App architecture modifications.

Now GUI and the app itself is divided into two different binaries.
The app also provides system tray icon.
Whereas the GUI can be used to configure the app.

app/src/db.rs

@@ -0,0 +1,51 @@
+pub mod structs;
+use crate::{config, APP_CONFIG_DIR};
+
+use std::path::PathBuf;
+use std::fs::File;
+use std::io::{BufReader, Read};
+use log::info;
+
+use serde_json;
+
+fn get_db_file_path() -> PathBuf {
+    PathBuf::from(format!("{}/{}", APP_CONFIG_DIR.get().unwrap().display(), config::DB_FILE_NAME))
+}
+
+pub fn init_settings() -> structs::Settings {
+    let mut db = None;
+    let db_file_path = get_db_file_path();
+
+    info!("Loading settings db file located at: {}", db_file_path.display());
+
+    if db_file_path.exists() {
+        // try load existing settings
+        if let Ok(mut db_file) = File::open(db_file_path) {
+            let reader = BufReader::new(db_file);
+            if let Ok(parsed_json) = serde_json::from_reader(reader) {
+                info!("Settings loaded.");
+                db = Some(parsed_json);
+            }
+        }
+    }
+
+    if db.is_none() {
+        // create default settings db file
+        warn!("No settings file found or there was an error parsing it. Creating default struct.");
+        db = Some(structs::Settings::default());
+    }
+
+    db.unwrap()
+}
+
+pub fn save_settings(settings: &structs::Settings) -> Result<(), std::io::Error> {
+    let db_file_path = get_db_file_path();
+
+    std::fs::write(
+        db_file_path,
+        serde_json::to_string_pretty(&settings).unwrap()
+    )?;
+
+    info!("Settings saved.");
+    Ok(())
+}