From ed844a997cf7211a61a317a7103b6c131c74aaf9 Mon Sep 17 00:00:00 2001
From: Bert Peters <bert@bertptrs.nl>
Date: Thu, 2 Dec 2021 08:34:14 +0100
Subject: [PATCH] Create reusable line reader

---
 2021/src/common.rs | 43 ++++++++++++++++++++++++++++++-------------
 2021/src/day02.rs  | 14 +++++---------
 2 files changed, 35 insertions(+), 22 deletions(-)

diff --git a/2021/src/common.rs b/2021/src/common.rs
index 3cb3826..ad978b3 100644
--- a/2021/src/common.rs
+++ b/2021/src/common.rs
@@ -4,6 +4,33 @@ use std::io::Read;
 use std::marker::PhantomData;
 use std::str::FromStr;
 
+pub struct LineIter<'a> {
+    reader: BufReader<&'a mut dyn Read>,
+    buffer: String,
+}
+
+impl<'a> LineIter<'a> {
+    pub fn new(input: &'a mut dyn Read) -> Self {
+        Self {
+            reader: BufReader::new(input),
+            buffer: String::new(),
+        }
+    }
+
+    /// Get the next line, or None
+    ///
+    /// This is deliberately not an [Iterator] impl as those cannot hand out references to self.
+    pub fn next(&mut self) -> Option<&str> {
+        self.buffer.clear();
+
+        if matches!(self.reader.read_line(&mut self.buffer), Ok(n) if n > 0) {
+            Some(self.buffer.trim_end_matches('\n'))
+        } else {
+            None
+        }
+    }
+}
+
 /// Line-based iterator/parser
 ///
 /// For each line of the input, attempt to parse it as the requested type. Iteration is stopped on
@@ -13,33 +40,23 @@ pub struct LineParser<'a, I>
 where
     I: FromStr,
 {
-    reader: BufReader<&'a mut dyn Read>,
-    buffer: String,
+    iter: LineIter<'a>,
     _data: PhantomData<I>,
 }
 
 impl<'a, I: FromStr> LineParser<'a, I> {
     pub fn new(input: &'a mut dyn Read) -> Self {
         Self {
-            reader: BufReader::new(input),
-            buffer: String::new(),
+            iter: LineIter::new(input),
             _data: PhantomData,
         }
     }
-
-    fn next_line(&mut self) -> Option<&str> {
-        self.buffer.clear();
-
-        self.reader.read_line(&mut self.buffer).ok()?;
-
-        Some(self.buffer.trim())
-    }
 }
 
 impl<'a, I: FromStr> Iterator for LineParser<'a, I> {
     type Item = I;
 
     fn next(&mut self) -> Option<Self::Item> {
-        self.next_line()?.parse().ok()
+        self.iter.next()?.parse().ok()
     }
 }
diff --git a/2021/src/day02.rs b/2021/src/day02.rs
index 1e29efb..d68b612 100644
--- a/2021/src/day02.rs
+++ b/2021/src/day02.rs
@@ -1,7 +1,7 @@
-use std::io::BufRead;
-use std::io::BufReader;
 use std::io::Read;
 
+use crate::common::LineIter;
+
 enum Dir {
     Up,
     Down,
@@ -9,13 +9,11 @@ enum Dir {
 }
 
 fn parse_input(input: &mut dyn Read) -> Vec<(Dir, i32)> {
-    let mut reader = BufReader::new(input);
-    let mut buffer = String::new();
-
+    let mut reader = LineIter::new(input);
     let mut moves = Vec::new();
 
-    while matches!(reader.read_line(&mut buffer), Ok(n) if n > 0) {
-        let (dir, amount) = buffer.trim().split_once(" ").unwrap();
+    while let Some(line) = reader.next() {
+        let (dir, amount) = line.split_once(" ").unwrap();
 
         let dir = match dir {
             "up" => Dir::Up,
@@ -25,8 +23,6 @@ fn parse_input(input: &mut dyn Read) -> Vec<(Dir, i32)> {
         };
 
         moves.push((dir, amount.parse().unwrap()));
-
-        buffer.clear();
     }
 
     moves