day4 refactor with nom and allow tests

day4/Cargo.toml

@@ -8,3 +8,4 @@ repository.workspace = true
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+nom.workspace = true

day4/src/main.rs

@@ -1,51 +1,79 @@
 #![warn(clippy::all, clippy::pedantic)]
 
-use std::fs::File;
-use std::io::{prelude::*, BufReader};
+use std::fs;
 
+use nom::{
+    bytes::complete::tag,
+    character::complete::{self, newline},
+    multi::separated_list0,
+    sequence::separated_pair,
+};
+
+fn parse_range(input: &str) -> nom::IResult<&str, (i32, i32)> {
+    separated_pair(complete::i32, tag("-"), complete::i32)(input)
+}
+fn parse_line(input: &str) -> nom::IResult<&str, ((i32, i32), (i32, i32))> {
+    separated_pair(parse_range, tag(","), parse_range)(input)
+}
+fn process_input(input: &str) -> nom::IResult<&str, Vec<((i32, i32), (i32, i32))>> {
+    separated_list0(newline, parse_line)(input)
+}
+
+fn part1(input: &str) -> String {
+    do_part(input, |(a, b)| {
+        i32::from((a.0 <= b.0 && a.1 >= b.1) || (a.0 >= b.0 && a.1 <= b.1))
+    })
+}
+fn part2(input: &str) -> String {
+    do_part(input, |(a, b)| {
+        i32::from(
+            (a.0 >= b.0 && a.0 <= b.1)
+                || (a.1 >= b.0 && a.1 <= b.1)
+                || (b.0 >= a.0 && b.0 <= a.1)
+                || (b.1 >= a.0 && b.1 <= a.1),
+        )
+    })
+}
+
+fn do_part(input: &str, f: impl Fn((&(i32, i32), &(i32, i32))) -> i32) -> String {
+    let (_, ranges) = process_input(input).unwrap();
+    ranges
+        .iter()
+        .map(|(a, b)| f((a, b)))
+        .fold(0, |mut acc: i32, x: i32| {
+            acc += x;
+            acc
+        })
+        .to_string()
+}
 fn main() -> std::io::Result<()> {
     //Read in file
-    let file = File::open("input")?;
-    let reader = BufReader::new(file);
+    let file = fs::read_to_string("input")?;
 
-    let value = reader
-        .lines()
-        .map(|line| {
-            let line = line.unwrap();
-            // split and parse
-            let (a, b) = match line.split(',').take(2).collect::<Vec<&str>>()[..] {
-                [a, b] => (
-                    a.split('-')
-                        .take(2)
-                        .map(|x| x.parse::<i32>().unwrap())
-                        .collect::<Vec<i32>>(),
-                    b.split('-')
-                        .take(2)
-                        .map(|x| x.parse::<i32>().unwrap())
-                        .collect::<Vec<i32>>(),
-                ),
-                _ => panic!("no good"),
-            };
-            (
-                // part 1 wholly overlapping
-                i32::from((a[0] <= b[0] && a[1] >= b[1]) || (a[0] >= b[0] && a[1] <= b[1])),
-                // part 2 any overlapping
-                i32::from(
-                    (a[0] >= b[0] && a[0] <= b[1])
-                        || (a[1] >= b[0] && a[1] <= b[1])
-                        || (b[0] >= a[0] && b[0] <= a[1])
-                        || (b[1] >= a[0] && b[1] <= a[1]),
-                ),
-            )
-        })
-        // using folding instead of sum() so that we can do both parts in one call
-        .fold((0, 0), |mut acc: (i32, i32), x| {
-            acc.0 += x.0;
-            acc.1 += x.1;
-            acc
-        });
-    println!("Part 1: {}", value.0);
-    println!("Part 2: {}", value.1);
+    println!("Part 1: {}", part1(&file));
+    println!("Part 2: {}", part2(&file));
 
     Ok(())
 }
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    const INPUT: &str = "2-4,6-8
+2-3,4-5
+5-7,7-9
+2-8,3-7
+6-6,4-6
+2-6,4-8";
+
+    #[test]
+    fn part1_works() {
+        assert_eq!(part1(INPUT), "2")
+    }
+
+    #[test]
+    fn part2_works() {
+        assert_eq!(part2(INPUT), "4")
+    }
+}