Split lib and main source and add PathTimes

Cargo.toml

@@ -11,3 +11,7 @@ clap = "4.4.2"
 ion-rs = "0.18.1"
 ion-schema = "0.9.1"
 thiserror = "1.0.48"
+
+[[bin]]
+name = "usysconf"
+path = "src/bin/usysconf/main.rs"

src/main.rs → src/bin/usysconf/main.rs

@@ -3,6 +3,7 @@
 // SPDX-License-Identifier: MPL-2.0
 
 mod cli;
+mod pathtimes;
 
 fn main() -> Result<(), cli::Error> {
     cli::process()

src/bin/usysconf/pathtimes.rs

@@ -0,0 +1,30 @@
+use std::collections::HashMap;
+use std::io::{Read, Write};
+
+type Path = String;
+type Mtime = i64;
+
+#[derive(Default)]
+pub struct PathTimes {
+    map: HashMap<Path, Mtime>,
+}
+
+impl PathTimes {
+    pub fn new(source: impl Read) -> Result<Self, bincode::Error> {
+        Ok(Self {
+            map: bincode::deserialize_from(source)?,
+        })
+    }
+
+    pub fn update(&mut self, path: Path, mtime: Mtime) {
+        self.map.insert(path, mtime);
+    }
+
+    pub fn get(&self, path: &Path) -> Option<Mtime> {
+        self.map.get(path).copied()
+    }
+
+    pub fn save(&mut self, writer: impl Write) -> Result<(), bincode::Error> {
+        bincode::serialize_into(writer, &self.map)
+    }
+}