fc-common: GitHub rate limit state extraction

Extract `X-RateLimit-*` headers from responses and calculate an adaptive
delay. Minimum delay is 1 seconds to prevent division by 0.

Signed-off-by: NotAShelf <raf@notashelf.dev>
Change-Id: Ib35b0d0e720098e2c68ced88a8821c7b6a6a6964

crates/common/tests/mod.rs

@@ -1,5 +1,7 @@
 //! Integration tests for database and configuration
 
+mod notifications_tests;
+
 use fc_common::{
   Database,
   config::{Config, DatabaseConfig},

crates/common/tests/notifications_tests.rs

@@ -0,0 +1,59 @@
+use fc_common::notifications::*;
+use std::time::{SystemTime, UNIX_EPOCH};
+
+#[test]
+fn test_rate_limit_extraction() {
+  let mut headers = reqwest::header::HeaderMap::new();
+  headers.insert("X-RateLimit-Limit", "5000".parse().unwrap());
+  headers.insert("X-RateLimit-Remaining", "1234".parse().unwrap());
+  headers.insert("X-RateLimit-Reset", "1735689600".parse().unwrap());
+
+  let state = extract_rate_limit_from_headers(&headers);
+  assert!(state.is_some());
+
+  let state = state.unwrap();
+  assert_eq!(state.limit, 5000);
+  assert_eq!(state.remaining, 1234);
+  assert_eq!(state.reset_at, 1735689600);
+}
+
+#[test]
+fn test_rate_limit_missing_headers() {
+  let headers = reqwest::header::HeaderMap::new();
+  let state = extract_rate_limit_from_headers(&headers);
+  assert!(state.is_none());
+}
+
+#[test]
+fn test_sleep_duration_calculation() {
+  let now = SystemTime::now()
+    .duration_since(UNIX_EPOCH)
+    .unwrap()
+    .as_secs();
+
+  let state = RateLimitState {
+    limit: 5000,
+    remaining: 500,
+    reset_at: now + 3600,
+  };
+
+  let delay = calculate_delay(&state, now);
+  assert!(delay >= 6 && delay <= 7);
+}
+
+#[test]
+fn test_sleep_duration_minimum() {
+  let now = SystemTime::now()
+    .duration_since(UNIX_EPOCH)
+    .unwrap()
+    .as_secs();
+
+  let state = RateLimitState {
+    limit: 5000,
+    remaining: 4999,
+    reset_at: now + 10000,
+  };
+
+  let delay = calculate_delay(&state, now);
+  assert_eq!(delay, 1);
+}