// 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 notifications

import (
	"encoding/json"

	"code.vikunja.io/api/pkg/db"
	"code.vikunja.io/api/pkg/log"

	"xorm.io/xorm"
)

// Notification is a notification which can be sent via mail or db.
type Notification interface {
	ToMail(lang string) *Mail
	ToDB() interface{}
	Name() string
}

type SubjectID interface {
	SubjectID() int64
}

type NotificationWithSubject interface {
	Notification
	SubjectID
}

type ThreadID interface {
	ThreadID() string
}

// Titler is an optional capability for notifications that can render a
// one-line, translated title. Used as the mail subject when ToMail does not
// set one explicitly, and as the item title in the notifications feed.
type Titler interface {
	ToTitle(lang string) string
}

var registry = map[string]func() Notification{}

// Register makes a notification type discoverable by name. It should be
// called from init() in the package that defines the type. Only notifications
// that persist to the database need to register, since only persisted
// notifications are re-hydrated from JSON (e.g. by the feed handler).
// The name is derived from the notification's own Name() method, so it stays
// in one place.
func Register(factory func() Notification) {
	registry[factory().Name()] = factory
}

// Lookup returns a fresh, empty instance of the notification type registered
// under the given name. The second return value is false if no type is
// registered with that name.
func Lookup(name string) (Notification, bool) {
	f, ok := registry[name]
	if !ok {
		return nil, false
	}
	return f(), true
}

// Notifiable is an entity which can be notified. Usually a user.
type Notifiable interface {
	// RouteForMail should return the email address this notifiable has.
	RouteForMail() (string, error)
	// RouteForDB should return the id of the notifiable entity to save it in the database.
	RouteForDB() int64
	// ShouldNotify provides a last-minute way to cancel a notification. It will be called immediately before
	// sending a notification. An optional session can be passed to reuse an existing transaction.
	ShouldNotify(sessions ...*xorm.Session) (should bool, err error)
	// Lang provides the language which should be used for translations in the mail.
	Lang() string
}

// Notify notifies a notifiable of a notification.
// An optional xorm session can be passed to reuse an existing transaction for the DB notification.
func Notify(notifiable Notifiable, notification Notification, sessions ...*xorm.Session) (err error) {
	if isUnderTest {
		sentTestNotifications = append(sentTestNotifications, notification)
		return nil
	}

	should, err := notifiable.ShouldNotify(sessions...)
	if err != nil || !should {
		log.Debugf("Not notifying user %d because they are disabled", notifiable.RouteForDB())
		return err
	}

	err = notifyMail(notifiable, notification)
	if err != nil {
		return
	}

	var s *xorm.Session
	if len(sessions) > 0 && sessions[0] != nil {
		s = sessions[0]
	}

	return notifyDB(notifiable, notification, s)
}

func notifyMail(notifiable Notifiable, notification Notification) error {
	mail := notification.ToMail(notifiable.Lang())
	if mail == nil {
		return nil
	}

	if mail.subject == "" {
		if t, is := notification.(Titler); is {
			mail.subject = t.ToTitle(notifiable.Lang())
		}
	}

	to, err := notifiable.RouteForMail()
	if err != nil {
		return err
	}
	mail.To(to)

	if threadID, is := notification.(ThreadID); is {
		mail.ThreadID(threadID.ThreadID())
	}

	return SendMail(mail, notifiable.Lang())
}

func notifyDB(notifiable Notifiable, notification Notification, existingSession *xorm.Session) (err error) {

	dbContent := notification.ToDB()
	if dbContent == nil {
		return nil
	}

	content, err := json.Marshal(dbContent)
	if err != nil {
		return err
	}

	dbNotification := &DatabaseNotification{
		NotifiableID: notifiable.RouteForDB(),
		Notification: json.RawMessage(content),
		Name:         notification.Name(),
	}

	if subject, is := notification.(SubjectID); is {
		dbNotification.SubjectID = subject.SubjectID()
	}

	if existingSession != nil {
		_, err = existingSession.Insert(dbNotification)
		return err
	}

	s := db.NewSession()
	defer s.Close()

	_, err = s.Insert(dbNotification)
	if err != nil {
		_ = s.Rollback()
		return err
	}

	return s.Commit()
}