package mail

import (
	"bytes"
	"io"
	"mime"
	"mime/multipart"
	"mime/quotedprintable"
	"net/mail"
	"strings"
	"testing"
)

// Every part must declare quoted-printable and put only 7-bit bytes on the
// wire. Raw UTF-8 under an implied 7bit encoding scored R_BAD_CTE_7BIT in
// rspamd, went out without a DKIM signature, and landed in Gmail's spam.
func TestEnvelopePartsAreQuotedPrintable(t *testing.T) {
	s := Sender{From: "Vantage <support@example.com>"}
	m := message{
		To:      "a@example.com",
		Subject: "Smith & Sons · restored",
		Text:    "VANTAGE · Account\nBilling has resumed.",
		HTML:    "<p>VANTAGE · Account</p><p>" + strings.Repeat("x", 2000) + "</p>",
	}
	raw, err := s.envelope(m)
	if err != nil {
		t.Fatal(err)
	}
	for i, c := range raw {
		if c > 0x7e && c != '\r' && c != '\n' {
			t.Fatalf("byte %d is 0x%x: the wire must be 7-bit", i, c)
		}
	}
	for _, line := range strings.Split(string(raw), "\r\n") {
		if len(line) > 998 {
			t.Fatalf("line of %d bytes exceeds SMTP's 998", len(line))
		}
	}

	msg, err := mail.ReadMessage(bytes.NewReader(raw))
	if err != nil {
		t.Fatal(err)
	}
	_, params, err := mime.ParseMediaType(msg.Header.Get("Content-Type"))
	if err != nil {
		t.Fatal(err)
	}
	r := multipart.NewReader(msg.Body, params["boundary"])
	want := []string{m.Text, m.HTML}
	for i := range want {
		p, err := r.NextRawPart()
		if err != nil {
			t.Fatalf("part %d: %v", i, err)
		}
		if cte := p.Header.Get("Content-Transfer-Encoding"); cte != "quoted-printable" {
			t.Fatalf("part %d Content-Transfer-Encoding = %q", i, cte)
		}
		// NextPart would decode for us; NextRawPart keeps the check honest by
		// decoding here, so a missing header cannot pass by accident.
		body, err := io.ReadAll(quotedprintable.NewReader(p))
		if err != nil {
			t.Fatal(err)
		}
		// Quoted-printable text mode writes line breaks as CRLF, which is the
		// canonical form on the wire.
		if strings.ReplaceAll(string(body), "\r\n", "\n") != want[i] {
			t.Fatalf("part %d decodes to %q", i, body)
		}
	}
}