Logging (#8)

- Add `Logger`, `Config`
- Back to `nixos-unstable`
- `nix flake update`

src/config.rs

@@ -0,0 +1,34 @@
+use crate::constants::APP_NAME;
+use color_eyre::eyre::{eyre, Result};
+use directories::ProjectDirs;
+use std::fs;
+use std::path::PathBuf;
+pub struct Config {
+    pub log_dir: PathBuf,
+}
+
+impl Config {
+    pub fn init() -> Result<Self> {
+        let log_dir = get_default_state_dir()?.join("logs");
+        fs::create_dir_all(&log_dir)?;
+
+        Ok(Self { log_dir })
+    }
+}
+
+// fn new
+pub fn get_project_dir() -> Result<ProjectDirs> {
+    let dirs = ProjectDirs::from("", "", APP_NAME)
+        .ok_or_else(|| eyre!("Failed to get project directories"))?;
+
+    Ok(dirs)
+}
+
+fn get_default_state_dir() -> Result<PathBuf> {
+    let directory = get_project_dir()?
+        .state_dir()
+        .map(|d| d.to_path_buf())
+        .ok_or_else(|| eyre!("Failed to get state directory"))?;
+
+    Ok(directory)
+}