From a69f1e59006b6fd5709e470d9f5af54879cffde4 Mon Sep 17 00:00:00 2001
From: Josh Kingsley <josh@joshkingsley.me>
Date: Thu, 4 Dec 2025 14:33:59 +0200
Subject: Day 3: parse input

---
 day3/Cargo.toml  |  6 +++++
 day3/src/main.rs | 72 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 78 insertions(+)
 create mode 100644 day3/Cargo.toml
 create mode 100644 day3/src/main.rs

(limited to 'day3')

diff --git a/day3/Cargo.toml b/day3/Cargo.toml
new file mode 100644
index 0000000..5111c7d
--- /dev/null
+++ b/day3/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "day3"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
diff --git a/day3/src/main.rs b/day3/src/main.rs
new file mode 100644
index 0000000..dbbd303
--- /dev/null
+++ b/day3/src/main.rs
@@ -0,0 +1,72 @@
+use std::{env, fs, num::ParseIntError, str::FromStr};
+
+#[derive(Debug)]
+struct BatteryBank(Vec<u8>);
+
+struct ParseBatteryBankError;
+
+impl From<ParseIntError> for ParseBatteryBankError {
+    fn from(_: ParseIntError) -> Self {
+        Self
+    }
+}
+
+impl FromStr for BatteryBank {
+    type Err = ParseBatteryBankError;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        Ok(Self(
+            s.chars()
+                .map(|ch| ch.to_string().parse())
+                .collect::<Result<_, _>>()?,
+        ))
+    }
+}
+
+#[derive(Debug)]
+struct Input(Vec<BatteryBank>);
+
+#[derive(Debug)]
+enum ParseInputError {
+    BadBank(String),
+}
+
+impl FromStr for Input {
+    type Err = ParseInputError;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        Ok(Self(
+            s.split_whitespace()
+                .map(|bank| bank.parse().map_err(|_| ParseInputError::BadBank(s.into())))
+                .collect::<Result<_, _>>()?,
+        ))
+    }
+}
+
+#[derive(Debug)]
+enum Error {
+    BadArgument,
+    BadInput(ParseInputError),
+}
+
+impl From<std::io::Error> for Error {
+    fn from(value: std::io::Error) -> Self {
+        Self::BadArgument
+    }
+}
+
+impl From<ParseInputError> for Error {
+    fn from(value: ParseInputError) -> Self {
+        Self::BadInput(value)
+    }
+}
+
+fn main() -> Result<(), Error> {
+    let mut args = env::args();
+    let input_path = args.nth(1).ok_or(Error::BadArgument)?;
+    let input: Input = fs::read_to_string(input_path)?.parse()?;
+
+    dbg!(input);
+
+    Ok(())
+}
-- 
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