fix: listen on PORT instead of 8080

Author: Yuanlin Lin

src/my_web_app.gleam

@@ -2,12 +2,24 @@ import mist
 import gleam/erlang/process
 import gleam/bytes_builder
 import gleam/http/response.{Response}
+import gleam/erlang/os
+import gleam/int
+
+pub fn get_port() -> Int {
+  case os.get_env("PORT") {
+    Ok(value) -> case int.parse(value) {
+      Error(e) -> 8080
+      Ok(i) -> i
+    }
+    Error(_) -> 8080  // If the environment variable is not set, fallback to 8080
+  }
+}
 
 pub fn main() {
   let assert Ok(_) =
     web_service
     |> mist.new
-    |> mist.port(8080)
+    |> mist.port(get_port())
     |> mist.start_http
   process.sleep_forever()
 }