Error Handling with Result and Option (page 31)

src/main.rs

@@ -1,5 +1,6 @@
 use clap::{Parser, Subcommand};
 use serde::{Deserialize, Serialize};
+use std::fmt;
 use std::fs;
 use std::path::Path;
 
@@ -32,6 +33,27 @@ struct TodoList {
     next_id: usize,
 }
 
+#[derive(Debug)]
+enum TodoError {
+    FileError(String),
+    ParseError(String),
+    TaskNotFound(usize),
+    InvalidInput(String),
+}
+
+impl fmt::Display for TodoError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            TodoError::FileError(msg) => write!(f, "File error: {}", msg),
+            TodoError::ParseError(msg) => write!(f, "Parse error: {}", msg),
+            TodoError::TaskNotFound(id) => write!(f, "Task {} not found", id),
+            TodoError::InvalidInput(msg) => write!(f, "Invalid input: {}", msg),
+        }
+    }
+}
+
+impl std::error::Error for TodoError {}
+
 impl TodoList {
     fn new() -> Self {
         TodoList {