use config struct to load the env variable into struct

.env.example

@@ -1,2 +1,3 @@
 DATABASE_URL=postgres://shuttle_test:password@localhost:5432/shuttle
-GEOCODING_API_KEY=
+GEOCODING_API_KEY=
+PORT=8000

src/config.rs

@@ -0,0 +1,11 @@
+#[derive(clap::Parser, Clone, Debug)]
+pub struct Config {
+    #[clap(long, env)]
+    pub database_url: String,
+
+    #[clap(long, env)]
+    pub geocoding_api_key: String,
+
+    #[clap(long, env, default_value = "8000")]
+    pub port: u16,
+}

src/main.rs

@@ -1,17 +1,39 @@
-use std::env;
+use std::{error::Error, net::SocketAddr};
 
 use axum::Router;
+use clap::Parser;
 use sqlx::{PgPool, Pool, Postgres};
 
+mod config;
 mod handlers;
-fn app(pool: Pool<Postgres>) -> Router {
-    handlers::router(pool)
+
+fn app(pool: Pool<Postgres>, geocoding_api_key: String) -> Router {
+    handlers::router(pool, geocoding_api_key)
 }
 
-#[shuttle_runtime::main]
-async fn shuttle_service() -> shuttle_axum::ShuttleAxum {
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn Error>> {
+    // load environment variable from .env file
     dotenv::dotenv().ok();
-    let database_url = env::var("DATABASE_URL").expect("DATABASE_URL must be set the env variable");
-    let pool = PgPool::connect(&database_url).await.unwrap();
-    Ok(app(pool).into())
+
+    // initialize the tracing
+    tracing_subscriber::fmt().init();
+
+    // load the env variable into config struct
+    let config = config::Config::parse();
+    tracing::info!("config .env {:?}", config);
+
+    // initialize the database pool
+    let pool = PgPool::connect(&config.database_url).await.unwrap();
+
+    // bind an address from the env port
+    let addr = SocketAddr::from(([0, 0, 0, 0], config.port));
+    tracing::info!("listening on {}", addr);
+
+    // start the server
+    axum::Server::bind(&addr)
+        .serve(app(pool, config.geocoding_api_key).into_make_service())
+        .await
+        .unwrap();
+    Ok(())
 }