Move user_follow to separate file (#1210)

Also add unit tests

models/user_follow.go

@@ -0,0 +1,71 @@
+// Copyright 2017 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 models
+
+// Follow represents relations of user and his/her followers.
+type Follow struct {
+	ID       int64 `xorm:"pk autoincr"`
+	UserID   int64 `xorm:"UNIQUE(follow)"`
+	FollowID int64 `xorm:"UNIQUE(follow)"`
+}
+
+// IsFollowing returns true if user is following followID.
+func IsFollowing(userID, followID int64) bool {
+	has, _ := x.Get(&Follow{UserID: userID, FollowID: followID})
+	return has
+}
+
+// FollowUser marks someone be another's follower.
+func FollowUser(userID, followID int64) (err error) {
+	if userID == followID || IsFollowing(userID, followID) {
+		return nil
+	}
+
+	sess := x.NewSession()
+	defer sessionRelease(sess)
+	if err = sess.Begin(); err != nil {
+		return err
+	}
+
+	if _, err = sess.Insert(&Follow{UserID: userID, FollowID: followID}); err != nil {
+		return err
+	}
+
+	if _, err = sess.Exec("UPDATE `user` SET num_followers = num_followers + 1 WHERE id = ?", followID); err != nil {
+		return err
+	}
+
+	if _, err = sess.Exec("UPDATE `user` SET num_following = num_following + 1 WHERE id = ?", userID); err != nil {
+		return err
+	}
+	return sess.Commit()
+}
+
+// UnfollowUser unmarks someone as another's follower.
+func UnfollowUser(userID, followID int64) (err error) {
+	if userID == followID || !IsFollowing(userID, followID) {
+		return nil
+	}
+
+	sess := x.NewSession()
+	defer sessionRelease(sess)
+	if err = sess.Begin(); err != nil {
+		return err
+	}
+
+	if _, err = sess.Delete(&Follow{UserID: userID, FollowID: followID}); err != nil {
+		return err
+	}
+
+	if _, err = sess.Exec("UPDATE `user` SET num_followers = num_followers - 1 WHERE id = ?", followID); err != nil {
+		return err
+	}
+
+	if _, err = sess.Exec("UPDATE `user` SET num_following = num_following - 1 WHERE id = ?", userID); err != nil {
+		return err
+	}
+	return sess.Commit()
+}
+