module smtp

/*
*
* smtp module
* Created by: nedimf (07/2020)
*/
import net
import net.ssl
import encoding.base64
import strings
import time
import io
import rand

const recv_size = 128

enum ReplyCode {
    ready      = 220
    close      = 221
    auth_ok    = 235
    action_ok  = 250
    mail_start = 354
}

pub enum BodyType {
    text
    html
}

// Message stores one body variant and optional attachments for a Mail.
pub struct Message {
pub:
    body        string
    attachments []Attachment
}

// Config stores the settings used to connect a new SMTP client.
pub struct Config {
pub:
    server   string
    port     int = 25
    username string
    password string
    from     string
    ssl      bool
    starttls bool
    timeout  time.Duration
}

pub struct Client {
    Config
mut:
    conn     net.TcpConn
    ssl_conn &ssl.SSLConn = unsafe { nil }
    reader   ?&io.BufferedReader
pub mut:
    is_open   bool
    encrypted bool
}

// Mail stores the message headers and MIME payload sent by Client.send.
pub struct Mail {
pub:
    from        string
    to          string
    cc          string
    bcc         string
    date        time.Time = time.now()
    subject     string
    body_type   BodyType
    body        string
    attachments []Attachment
    html        Message
    text        Message
    boundary    string
}

pub struct Attachment {
pub:
    cid      string
    filename string
    bytes    []u8
}

// new_client returns a new SMTP client and connects to it
pub fn new_client(config Config) !&Client {
    if config.ssl && config.starttls {
        return error('Can not use both implicit SSL and STARTTLS')
    }

    mut c := &Client{
        Config: config
    }
    c.reconnect()!
    return c
}

// reconnect reconnects to the SMTP server if the connection was closed
pub fn (mut c Client) reconnect() ! {
    if c.is_open {
        return error('Already connected to server')
    }

    mut conn := net.dial_tcp('${c.server}:${c.port}') or {
        return error('Connecting to server failed')
    }
    if c.timeout != 0 {
        conn.set_read_timeout(c.timeout)
        conn.set_write_timeout(c.timeout)
    }
    c.conn = conn

    if c.ssl || c.encrypted {
        c.connect_ssl()!
    } else {
        c.reader = io.new_buffered_reader(reader: c.conn)
    }

    c.expect_reply(.ready) or { return error('Received invalid response from server') }
    c.send_ehlo() or { return error('Sending EHLO packet failed') }

    if c.starttls && !c.encrypted {
        c.send_starttls() or { return error('Sending STARTTLS failed') }
    }

    c.send_auth() or { return error('Authenticating to server failed') }
    c.is_open = true
}

// send sends an email
pub fn (mut c Client) send(config Mail) ! {
    if !c.is_open {
        return error('Disconnected from server')
    }
    from := if config.from != '' { config.from } else { c.from }
    c.send_mailfrom(from) or { return error('Sending mailfrom failed') }
    c.send_mailto(config.to) or { return error('Sending mailto failed') }
    c.send_data() or { return error('Sending mail data failed') }
    c.send_body(Mail{
        ...config
        from:     from
        boundary: rand.uuid_v4()
    }) or { return error('Sending mail body failed') }
}

// quit closes the connection to the server
pub fn (mut c Client) quit() ! {
    c.send_str('QUIT\r\n')!
    c.expect_reply(.close)!
    if c.encrypted {
        c.ssl_conn.shutdown()!
    } else {
        c.conn.close()!
    }
    c.is_open = false
    c.encrypted = false
}

fn (mut c Client) connect_ssl() ! {
    c.ssl_conn = ssl.new_ssl_conn()!
    c.ssl_conn.connect(mut c.conn, c.server) or {
        return error('Connecting to server using OpenSSL failed: ${err}')
    }

    c.reader = io.new_buffered_reader(reader: c.ssl_conn)
    c.encrypted = true
}

// expect_reply checks if the SMTP server replied with the expected reply code
fn (mut c Client) expect_reply(expected ReplyCode) ! {
    mut str := ''
    for {
        str = c.reader or { return error('the Client.reader field is not set') }.read_line()!
        if str.len < 4 {
            return error('Invalid SMTP response: ${str}')
        }

        if str.runes()[3] == `-` {
            continue
        } else {
            break
        }
    }

    $if smtp_debug ? {
        eprintln('\n\n[RECV]')
        eprint(str)
    }

    if str.len >= 3 {
        status := str[..3].int()
        if unsafe { ReplyCode(status) } != expected {
            return error('Received unexpected status code ${status}, expecting ${expected}')
        }
    } else {
        return error('Received unexpected SMTP data: ${str}')
    }
}

@[inline]
fn (mut c Client) send_str(s string) ! {
    $if smtp_debug ? {
        eprintln('\n\n[SEND START]')
        eprint(s.trim_space())
        eprintln('\n[SEND END]')
    }

    if c.encrypted {
        c.ssl_conn.write(s.bytes())!
    } else {
        c.conn.write(s.bytes())!
    }
}

@[inline]
fn (mut c Client) send_ehlo() ! {
    c.send_str('EHLO ${c.server}\r\n')!
    c.expect_reply(.action_ok)!
}

@[inline]
fn (mut c Client) send_starttls() ! {
    c.send_str('STARTTLS\r\n')!
    c.expect_reply(.ready)!
    c.connect_ssl()!
}

@[inline]
fn (mut c Client) send_auth() ! {
    if c.username.len == 0 {
        return
    }
    mut sb := strings.new_builder(100)
    sb.write_u8(0)
    sb.write_string(c.username)
    sb.write_u8(0)
    sb.write_string(c.password)
    a := sb.str()
    auth := 'AUTH PLAIN ${base64.encode_str(a)}\r\n'
    c.send_str(auth)!
    c.expect_reply(.auth_ok)!
}

// envelope_addr extracts the bare mailbox from an address that may include a
// display name. The SMTP envelope (`MAIL FROM:` / `RCPT TO:`) only accepts a
// bare mailbox (RFC 5321), while `Mail.from`/`Mail.to` may also be written in
// the RFC 5322 `Display Name <[email protected]>` form for the message header.
//
// Only strip an angle-addr wrapper when the input actually ends in `>`; bare
// mailboxes are returned unchanged. When walking for the opening `<`, quoted
// strings are skipped so a quoted local-part like `"a<b"@example.com` is
// preserved intact.
fn envelope_addr(s string) string {
    trimmed := s.trim_space()
    if !trimmed.ends_with('>') {
        return trimmed
    }
    mut in_quote := false
    mut i := 0
    for i < trimmed.len - 1 {
        c := trimmed[i]
        if c == `"` {
            in_quote = !in_quote
        } else if in_quote && c == `\\` && i + 1 < trimmed.len {
            i++
        } else if c == `<` && !in_quote {
            return trimmed[i + 1..trimmed.len - 1]
        }
        i++
    }
    return trimmed
}

fn (mut c Client) send_mailfrom(from string) ! {
    c.send_str('MAIL FROM:<${envelope_addr(from)}>\r\n')!
    c.expect_reply(.action_ok)!
}

fn (mut c Client) send_mailto(to string) ! {
    for rcpt in to.split(';') {
        c.send_str('RCPT TO:<${envelope_addr(rcpt)}>\r\n')!
        c.expect_reply(.action_ok)!
    }
}

fn (mut c Client) send_data() ! {
    c.send_str('DATA\r\n')!
    c.expect_reply(.mail_start)!
}

fn (mut c Client) send_body(cfg Mail) ! {
    c.send_str(cfg.message_data())!
    c.expect_reply(.action_ok)!
}

fn (cfg &Mail) message_data() string {
    date := cfg.date.custom_format('ddd, D MMM YYYY HH:mm ZZ')
    nonascii_subject := cfg.subject.bytes().any(it < u8(` `) || it > u8(`~`))
    parts, attachments := cfg.mime_parts()
    mut sb := strings.new_builder(200 + cfg.body.len + cfg.text.body.len + cfg.html.body.len +
        (cfg.attachments.len + cfg.text.attachments.len + cfg.html.attachments.len) * 200)
    sb.write_string('From: ${cfg.from}\r\n')
    sb.write_string('To: <${cfg.to.split(';').join('>; <')}>\r\n')
    sb.write_string('Cc: <${cfg.cc.split(';').join('>; <')}>\r\n')
    sb.write_string('Bcc: <${cfg.bcc.split(';').join('>; <')}>\r\n')
    sb.write_string('Date: ${date}\r\n')
    if nonascii_subject {
        // handle UTF-8 subjects according RFC 1342
        sb.write_string('Subject: =?utf-8?B?' + base64.encode_str(cfg.subject) + '?=\r\n')
    } else {
        sb.write_string('Subject: ${cfg.subject}\r\n')
    }
    if parts.len > 1 || attachments.len > 0 {
        sb.write_string('MIME-Version: 1.0\r\n')
    }

    boundary := cfg.mime_boundary()
    if parts.len > 1 && attachments.len > 0 {
        alternative_boundary := '${boundary}-alternative'
        write_multipart_header(mut sb, 'multipart/mixed', boundary)
        write_multipart_boundary(mut sb, boundary)
        write_multipart_header(mut sb, 'multipart/alternative', alternative_boundary)
        for part in parts {
            write_multipart_boundary(mut sb, alternative_boundary)
            write_message_part(mut sb, part)
        }
        write_multipart_end(mut sb, alternative_boundary)
        write_attachments(mut sb, attachments, boundary)
    } else if parts.len > 1 {
        write_multipart_header(mut sb, 'multipart/alternative', boundary)
        for part in parts {
            write_multipart_boundary(mut sb, boundary)
            write_message_part(mut sb, part)
        }
        write_multipart_end(mut sb, boundary)
    } else if attachments.len > 0 {
        write_multipart_header(mut sb, 'multipart/mixed', boundary)
        write_multipart_boundary(mut sb, boundary)
        write_message_part(mut sb, parts[0])
        write_attachments(mut sb, attachments, boundary)
    } else {
        write_message_part(mut sb, parts[0])
    }
    sb.write_string('.\r\n')
    return sb.str()
}

struct MimePart {
    body_type BodyType
    body      string
}

fn (cfg &Mail) mime_parts() ([]MimePart, []Attachment) {
    if cfg.text.body != '' || cfg.html.body != '' {
        mut parts := []MimePart{cap: 2}
        mut attachments := []Attachment{cap: cfg.text.attachments.len + cfg.html.attachments.len}
        if cfg.text.body != '' {
            parts << MimePart{
                body_type: .text
                body:      cfg.text.body
            }
        }
        attachments << cfg.text.attachments
        if cfg.html.body != '' {
            parts << MimePart{
                body_type: .html
                body:      cfg.html.body
            }
        }
        attachments << cfg.html.attachments
        return parts, attachments
    }
    return [MimePart{
        body_type: cfg.body_type
        body:      cfg.body
    }], cfg.attachments
}

fn (cfg &Mail) mime_boundary() string {
    if cfg.boundary != '' {
        return cfg.boundary
    }
    return 'v-smtp-boundary'
}

fn write_multipart_header(mut sb strings.Builder, multipart_type string, boundary string) {
    sb.write_string('Content-Type: ${multipart_type}; boundary="${boundary}"\r\n\r\n')
}

fn write_multipart_boundary(mut sb strings.Builder, boundary string) {
    sb.write_string('--${boundary}\r\n')
}

fn write_multipart_end(mut sb strings.Builder, boundary string) {
    sb.write_string('--${boundary}--\r\n')
}

fn write_message_part(mut sb strings.Builder, part MimePart) {
    if part.body_type == .html {
        sb.write_string('Content-Type: text/html; charset=UTF-8\r\n')
    } else {
        sb.write_string('Content-Type: text/plain; charset=UTF-8\r\n')
    }
    sb.write_string('Content-Transfer-Encoding: base64\r\n\r\n')
    sb.write_string(fold_base64(base64.encode_str(part.body)))
    sb.write_string('\r\n')
}

fn write_attachments(mut sb strings.Builder, attachments []Attachment, boundary string) {
    for attachment in attachments {
        write_multipart_boundary(mut sb, boundary)
        sb.write_string(attachment.to_string())
        sb.write_string('\r\n')
    }
    write_multipart_end(mut sb, boundary)
}

fn (a &Attachment) to_string() string {
    crlf := '\r\n'
    cid := if a.cid != '' {
        'Content-ID: <${a.cid}>${crlf}'
    } else {
        ''
    }
    return 'Content-Type: application/octet-stream${crlf}${cid}Content-Transfer-Encoding: base64${crlf}Content-Disposition: attachment; filename="${a.filename}"${crlf}${crlf}${fold_base64(base64.encode(a.bytes))}'
}

fn fold_base64(encoded string) string {
    if encoded.len <= 76 {
        return encoded
    }
    mut sb := strings.new_builder(encoded.len + encoded.len / 76 * 2)
    for start := 0; start < encoded.len; start += 76 {
        end := if start + 76 < encoded.len { start + 76 } else { encoded.len }
        sb.write_string(encoded[start..end])
        if end < encoded.len {
            sb.write_string('\r\n')
        }
    }
    return sb.str()
}