// Vikunja is a to-do list application to facilitate your life.
// Copyright 2018-present Vikunja and contributors. All rights reserved.
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.

package models

import (
	"time"

	"code.vikunja.io/api/pkg/config"
	"code.vikunja.io/api/pkg/cron"
	"code.vikunja.io/api/pkg/db"
	"code.vikunja.io/api/pkg/events"
	"code.vikunja.io/api/pkg/log"
	"code.vikunja.io/api/pkg/notifications"
	"code.vikunja.io/api/pkg/user"
	"code.vikunja.io/api/pkg/utils"

	"xorm.io/builder"
	"xorm.io/xorm"
)

// ReminderRelation represents the date attribute of the task which a period based reminder relates to
type ReminderRelation string

// All valid ReminderRelations
const (
	ReminderRelationDueDate   ReminderRelation = `due_date`
	ReminderRelationStartDate ReminderRelation = `start_date`
	ReminderRelationEndDate   ReminderRelation = `end_date`
)

// TaskReminder holds a reminder on a task.
// If RelativeTo and the assciated date field are defined, then the attribute Reminder will be computed.
// If RelativeTo is missing, than Reminder must be given.
type TaskReminder struct {
	ID     int64 `xorm:"bigint autoincr not null unique pk" json:"-"`
	TaskID int64 `xorm:"bigint not null INDEX" json:"-"`
	// The absolute time when the user wants to be reminded of the task.
	Reminder time.Time `xorm:"DATETIME not null INDEX 'reminder'" json:"reminder"`
	Created  time.Time `xorm:"created not null" json:"-"`
	// A period in seconds relative to another date argument. Negative values mean the reminder triggers before the date. Default: 0, tiggers when RelativeTo is due.
	RelativePeriod int64 `xorm:"bigint null" json:"relative_period"`
	// The name of the date field to which the relative period refers to.
	RelativeTo ReminderRelation `xorm:"varchar(50) null" json:"relative_to"`
}

// TableName returns a pretty table name
func (TaskReminder) TableName() string {
	return "task_reminders"
}

type taskUser struct {
	Task *Task      `xorm:"extends"`
	User *user.User `xorm:"extends"`
}

const dbTimeFormat = `2006-01-02 15:04:05`

//nolint:gocyclo
func getTaskUsersForTasks(s *xorm.Session, taskIDs []int64, cond builder.Cond) (taskUsers []*taskUser, err error) {
	if len(taskIDs) == 0 {
		return
	}

	taskUsers = []*taskUser{}
	taskMap := make(map[int64]*Task, len(taskIDs))
	err = s.In("id", taskIDs).Find(&taskMap)
	if err != nil {
		return
	}

	projectIDs := []int64{}
	for _, task := range taskMap {
		projectIDs = append(projectIDs, task.ProjectID)
	}
	projects := make(map[int64]*Project)
	err = s.In("id", projectIDs).Find(&projects)
	if err != nil {
		return
	}

	// user_id -> project_id -> has read access
	userPermissionOnProject := make(map[int64]map[int64]bool)

	seen := make(map[int64]map[int64]struct{})
	appendUser := func(taskID int64, u *user.User) (err error) {
		if u == nil {
			return
		}
		task, hasTask := taskMap[taskID]
		if !hasTask {
			return
		}
		if seen[taskID] == nil {
			seen[taskID] = make(map[int64]struct{})
		}
		if _, exists := seen[taskID][u.ID]; exists {
			return
		}
		seen[taskID][u.ID] = struct{}{}

		userProjects, has := userPermissionOnProject[u.ID]
		if !has {
			userPermissionOnProject[u.ID] = make(map[int64]bool)
			userProjects = userPermissionOnProject[u.ID]
		}
		_, projectExists := userProjects[task.ProjectID]
		if !projectExists {
			p, exists := projects[task.ProjectID]
			if !exists {
				return
			}

			userProjects[task.ProjectID] = p.isOwner(u)

			if !p.isOwner(u) {
				userProjects[task.ProjectID], _, err = p.checkPermission(s, u, PermissionRead, PermissionWrite, PermissionAdmin)
				if err != nil {
					return err
				}
			}
		}

		if !userProjects[task.ProjectID] {
			return
		}

		taskUsers = append(taskUsers, &taskUser{Task: task, User: u})

		return
	}

	type userWithTask struct {
		TaskID    int64
		user.User `xorm:"extends"`
	}

	conditions := []builder.Cond{
		builder.In("tasks.id", taskIDs),
		builder.Eq{"users.status": user.StatusActive},
	}
	if cond != nil {
		conditions = append(conditions, cond)
	}

	creators := []*userWithTask{}
	err = s.Table("tasks").
		Select("DISTINCT tasks.id AS task_id, users.id, users.name, users.username, users.email, users.email_reminders_enabled, users.overdue_tasks_reminders_enabled, users.overdue_tasks_reminders_time, users.language, users.timezone, users.created, users.updated").
		Join("INNER", "users", "tasks.created_by_id = users.id").
		Where(builder.And(conditions...)).
		Find(&creators)
	if err != nil {
		return
	}

	for _, creator := range creators {
		err = appendUser(creator.TaskID, &creator.User)
		if err != nil {
			return
		}
	}

	assigneeConds := []builder.Cond{
		builder.In("task_assignees.task_id", taskIDs),
	}
	if cond != nil {
		assigneeConds = append(assigneeConds, cond)
	}

	assignees := []*TaskAssigneeWithUser{}
	err = s.Table("task_assignees").
		Select("DISTINCT task_assignees.task_id, users.id, users.name, users.username, users.email, users.email_reminders_enabled, users.overdue_tasks_reminders_enabled, users.overdue_tasks_reminders_time, users.language, users.timezone, users.created, users.updated").
		Join("INNER", "users", "task_assignees.user_id = users.id").
		Where(builder.And(assigneeConds...)).
		Find(&assignees)
	if err != nil {
		return
	}

	for i := range assignees {
		err = appendUser(assignees[i].TaskID, &assignees[i].User)
		if err != nil {
			return
		}
	}

	subscriptions, err := GetSubscriptionsForEntities(s, SubscriptionEntityTask, taskIDs)
	if err != nil {
		return nil, err
	}

	subscriberIDs := []int64{}
	for _, subs := range subscriptions {
		for _, sub := range subs {
			subscriberIDs = append(subscriberIDs, sub.UserID)
		}
	}

	if len(subscriberIDs) == 0 {
		return
	}

	subscriberCond := []builder.Cond{
		builder.In("id", subscriberIDs),
	}
	if cond != nil {
		subscriberCond = append(subscriberCond, cond)
	}

	subscribers, err := user.GetUsersByCond(s, builder.And(subscriberCond...))
	if err != nil {
		return nil, err
	}

	for taskID, subs := range subscriptions {
		for _, sub := range subs {
			u, has := subscribers[sub.UserID]
			if !has {
				continue
			}
			err = appendUser(taskID, u)
			if err != nil {
				return
			}
		}
	}

	return
}

func getTasksWithRemindersDueAndTheirUsers(s *xorm.Session, now time.Time) (reminderNotifications []*ReminderDueNotification, err error) {
	now = utils.GetTimeWithoutNanoSeconds(now)
	reminderNotifications = []*ReminderDueNotification{}

	nextMinute := now.Add(1 * time.Minute)

	log.Debugf("[Task Reminder Cron] Looking for reminders between %s and %s to send...", now, nextMinute)

	reminders := []*TaskReminder{}
	err = s.
		Join("INNER", "tasks", "tasks.id = task_reminders.task_id").
		// All reminders from -12h to +14h to include all time zones
		Where("reminder >= ? and reminder < ?", now.Add(time.Hour*-12).Format(dbTimeFormat), nextMinute.Add(time.Hour*14).Format(dbTimeFormat)).
		And("tasks.done = false").
		Find(&reminders)
	if err != nil {
		return
	}

	log.Debugf("[Task Reminder Cron] Found %d reminders", len(reminders))

	if len(reminders) == 0 {
		return
	}

	var taskIDs []int64
	for _, r := range reminders {
		taskIDs = append(taskIDs, r.TaskID)
	}

	if len(taskIDs) == 0 {
		return
	}

	usersWithReminders, err := getTaskUsersForTasks(s, taskIDs, builder.Eq{"users.email_reminders_enabled": true})
	if err != nil {
		return
	}

	usersPerTask := make(map[int64][]*taskUser, len(usersWithReminders))
	for _, ur := range usersWithReminders {
		usersPerTask[ur.Task.ID] = append(usersPerTask[ur.Task.ID], ur)
	}

	seen := make(map[int64]map[int64]bool)

	projects, err := GetProjectsMapSimpleByTaskIDs(s, taskIDs)
	if err != nil {
		return
	}

	// Time zone cache per time zone string to avoid parsing the same time zone over and over again
	tzs := make(map[string]*time.Location)
	// Figure out which reminders are actually due in the time zone of the users
	for _, r := range reminders {

		for _, u := range usersPerTask[r.TaskID] {

			// This ensures we send each reminder only once to each user
			if seen[r.TaskID] == nil {
				seen[r.TaskID] = make(map[int64]bool)
			}

			if _, exists := seen[r.TaskID][u.User.ID]; exists {
				continue
			}

			if u.User.Timezone == "" {
				u.User.Timezone = config.GetTimeZone().String()
			}

			// I think this will break once there's more reminders than what we can handle in one minute
			tz, exists := tzs[u.User.Timezone]
			if !exists {
				tz, err = time.LoadLocation(u.User.Timezone)
				if err != nil {
					return
				}
				tzs[u.User.Timezone] = tz
			}

			actualReminder := r.Reminder.In(tz)
			if (actualReminder.After(now) && actualReminder.Before(now.Add(time.Minute))) || actualReminder.Equal(now) {
				seen[r.TaskID][u.User.ID] = true

				reminderNotifications = append(reminderNotifications, &ReminderDueNotification{
					User:    u.User,
					Task:    u.Task,
					Project: projects[u.Task.ProjectID],
				})
			}
		}
	}

	return
}

// RegisterReminderCron registers a cron function which runs every minute to check if any reminders are due the
// next minute to send emails.
func RegisterReminderCron() {
	tz := config.GetTimeZone()

	log.Debugf("[Task Reminder Cron] Timezone is %s", tz)

	err := cron.Schedule("* * * * *", func() {
		s := db.NewSession()
		defer s.Close()

		now := time.Now()
		reminders, err := getTasksWithRemindersDueAndTheirUsers(s, now)
		if err != nil {
			log.Errorf("[Task Reminder Cron] Could not get tasks with reminders in the next minute: %s", err)
			return
		}

		if len(reminders) == 0 {
			return
		}

		log.Debugf("[Task Reminder Cron] Sending %d reminders", len(reminders))

		// Dispatch webhook events, deduplicated by task ID
		dispatchedTasks := make(map[int64]bool)
		for _, n := range reminders {
			if dispatchedTasks[n.Task.ID] {
				continue
			}
			dispatchedTasks[n.Task.ID] = true
			err = events.Dispatch(&TaskReminderFiredEvent{
				Task:    n.Task,
				Project: n.Project,
			})
			if err != nil {
				log.Errorf("[Task Reminder Cron] Could not dispatch reminder event for task %d: %s", n.Task.ID, err)
			}
		}

		if !config.ServiceEnableEmailReminders.GetBool() || !config.MailerEnabled.GetBool() {
			return
		}

		for _, n := range reminders {
			err = notifications.Notify(n.User, n, s)
			if err != nil {
				log.Errorf("[Task Reminder Cron] Could not notify user %d: %s", n.User.ID, err)
				return
			}

			log.Debugf("[Task Reminder Cron] Sent reminder email for task %d to user %d", n.Task.ID, n.User.ID)
		}

		if err := s.Commit(); err != nil {
			log.Errorf("[Task Reminder Cron] Could not commit: %s", err)
		}
	})
	if err != nil {
		log.Fatalf("Could not register reminder cron: %s", err)
	}
}