[MM-44765] Add API method for getting post's information from permalink (#21518)

* add api for getting post's information

* add information about current user state

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

app/app_iface.go

@@ -712,6 +712,7 @@ type AppIface interface {
 	GetPostIdAfterTime(channelID string, time int64, collapsedThreads bool) (string, *model.AppError)
 	GetPostIdBeforeTime(channelID string, time int64, collapsedThreads bool) (string, *model.AppError)
 	GetPostIfAuthorized(c request.CTX, postID string, session *model.Session, includeDeleted bool) (*model.Post, *model.AppError)
+	GetPostInfo(c request.CTX, postID string) (*model.PostInfo, *model.AppError)
 	GetPostThread(postID string, opts model.GetPostsOptions, userID string) (*model.PostList, *model.AppError)
 	GetPosts(channelID string, offset int, limit int) (*model.PostList, *model.AppError)
 	GetPostsAfterPost(options model.GetPostsOptions) (*model.PostList, *model.AppError)

app/opentracing/opentracing_layer.go

@@ -7952,6 +7952,28 @@ func (a *OpenTracingAppLayer) GetPostIfAuthorized(c request.CTX, postID string,
 	return resultVar0, resultVar1
 }
 
+func (a *OpenTracingAppLayer) GetPostInfo(c request.CTX, postID string) (*model.PostInfo, *model.AppError) {
+	origCtx := a.ctx
+	span, newCtx := tracing.StartSpanWithParentByContext(a.ctx, "app.GetPostInfo")
+
+	a.ctx = newCtx
+	a.app.Srv().Store().SetContext(newCtx)
+	defer func() {
+		a.app.Srv().Store().SetContext(origCtx)
+		a.ctx = origCtx
+	}()
+
+	defer span.Finish()
+	resultVar0, resultVar1 := a.app.GetPostInfo(c, postID)
+
+	if resultVar1 != nil {
+		span.LogFields(spanlog.Error(resultVar1))
+		ext.Error.Set(span, true)
+	}
+
+	return resultVar0, resultVar1
+}
+
 func (a *OpenTracingAppLayer) GetPostThread(postID string, opts model.GetPostsOptions, userID string) (*model.PostList, *model.AppError) {
 	origCtx := a.ctx
 	span, newCtx := tracing.StartSpanWithParentByContext(a.ctx, "app.GetPostThread")

app/post.go

@@ -2151,6 +2151,74 @@ func (a *App) CheckPostReminders() {
 
 }
 
+func (a *App) GetPostInfo(c request.CTX, postID string) (*model.PostInfo, *model.AppError) {
+	userID := c.Session().UserId
+	post, appErr := a.GetSinglePost(postID, false)
+	if appErr != nil {
+		return nil, appErr
+	}
+
+	channel, appErr := a.GetChannel(c, post.ChannelId)
+	if appErr != nil {
+		return nil, appErr
+	}
+
+	notFoundError := model.NewAppError("GetPostInfo", "app.post.get.app_error", nil, "", http.StatusNotFound)
+
+	var team *model.Team
+	hasPermissionToAccessTeam := false
+	if channel.TeamId != "" {
+		team, appErr = a.GetTeam(channel.TeamId)
+		if appErr != nil {
+			return nil, appErr
+		}
+
+		if team.Type == model.TeamOpen {
+			hasPermissionToAccessTeam = a.HasPermissionToTeam(userID, team.Id, model.PermissionJoinPublicTeams)
+		} else if team.Type == model.TeamInvite {
+			hasPermissionToAccessTeam = a.HasPermissionToTeam(userID, team.Id, model.PermissionJoinPrivateTeams)
+		}
+	} else {
+		// This happens in case of DMs and GMs.
+		hasPermissionToAccessTeam = true
+	}
+
+	if !hasPermissionToAccessTeam {
+		return nil, notFoundError
+	}
+
+	hasPermissionToAccessChannel := false
+	if channel.Type == model.ChannelTypeOpen {
+		hasPermissionToAccessChannel = true
+	} else if channel.Type == model.ChannelTypePrivate {
+		hasPermissionToAccessChannel = a.HasPermissionToChannel(c, userID, channel.Id, model.PermissionManagePrivateChannelMembers)
+	} else if channel.Type == model.ChannelTypeDirect || channel.Type == model.ChannelTypeGroup {
+		hasPermissionToAccessChannel = a.HasPermissionToChannel(c, userID, channel.Id, model.PermissionReadChannel)
+	}
+
+	if !hasPermissionToAccessChannel {
+		return nil, notFoundError
+	}
+
+	_, channelMemberErr := a.GetChannelMember(c, channel.Id, userID)
+
+	info := model.PostInfo{
+		ChannelId:          channel.Id,
+		ChannelType:        channel.Type,
+		ChannelDisplayName: channel.DisplayName,
+		HasJoinedChannel:   channelMemberErr == nil,
+	}
+	if team != nil {
+		_, teamMemberErr := a.GetTeamMember(team.Id, userID)
+
+		info.TeamId = team.Id
+		info.TeamType = team.Type
+		info.TeamDisplayName = team.DisplayName
+		info.HasJoinedTeam = teamMemberErr == nil
+	}
+	return &info, nil
+}
+
 func includeEmbedsAndImages(a *App, c request.CTX, topThreadList *model.TopThreadList, userID string) (*model.TopThreadList, error) {
 	for _, topThread := range topThreadList.Items {
 		topThread.Post = a.PreparePostForClientWithEmbedsAndImages(c, topThread.Post, false, false, true)