feat(zarinhub): automate access token refresh

backend/internal/zarinhub/client.go

@@ -16,28 +16,60 @@ import (
 const maxResponseBodySize = 1 << 20
 
 type Client struct {
-	httpClient  *http.Client
-	endpointURL string
-	accessToken string
+	httpClient    *http.Client
+	endpointURL   string
+	tokenProvider TokenProvider
 }
 
 var _ service.CardToIBANClient = (*Client)(nil)
 
+type TokenProvider interface {
+	AccessToken(ctx context.Context) (string, error)
+	Invalidate(token string)
+}
+
 func NewClient(
 	httpClient *http.Client,
 	endpointURL string,
-	accessToken string,
+	tokenProvider TokenProvider,
 ) *Client {
 	return &Client{
-		httpClient:  httpClient,
-		endpointURL: endpointURL,
-		accessToken: accessToken,
+		httpClient:    httpClient,
+		endpointURL:   endpointURL,
+		tokenProvider: tokenProvider,
 	}
 }
 
 func (c *Client) Convert(
 	ctx context.Context,
 	cardNumber string,
+) (service.ConversionResult, error) {
+	accessToken, err := c.tokenProvider.AccessToken(ctx)
+	if err != nil {
+		return service.ConversionResult{},
+			fmt.Errorf("get zarinhub access token: %w", err)
+	}
+
+	result, err := c.convert(ctx, cardNumber, accessToken)
+	if !errors.Is(err, ErrAuthentication) ||
+		result.UpstreamHTTPStatus != http.StatusUnauthorized {
+		return result, err
+	}
+
+	c.tokenProvider.Invalidate(accessToken)
+
+	accessToken, err = c.tokenProvider.AccessToken(ctx)
+	if err != nil {
+		return result, fmt.Errorf("refresh zarinhub access token: %w", err)
+	}
+
+	return c.convert(ctx, cardNumber, accessToken)
+}
+
+func (c *Client) convert(
+	ctx context.Context,
+	cardNumber string,
+	accessToken string,
 ) (service.ConversionResult, error) {
 	payload, err := json.Marshal(convertRequest{
 		Card: cardNumber,
@@ -60,7 +92,7 @@ func (c *Client) Convert(
 
 	req.Header.Set(
 		"Authorization",
-		"Bearer "+c.accessToken,
+		"Bearer "+accessToken,
 	)
 
 	req.Header.Set(