add memory cache for gemini identities search

src/profile/identity/gemini/memory.rs

@@ -0,0 +1,39 @@
+mod error;
+use error::Error;
+
+use std::{cell::RefCell, collections::HashMap};
+
+/// Reduce disk usage by cache index in memory
+pub struct Memory {
+    index: RefCell<HashMap<i64, String>>,
+}
+
+impl Memory {
+    // Constructors
+
+    /// Create new `Self`
+    pub fn new() -> Self {
+        Self {
+            index: RefCell::new(HashMap::new()),
+        }
+    }
+
+    // Actions
+
+    /// Add new record with `id` as key and `pem` as value
+    /// * validate record with same key does not exist yet
+    pub fn add(&self, id: i64, pem: String) -> Result<(), Error> {
+        match self.index.borrow_mut().insert(id, pem) {
+            Some(_) => Err(Error::Overwrite), // @TODO prevent?
+            None => Ok(()),
+        }
+    }
+
+    /// Get `pem` clone by `id` from memory index
+    pub fn get(&self, id: i64) -> Result<String, Error> {
+        match self.index.borrow().get(&id) {
+            Some(pem) => Ok(pem.clone()),
+            None => Err(Error::NotFound),
+        }
+    }
+}

src/profile/identity/gemini/memory/error.rs

@@ -0,0 +1,5 @@
+#[derive(Debug)]
+pub enum Error {
+    NotFound,
+    Overwrite,
+}