start error handling

error-handling/Cargo.toml

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+[package]
+name = "error_handling"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]

error-handling/src/main.rs

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+use std::fs::{self, File};
+use std::io::{self, Read};
+
+fn main() {
+    let username = get_username_or_create_file().unwrap();
+    if username == "" {
+        println!("empty!");
+    } else {
+        println!("{:?}", username);
+    }
+}
+
+fn get_username_or_create_file() -> Result<String, io::Error> {
+    let check_username_file = File::open("username.txt");
+
+    let mut username_file = match check_username_file {
+        Ok(filename) => filename,
+        Err(e) => match e.kind() {
+            std::io::ErrorKind::NotFound => match File::create("username.txt") {
+                Ok(file_created) => {
+                    println!("created file, now writing...");
+                    fs::write("{file_created}", "admin");
+                    file_created
+                }
+                Err(error_creating_file) => {
+                    panic!("error creating file! {error_creating_file:?}")
+                }
+            },
+            _ => panic!("cant open file!"),
+        },
+    };
+
+    let mut username = String::new();
+
+    match username_file.read_to_string(&mut username) {
+        Ok(_) => Ok(username),
+        Err(e) => Err(e),
+    }
+}

error-handling/{file_created}

@@ -0,0 +1 @@
+admin