PLT-3647 Email Batching (#3718)

* PLT-3647 Added config settings for email batching

* PLT-3647 Refactored generation of email notification

* PLT-3647 Added serverside code for email batching

* PLT-3647 Updated settings UI to enable email batching

* PLT-3647 Removed debug code

* PLT-3647 Fixed 0-padding of minutes in batched notification

* PLT-3647 Updated clientside UI for when email batching is disabled

* Go fmt

* PLT-3647 Changed email batching to be disabled by default

* Updated batched email message

* Added email batching toggle to system console

* Changed Email Notifications > Immediate setting to a 30 second batch interval

* Go fmt

* Fixed link to Mattermost icon in batched email notification

* Updated users to use 30 second email batching by default

* Fully disabled email batching when clustering is enabled

* Fixed email batching setting in the system console

* Fixed casing of 'Send Email notifications' -> 'Send email notifications'

* Updating UI Improvements for email batching (#3736)

* Updated text for notification settings and SiteURL.

* Prevented enabling email batching when SiteURL isn't set in the system console

* Re-added a couple debug messages

* Added warning text when clustering is enabled

3 files changed, 66 insertions, 2 deletions

diff --git a/model/config.go b/model/config.go
index f73cb290b..32cb501a0 100644
--- a/model/config.go
+++ b/model/config.go
@@ -47,6 +47,9 @@ const (
 	RESTRICT_EMOJI_CREATION_ADMIN        = "admin"
 	RESTRICT_EMOJI_CREATION_SYSTEM_ADMIN = "system_admin"
 
+	EMAIL_BATCHING_BUFFER_SIZE = 256
+	EMAIL_BATCHING_INTERVAL    = 30
+
 	SITENAME_MAX_LENGTH = 30
 )
 
@@ -166,6 +169,9 @@ type EmailSettings struct {
 	SendPushNotifications    *bool
 	PushNotificationServer   *string
 	PushNotificationContents *string
+	EnableEmailBatching      *bool
+	EmailBatchingBufferSize  *int
+	EmailBatchingInterval    *int
 }
 
 type RateLimitSettings struct {
@@ -508,6 +514,21 @@ func (o *Config) SetDefaults() {
 		*o.EmailSettings.FeedbackOrganization = ""
 	}
 
+	if o.EmailSettings.EnableEmailBatching == nil {
+		o.EmailSettings.EnableEmailBatching = new(bool)
+		*o.EmailSettings.EnableEmailBatching = false
+	}
+
+	if o.EmailSettings.EmailBatchingBufferSize == nil {
+		o.EmailSettings.EmailBatchingBufferSize = new(int)
+		*o.EmailSettings.EmailBatchingBufferSize = EMAIL_BATCHING_BUFFER_SIZE
+	}
+
+	if o.EmailSettings.EmailBatchingInterval == nil {
+		o.EmailSettings.EmailBatchingInterval = new(int)
+		*o.EmailSettings.EmailBatchingInterval = EMAIL_BATCHING_INTERVAL
+	}
+
 	if !IsSafeLink(o.SupportSettings.TermsOfServiceLink) {
 		o.SupportSettings.TermsOfServiceLink = nil
 	}
@@ -871,6 +892,14 @@ func (o *Config) IsValid() *AppError {
 		return NewLocAppError("Config.IsValid", "model.config.is_valid.listen_address.app_error", nil, "")
 	}
 
+	if *o.ClusterSettings.Enable && *o.EmailSettings.EnableEmailBatching {
+		return NewLocAppError("Config.IsValid", "model.config.is_valid.cluster_email_batching.app_error", nil, "")
+	}
+
+	if len(*o.ServiceSettings.SiteURL) == 0 && *o.EmailSettings.EnableEmailBatching {
+		return NewLocAppError("Config.IsValid", "model.config.is_valid.site_url_email_batching.app_error", nil, "")
+	}
+
 	if o.TeamSettings.MaxUsersPerTeam <= 0 {
 		return NewLocAppError("Config.IsValid", "model.config.is_valid.max_users.app_error", nil, "")
 	}
@@ -947,6 +976,14 @@ func (o *Config) IsValid() *AppError {
 		return NewLocAppError("Config.IsValid", "model.config.is_valid.email_reset_salt.app_error", nil, "")
 	}
 
+	if *o.EmailSettings.EmailBatchingBufferSize <= 0 {
+		return NewLocAppError("Config.IsValid", "model.config.is_valid.email_batching_buffer_size.app_error", nil, "")
+	}
+
+	if *o.EmailSettings.EmailBatchingInterval < 30 {
+		return NewLocAppError("Config.IsValid", "model.config.is_valid.email_batching_interval.app_error", nil, "")
+	}
+
 	if o.RateLimitSettings.MemoryStoreSize <= 0 {
 		return NewLocAppError("Config.IsValid", "model.config.is_valid.rate_mem.app_error", nil, "")
 	}
diff --git a/model/preference.go b/model/preference.go
index 5787fe6ef..cc35768cb 100644
--- a/model/preference.go
+++ b/model/preference.go
@@ -17,8 +17,13 @@ const (
 	PREFERENCE_CATEGORY_ADVANCED_SETTINGS   = "advanced_settings"
 	PREFERENCE_CATEGORY_FLAGGED_POST        = "flagged_post"
 
-	PREFERENCE_CATEGORY_DISPLAY_SETTINGS = "display_settings"
-	PREFERENCE_NAME_COLLAPSE_SETTING     = "collapse_previews"
+	PREFERENCE_CATEGORY_DISPLAY_SETTINGS   = "display_settings"
+	PREFERENCE_NAME_COLLAPSE_SETTING       = "collapse_previews"
+	PREFERENCE_NAME_DISPLAY_NAME_FORMAT    = "name_format"
+	PREFERENCE_VALUE_DISPLAY_NAME_NICKNAME = "nickname_full_name"
+	PREFERENCE_VALUE_DISPLAY_NAME_FULL     = "full_name"
+	PREFERENCE_VALUE_DISPLAY_NAME_USERNAME = "username"
+	PREFERENCE_DEFAULT_DISPLAY_NAME_FORMAT = PREFERENCE_VALUE_DISPLAY_NAME_USERNAME
 
 	PREFERENCE_CATEGORY_THEME = "theme"
 	// the name for theme props is the team id
@@ -28,6 +33,10 @@ const (
 
 	PREFERENCE_CATEGORY_LAST     = "last"
 	PREFERENCE_NAME_LAST_CHANNEL = "channel"
+
+	PREFERENCE_CATEGORY_NOTIFICATIONS = "notifications"
+	PREFERENCE_NAME_EMAIL_INTERVAL    = "email_interval"
+	PREFERENCE_DEFAULT_EMAIL_INTERVAL = "30" // default to match the interval of the "immediate" setting (ie 30 seconds)
 )
 
 type Preference struct {
diff --git a/model/user.go b/model/user.go
index bad616d73..d8ad54065 100644
--- a/model/user.go
+++ b/model/user.go
@@ -295,6 +295,24 @@ func (u *User) GetDisplayName() string {
 	}
 }
 
+func (u *User) GetDisplayNameForPreference(nameFormat string) string {
+	displayName := u.Username
+
+	if nameFormat == PREFERENCE_VALUE_DISPLAY_NAME_NICKNAME {
+		if u.Nickname != "" {
+			displayName = u.Nickname
+		} else if fullName := u.GetFullName(); fullName != "" {
+			displayName = fullName
+		}
+	} else if nameFormat == PREFERENCE_VALUE_DISPLAY_NAME_FULL {
+		if fullName := u.GetFullName(); fullName != "" {
+			displayName = fullName
+		}
+	}
+
+	return displayName
+}
+
 func IsValidUserRoles(userRoles string) bool {
 
 	roles := strings.Split(userRoles, " ")