Rearranged the existing code to make it more manageable.

src/gtfs/mod.rs

@@ -0,0 +1,30 @@
+mod loader;
+mod utils;
+mod structs;
+use std::{
+    collections::{HashMap, HashSet},
+    fs::File,
+};
+use crate::gtfs::{loader::load_gtfs, structs::Gtfs};
+
+
+/// Load a GTFS structure from a zip file
+pub fn load(src_file: &str, route_numbers: HashSet<String>, stop_codes: HashSet<String>) -> Gtfs {
+    // Open zip file
+    let mut zip_reader = zip::ZipArchive::new(File::open(src_file).unwrap()).unwrap();
+
+    let mut gtfs: Gtfs = Gtfs {
+        agencies: Vec::new(),
+        calendar: HashMap::new(),
+        calendar_dates: HashMap::new(),
+        routes: HashMap::new(),
+        stops: HashMap::new(),
+        trips: HashMap::new(),
+        stop_times: HashMap::new(),
+    };
+
+
+    load_gtfs(&mut gtfs, &mut zip_reader, route_numbers, stop_codes);
+
+    return gtfs;
+}