/*
Copyright 2017-2022 CAcert Inc.
SPDX-License-Identifier: Apache-2.0

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package notifications

import (
	"bytes"
	"fmt"
	"log"
	"net"
	"os"
	"path"
	"text/template"
	"time"

	"github.com/Masterminds/sprig/v3"
	"gopkg.in/mail.v2"

	"git.cacert.org/cacert-boardvoting/internal"
	"git.cacert.org/cacert-boardvoting/internal/models"
)

type MailConfig struct {
	SMTPHost                  string        `yaml:"smtp_host"`
	SMTPPort                  int           `yaml:"smtp_port"`
	SMTPTimeOut               time.Duration `yaml:"smtp_timeout,omitempty"`
	NotificationSenderAddress string        `yaml:"notification_sender_address"`
	NoticeMailAddress         string        `yaml:"notice_mail_address"`
	VoteNoticeMailAddress     string        `yaml:"vote_notice_mail_address"`
	BaseURL                   string        `yaml:"base_url"`
}

type recipientData struct {
	field, address, name string
}

type NotificationContent struct {
	template   string
	data       interface{}
	subject    string
	headers    map[string][]string
	recipients []recipientData
}

type NotificationMail interface {
	GetNotificationContent(*MailConfig) *NotificationContent
}

type MailNotifier struct {
	notifyChannel     chan NotificationMail
	senderAddress     string
	dialer            *mail.Dialer
	quitChannel       chan struct{}
	infoLog, errorLog *log.Logger
	mailConfig        *MailConfig
}

type Option func(*MailNotifier)

func NewMailNotifier(config *MailConfig, opts ...Option) *MailNotifier {
	n := &MailNotifier{
		notifyChannel: make(chan NotificationMail, 1),
		senderAddress: config.NotificationSenderAddress,
		dialer:        mail.NewDialer(config.SMTPHost, config.SMTPPort, "", ""),
		quitChannel:   make(chan struct{}),
		infoLog:       log.New(os.Stdout, "", 0),
		errorLog:      log.New(os.Stderr, "", 0),
		mailConfig:    config,
	}

	for _, o := range opts {
		o(n)
	}

	return n
}

func NotifierLog(infoLog, errorLog *log.Logger) Option {
	return func(n *MailNotifier) {
		n.infoLog = infoLog
		n.errorLog = errorLog
	}
}

func (mn *MailNotifier) Start() {
	mn.infoLog.Print("Launching mail notifier")

	for {
		select {
		case notification := <-mn.notifyChannel:
			content := notification.GetNotificationContent(mn.mailConfig)

			mailText, err := content.buildMail(mn.mailConfig.BaseURL)
			if err != nil {
				mn.errorLog.Printf("building mail failed: %v", err)

				continue
			}

			m := mail.NewMessage()

			m.SetHeaders(content.headers)
			m.SetAddressHeader("From", mn.senderAddress, "CAcert board voting system")

			for _, recipient := range content.recipients {
				m.SetAddressHeader(recipient.field, recipient.address, recipient.name)
			}

			m.SetHeader("Subject", content.subject)

			m.SetBody("text/plain", mailText.String())

			if err = mn.dialer.DialAndSend(m); err != nil {
				mn.errorLog.Printf("sending mail failed: %v", err)
			}
		case <-mn.quitChannel:
			mn.infoLog.Print("ending mail notifier")

			return
		}
	}
}

func (mn *MailNotifier) Quit() {
	mn.quitChannel <- struct{}{}
}

func (mn *MailNotifier) Notify(w NotificationMail) {
	mn.notifyChannel <- w
}

func (mn *MailNotifier) Ping() error {
	conn, err := net.DialTimeout(
		"tcp",
		fmt.Sprintf("%s:%d", mn.mailConfig.SMTPHost, mn.mailConfig.SMTPPort),
		mn.mailConfig.SMTPTimeOut,
	)
	if err != nil {
		return fmt.Errorf("could not connect to SMTP server: %w", err)
	}

	defer func(conn net.Conn) {
		_ = conn.Close()
	}(conn)

	return nil
}

func (n *NotificationContent) buildMail(baseURL string) (fmt.Stringer, error) {
	// TODO: implement a template cache for mail templates too
	b, err := internal.MailTemplates.ReadFile(path.Join("mailtemplates", n.template))
	if err != nil {
		return nil, fmt.Errorf("could not read mail template %s: %w", n.template, err)
	}

	t, err := template.New(n.template).Funcs(sprig.GenericFuncMap()).Parse(string(b))
	if err != nil {
		return nil, fmt.Errorf("could not parse mail template %s: %w", n.template, err)
	}

	data := struct {
		Data    any
		BaseURL string
	}{Data: n.data, BaseURL: baseURL}

	mailText := bytes.NewBuffer(make([]byte, 0))
	if err = t.Execute(mailText, data); err != nil {
		return nil, fmt.Errorf(
			"failed to execute template %s with context %v: %w", n.template, n.data, err)
	}

	return mailText, nil
}

func defaultRecipient(mc *MailConfig) recipientData {
	return recipientData{
		field:   "To",
		address: mc.NoticeMailAddress,
		name:    "CAcert board mailing list",
	}
}

func voteNoticeRecipient(mc *MailConfig) recipientData {
	return recipientData{
		field:   "To",
		address: mc.VoteNoticeMailAddress,
		name:    "CAcert board votes mailing list",
	}
}

func motionReplyHeaders(m *models.Motion) map[string][]string {
	return map[string][]string{
		"References":  {fmt.Sprintf("<%s>", m.Tag)},
		"In-Reply-To": {fmt.Sprintf("<%s>", m.Tag)},
	}
}

type RemindVoterNotification struct {
	Voter     *models.User
	Decisions []*models.Motion
}

func (r RemindVoterNotification) GetNotificationContent(*MailConfig) *NotificationContent {
	recipientAddress := make([]recipientData, 0)

	if r.Voter.Reminder.Valid {
		recipientAddress = append(recipientAddress, recipientData{
			field:   "To",
			address: r.Voter.Reminder.String,
			name:    r.Voter.Name,
		})
	}

	return &NotificationContent{
		template: "remind_voter_mail.txt",
		data: struct {
			Decisions []*models.Motion
			Name      string
		}{Decisions: r.Decisions, Name: r.Voter.Name},
		subject:    "Outstanding CAcert board votes",
		recipients: recipientAddress,
	}
}

type ClosedDecisionNotification struct {
	Decision *models.Motion
}

func (c *ClosedDecisionNotification) GetNotificationContent(mc *MailConfig) *NotificationContent {
	return &NotificationContent{
		template: "closed_motion_mail.txt",
		data: struct {
			*models.Motion
		}{Motion: c.Decision},
		subject:    fmt.Sprintf("Re: %s - %s - finalized", c.Decision.Tag, c.Decision.Title),
		headers:    motionReplyHeaders(c.Decision),
		recipients: []recipientData{defaultRecipient(mc)},
	}
}

type NewDecisionNotification struct {
	Decision *models.Motion
	Proposer *models.User
}

func (n NewDecisionNotification) GetNotificationContent(mc *MailConfig) *NotificationContent {
	voteURL := fmt.Sprintf("/vote/%s", n.Decision.Tag)
	unvotedURL := "/motions/?unvoted=1"

	return &NotificationContent{
		template: "create_motion_mail.txt",
		data: struct {
			*models.Motion
			Name       string
			VoteURL    string
			UnvotedURL string
		}{
			Motion:     n.Decision,
			Name:       n.Proposer.Name,
			VoteURL:    voteURL,
			UnvotedURL: unvotedURL,
		},
		subject:    fmt.Sprintf("%s - %s", n.Decision.Tag, n.Decision.Title),
		headers:    n.getHeaders(),
		recipients: []recipientData{defaultRecipient(mc)},
	}
}

func (n NewDecisionNotification) getHeaders() map[string][]string {
	return map[string][]string{
		"Message-ID": {fmt.Sprintf("<%s>", n.Decision.Tag)},
	}
}

type UpdateDecisionNotification struct {
	Decision *models.Motion
	User     *models.User
}

func (u UpdateDecisionNotification) GetNotificationContent(mc *MailConfig) *NotificationContent {
	voteURL := fmt.Sprintf("/vote/%s", u.Decision.Tag)
	unvotedURL := "/motions/?unvoted=1"

	return &NotificationContent{
		template: "update_motion_mail.txt",
		data: struct {
			*models.Motion
			Name       string
			VoteURL    string
			UnvotedURL string
		}{
			Motion:     u.Decision,
			Name:       u.User.Name,
			VoteURL:    voteURL,
			UnvotedURL: unvotedURL,
		},
		subject:    fmt.Sprintf("%s - %s", u.Decision.Tag, u.Decision.Title),
		headers:    motionReplyHeaders(u.Decision),
		recipients: []recipientData{defaultRecipient(mc)},
	}
}

type DirectVoteNotification struct {
	Decision *models.Motion
	User     *models.User
	Choice   *models.VoteChoice
}

func (d DirectVoteNotification) GetNotificationContent(mc *MailConfig) *NotificationContent {
	return &NotificationContent{
		template: "direct_vote_mail.txt",
		data: struct {
			*models.Motion
			Name   string
			Choice *models.VoteChoice
		}{
			Motion: d.Decision,
			Name:   d.User.Name,
			Choice: d.Choice,
		},
		subject:    fmt.Sprintf("Re: %s - %s", d.Decision.Tag, d.Decision.Title),
		headers:    motionReplyHeaders(d.Decision),
		recipients: []recipientData{voteNoticeRecipient(mc)},
	}
}

type ProxyVoteNotification struct {
	Decision      *models.Motion
	User          *models.User
	Voter         *models.User
	Choice        *models.VoteChoice
	Justification string
}

func (p ProxyVoteNotification) GetNotificationContent(mc *MailConfig) *NotificationContent {
	return &NotificationContent{
		template: "proxy_vote_mail.txt",
		data: struct {
			*models.Motion
			Name          string
			Voter         string
			Choice        *models.VoteChoice
			Justification string
		}{
			Motion:        p.Decision,
			Name:          p.User.Name,
			Voter:         p.Voter.Name,
			Choice:        p.Choice,
			Justification: p.Justification,
		},
		subject:    fmt.Sprintf("Re: %s - %s", p.Decision.Tag, p.Decision.Title),
		headers:    motionReplyHeaders(p.Decision),
		recipients: []recipientData{voteNoticeRecipient(mc)},
	}
}

type WithDrawMotionNotification struct {
	Motion *models.Motion
	Voter  *models.User
}

func (w WithDrawMotionNotification) GetNotificationContent(mc *MailConfig) *NotificationContent {
	return &NotificationContent{
		template: "withdraw_motion_mail.txt",
		data: struct {
			*models.Motion
			Name string
		}{Motion: w.Motion, Name: w.Voter.Name},
		subject:    fmt.Sprintf("Re: %s - %s", w.Motion.Tag, w.Motion.Title),
		headers:    motionReplyHeaders(w.Motion),
		recipients: []recipientData{defaultRecipient(mc)},
	}
}