feat: add support for configuring through environment variables

src/config.rs

@@ -1,10 +1,18 @@
-use std::path::PathBuf;
-
 use rustc_hash::FxHashMap;
 use serde::Deserialize;
+use std::env;
+use std::mem;
+use std::path::PathBuf;
 
 use crate::error;
 
+// We can't assign `a` to `b` in the loop in `Config::load`, so we'll have to use swap. It looks ugly so now we have a macro for it.
+macro_rules! swap {
+    ($a:expr, $b:expr) => {
+        mem::swap(&mut $a, &mut $b)
+    };
+}
+
 #[derive(Clone, Deserialize)]
 #[serde(rename_all = "snake_case")]
 pub enum Theme {
@@ -78,8 +86,41 @@ impl Config {
         }
     }
 
+    /// Loads file and env config and merges them
+    pub fn load(&mut self, path: Option<PathBuf>) -> Self {
+        let mut config = self.load_file(path);
+
+        // Get environment variables with CUP_ prefix
+        let env_vars: FxHashMap<String, String> =
+            env::vars().filter(|(k, _)| k.starts_with("CUP_")).collect();
+
+        if !env_vars.is_empty() {
+            if let Ok(mut cfg) = envy::prefixed("CUP_").from_env::<Config>() {
+                // If we have environment variables, override config.json options
+                for (key, _) in env_vars {
+                    match key.as_str() {
+                        "CUP_AGENT" => config.agent = cfg.agent,
+                        #[rustfmt::skip]
+                        "CUP_IGNORE_UPDATE_TYPE" => swap!(config.ignore_update_type, cfg.ignore_update_type),
+                        #[rustfmt::skip]
+                        "CUP_REFRESH_INTERVAL" => swap!(config.refresh_interval, cfg.refresh_interval),
+                        "CUP_SOCKET" => swap!(config.socket, cfg.socket),
+                        "CUP_THEME" => swap!(config.theme, cfg.theme),
+                        // The syntax for these is slightly more complicated, not sure if they should be enabled or not. Let's stick to simple types for now.
+                        // "CUP_IMAGES" => swap!(config.images, cfg.images),
+                        // "CUP_REGISTRIES" => swap!(config.registries, cfg.registries),
+                        // "CUP_SERVERS" => swap!(config.servers, cfg.servers),
+                        _ => (), // Maybe print a warning if other CUP_ variables are detected
+                    }
+                }
+            }
+        }
+
+        config
+    }
+
     /// Reads the config from the file path provided and returns the parsed result.
-    pub fn load(&self, path: Option<PathBuf>) -> Self {
+    fn load_file(&self, path: Option<PathBuf>) -> Self {
         let raw_config = match &path {
             Some(path) => std::fs::read_to_string(path),
             None => return Self::new(), // Empty config
@@ -93,7 +134,7 @@ impl Config {
         self.parse(&raw_config.unwrap()) // We can safely unwrap here
     }
     /// Parses and validates the config.
-    pub fn parse(&self, raw_config: &str) -> Self {
+    fn parse(&self, raw_config: &str) -> Self {
         let config: Self = match serde_json::from_str(raw_config) {
             Ok(config) => config,
             Err(e) => error!("Unexpected error occured while parsing config: {}", e),