// Copyright (C) 2019 Storj Labs, Inc.
// See LICENSE for copying information

package mailservice

import (
	"bytes"
	"context"
	htmltemplate "html/template"
	"path/filepath"
	"sync"
	"time"

	"github.com/spacemonkeygo/monkit/v3"
	"go.uber.org/zap"

	"storj.io/common/context2"
	"storj.io/storj/private/post"
)

// Config defines values needed by mailservice service.
type Config struct {
	SMTPServerAddress string `help:"smtp server address" default:""`
	TemplatePath      string `help:"path to email templates source" default:""`
	From              string `help:"sender email address" default:""`
	AuthType          string `help:"smtp authentication type" releaseDefault:"login" devDefault:"simulate"`
	Login             string `help:"plain/login auth user login" default:""`
	Password          string `help:"plain/login auth user password" default:""`
	RefreshToken      string `help:"refresh token used to retrieve new access token" default:""`
	ClientID          string `help:"oauth2 app's client id" default:""`
	ClientSecret      string `help:"oauth2 app's client secret" default:""`
	TokenURI          string `help:"uri which is used when retrieving new access token" default:""`
}

var (
	mon = monkit.Package()
)

// Sender sends emails.
//
// architecture: Service
type Sender interface {
	SendEmail(ctx context.Context, msg *post.Message) error
	FromAddress() post.Address
}

// Message defines mailservice template-backed message for SendRendered method.
type Message interface {
	Template() string
	Subject() string
}

// Service sends template-backed email messages through SMTP.
//
// architecture: Service
type Service struct {
	log    *zap.Logger
	sender Sender

	html *htmltemplate.Template
	// TODO(yar): prepare plain text version
	// text *texttemplate.Template

	sending sync.WaitGroup
}

// New creates new service.
func New(log *zap.Logger, sender Sender, templatePath string) (*Service, error) {
	var err error
	service := &Service{log: log, sender: sender}

	// TODO(yar): prepare plain text version
	// service.text, err = texttemplate.ParseGlob(filepath.Join(templatePath, "*.txt"))
	// if err != nil {
	// 	return nil, err
	// }

	service.html, err = htmltemplate.ParseGlob(filepath.Join(templatePath, "*.html"))
	if err != nil {
		return nil, err
	}

	return service, nil
}

// Close closes and waits for any pending actions.
func (service *Service) Close() error {
	service.sending.Wait()
	return nil
}

// Send is generalized method for sending custom email message.
func (service *Service) Send(ctx context.Context, msg *post.Message) (err error) {
	defer mon.Task()(&ctx)(&err)
	return service.sender.SendEmail(ctx, msg)
}

// SendRenderedAsync renders content from htmltemplate and texttemplate templates then sends it asynchronously.
func (service *Service) SendRenderedAsync(ctx context.Context, to []post.Address, msg Message) {
	// TODO: think of a better solution
	service.sending.Add(1)
	go func() {
		defer service.sending.Done()

		ctx, cancel := context.WithTimeout(context2.WithoutCancellation(ctx), 5*time.Second)
		defer cancel()

		err := service.SendRendered(ctx, to, msg)

		var recipients []string
		for _, recipient := range to {
			recipients = append(recipients, recipient.String())
		}

		if err != nil {
			service.log.Error("fail sending email",
				zap.Strings("recipients", recipients),
				zap.Error(err))
		} else {
			service.log.Info("email sent successfully",
				zap.Strings("recipients", recipients))
		}
	}()
}

// SendRendered renders content from htmltemplate and texttemplate templates then sends it.
func (service *Service) SendRendered(ctx context.Context, to []post.Address, msg Message) (err error) {
	defer mon.Task()(&ctx)(&err)

	var htmlBuffer bytes.Buffer
	var textBuffer bytes.Buffer

	// TODO(yar): prepare plain text version
	// if err = service.text.ExecuteTemplate(&textBuffer, msg.Template() + ".txt", msg); err != nil {
	// 	return
	// }

	if err = service.html.ExecuteTemplate(&htmlBuffer, msg.Template()+".html", msg); err != nil {
		return
	}

	m := &post.Message{
		From:      service.sender.FromAddress(),
		To:        to,
		Subject:   msg.Subject(),
		PlainText: textBuffer.String(),
		Parts: []post.Part{
			{
				Type:    "text/html; charset=UTF-8",
				Content: htmlBuffer.String(),
			},
		},
	}

	return service.sender.SendEmail(ctx, m)
}