feat: out-of-box experience (#2)

Reviewed-on: https://git.reya.su/reya/signed/pulls/2

crates/signed_state/src/git_store.rs

@@ -0,0 +1,44 @@
+use std::path::PathBuf;
+
+use gpui::{App, Global};
+use signed_git::GitCache;
+
+struct GlobalGitStore(GitCache);
+
+impl Global for GlobalGitStore {}
+
+/// Global access to the on-disk git clone cache (grasp mirrors).
+///
+/// Installed at startup via [`GitStore::set_global`]; see also
+/// [`signed_state::init`].
+#[derive(Debug, Clone)]
+pub struct GitStore(GitCache);
+
+impl GitStore {
+    /// Register the clone cache rooted at `root` as an app-wide global.
+    /// Replaces any previously installed store (see [`signed_state::init`], which
+    /// installs an empty one).
+    pub fn set_global(root: impl Into<PathBuf>, cx: &mut App) -> Self {
+        let store = Self::new(root);
+        cx.set_global(GlobalGitStore(store.0.clone()));
+        store
+    }
+
+    /// The app-wide clone cache.
+    ///
+    /// # Panics
+    ///
+    /// Panics if [`GitStore::set_global`] was never called.
+    pub fn global(cx: &App) -> Self {
+        Self(cx.global::<GlobalGitStore>().0.clone())
+    }
+
+    fn new(root: impl Into<PathBuf>) -> Self {
+        Self(GitCache::new(root.into()))
+    }
+
+    /// Underlying clone cache.
+    pub fn cache(&self) -> &GitCache {
+        &self.0
+    }
+}