fix: enforce global rate limit in jikan client and handle relation errors

internal/jikan/client.go

@@ -5,15 +5,18 @@ import (
 	"encoding/json"
 	"fmt"
 	"net/http"
+	"sync"
 	"time"
 
 	"mal/internal/database"
 )
 
 type Client struct {
-	httpClient *http.Client
-	baseURL    string
-	db         database.Querier
+	httpClient  *http.Client
+	baseURL     string
+	db          database.Querier
+	mu          sync.Mutex
+	lastReqTime time.Time
 }
 
 func NewClient(db database.Querier) *Client {
@@ -24,6 +27,20 @@ func NewClient(db database.Querier) *Client {
 	}
 }
 
+func (c *Client) waitRateLimit() {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	now := time.Now()
+	nextAllowed := c.lastReqTime.Add(340 * time.Millisecond)
+	if now.Before(nextAllowed) {
+		time.Sleep(nextAllowed.Sub(now))
+		c.lastReqTime = time.Now()
+	} else {
+		c.lastReqTime = now
+	}
+}
+
 func (c *Client) getCache(key string, out interface{}) bool {
 	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
 	defer cancel()
@@ -57,8 +74,7 @@ func (c *Client) setCache(key string, data interface{}, ttl time.Duration) {
 func (c *Client) fetchWithRetry(urlStr string, out interface{}) error {
 	maxRetries := 3
 	for i := 0; i < maxRetries; i++ {
-		// Base delay for Jikan rate limiting (3 requests per second)
-		time.Sleep(340 * time.Millisecond)
+		c.waitRateLimit()
 
 		resp, err := c.httpClient.Get(urlStr)
 		if err != nil {