Rewrite delivery of issue and comment mails (#9009)

* Mail issue subscribers, rework the function

* Simplify a little more

* Fix unused variable

* Refactor mail delivery to avoid heavy load on server

* Avoid splitting into too many goroutines

* Fix comments and optimize GetMaileableUsersByIDs()

* Fix return on errors

5 files changed, 63 insertions, 0 deletions

diff --git a/models/issue.go b/models/issue.go
index 1fe9140dad..0113f0a404 100644
--- a/models/issue.go
+++ b/models/issue.go
@@ -1219,6 +1219,19 @@ func Issues(opts *IssuesOptions) ([]*Issue, error) {
 	return issues, nil
 }
 
+// GetParticipantsIDsByIssueID returns the IDs of all users who participated in comments of an issue,
+// but skips joining with `user` for performance reasons.
+// User permissions must be verified elsewhere if required.
+func GetParticipantsIDsByIssueID(issueID int64) ([]int64, error) {
+	userIDs := make([]int64, 0, 5)
+	return userIDs, x.Table("comment").
+		Cols("poster_id").
+		Where("issue_id = ?", issueID).
+		And("type in (?,?,?)", CommentTypeComment, CommentTypeCode, CommentTypeReview).
+		Distinct("poster_id").
+		Find(&userIDs)
+}
+
 // GetParticipantsByIssueID returns all users who are participated in comments of an issue.
 func GetParticipantsByIssueID(issueID int64) ([]*User, error) {
 	return getParticipantsByIssueID(x, issueID)
diff --git a/models/issue_assignees.go b/models/issue_assignees.go
index 4d71cc6e51..08a567c4eb 100644
--- a/models/issue_assignees.go
+++ b/models/issue_assignees.go
@@ -41,6 +41,18 @@ func (issue *Issue) loadAssignees(e Engine) (err error) {
 	return
 }
 
+// GetAssigneeIDsByIssue returns the IDs of users assigned to an issue
+// but skips joining with `user` for performance reasons.
+// User permissions must be verified elsewhere if required.
+func GetAssigneeIDsByIssue(issueID int64) ([]int64, error) {
+	userIDs := make([]int64, 0, 5)
+	return userIDs, x.Table("issue_assignees").
+		Cols("assignee_id").
+		Where("issue_id = ?", issueID).
+		Distinct("assignee_id").
+		Find(&userIDs)
+}
+
 // GetAssigneesByIssue returns everyone assigned to that issue
 func GetAssigneesByIssue(issue *Issue) (assignees []*User, err error) {
 	return getAssigneesByIssue(x, issue)
diff --git a/models/issue_watch.go b/models/issue_watch.go
index 1ae0c9d474..3d7d48a125 100644
--- a/models/issue_watch.go
+++ b/models/issue_watch.go
@@ -60,6 +60,18 @@ func getIssueWatch(e Engine, userID, issueID int64) (iw *IssueWatch, exists bool
 	return
 }
 
+// GetIssueWatchersIDs returns IDs of subscribers to a given issue id
+// but avoids joining with `user` for performance reasons
+// User permissions must be verified elsewhere if required
+func GetIssueWatchersIDs(issueID int64) ([]int64, error) {
+	ids := make([]int64, 0, 64)
+	return ids, x.Table("issue_watch").
+		Where("issue_id=?", issueID).
+		And("is_watching = ?", true).
+		Select("user_id").
+		Find(&ids)
+}
+
 // GetIssueWatchers returns watchers/unwatchers of a given issue
 func GetIssueWatchers(issueID int64) (IssueWatchList, error) {
 	return getIssueWatchers(x, issueID)
diff --git a/models/repo_watch.go b/models/repo_watch.go
index 2de4f8b320..2279dcb115 100644
--- a/models/repo_watch.go
+++ b/models/repo_watch.go
@@ -140,6 +140,18 @@ func GetWatchers(repoID int64) ([]*Watch, error) {
 	return getWatchers(x, repoID)
 }
 
+// GetRepoWatchersIDs returns IDs of watchers for a given repo ID
+// but avoids joining with `user` for performance reasons
+// User permissions must be verified elsewhere if required
+func GetRepoWatchersIDs(repoID int64) ([]int64, error) {
+	ids := make([]int64, 0, 64)
+	return ids, x.Table("watch").
+		Where("watch.repo_id=?", repoID).
+		And("watch.mode<>?", RepoWatchModeDont).
+		Select("user_id").
+		Find(&ids)
+}
+
 // GetWatchers returns range of users watching given repository.
 func (repo *Repository) GetWatchers(page int) ([]*User, error) {
 	users := make([]*User, 0, ItemsPerPage)
diff --git a/models/user.go b/models/user.go
index 4a8c644ccd..ce78e5bfce 100644
--- a/models/user.go
+++ b/models/user.go
@@ -1307,6 +1307,20 @@ func getUserEmailsByNames(e Engine, names []string) []string {
 	return mails
 }
 
+// GetMaileableUsersByIDs gets users from ids, but only if they can receive mails
+func GetMaileableUsersByIDs(ids []int64) ([]*User, error) {
+	if len(ids) == 0 {
+		return nil, nil
+	}
+	ous := make([]*User, 0, len(ids))
+	return ous, x.In("id", ids).
+		Where("`type` = ?", UserTypeIndividual).
+		And("`prohibit_login` = ?", false).
+		And("`is_active` = ?", true).
+		And("`email_notifications_preference` = ?", EmailNotificationsEnabled).
+		Find(&ous)
+}
+
 // GetUsersByIDs returns all resolved users from a list of Ids.
 func GetUsersByIDs(ids []int64) ([]*User, error) {
 	ous := make([]*User, 0, len(ids))