Moving slash-commands out of app package (#14979)

* Moving slash-commands out of app package

* Fixing golint checks

* Fixing golangci-lint

* Fixing golangci-lint errors

app/slashcommands/command_echo.go

@@ -0,0 +1,98 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package slashcommands
+
+import (
+	"strconv"
+	"strings"
+	"time"
+
+	goi18n "github.com/mattermost/go-i18n/i18n"
+	"github.com/mattermost/mattermost-server/v5/app"
+	"github.com/mattermost/mattermost-server/v5/mlog"
+	"github.com/mattermost/mattermost-server/v5/model"
+)
+
+var echoSem chan bool
+
+type EchoProvider struct {
+}
+
+const (
+	CMD_ECHO = "echo"
+)
+
+func init() {
+	app.RegisterCommandProvider(&EchoProvider{})
+}
+
+func (me *EchoProvider) GetTrigger() string {
+	return CMD_ECHO
+}
+
+func (me *EchoProvider) GetCommand(a *app.App, T goi18n.TranslateFunc) *model.Command {
+	return &model.Command{
+		Trigger:          CMD_ECHO,
+		AutoComplete:     true,
+		AutoCompleteDesc: T("api.command_echo.desc"),
+		AutoCompleteHint: T("api.command_echo.hint"),
+		DisplayName:      T("api.command_echo.name"),
+	}
+}
+
+func (me *EchoProvider) DoCommand(a *app.App, args *model.CommandArgs, message string) *model.CommandResponse {
+	if len(message) == 0 {
+		return &model.CommandResponse{Text: args.T("api.command_echo.message.app_error"), ResponseType: model.COMMAND_RESPONSE_TYPE_EPHEMERAL}
+	}
+
+	maxThreads := 100
+
+	delay := 0
+	if endMsg := strings.LastIndex(message, "\""); string(message[0]) == "\"" && endMsg > 1 {
+		if checkDelay, err := strconv.Atoi(strings.Trim(message[endMsg:], " \"")); err == nil {
+			delay = checkDelay
+		}
+		message = message[1:endMsg]
+	} else if strings.Contains(message, " ") {
+		delayIdx := strings.LastIndex(message, " ")
+		delayStr := strings.Trim(message[delayIdx:], " ")
+
+		if checkDelay, err := strconv.Atoi(delayStr); err == nil {
+			delay = checkDelay
+			message = message[:delayIdx]
+		}
+	}
+
+	if delay > 10000 {
+		return &model.CommandResponse{Text: args.T("api.command_echo.delay.app_error"), ResponseType: model.COMMAND_RESPONSE_TYPE_EPHEMERAL}
+	}
+
+	if echoSem == nil {
+		// We want one additional thread allowed so we never reach channel lockup
+		echoSem = make(chan bool, maxThreads+1)
+	}
+
+	if len(echoSem) >= maxThreads {
+		return &model.CommandResponse{Text: args.T("api.command_echo.high_volume.app_error"), ResponseType: model.COMMAND_RESPONSE_TYPE_EPHEMERAL}
+	}
+
+	echoSem <- true
+	a.Srv().Go(func() {
+		defer func() { <-echoSem }()
+		post := &model.Post{}
+		post.ChannelId = args.ChannelId
+		post.RootId = args.RootId
+		post.ParentId = args.ParentId
+		post.Message = message
+		post.UserId = args.UserId
+
+		time.Sleep(time.Duration(delay) * time.Second)
+
+		if _, err := a.CreatePostMissingChannel(post, true); err != nil {
+			mlog.Error("Unable to create /echo post.", mlog.Err(err))
+		}
+	})
+
+	return &model.CommandResponse{}
+}