prefix, app_config.app.debug)

    @application.get(f"{prefix}/docs", include_in_schema=False)
    async def custom_swagger_ui_html():
        return get_swagger_ui_html(
            openapi_url=application.openapi_url,
            title=application.title + " - Swagger UI",
            oauth2_redirect_url=app.swagger_ui_oauth2_redirect_url,
            swagger_js_url="https://unpkg.com/swagger-ui-dist@5.11.7/swagger-ui-bundle.js",
            swagger_css_url="https://unpkg.com/swagger-ui-dist@5.11.7/swagger-ui.css",
        )

    application.add_middleware(
        CORSMiddleware,
        allow_origins=app_config.app.cors.allow_origins,
        allow_credentials=app_config.app.cors.allow_credentials,
        allow_methods=app_config.app.cors.allow_methods,
        allow_headers=app_config.app.cors.allow_headers,
    )
    application.add_middleware(GZipMiddleware, minimum_size=1000, compresslevel=5)

    application.state.config = app_config

    logger = configure_logging(
        app_config.observability.logging,
        tracing_enabled=app_config.observability.jaeger is not None,
    )
    metrics = init_metrics()
    exception_mapper = _get_exception_mapper(app_config.app.debug)
    connection_manager = PostgresConnectionManager(
        master=app_config.db.master,
        replicas=app_config.db.replicas,
        logger=logger,
        application_name=f"{{project_slug}}_{VERSION}",
    )
    urls_mapper = URLsMapper(app_config.observability.prometheus.urls_mapping)

    connection_manager_dep.init_dispencer(application, connection_manager)
    metrics_dep.init_dispencer(application, metrics)
    logger_dep.init_dispencer(application, logger)

    application.add_middleware(
        ObservabilityMiddleware,
        exception_mapper=exception_mapper,
        metrics=metrics,
        urls_mapper=urls_mapper,
    )
    application.add_middleware(
        ExceptionHandlerMiddleware,
        debug=[app_config.app.debug],
        exception_mapper=exception_mapper,
    )

    return application


@asynccontextmanager
async def lifespan(application: FastAPI):
    """Lifespan function.

    Initializes database connection in pass_services_dependencies middleware.
    """
    app_config: {{ProjectName}}Config = application.state.config
    logger = logger_dep.obtain(application)

    await logger.ainfo("application is being configured", config=app_config.to_order_dict())

    for middleware in application.user_middleware:
        if middleware.cls == ExceptionHandlerMiddleware:
            middleware.kwargs["debug"][0] = app_config.app.debug

    otel_agent = OpenTelemetryAgent(
        app_config.observability.prometheus,
        app_config.observability.jaeger,
    )

    yield

    otel_agent.shutdown()


app = get_app()