PLT-6408 Framework for job server (#6404)

* Added initial job server

* Added job server to be ran as part of platform

* Added test job to the enterprise repo

* Fixed job server not loading license

* Renamed job package to jobs

* Fixed TE not being buildable

* Added JobStatus table to database

* Changed fields used by JobStatus

* Added APIs to query job status

* Added config change listener to server

* Added option to run job server from Makefile

* Added ability to enable/disable jobs from config

* Commented out placeholder for search indexing job

* Fixed govet

* Removed debug messages and fixed job api init message

model/scheduled_task.go

@@ -0,0 +1,110 @@
+// Copyright (c) 2016-present Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package model
+
+import (
+	"fmt"
+	"sync"
+	"time"
+)
+
+type TaskFunc func()
+
+type ScheduledTask struct {
+	Name      string        `json:"name"`
+	Interval  time.Duration `json:"interval"`
+	Recurring bool          `json:"recurring"`
+	function  TaskFunc
+	timer     *time.Timer
+}
+
+var taskMutex = sync.Mutex{}
+var tasks = make(map[string]*ScheduledTask)
+
+func addTask(task *ScheduledTask) {
+	taskMutex.Lock()
+	defer taskMutex.Unlock()
+	tasks[task.Name] = task
+}
+
+func removeTaskByName(name string) {
+	taskMutex.Lock()
+	defer taskMutex.Unlock()
+	delete(tasks, name)
+}
+
+func GetTaskByName(name string) *ScheduledTask {
+	taskMutex.Lock()
+	defer taskMutex.Unlock()
+	if task, ok := tasks[name]; ok {
+		return task
+	}
+	return nil
+}
+
+func GetAllTasks() *map[string]*ScheduledTask {
+	taskMutex.Lock()
+	defer taskMutex.Unlock()
+	return &tasks
+}
+
+func CreateTask(name string, function TaskFunc, timeToExecution time.Duration) *ScheduledTask {
+	task := &ScheduledTask{
+		Name:      name,
+		Interval:  timeToExecution,
+		Recurring: false,
+		function:  function,
+	}
+
+	taskRunner := func() {
+		go task.function()
+		removeTaskByName(task.Name)
+	}
+
+	task.timer = time.AfterFunc(timeToExecution, taskRunner)
+
+	addTask(task)
+
+	return task
+}
+
+func CreateRecurringTask(name string, function TaskFunc, interval time.Duration) *ScheduledTask {
+	task := &ScheduledTask{
+		Name:      name,
+		Interval:  interval,
+		Recurring: true,
+		function:  function,
+	}
+
+	taskRecurer := func() {
+		go task.function()
+		task.timer.Reset(task.Interval)
+	}
+
+	task.timer = time.AfterFunc(interval, taskRecurer)
+
+	addTask(task)
+
+	return task
+}
+
+func (task *ScheduledTask) Cancel() {
+	task.timer.Stop()
+	removeTaskByName(task.Name)
+}
+
+// Executes the task immediatly. A recurring task will be run regularally after interval.
+func (task *ScheduledTask) Execute() {
+	task.function()
+	task.timer.Reset(task.Interval)
+}
+
+func (task *ScheduledTask) String() string {
+	return fmt.Sprintf(
+		"%s\nInterval: %s\nRecurring: %t\n",
+		task.Name,
+		task.Interval.String(),
+		task.Recurring,
+	)
+}