With iterator!

day1/src/main.rs

@@ -1,10 +1,47 @@
 use std::fs::File;
 use std::io::BufRead;
 use std::io::BufReader;
+use std::io::Lines;
 
 use clap::Arg;
 use clap::Command;
 
+struct Accumulator<B> {
+    lines: Lines<B>,
+    current: u32,
+}
+
+trait Elvish<B> {
+    fn elf(self) -> Accumulator<B>;
+}
+
+impl<B> Elvish<B> for Lines<B> {
+    fn elf(self) -> Accumulator<B> {
+        Accumulator {
+            lines: self,
+            current: 0,
+        }
+    }
+}
+
+impl<B: BufRead> Iterator for Accumulator<B> {
+    type Item = u32;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        while let Some(Ok(line)) = self.lines.next() {
+            let line = line.trim();
+            if line.is_empty() {
+                let result = self.current;
+                self.current = 0;
+                return Some(result);
+            } else {
+                self.current += line.parse::<u32>().unwrap();
+            }
+        }
+        None
+    }
+}
+
 fn main() {
     let matches = Command::new("Day1").arg(Arg::new("filename")).get_matches();
     let filename = matches
@@ -15,23 +52,5 @@ fn main() {
     let file = File::open(filename).expect("Can't read file");
     let reader = BufReader::new(file);
 
-    let mut max_calories = 0;
-    let mut elf_calories = 0;
-
-    for line in reader.lines() {
-        let line = line.unwrap();
-        let line = line.trim();
-
-        // XXX I want to do this with an iterator!
-        if line.is_empty() {
-            if elf_calories > max_calories {
-                max_calories = elf_calories;
-            }
-            elf_calories = 0;
-        } else {
-            println!("Line: {}", line);
-            elf_calories += line.parse::<u32>().unwrap();
-        }
-    }
-    println!("Max: {}", max_calories);
+    println!("Max: {:?}", reader.lines().elf().max())
 }