feat(config)!: use XDG spec environment variables

Depending on the existence of a file in the original config location, uses that or
the new location.

Linux users will see no change if they haven't set any XDG_* environment
variable. Windows and Mac OS users may see their cache folder move,
adjusting it to the dirs_next advised location.

Everyone will have the option to establish their settings in their
$XDG_CONFIG_HOME directory and their cache location analogously.

README.md

@@ -380,15 +380,15 @@ To move the focus from the search input to the other windows such as track resul
 
 ## Configurations
 
-By default, `spotify_player` will look into `$HOME/.config/spotify-player` for application's configuration files. This can be changed by either specifying `-c <FOLDER_PATH>` or `--config-folder <FOLDER_PATH>` option.
+By default, `spotify_player` will look into the `$XDG_CONFIG_HOME/spotify-player` directory for application's configuration files, falling back on `$HOME/.config/spotify-player`. This can be changed by either specifying `-c <FOLDER_PATH>` or `--config-folder <FOLDER_PATH>` option.
 
 If an application configuration file is not found, one will be created with default values.
 
 Please refer to [the configuration documentation](docs/config.md) for more details on the configuration options.
 
 ## Caches
 
-By default, `spotify_player` will look into `$HOME/.cache/spotify-player` for application's cache files, which include log files, Spotify's authorization credentials, audio cache files, etc. This can be changed by either specifying `-C <FOLDER_PATH>` or `--cache-folder <FOLDER_PATH>` option.
+By default, `spotify_player` will look into `$XDG_CACHE_HOME/spotify-player` for application's cache files, which include log files, Spotify's authorization credentials, audio cache files, etc, falling back on `$HOME/.cache/spotify-player`. This can be changed by either specifying `-C <FOLDER_PATH>` or `--cache-folder <FOLDER_PATH>` option.
 
 ### Logging
 

spotify_player/src/config/mod.rs

@@ -2,7 +2,6 @@ mod keymap;
 mod theme;
 
 const DEFAULT_CONFIG_FOLDER: &str = ".config/spotify-player";
-const DEFAULT_CACHE_FOLDER: &str = ".cache/spotify-player";
 const APP_CONFIG_FILE: &str = "app.toml";
 const THEME_CONFIG_FILE: &str = "theme.toml";
 const KEYMAP_CONFIG_FILE: &str = "keymap.toml";
@@ -321,18 +320,27 @@ impl AppConfig {
     }
 }
 
+const APP_NAME: &str = "spotify-player";
+
 /// gets the application's configuration folder path
 pub fn get_config_folder_path() -> Result<PathBuf> {
-    match dirs_next::home_dir() {
-        Some(home) => Ok(home.join(DEFAULT_CONFIG_FOLDER)),
-        None => Err(anyhow!("cannot find the $HOME folder")),
+    if let Some(home) = dirs_next::home_dir() {
+        let old_path = home.join(DEFAULT_CONFIG_FOLDER);
+        if old_path.exists() {
+            return Ok(old_path);
+        }
     }
+    if let Some(config_home) = dirs_next::config_dir() {
+        return Ok(config_home.join(APP_NAME));
+    }
+
+    Err(anyhow!("cannot find the $HOME folder"))
 }
 
 /// gets the application's cache folder path
 pub fn get_cache_folder_path() -> Result<PathBuf> {
-    match dirs_next::home_dir() {
-        Some(home) => Ok(home.join(DEFAULT_CACHE_FOLDER)),
+    match dirs_next::cache_dir() {
+        Some(cache_home) => Ok(cache_home.join(APP_NAME)),
         None => Err(anyhow!("cannot find the $HOME folder")),
     }
 }