chore: rewrite the backend (not tested) (#203)

* wip: refactor

* refactor

* clean up

* .

* rename

* add relay auth

* .

* .

* optimize

* .

* clean up

* add encryption crate

* .

* .

* .

* .

* .

* add encryption crate

* .

* refactor nip4e

* .

* fix endless loop

* fix metadata fetching

crates/common/src/paths.rs

@@ -0,0 +1,64 @@
+use std::path::PathBuf;
+use std::sync::OnceLock;
+
+/// Returns the path to the user's home directory.
+pub fn home_dir() -> &'static PathBuf {
+    static HOME_DIR: OnceLock<PathBuf> = OnceLock::new();
+    HOME_DIR.get_or_init(|| dirs::home_dir().expect("failed to determine home directory"))
+}
+
+/// Returns the path to the configuration directory used by Coop.
+pub fn config_dir() -> &'static PathBuf {
+    static CONFIG_DIR: OnceLock<PathBuf> = OnceLock::new();
+    CONFIG_DIR.get_or_init(|| {
+        if cfg!(target_os = "windows") {
+            return dirs::config_dir()
+                .expect("failed to determine RoamingAppData directory")
+                .join("Coop");
+        }
+
+        if cfg!(any(target_os = "linux", target_os = "freebsd")) {
+            return if let Ok(flatpak_xdg_config) = std::env::var("FLATPAK_XDG_CONFIG_HOME") {
+                flatpak_xdg_config.into()
+            } else {
+                dirs::config_dir().expect("failed to determine XDG_CONFIG_HOME directory")
+            }
+            .join("coop");
+        }
+
+        home_dir().join(".config").join("coop")
+    })
+}
+
+/// Returns the path to the support directory used by Coop.
+pub fn support_dir() -> &'static PathBuf {
+    static SUPPORT_DIR: OnceLock<PathBuf> = OnceLock::new();
+    SUPPORT_DIR.get_or_init(|| {
+        if cfg!(target_os = "macos") {
+            return home_dir().join("Library/Application Support/Coop");
+        }
+
+        if cfg!(any(target_os = "linux", target_os = "freebsd")) {
+            return if let Ok(flatpak_xdg_data) = std::env::var("FLATPAK_XDG_DATA_HOME") {
+                flatpak_xdg_data.into()
+            } else {
+                dirs::data_local_dir().expect("failed to determine XDG_DATA_HOME directory")
+            }
+            .join("coop");
+        }
+
+        if cfg!(target_os = "windows") {
+            return dirs::data_local_dir()
+                .expect("failed to determine LocalAppData directory")
+                .join("coop");
+        }
+
+        config_dir().clone()
+    })
+}
+
+/// Returns the path to the `nostr` file.
+pub fn nostr_file() -> &'static PathBuf {
+    static NOSTR_FILE: OnceLock<PathBuf> = OnceLock::new();
+    NOSTR_FILE.get_or_init(|| support_dir().join("nostr-db"))
+}