add memory cache for auth index

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

@@ -0,0 +1,52 @@
+mod error;
+use error::Error;
+
+use std::{cell::RefCell, collections::HashMap};
+
+/// Reduce disk usage by cache Auth index in memory
+pub struct Memory {
+    index: RefCell<HashMap<String, i64>>,
+}
+
+impl Memory {
+    // Constructors
+
+    /// Create new `Self`
+    pub fn new() -> Self {
+        Self {
+            index: RefCell::new(HashMap::new()),
+        }
+    }
+
+    // Actions
+
+    /// Add new record with `url` as key and `profile_identity_gemini_id` as value
+    /// * validate record with same key does not exist yet
+    pub fn add(&self, url: String, profile_identity_gemini_id: i64) -> Result<(), Error> {
+        match self
+            .index
+            .borrow_mut()
+            .insert(url, profile_identity_gemini_id)
+        {
+            Some(_) => Err(Error::Overwrite), // @TODO prevent?
+            None => Ok(()),
+        }
+    }
+
+    /* @TODO update feature
+    /// Cleanup index
+    pub fn clear(&self, url: &str) {
+        self.index.borrow_mut().clear()
+    } */
+
+    /// Search for `profile_identity_gemini_id` by `url` starts with given substring
+    pub fn starts_with(&self, prefix: &str) -> Vec<i64> {
+        let mut result = Vec::new();
+        for (url, &profile_identity_gemini_id) in self.index.borrow().iter() {
+            if url.starts_with(prefix) {
+                result.push(profile_identity_gemini_id)
+            }
+        }
+        result
+    }
+}