package mailbox

import (
	"bytes"
	"fmt"
	"mime"
	"net"
	"net/smtp"
	"strings"
	"time"
)

// buildRFC822 renders a draft as an RFC 5322 message (CRLF line endings, UTF-8
// text body). It returns the bytes and the generated Message-ID.
func buildRFC822(from string, d Draft) ([]byte, string) {
	domain := "localhost"
	if at := strings.LastIndexByte(from, '@'); at >= 0 {
		domain = from[at+1:]
	}
	msgID := fmt.Sprintf("<%s@%s>", randToken(), domain)

	var b bytes.Buffer
	wh := func(k, v string) { fmt.Fprintf(&b, "%s: %s\r\n", k, v) }
	wh("From", from)
	wh("To", headerAddrs(d.To))
	if len(d.CC) > 0 {
		wh("Cc", headerAddrs(d.CC))
	}
	wh("Subject", mime.QEncoding.Encode("utf-8", d.Subject))
	wh("Date", time.Now().Format(time.RFC1123Z))
	wh("Message-Id", msgID)
	if d.InReplyTo != "" {
		wh("In-Reply-To", d.InReplyTo)
		wh("References", d.InReplyTo)
	}
	wh("MIME-Version", "1.0")
	wh("Content-Type", "text/plain; charset=utf-8")
	wh("Content-Transfer-Encoding", "8bit")
	b.WriteString("\r\n")
	b.WriteString(strings.ReplaceAll(d.Text, "\n", "\r\n"))
	return b.Bytes(), msgID
}

// headerAddrs renders an address list for a header, encoding display names.
func headerAddrs(list []Address) string {
	parts := make([]string, len(list))
	for i, a := range list {
		if a.Name == "" {
			parts[i] = a.Address
		} else {
			parts[i] = fmt.Sprintf("%s <%s>", mime.QEncoding.Encode("utf-8", a.Name), a.Address)
		}
	}
	return strings.Join(parts, ", ")
}

// recipients flattens To+Cc+Bcc into envelope recipient addresses.
func recipients(d Draft) []string {
	var out []string
	for _, l := range [][]Address{d.To, d.CC, d.BCC} {
		for _, a := range l {
			out = append(out, a.Address)
		}
	}
	return out
}

// smtpSend submits a built message via SMTP. With a non-empty user it does
// STARTTLS + AUTH (e.g. smtp.profullstack.com:587); with an empty user it sends
// unauthenticated, for a trusted local relay (e.g. the co-located Postfix).
func smtpSend(addr, user, pass, from string, rcpts []string, msg []byte) error {
	host, _, err := net.SplitHostPort(addr)
	if err != nil {
		return fmt.Errorf("smtp addr %q: %w", addr, err)
	}
	var auth smtp.Auth
	if user != "" {
		auth = smtp.PlainAuth("", user, pass, host)
	}
	return smtp.SendMail(addr, auth, from, rcpts, msg)
}