[MM-9904] Add /invite slash command to invite users to a channel (#8482)

* [MM-9904] Add /invite slash command to invite users to a channel

* Update en.json

4 files changed, 272 insertions, 0 deletions

diff --git a/app/apptestlib.go b/app/apptestlib.go
index 6c2273c6e..1b22831c9 100644
--- a/app/apptestlib.go
+++ b/app/apptestlib.go
@@ -218,6 +218,20 @@ func (me *TestHelper) createChannel(team *model.Team, channelType string) *model
 	return channel
 }
 
+func (me *TestHelper) CreateDmChannel(user *model.User) *model.Channel {
+	utils.DisableDebugLogForTest()
+	var err *model.AppError
+	var channel *model.Channel
+	if channel, err = me.App.CreateDirectChannel(me.BasicUser.Id, user.Id); err != nil {
+		l4g.Error(err.Error())
+		l4g.Close()
+		time.Sleep(time.Second)
+		panic(err)
+	}
+	utils.EnableDebugLogForTest()
+	return channel
+}
+
 func (me *TestHelper) CreatePost(channel *model.Channel) *model.Post {
 	id := model.NewId()
 
diff --git a/app/command_invite.go b/app/command_invite.go
new file mode 100644
index 000000000..ce443bf3d
--- /dev/null
+++ b/app/command_invite.go
@@ -0,0 +1,102 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package app
+
+import (
+	"strings"
+
+	l4g "github.com/alecthomas/log4go"
+	"github.com/mattermost/mattermost-server/model"
+	goi18n "github.com/nicksnyder/go-i18n/i18n"
+)
+
+type InviteProvider struct {
+}
+
+const (
+	CMD_INVITE = "invite"
+)
+
+func init() {
+	RegisterCommandProvider(&InviteProvider{})
+}
+
+func (me *InviteProvider) GetTrigger() string {
+	return CMD_INVITE
+}
+
+func (me *InviteProvider) GetCommand(a *App, T goi18n.TranslateFunc) *model.Command {
+	return &model.Command{
+		Trigger:          CMD_INVITE,
+		AutoComplete:     true,
+		AutoCompleteDesc: T("api.command_invite.desc"),
+		AutoCompleteHint: T("api.command_invite.hint"),
+		DisplayName:      T("api.command_invite.name"),
+	}
+}
+
+func (me *InviteProvider) DoCommand(a *App, args *model.CommandArgs, message string) *model.CommandResponse {
+	if message == "" {
+		return &model.CommandResponse{Text: args.T("api.command_invite.missing_message.app_error"), ResponseType: model.COMMAND_RESPONSE_TYPE_EPHEMERAL}
+	}
+
+	l4g.Debug(message)
+
+	splitMessage := strings.SplitN(message, " ", 2)
+	targetUsername := splitMessage[0]
+	targetUsername = strings.TrimPrefix(targetUsername, "@")
+
+	var userProfile *model.User
+	if result := <-a.Srv.Store.User().GetByUsername(targetUsername); result.Err != nil {
+		l4g.Error(result.Err.Error())
+		return &model.CommandResponse{Text: args.T("api.command_invite.missing_user.app_error"), ResponseType: model.COMMAND_RESPONSE_TYPE_EPHEMERAL}
+	} else {
+		userProfile = result.Data.(*model.User)
+	}
+
+	var channelToJoin *model.Channel
+	var err *model.AppError
+	// User set a channel to add the invited user
+	if len(splitMessage) > 1 && splitMessage[1] != "" {
+		targetChannelName := strings.TrimPrefix(strings.TrimSpace(splitMessage[1]), "~")
+
+		if channelToJoin, err = a.GetChannelByName(targetChannelName, args.TeamId); err != nil {
+			return &model.CommandResponse{Text: args.T("api.command_invite.channel.error", map[string]interface{}{"Channel": targetChannelName}), ResponseType: model.COMMAND_RESPONSE_TYPE_EPHEMERAL}
+		}
+	} else {
+		channelToJoin, err = a.GetChannel(args.ChannelId)
+		if err != nil {
+			return &model.CommandResponse{Text: args.T("api.command_invite.channel.app_error"), ResponseType: model.COMMAND_RESPONSE_TYPE_EPHEMERAL}
+		}
+	}
+
+	// Check if is a Direct Channel
+	if channelToJoin.Type == model.CHANNEL_DIRECT || channelToJoin.Type == model.CHANNEL_GROUP {
+		return &model.CommandResponse{Text: args.T("api.command_invite.directchannel.app_error"), ResponseType: model.COMMAND_RESPONSE_TYPE_EPHEMERAL}
+	}
+
+	// Check if user is already in the channel
+	_, err = a.GetChannelMember(channelToJoin.Id, userProfile.Id)
+	if err == nil {
+		return &model.CommandResponse{Text: args.T("api.command_invite.user_already_in_channel.app_error", map[string]interface{}{"User": userProfile.Username}), ResponseType: model.COMMAND_RESPONSE_TYPE_EPHEMERAL}
+	}
+
+	if channelToJoin.Type == model.CHANNEL_OPEN && !a.SessionHasPermissionToChannel(args.Session, channelToJoin.Id, model.PERMISSION_MANAGE_PUBLIC_CHANNEL_MEMBERS) {
+		return &model.CommandResponse{Text: args.T("api.command_invite.permission.app_error", map[string]interface{}{"User": userProfile.Username, "Channel": channelToJoin.Name}), ResponseType: model.COMMAND_RESPONSE_TYPE_EPHEMERAL}
+	}
+
+	if channelToJoin.Type == model.CHANNEL_PRIVATE && !a.SessionHasPermissionToChannel(args.Session, channelToJoin.Id, model.PERMISSION_MANAGE_PRIVATE_CHANNEL_MEMBERS) {
+		return &model.CommandResponse{Text: args.T("api.command_invite.permission.app_error", map[string]interface{}{"User": userProfile.Username, "Channel": channelToJoin.Name}), ResponseType: model.COMMAND_RESPONSE_TYPE_EPHEMERAL}
+	}
+
+	if _, err := a.AddChannelMember(userProfile.Id, channelToJoin, args.Session.UserId, ""); err != nil {
+		return &model.CommandResponse{Text: args.T("api.command_invite.fail.app_error"), ResponseType: model.COMMAND_RESPONSE_TYPE_EPHEMERAL}
+	}
+
+	if args.ChannelId != channelToJoin.Id {
+		return &model.CommandResponse{Text: args.T("api.command_invite.success", map[string]interface{}{"User": userProfile.Username, "Channel": channelToJoin.Name}), ResponseType: model.COMMAND_RESPONSE_TYPE_EPHEMERAL}
+	}
+
+	return &model.CommandResponse{}
+}
diff --git a/app/command_invite_test.go b/app/command_invite_test.go
new file mode 100644
index 000000000..c46bc4628
--- /dev/null
+++ b/app/command_invite_test.go
@@ -0,0 +1,108 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package app
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+
+	"github.com/mattermost/mattermost-server/model"
+)
+
+func TestInviteProvider(t *testing.T) {
+	th := Setup().InitBasic()
+	defer th.TearDown()
+
+	channel := th.createChannel(th.BasicTeam, model.CHANNEL_OPEN)
+	privateChannel := th.createChannel(th.BasicTeam, model.CHANNEL_PRIVATE)
+	dmChannel := th.CreateDmChannel(th.BasicUser2)
+
+	basicUser3 := th.CreateUser()
+	th.LinkUserToTeam(basicUser3, th.BasicTeam)
+	basicUser4 := th.CreateUser()
+
+	InviteP := InviteProvider{}
+	args := &model.CommandArgs{
+		T:         func(s string, args ...interface{}) string { return s },
+		ChannelId: th.BasicChannel.Id,
+		TeamId:    th.BasicTeam.Id,
+		Session:   model.Session{UserId: th.BasicUser.Id, TeamMembers: []*model.TeamMember{{TeamId: th.BasicTeam.Id, Roles: model.TEAM_USER_ROLE_ID}}},
+	}
+
+	userAndWrongChannel := "@" + th.BasicUser2.Username + " wrongchannel1"
+	userAndChannel := "@" + th.BasicUser2.Username + " ~" + channel.Name + " "
+	userAndDisplayChannel := "@" + th.BasicUser2.Username + " ~" + channel.DisplayName + " "
+	userAndPrivateChannel := "@" + th.BasicUser2.Username + " ~" + privateChannel.Name
+	userAndDMChannel := "@" + basicUser3.Username + " ~" + dmChannel.Name
+
+	tests := []struct {
+		desc     string
+		expected string
+		msg      string
+	}{
+		{
+			desc:     "Missing user and channel in the command",
+			expected: "api.command_invite.missing_message.app_error",
+			msg:      "",
+		},
+		{
+			desc:     "User added in the current channel",
+			expected: "",
+			msg:      th.BasicUser2.Username,
+		},
+		{
+			desc:     "Add user to another channel not the current",
+			expected: "api.command_invite.success",
+			msg:      userAndChannel,
+		},
+		{
+			desc:     "try to add a user to a direct channel",
+			expected: "api.command_invite.directchannel.app_error",
+			msg:      userAndDMChannel,
+		},
+		{
+			desc:     "Try to add a user to a invalid channel",
+			expected: "api.command_invite.channel.error",
+			msg:      userAndWrongChannel,
+		},
+		{
+			desc:     "Try to add a user to an private channel",
+			expected: "api.command_invite.success",
+			msg:      userAndPrivateChannel,
+		},
+		{
+			desc:     "Using display channel name which is different form Channel name",
+			expected: "api.command_invite.channel.error",
+			msg:      userAndDisplayChannel,
+		},
+		{
+			desc:     "Invalid user to current channel",
+			expected: "api.command_invite.missing_user.app_error",
+			msg:      "@invalidUser123",
+		},
+		{
+			desc:     "Invalid user to current channel without @",
+			expected: "api.command_invite.missing_user.app_error",
+			msg:      "invalidUser321",
+		},
+		{
+			desc:     "try to add a user which is not part of the team",
+			expected: "api.command_invite.fail.app_error",
+			msg:      basicUser4.Username,
+		},
+		{
+			desc:     "try to add a user to a direct channel",
+			expected: "api.command_invite.directchannel.app_error",
+			msg:      userAndDMChannel,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.desc, func(t *testing.T) {
+			actual := InviteP.DoCommand(th.App, args, test.msg).Text
+			assert.Equal(t, test.expected, actual)
+		})
+	}
+}
diff --git a/i18n/en.json b/i18n/en.json
index 02ac46e70..c7276b6cc 100644
--- a/i18n/en.json
+++ b/i18n/en.json
@@ -815,6 +815,54 @@
     "translation": "Joined channel."
   },
   {
+    "id": "api.command_invite.hint",
+    "translation": "@[username] ~[channel]"
+  },
+  {
+    "id": "api.command_invite.name",
+    "translation": "invite"
+  },
+  {
+    "id": "api.command_invite.desc",
+    "translation": "Invite a user to a channel"
+  },
+  {
+    "id": "api.command_invite.missing_message.app_error",
+    "translation": "Missing Username and Channel."
+  },
+  {
+    "id": "api.command_invite.missing_user.app_error",
+    "translation": "We couldn't find the user."
+  },
+  {
+    "id": "api.command_invite.channel.app_error",
+    "translation": "Error to retrieve the current channel."
+  },
+  {
+    "id": "api.command_invite.channel.error",
+    "translation": "Could not find the channel {{.Channel}}. Please use the [channel handle](https://about.mattermost.com/default-channel-handle-documentation) to identify channels."
+  },
+  {
+    "id": "api.command_invite.fail.app_error",
+    "translation": "An error occurred while joining the channel."
+  },
+  {
+    "id": "api.command_invite.permission.app_error",
+    "translation": "You don't have enough permissions to add {{.User}} in {{.Channel}}."
+  },
+  {
+    "id": "api.command_invite.directchannel.app_error",
+    "translation": "You can't add someone to a direct message channel."
+  },
+  {
+    "id": "api.command_invite.user_already_in_channel.app_error",
+    "translation": "{{.User}} is already in the channel."
+  },
+  {
+    "id": "api.command_invite.success",
+    "translation": "{{.User}} added to {{.Channel}} channel."
+  },
+  {
     "id": "api.command_kick.name",
     "translation": "kick"
   },