[MM-55726] Create batch report worker, add batch report job for exporting users to CSV (#25832)

* Split out migration logic and create generic BatchWorker

* WIP

* WIP

* POC batch reporting

* Oops

* Job hookup

* Working export to file

* PR feedback

* Merge'd

* Fix error handling

* Add API to start report, translations, couple fixes

* Add DMs to send reports to users

* Merge'd

* Update types

* A bit of cleanup

* Some fixes

* Add missing API doc

* PR feedback

* Fix generated

* Fix bug with post creation

* PR feedback

* Add some tests

* PR feedback

* Fix lint

* Some test changes

* Fix tests

* Add comment to explain why we forcibly stop

* Rework of some tests

* Batch report test

* Restrict batch exports to Pro and Enterprise licenses

* Fix erroneous comment

---------

Co-authored-by: Mattermost Build <build@mattermost.com>

server/channels/jobs/export_users_to_csv/export_users_to_csv.go

@@ -0,0 +1,107 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package export_users_to_csv
+
+import (
+	"strconv"
+	"time"
+
+	"github.com/mattermost/mattermost/server/public/model"
+	"github.com/mattermost/mattermost/server/v8/channels/jobs"
+	"github.com/mattermost/mattermost/server/v8/channels/store"
+	"github.com/pkg/errors"
+)
+
+const (
+	timeBetweenBatches = 1 * time.Second
+)
+
+type ExportUsersToCSVAppIFace interface {
+	jobs.BatchReportWorkerAppIFace
+	GetUsersForReporting(filter *model.UserReportOptions) ([]*model.UserReport, *model.AppError)
+}
+
+// MakeWorker creates a batch report worker to generate CSV user reports.
+func MakeWorker(jobServer *jobs.JobServer, store store.Store, app ExportUsersToCSVAppIFace) model.Worker {
+	return jobs.MakeBatchReportWorker(
+		jobServer,
+		store,
+		app,
+		timeBetweenBatches,
+		"csv",
+		[]string{
+			"Id",
+			"Username",
+			"Email",
+			"CreateAt",
+			"Name",
+			"Roles",
+			"LastLogin",
+			"LastStatusAt",
+			"LastPostDate",
+			"DaysActive",
+			"TotalPosts",
+		},
+		getData(app),
+	)
+}
+
+// parseJobMetadata parses the opaque job metadata to return the information needed to decide which
+// batch to process next.
+func parseJobMetadata(data model.StringMap) (*model.UserReportOptions, error) {
+	startAt, err := strconv.ParseInt(data["start_at"], 10, 64)
+	if err != nil {
+		return nil, err
+	}
+	endAt, err := strconv.ParseInt(data["end_at"], 10, 64)
+	if err != nil {
+		return nil, err
+	}
+
+	options := model.UserReportOptions{
+		ReportingBaseOptions: model.ReportingBaseOptions{
+			SortColumn:      "Username",
+			PageSize:        100,
+			FromColumnValue: data["last_column_value"],
+			FromId:          data["last_user_id"],
+			StartAt:         startAt,
+			EndAt:           endAt,
+		},
+	}
+
+	return &options, nil
+}
+
+// makeJobMetadata encodes the information needed to decide which batch to process next back into
+// the opaque job metadata.
+func makeJobMetadata(jobData model.StringMap, lastColumnValue string, userID string) model.StringMap {
+	jobData["last_column_value"] = lastColumnValue
+	jobData["last_user_id"] = userID
+	return jobData
+}
+
+func getData(app ExportUsersToCSVAppIFace) func(jobData model.StringMap) ([]model.ReportableObject, model.StringMap, bool, error) {
+	return func(jobData model.StringMap) ([]model.ReportableObject, model.StringMap, bool, error) {
+		filter, err := parseJobMetadata(jobData)
+		if err != nil {
+			return nil, nil, false, errors.Wrap(err, "failed to parse job metadata")
+		}
+
+		users, appErr := app.GetUsersForReporting(filter)
+		if appErr != nil {
+			return nil, nil, false, errors.Wrapf(err, "failed to get the next batch (column_value=%v, user_id=%v)", filter.FromColumnValue, filter.FromId)
+		}
+
+		if len(users) == 0 {
+			return nil, nil, true, nil
+		}
+
+		reportableObjects := []model.ReportableObject{}
+		for i := 0; i < len(users); i++ {
+			reportableObjects = append(reportableObjects, users[i])
+		}
+
+		return reportableObjects, makeJobMetadata(jobData, users[len(users)-1].Username, users[len(users)-1].Id), false, nil
+	}
+}