paypal 在到期结束前的一半时间内，自动刷新token (#365)

* paypal 在到期结束前的一半时间内，自动刷新token

paypal/client.go

@@ -2,6 +2,8 @@ package paypal
 
 import (
 	"context"
+	"github.com/go-pay/gopay/pkg/xlog"
+	"time"
 
 	"github.com/go-pay/gopay"
 	"github.com/go-pay/gopay/pkg/util"
@@ -34,10 +36,26 @@ func NewClient(clientid, secret string, isProd bool) (client *Client, err error)
 		DebugSwitch: gopay.DebugOff,
 		hc:          xhttp.NewClient(),
 	}
-	_, err = client.GetAccessToken()
+	token, err := client.GetAccessToken()
 	if err != nil {
 		return nil, err
 	}
+	// 在到期结束前的一半时间内，自动刷新token
+	go func(token *AccessToken) {
+		ticker := time.NewTicker(time.Duration(token.ExpiresIn/2) * time.Second)
+		for {
+			select {
+			case <-ticker.C:
+				tokenNew, err := client.GetAccessToken()
+				if err != nil {
+					xlog.Errorf("PayPal GetAccessToken Error: %s", err.Error())
+					continue
+				}
+				client.AccessToken = tokenNew.AccessToken
+			}
+		}
+	}(token)
+
 	return client, nil
 }