doc: Add note in to-do list about improving the clap API

TODO.md

@@ -2,4 +2,5 @@
 - Report that "ReadableConfig" error, which was super unhelpful and very annoying when you don't know why it's bugging.
 - Find a better notation for the error-handling in read_config_template() – although the custom error message is desirable, it's very bad
 to have to implement it using such a ridiculously long line...
-- Refactor so as to allow *either* OAuth2 or password to be filled in, depending on which was entered (with preference for OAuth2).
+- Look at clap feature to allow deriving an arg-group from an enum to vastly simplify the structs required for parsing
+auth method.

src/main.rs

@@ -75,18 +75,21 @@ fn read_config_template() -> Result<String, std::io::Error> {
     std::fs::read_to_string(CONFIG_TEMPLATE_PATH).or(Err(std::io::Error::new(std::io::ErrorKind::NotFound, format!("Unable to find {}; did you execute the script from the same directory?", CONFIG_TEMPLATE_PATH))))
 }
 
+fn create_toml_line(field_name: &str, value: &str) -> String {
+    format!("{} = \"{}\"\n", field_name, value)
+}
+
 fn fill_config_template(config_template: String, args: SetupArgs) -> String {
     let mut filled = formatx!(config_template, args.api_url, args.rest_url, args.username).unwrap();
-    let chosen_method: AuthMethod = args.auth_phrase.into();
-    match chosen_method {
+    let auth_method: AuthMethod = args.auth_phrase.into();
+    match auth_method {
         AuthMethod::Password(password) => {
-            filled.push_str(format!("password = \"{}\"", password).as_str());
+            filled.push_str(&create_toml_line("password", &password));
         },
         AuthMethod::OAuth2Token(oauth2_token) => {
-            filled.push_str(format!("oauth2_token = \"{}\"", oauth2_token).as_str());
+            filled.push_str(&create_toml_line("oauth2_token", &oauth2_token));
         }
     }
-    filled.push('\n');
     filled
 }