day(02): refine parsing

Signed-off-by: Matej Focko <mfocko@redhat.com>

src/bin/day02.rs

@@ -1,7 +1,9 @@
+use std::str::FromStr;
+
 use aoc_2022::*;
 
 use color_eyre::eyre::Result;
-use itertools::Itertools;
+use thiserror::Error;
 use tracing::*;
 use tracing_subscriber::EnvFilter;
 
@@ -22,6 +24,32 @@ impl Shape {
     }
 }
 
+#[derive(Error, Debug)]
+enum ShapeError {
+    #[error("empty string given")]
+    Empty,
+    
+    #[error("unknown shape ‹{0}›")]
+    UnknownShape(String),
+}
+
+impl FromStr for Shape {
+    type Err = ShapeError;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        if s.is_empty() {
+            return Err(ShapeError::Empty);
+        }
+
+        match s {
+            "A" | "X" => Ok(Shape::Rock),
+            "B" | "Y" => Ok(Shape::Paper),
+            "C" | "Z" => Ok(Shape::Scissors),
+            _ => Err(ShapeError::UnknownShape(s.to_string())),
+        }
+    }
+}
+
 #[derive(Debug, Clone, Copy)]
 enum Outcome {
     Lose,
@@ -35,6 +63,28 @@ struct Round {
     me: Shape,
 }
 
+#[derive(Error, Debug)]
+enum RoundError {
+    #[error("invalid shape ‹{0}›")]
+    InvalidShape(#[from] ShapeError),
+}
+
+impl FromStr for Round {
+    type Err = RoundError;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        let mut split_str = s.split(' ');
+
+        let opponent = split_str.next().unwrap().parse::<Shape>();
+        let me = split_str.next().unwrap().parse::<Shape>();
+
+        Ok(Round {
+            opponent: opponent?,
+            me: me?,
+        })
+    }
+}
+
 impl Round {
     fn score(&self) -> i32 {
         let shape_score = self.me.score();
@@ -93,30 +143,7 @@ fn part_2(input: &Input) -> Output {
 }
 
 fn parse_input(pathname: &str) -> Input {
-    file_to_lines(pathname)
-        .iter()
-        .map(|s| {
-            let mut split_str = s.split(" ");
-
-            let opponent = split_str.next().unwrap();
-            let me = split_str.next().unwrap();
-
-            Round {
-                opponent: match opponent {
-                    "A" => Shape::Rock,
-                    "B" => Shape::Paper,
-                    "C" => Shape::Scissors,
-                    _ => panic!("invalid choice"),
-                },
-                me: match me {
-                    "X" => Shape::Rock,
-                    "Y" => Shape::Paper,
-                    "Z" => Shape::Scissors,
-                    _ => panic!("invalid choice"),
-                },
-            }
-        })
-        .collect()
+    file_to_structs(pathname)
 }
 
 fn main() -> Result<()> {