// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in https://raw.githubusercontent.com/golang/go/master/LICENSE

// Package mail implements the Simple Mail Transfer Protocol as defined in RFC 5321.
// It also implements the following extensions:
//	8BITMIME  RFC 1652
//	AUTH      RFC 2554
//	STARTTLS  RFC 3207
// Additional extensions may be handled by clients using smtp.go in golang source code or pull request Go Simple Mail

// smtp.go file is a modification of smtp golang package what is frozen and is not accepting new features.

package mail

import (
	"crypto/tls"
	"encoding/base64"
	"errors"
	"fmt"
	"io"
	"net"
	"net/textproto"
	"strings"
)

// A Client represents a client connection to an SMTP server.
type smtpClient struct {
	// Text is the textproto.Conn used by the Client.
	text *textproto.Conn
	// keep a reference to the connection so it can be used to create a TLS
	// connection later
	conn net.Conn
	// whether the Client is using TLS
	tls        bool
	serverName string
	// map of supported extensions
	ext map[string]string
	// supported auth mechanisms
	a          []string
	localName  string // the name to use in HELO/EHLO
	didHello   bool   // whether we've said HELO/EHLO
	helloError error  // the error from the hello
}

// newClient returns a new smtpClient using an existing connection and host as a
// server name to be used when authenticating.
func newClient(conn net.Conn, host string) (*smtpClient, error) {
	text := textproto.NewConn(conn)
	_, _, err := text.ReadResponse(220)
	if err != nil {
		text.Close()
		return nil, err
	}
	c := &smtpClient{text: text, conn: conn, serverName: host, localName: "localhost"}
	_, c.tls = conn.(*tls.Conn)
	return c, nil
}

// Close closes the connection.
func (c *smtpClient) close() error {
	return c.text.Close()
}

// hello runs a hello exchange if needed.
func (c *smtpClient) hello() error {
	if !c.didHello {
		c.didHello = true
		err := c.ehlo()
		if err != nil {
			c.helloError = c.helo()
		}
	}
	return c.helloError
}

// hi sends a HELO or EHLO to the server as the given host name.
// Calling this method is only necessary if the client needs control
// over the host name used. The client will introduce itself as "localhost"
// automatically otherwise. If Hello is called, it must be called before
// any of the other methods.
func (c *smtpClient) hi(localName string) error {
	if err := validateLine(localName); err != nil {
		return err
	}
	if c.didHello {
		return errors.New("smtp: Hello called after other methods")
	}
	c.localName = localName
	return c.hello()
}

// cmd is a convenience function that sends a command and returns the response
func (c *smtpClient) cmd(expectCode int, format string, args ...interface{}) (int, string, error) {
	id, err := c.text.Cmd(format, args...)
	if err != nil {
		return 0, "", err
	}
	c.text.StartResponse(id)
	defer c.text.EndResponse(id)
	code, msg, err := c.text.ReadResponse(expectCode)
	return code, msg, err
}

// helo sends the HELO greeting to the server. It should be used only when the
// server does not support ehlo.
func (c *smtpClient) helo() error {
	c.ext = nil
	_, _, err := c.cmd(250, "HELO %s", c.localName)
	return err
}

// ehlo sends the EHLO (extended hello) greeting to the server. It
// should be the preferred greeting for servers that support it.
func (c *smtpClient) ehlo() error {
	_, msg, err := c.cmd(250, "EHLO %s", c.localName)
	if err != nil {
		return err
	}
	ext := make(map[string]string)
	extList := strings.Split(msg, "\n")
	if len(extList) > 1 {
		extList = extList[1:]
		for _, line := range extList {
			args := strings.SplitN(line, " ", 2)
			if len(args) > 1 {
				ext[args[0]] = args[1]
			} else {
				ext[args[0]] = ""
			}
		}
	}
	if mechs, ok := ext["AUTH"]; ok {
		c.a = strings.Split(mechs, " ")
	}
	c.ext = ext
	return err
}

// startTLS sends the STARTTLS command and encrypts all further communication.
// Only servers that advertise the STARTTLS extension support this function.
func (c *smtpClient) startTLS(config *tls.Config) error {
	if err := c.hello(); err != nil {
		return err
	}
	_, _, err := c.cmd(220, "STARTTLS")
	if err != nil {
		return err
	}
	c.conn = tls.Client(c.conn, config)
	c.text = textproto.NewConn(c.conn)
	c.tls = true
	return c.ehlo()
}

// authenticate authenticates a client using the provided authentication mechanism.
// A failed authentication closes the connection.
// Only servers that advertise the AUTH extension support this function.
func (c *smtpClient) authenticate(a auth) error {
	if err := c.hello(); err != nil {
		return err
	}
	encoding := base64.StdEncoding
	mech, resp, err := a.start(&serverInfo{c.serverName, c.tls, c.a})
	if err != nil {
		c.quit()
		return err
	}
	resp64 := make([]byte, encoding.EncodedLen(len(resp)))
	encoding.Encode(resp64, resp)
	code, msg64, err := c.cmd(0, strings.TrimSpace(fmt.Sprintf("AUTH %s %s", mech, resp64)))
	for err == nil {
		var msg []byte
		switch code {
		case 334:
			msg, err = encoding.DecodeString(msg64)
		case 235:
			// the last message isn't base64 because it isn't a challenge
			msg = []byte(msg64)
		default:
			err = &textproto.Error{Code: code, Msg: msg64}
		}
		if err == nil {
			resp, err = a.next(msg, code == 334)
		}
		if err != nil {
			// abort the AUTH
			c.cmd(501, "*")
			c.quit()
			break
		}
		if resp == nil {
			break
		}
		resp64 = make([]byte, encoding.EncodedLen(len(resp)))
		encoding.Encode(resp64, resp)
		code, msg64, err = c.cmd(0, string(resp64))
	}
	return err
}

// mail issues a MAIL command to the server using the provided email address.
// If the server supports the 8BITMIME extension, Mail adds the BODY=8BITMIME
// parameter.
// This initiates a mail transaction and is followed by one or more Rcpt calls.
func (c *smtpClient) mail(from string) error {
	if err := validateLine(from); err != nil {
		return err
	}
	if err := c.hello(); err != nil {
		return err
	}
	cmdStr := "MAIL FROM:<%s>"
	if c.ext != nil {
		if _, ok := c.ext["8BITMIME"]; ok {
			cmdStr += " BODY=8BITMIME"
		}
	}
	_, _, err := c.cmd(250, cmdStr, from)
	return err
}

// rcpt issues a RCPT command to the server using the provided email address.
// A call to Rcpt must be preceded by a call to Mail and may be followed by
// a Data call or another Rcpt call.
func (c *smtpClient) rcpt(to string) error {
	if err := validateLine(to); err != nil {
		return err
	}
	_, _, err := c.cmd(25, "RCPT TO:<%s>", to)
	return err
}

type dataCloser struct {
	c *smtpClient
	io.WriteCloser
}

func (d *dataCloser) Close() error {
	d.WriteCloser.Close()
	_, _, err := d.c.text.ReadResponse(250)
	return err
}

// data issues a DATA command to the server and returns a writer that
// can be used to write the mail headers and body. The caller should
// close the writer before calling any more methods on c. A call to
// Data must be preceded by one or more calls to Rcpt.
func (c *smtpClient) data() (io.WriteCloser, error) {
	_, _, err := c.cmd(354, "DATA")
	if err != nil {
		return nil, err
	}
	return &dataCloser{c, c.text.DotWriter()}, nil
}

// extension reports whether an extension is support by the server.
// The extension name is case-insensitive. If the extension is supported,
// extension also returns a string that contains any parameters the
// server specifies for the extension.
func (c *smtpClient) extension(ext string) (bool, string) {
	if err := c.hello(); err != nil {
		return false, ""
	}
	if c.ext == nil {
		return false, ""
	}
	ext = strings.ToUpper(ext)
	param, ok := c.ext[ext]
	return ok, param
}

// reset sends the RSET command to the server, aborting the current mail
// transaction.
func (c *smtpClient) reset() error {
	if err := c.hello(); err != nil {
		return err
	}
	_, _, err := c.cmd(250, "RSET")
	return err
}

// noop sends the NOOP command to the server. It does nothing but check
// that the connection to the server is okay.
func (c *smtpClient) noop() error {
	if err := c.hello(); err != nil {
		return err
	}
	_, _, err := c.cmd(250, "NOOP")
	return err
}

// quit sends the QUIT command and closes the connection to the server.
func (c *smtpClient) quit() error {
	if err := c.hello(); err != nil {
		return err
	}
	_, _, err := c.cmd(221, "QUIT")
	if err != nil {
		return err
	}
	return c.text.Close()
}

// validateLine checks to see if a line has CR or LF as per RFC 5321
func validateLine(line string) error {
	if strings.ContainsAny(line, "\n\r") {
		return errors.New("smtp: A line must not contain CR or LF")
	}
	return nil
}
