PLT-6484 Add /leave command to leave a channel (#6402)

* PLT-6484 Add /leave command to leave a channel

* Text changes requeted on review.

* PLT-6484 Display the right error message when trying to /leave town-square

* PLT-6484 Be able to execute /leave command in direct and group message channels with the same effect as clicking x

* PLT-6484 Refactor to create new leave_private_channel_modal.jsx

* PLT-6484 Remove previous leave private channel logic to use new leave_private_channel_modal.jsx

* Remove dot in command description. Change localized error when leaving Town square.

* disable /leave command in reply threads on the right-hand sidebar, since it is not obvious which channel you should leave

app/command_leave.go

@@ -0,0 +1,55 @@
+// Copyright (c) 2017-present Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package app
+
+import (
+	"github.com/mattermost/platform/model"
+	goi18n "github.com/nicksnyder/go-i18n/i18n"
+)
+
+type LeaveProvider struct {
+}
+
+const (
+	CMD_LEAVE = "leave"
+)
+
+func init() {
+	RegisterCommandProvider(&LeaveProvider{})
+}
+
+func (me *LeaveProvider) GetTrigger() string {
+	return CMD_LEAVE
+}
+
+func (me *LeaveProvider) GetCommand(T goi18n.TranslateFunc) *model.Command {
+	return &model.Command{
+		Trigger:          CMD_LEAVE,
+		AutoComplete:     true,
+		AutoCompleteDesc: T("api.command_leave.desc"),
+		DisplayName:      T("api.command_leave.name"),
+	}
+}
+
+func (me *LeaveProvider) DoCommand(args *model.CommandArgs, message string) *model.CommandResponse {
+	var channel *model.Channel
+	var noChannelErr *model.AppError
+	if channel, noChannelErr = GetChannel(args.ChannelId); noChannelErr != nil {
+		return &model.CommandResponse{Text: args.T("api.command_leave.fail.app_error"), ResponseType: model.COMMAND_RESPONSE_TYPE_EPHEMERAL}
+	}
+	if channel.Name == model.DEFAULT_CHANNEL {
+		return &model.CommandResponse{Text: args.T("api.channel.leave.default.app_error", map[string]interface{}{"Channel": model.DEFAULT_CHANNEL}), ResponseType: model.COMMAND_RESPONSE_TYPE_EPHEMERAL}
+	}
+	err := LeaveChannel(args.ChannelId, args.UserId)
+	if err != nil {
+		return &model.CommandResponse{Text: args.T("api.command_leave.fail.app_error"), ResponseType: model.COMMAND_RESPONSE_TYPE_EPHEMERAL}
+	}
+
+	team, err := GetTeam(args.TeamId)
+	if err != nil {
+		return &model.CommandResponse{Text: args.T("api.command_leave.fail.app_error"), ResponseType: model.COMMAND_RESPONSE_TYPE_EPHEMERAL}
+	}
+
+	return &model.CommandResponse{GotoLocation: args.SiteURL + "/" + team.Name + "/channels/" + model.DEFAULT_CHANNEL, Text: args.T("api.command_leave.success"), ResponseType: model.COMMAND_RESPONSE_TYPE_EPHEMERAL}
+}