[Add] issue Un-/Subscription function (#214)

fix lint

add issue subscription function

Co-authored-by: 6543 <6543@obermui.de>
Reviewed-by: Andrew Thornton <art27@cantab.net>
Reviewed-by: techknowlogick <techknowlogick@gitea.io>

gitea/issue_subscription.go

@@ -0,0 +1,45 @@
+// Copyright 2020 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package gitea
+
+import (
+	"fmt"
+)
+
+// GetIssueSubscribers get list of users who subscribed on an issue
+func (c *Client) GetIssueSubscribers(owner, repo string, index int64) ([]*User, error) {
+	subscribers := make([]*User, 0, 10)
+	return subscribers, c.getParsedResponse("GET", fmt.Sprintf("/repos/%s/%s/issues/%d/subscriptions", owner, repo, index), nil, nil, &subscribers)
+}
+
+// AddIssueSubscription Subscribe user to issue
+func (c *Client) AddIssueSubscription(owner, repo string, index int64, user string) error {
+	_, err := c.getResponse("PUT", fmt.Sprintf("/repos/%s/%s/issues/%d/subscriptions/%s", owner, repo, index, user), nil, nil)
+	return err
+}
+
+// DeleteIssueSubscription unsubscribe user from issue
+func (c *Client) DeleteIssueSubscription(owner, repo string, index int64, user string) error {
+	_, err := c.getResponse("DELETE", fmt.Sprintf("/repos/%s/%s/issues/%d/subscriptions/%s", owner, repo, index, user), nil, nil)
+	return err
+}
+
+// IssueSubscribe subscribe current user to an issue
+func (c *Client) IssueSubscribe(owner, repo string, index int64) error {
+	u, err := c.GetMyUserInfo()
+	if err != nil {
+		return err
+	}
+	return c.AddIssueSubscription(owner, repo, index, u.UserName)
+}
+
+// IssueUnSubscribe unsubscribe current user from an issue
+func (c *Client) IssueUnSubscribe(owner, repo string, index int64) error {
+	u, err := c.GetMyUserInfo()
+	if err != nil {
+		return err
+	}
+	return c.DeleteIssueSubscription(owner, repo, index, u.UserName)
+}