// Copyright (C) 2019-2023 Nicola Murino
//
// 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, version 3.
//
// 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 smtp provides supports for sending emails
package smtp

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"html/template"
	"path/filepath"
	"time"

	"github.com/wneessen/go-mail"

	"github.com/drakkan/sftpgo/v2/internal/logger"
	"github.com/drakkan/sftpgo/v2/internal/util"
)

const (
	logSender = "smtp"
)

// EmailContentType defines the support content types for email body
type EmailContentType int

// Supported email body content type
const (
	EmailContentTypeTextPlain EmailContentType = iota
	EmailContentTypeTextHTML
)

const (
	templateEmailDir           = "email"
	templatePasswordReset      = "reset-password.html"
	templatePasswordExpiration = "password-expiration.html"
)

var (
	config         *Config
	emailTemplates = make(map[string]*template.Template)
)

// IsEnabled returns true if an SMTP server is configured
func IsEnabled() bool {
	return config != nil
}

// Config defines the SMTP configuration to use to send emails
type Config struct {
	// Location of SMTP email server. Leavy empty to disable email sending capabilities
	Host string `json:"host" mapstructure:"host"`
	// Port of SMTP email server
	Port int `json:"port" mapstructure:"port"`
	// From address, for example "SFTPGo <sftpgo@example.com>".
	// Many SMTP servers reject emails without a `From` header so, if not set,
	// SFTPGo will try to use the username as fallback, this may or may not be appropriate
	From string `json:"from" mapstructure:"from"`
	// SMTP username
	User string `json:"user" mapstructure:"user"`
	// SMTP password. Leaving both username and password empty the SMTP authentication
	// will be disabled
	Password string `json:"password" mapstructure:"password"`
	// 0 Plain
	// 1 Login
	// 2 CRAM-MD5
	AuthType int `json:"auth_type" mapstructure:"auth_type"`
	// 0 no encryption
	// 1 TLS
	// 2 start TLS
	Encryption int `json:"encryption" mapstructure:"encryption"`
	// Domain to use for HELO command, if empty localhost will be used
	Domain string `json:"domain" mapstructure:"domain"`
	// Path to the email templates. This can be an absolute path or a path relative to the config dir.
	// Templates are searched within a subdirectory named "email" in the specified path
	TemplatesPath string `json:"templates_path" mapstructure:"templates_path"`
}

// Initialize initialized and validates the SMTP configuration
func (c *Config) Initialize(configDir string) error {
	config = nil
	if c.Host == "" {
		logger.Debug(logSender, "", "configuration disabled, email capabilities will not be available")
		return nil
	}
	if c.Port <= 0 || c.Port > 65535 {
		return fmt.Errorf("smtp: invalid port %v", c.Port)
	}
	if c.AuthType < 0 || c.AuthType > 2 {
		return fmt.Errorf("smtp: invalid auth type %v", c.AuthType)
	}
	if c.Encryption < 0 || c.Encryption > 2 {
		return fmt.Errorf("smtp: invalid encryption %v", c.Encryption)
	}
	if c.From == "" && c.User == "" {
		return fmt.Errorf(`smtp: from address and user cannot both be empty`)
	}
	templatesPath := util.FindSharedDataPath(c.TemplatesPath, configDir)
	if templatesPath == "" {
		return fmt.Errorf("smtp: invalid templates path %#v", templatesPath)
	}
	loadTemplates(filepath.Join(templatesPath, templateEmailDir))
	config = c
	logger.Debug(logSender, "", "configuration successfully initialized, host: %q, port: %d, username: %q, auth: %d, encryption: %d, helo: %q",
		config.Host, config.Port, config.User, config.AuthType, config.Encryption, config.Domain)
	return nil
}

func (c *Config) getMailClientOptions() []mail.Option {
	options := []mail.Option{mail.WithPort(c.Port), mail.WithoutNoop()}

	switch c.Encryption {
	case 1:
		options = append(options, mail.WithSSL())
	case 2:
		options = append(options, mail.WithTLSPolicy(mail.TLSMandatory))
	default:
		options = append(options, mail.WithTLSPolicy(mail.NoTLS))
	}
	if config.User != "" {
		options = append(options, mail.WithUsername(config.User))
	}
	if config.Password != "" {
		options = append(options, mail.WithPassword(config.Password))
	}
	if config.User != "" || config.Password != "" {
		switch config.AuthType {
		case 1:
			options = append(options, mail.WithSMTPAuth(mail.SMTPAuthLogin))
		case 2:
			options = append(options, mail.WithSMTPAuth(mail.SMTPAuthCramMD5))
		default:
			options = append(options, mail.WithSMTPAuth(mail.SMTPAuthPlain))
		}
	}
	if config.Domain != "" {
		options = append(options, mail.WithHELO(config.Domain))
	}
	return options
}

func loadTemplates(templatesPath string) {
	logger.Debug(logSender, "", "loading templates from %#v", templatesPath)

	passwordResetPath := filepath.Join(templatesPath, templatePasswordReset)
	pwdResetTmpl := util.LoadTemplate(nil, passwordResetPath)
	passwordExpirationPath := filepath.Join(templatesPath, templatePasswordExpiration)
	pwdExpirationTmpl := util.LoadTemplate(nil, passwordExpirationPath)

	emailTemplates[templatePasswordReset] = pwdResetTmpl
	emailTemplates[templatePasswordExpiration] = pwdExpirationTmpl
}

// RenderPasswordResetTemplate executes the password reset template
func RenderPasswordResetTemplate(buf *bytes.Buffer, data any) error {
	if !IsEnabled() {
		return errors.New("smtp: not configured")
	}
	return emailTemplates[templatePasswordReset].Execute(buf, data)
}

// RenderPasswordExpirationTemplate executes the password expiration template
func RenderPasswordExpirationTemplate(buf *bytes.Buffer, data any) error {
	if !IsEnabled() {
		return errors.New("smtp: not configured")
	}
	return emailTemplates[templatePasswordExpiration].Execute(buf, data)
}

// SendEmail tries to send an email using the specified parameters.
func SendEmail(to []string, subject, body string, contentType EmailContentType, attachments ...*mail.File) error {
	if !IsEnabled() {
		return errors.New("smtp: not configured")
	}
	m := mail.NewMsg()

	var from string
	if config.From != "" {
		from = config.From
	} else {
		from = config.User
	}
	if err := m.From(from); err != nil {
		return fmt.Errorf("invalid from address: %w", err)
	}
	if err := m.To(to...); err != nil {
		return err
	}
	m.Subject(subject)
	m.SetDate()
	m.SetMessageID()
	m.SetAttachements(attachments)

	switch contentType {
	case EmailContentTypeTextPlain:
		m.SetBodyString(mail.TypeTextPlain, body)
	case EmailContentTypeTextHTML:
		m.SetBodyString(mail.TypeTextHTML, body)
	default:
		return fmt.Errorf("smtp: unsupported body content type %v", contentType)
	}

	c, err := mail.NewClient(config.Host, config.getMailClientOptions()...)
	if err != nil {
		return fmt.Errorf("unable to create mail client: %w", err)
	}
	ctx, cancelFn := context.WithTimeout(context.Background(), 10*time.Second)
	defer cancelFn()

	return c.DialAndSendWithContext(ctx, m)
}