// Copyright 2016 Documize Inc. <legal@documize.com>. All rights reserved.
//
// This software (Documize Community Edition) is licensed under
// GNU AGPL v3 http://www.gnu.org/licenses/agpl-3.0.en.html
//
// You can operate outside the AGPL restrictions by purchasing
// Documize Enterprise Edition and obtaining a commercial license
// by contacting <sales@documize.com>.
//
// https://documize.com

/*
Elements of the software in this file were modified from github.com/jordan-wright/email and
are subject to the licence below:

The MIT License (MIT)

Copyright (c) 2013 Jordan Wright

Permission is hereby granted, free of charge, to any person obtaining a copy of
this software and associated documentation files (the "Software"), to deal in
the Software without restriction, including without limitation the rights to
use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
the Software, and to permit persons to whom the Software is furnished to do so,
subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/

// Package mail sends transactional emails.
// The code in smtp.go is designed to provide an "email interface for humans".
// Designed to be robust and flexible, the email package aims to make sending email easy without getting in the way.
package mail

import (
	"bytes"
	"encoding/base64"
	"errors"
	"fmt"
	"io"
	"mime"
	"mime/multipart"
	"net/mail"
	"net/smtp"
	"net/textproto"
	"os"
	"path/filepath"
	"strings"
	"time"

	"github.com/documize/community/core/log"
)

const (
	// MaxLineLength is the maximum line length per RFC 2045
	MaxLineLength = 76
)

// Email is the type used for email messages
type Email struct {
	From        string
	To          []string
	Bcc         []string
	Cc          []string
	Subject     string
	Text        []byte // Plaintext message (optional)
	HTML        []byte // Html message (optional)
	Headers     textproto.MIMEHeader
	Attachments []*Attachment
	ReadReceipt []string
}

// NewEmail creates an Email, and returns the pointer to it.
func NewEmail() *Email {
	return &Email{Headers: textproto.MIMEHeader{}}
}

// Attach is used to attach content from an io.Reader to the email.
// Required parameters include an io.Reader, the desired filename for the attachment, and the Content-Type
// The function will return the created Attachment for reference, as well as nil for the error, if successful.
func (e *Email) Attach(r io.Reader, filename string, c string) (a *Attachment, err error) {
	var buffer bytes.Buffer
	if _, err = io.Copy(&buffer, r); err != nil {
		return
	}
	at := &Attachment{
		Filename: filename,
		Header:   textproto.MIMEHeader{},
		Content:  buffer.Bytes(),
	}
	// Get the Content-Type to be used in the MIMEHeader
	if c != "" {
		at.Header.Set("Content-Type", c)
	} else {
		// If the Content-Type is blank, set the Content-Type to "application/octet-stream"
		at.Header.Set("Content-Type", "application/octet-stream")
	}
	at.Header.Set("Content-Disposition", fmt.Sprintf("attachment;\r\n filename=\"%s\"", filename))
	at.Header.Set("Content-ID", fmt.Sprintf("<%s>", filename))
	at.Header.Set("Content-Transfer-Encoding", "base64")
	e.Attachments = append(e.Attachments, at)
	return at, nil
}

// AttachFile is used to attach content to the email.
// It attempts to open the file referenced by filename and, if successful, creates an Attachment.
// This Attachment is then appended to the slice of Email.Attachments.
// The function will then return the Attachment for reference, as well as nil for the error, if successful.
func (e *Email) AttachFile(filename string) (a *Attachment, err error) {
	f, err := os.Open(filename)
	if err != nil {
		return
	}
	ct := mime.TypeByExtension(filepath.Ext(filename))
	basename := filepath.Base(filename)
	return e.Attach(f, basename, ct)
}

// msgHeaders merges the Email's various fields and custom headers together in a
// standards compliant way to create a MIMEHeader to be used in the resulting
// message. It does not alter e.Headers.
//
// "e"'s fields To, Cc, From, Subject will be used unless they are present in
// e.Headers. Unless set in e.Headers, "Date" will filled with the current time.
func (e *Email) msgHeaders() textproto.MIMEHeader {
	res := make(textproto.MIMEHeader, len(e.Headers)+4)
	if e.Headers != nil {
		for _, h := range []string{"To", "Cc", "From", "Subject", "Date"} {
			if v, ok := e.Headers[h]; ok {
				res[h] = v
			}
		}
	}
	// Set headers if there are values.
	if _, ok := res["To"]; !ok && len(e.To) > 0 {
		res.Set("To", strings.Join(e.To, ", "))
	}
	if _, ok := res["Cc"]; !ok && len(e.Cc) > 0 {
		res.Set("Cc", strings.Join(e.Cc, ", "))
	}
	if _, ok := res["Subject"]; !ok && e.Subject != "" {
		res.Set("Subject", e.Subject)
	}
	// Date and From are required headers.
	if _, ok := res["From"]; !ok {
		res.Set("From", e.From)
	}
	if _, ok := res["Date"]; !ok {
		res.Set("Date", time.Now().Format(time.RFC1123Z))
	}
	if _, ok := res["Mime-Version"]; !ok {
		res.Set("Mime-Version", "1.0")
	}
	for field, vals := range e.Headers {
		if _, ok := res[field]; !ok {
			res[field] = vals
		}
	}
	return res
}

// Bytes converts the Email object to a []byte representation, including all needed MIMEHeaders, boundaries, etc.
func (e *Email) Bytes() ([]byte, error) {
	// TODO: better guess buffer size
	buff := bytes.NewBuffer(make([]byte, 0, 4096))

	headers := e.msgHeaders()
	w := multipart.NewWriter(buff)
	// TODO: determine the content type based on message/attachment mix.
	headers.Set("Content-Type", "multipart/mixed;\r\n boundary="+w.Boundary())
	headerToBytes(buff, headers)
	_, err := io.WriteString(buff, "\r\n")
	log.IfErr(err)
	// Start the multipart/mixed part
	fmt.Fprintf(buff, "--%s\r\n", w.Boundary())
	header := textproto.MIMEHeader{}
	// Check to see if there is a Text or HTML field
	if len(e.Text) > 0 || len(e.HTML) > 0 {
		subWriter := multipart.NewWriter(buff)
		// Create the multipart alternative part
		header.Set("Content-Type", fmt.Sprintf("multipart/alternative;\r\n boundary=%s\r\n", subWriter.Boundary()))
		// Write the header
		headerToBytes(buff, header)
		// Create the body sections
		if len(e.Text) > 0 {
			header.Set("Content-Type", fmt.Sprintf("text/plain; charset=UTF-8"))
			header.Set("Content-Transfer-Encoding", "quoted-printable")
			if _, err := subWriter.CreatePart(header); err != nil {
				return nil, err
			}
			// Write the text
			if err := quotePrintEncode(buff, e.Text); err != nil {
				return nil, err
			}
		}
		if len(e.HTML) > 0 {
			header.Set("Content-Type", fmt.Sprintf("text/html; charset=UTF-8"))
			header.Set("Content-Transfer-Encoding", "quoted-printable")
			if _, err := subWriter.CreatePart(header); err != nil {
				return nil, err
			}
			// Write the text
			if err := quotePrintEncode(buff, e.HTML); err != nil {
				return nil, err
			}
		}
		if err := subWriter.Close(); err != nil {
			return nil, err
		}
	}
	// Create attachment part, if necessary
	for _, a := range e.Attachments {
		ap, err := w.CreatePart(a.Header)
		if err != nil {
			return nil, err
		}
		// Write the base64Wrapped content to the part
		base64Wrap(ap, a.Content)
	}
	if err := w.Close(); err != nil {
		return nil, err
	}
	return buff.Bytes(), nil
}

// Send an email using the given host and SMTP auth (optional), returns any error thrown by smtp.SendMail
// This function merges the To, Cc, and Bcc fields and calls the smtp.SendMail function using the Email.Bytes() output as the message
func (e *Email) Send(addr string, a smtp.Auth) error {
	// Merge the To, Cc, and Bcc fields
	to := make([]string, 0, len(e.To)+len(e.Cc)+len(e.Bcc))
	to = append(append(append(to, e.To...), e.Cc...), e.Bcc...)
	for i := 0; i < len(to); i++ {
		addr, err := mail.ParseAddress(to[i])
		if err != nil {
			return err
		}
		to[i] = addr.Address
	}
	// Check to make sure there is at least one recipient and one "From" address
	if e.From == "" || len(to) == 0 {
		return errors.New("Must specify at least one From address and one To address")
	}
	from, err := mail.ParseAddress(e.From)
	if err != nil {
		return err
	}
	raw, err := e.Bytes()
	if err != nil {
		return err
	}
	return smtpSendMail(addr, a, from.Address, to, raw)
}

var smtpSendMail = smtp.SendMail // so that it can be overloaded for testing

// Attachment is a struct representing an email attachment.
// Based on the mime/multipart.FileHeader struct, Attachment contains the name, MIMEHeader, and content of the attachment in question
type Attachment struct {
	Filename string
	Header   textproto.MIMEHeader
	Content  []byte
}

// quotePrintEncode writes the quoted-printable text to the IO Writer (according to RFC 2045)
func quotePrintEncode(w io.Writer, body []byte) error {
	var buf [3]byte
	mc := 0
	for _, c := range body {
		// We're assuming Unix style text formats as input (LF line break), and
		// quoted-printable uses CRLF line breaks. (Literal CRs will become
		// "=0D", but probably shouldn't be there to begin with!)
		if c == '\n' {
			_, err := io.WriteString(w, "\r\n")
			if err != nil {
				return err
			}
			mc = 0
			continue
		}

		var nextOut []byte
		if isPrintable[c] {
			buf[0] = c
			nextOut = buf[:1]
		} else {
			nextOut = buf[:]
			qpEscape(nextOut, c)
		}

		// Add a soft line break if the next (encoded) byte would push this line
		// to or past the limit.
		if mc+len(nextOut) >= MaxLineLength {
			if _, err := io.WriteString(w, "=\r\n"); err != nil {
				return err
			}
			mc = 0
		}

		if _, err := w.Write(nextOut); err != nil {
			return err
		}
		mc += len(nextOut)
	}
	// No trailing end-of-line?? Soft line break, then. TODO: is this sane?
	if mc > 0 {
		_, err := io.WriteString(w, "=\r\n")
		if err != nil {
			return err
		}
	}
	return nil
}

// isPrintable holds true if the byte given is "printable" according to RFC 2045, false otherwise
var isPrintable [256]bool

func init() {
	for c := '!'; c <= '<'; c++ {
		isPrintable[c] = true
	}
	for c := '>'; c <= '~'; c++ {
		isPrintable[c] = true
	}
	isPrintable[' '] = true
	isPrintable['\n'] = true
	isPrintable['\t'] = true
}

// qpEscape is a helper function for quotePrintEncode which escapes a
// non-printable byte. Expects len(dest) == 3.
func qpEscape(dest []byte, c byte) {
	const nums = "0123456789ABCDEF"
	dest[0] = '='
	dest[1] = nums[(c&0xf0)>>4]
	dest[2] = nums[(c & 0xf)]
}

// base64Wrap encodes the attachment content, and wraps it according to RFC 2045 standards (every 76 chars)
// The output is then written to the specified io.Writer
func base64Wrap(w io.Writer, b []byte) {
	// 57 raw bytes per 76-byte base64 line.
	const maxRaw = 57
	// Buffer for each line, including trailing CRLF.
	buffer := make([]byte, MaxLineLength+len("\r\n"))
	copy(buffer[MaxLineLength:], "\r\n")
	// Process raw chunks until there's no longer enough to fill a line.
	for len(b) >= maxRaw {
		base64.StdEncoding.Encode(buffer, b[:maxRaw])
		_, err := w.Write(buffer)
		log.IfErr(err)
		b = b[maxRaw:]
	}
	// Handle the last chunk of bytes.
	if len(b) > 0 {
		out := buffer[:base64.StdEncoding.EncodedLen(len(b))]
		base64.StdEncoding.Encode(out, b)
		out = append(out, "\r\n"...)
		_, err := w.Write(out)
		log.IfErr(err)
	}
}

// headerToBytes renders "header" to "buff". If there are multiple values for a
// field, multiple "Field: value\r\n" lines will be emitted.
func headerToBytes(buff *bytes.Buffer, header textproto.MIMEHeader) {
	for field, vals := range header {
		for _, subval := range vals {
			_, err := io.WriteString(buff, field+": "+subval+"\r\n")
			log.IfErr(err)
		}
	}
}