support DATABASE_URL environment variable

src/config.rs

···
 });
 
 pub static POSTGRES_URL: LazyLock<String> = LazyLock::new(|| {
-    let Ok(user) = env::var("POSTGRES_USER") else {
-        panic!("POSTGRES_USER was not set. Cannot connect to database")
-    };
-    let Ok(password) = env::var("POSTGRES_PASSWORD") else {
-        panic!("POSTGRES_PASSWORD was not set. Cannot connect to database")
-    };
-    let Ok(host) = env::var("POSTGRES_HOST") else {
-        panic!("POSTGRES_HOST was not set. Cannot connect to database")
-    };
+    if let Ok(url) = env::var("DATABASE_URL") {
+        return url;
+    }
+
+    let user = env::var("POSTGRES_USER");
+    let db = env::var("POSTGRES_DATABASE").or_else(|_| user.clone());
+    let password = env::var("POSTGRES_PASSWORD");
+    let host = env::var("POSTGRES_HOST");
 
-    format!("postgres://{}:{}@{}/{}", user, password, host, user)
+    if let Ok(user) = user.clone()
+        && let Ok(db) = db.clone()
+        && let Ok(password) = password.clone()
+        && let Ok(host) = host.clone()
+    {
+        format!("postgres://{}:{}@{}/{}", user, password, host, db)
+    } else {
+        let missing = [
+            (user, "USER"),
+            (db, "DATABASE"),
+            (password, "PASSWORD"),
+            (host, "HOST"),
+        ]
+        .iter()
+        .filter_map(|x| {
+            if x.0.is_err() {
+                Some(String::from("POSTGRES_") + x.1)
+            } else {
+                None
+            }
+        })
+        .collect::<Vec<String>>()
+        .join(", ");
+
+        panic!("Could not generate database url. Missing environment variables {}. Set DATABASE_URL to define the postgres url manually", missing);
+    }
 });

src/db.rs

···
     let conn = match PgPool::connect(&config::POSTGRES_URL).await {
         Ok(val) => val,
         Err(err) => {
-            println!("Could not connect to the database. Got error {err}");
-            panic!()
+            panic!("Could not connect to the database. Got error {err}");
         }
     };
 

src/main.rs

···
     let conn: Pool<Postgres> = db::conn().await;
     println!("Database connected and initialized");
 
-    let pds = match utils::resolver::resolve(&config::USER).await {
-        Ok(val) => val,
-        Err(err) => panic!("{}", err),
-    };
+    let pds = utils::resolver::resolve(&config::USER)
+        .await
+        .unwrap_or_else(|err| panic!("{}", err));
 
     println!("Starting backfill");
     let timer = std::time::Instant::now();
 
-    if let Err(err) = backfill(&pds, &conn, Some(timer)).await {
-        println!("{}", err);
-        return Err(Error);
-    };
+    backfill(&pds, &conn, Some(timer))
+        .await
+        .unwrap_or_else(|err| panic!("{}", err));
 
     println!("Backfill complete. Took {:?}", timer.elapsed());