package smtp2shoutrrr

import (
	"encoding/base64"
	"net/mail"
	"strings"
	"testing"
	"unicode/utf8"

	"github.com/stretchr/testify/require"
)

func readMessage(t *testing.T, raw string) *mail.Message {
	t.Helper()

	msg, err := mail.ReadMessage(strings.NewReader(raw))
	require.NoError(t, err)

	return msg
}

// Regression: this header reached log.Fatalf, which exits the process. The
// value is attacker-controlled and needs nothing but the ability to deliver a
// message.
func TestBodyRejectsMalformedContentType(t *testing.T) {
	for name, contentType := range map[string]string{
		"parameter without a value": "text/plain; charset",
		"duplicate parameter":       "text/plain; charset=utf-8; charset=ascii",
		"no media type":             ";",
		"unterminated quoted value": `multipart/mixed; boundary="unterminated`,
	} {
		t.Run(name, func(t *testing.T) {
			email := ReceivedEmail{
				Msg: readMessage(t, "Subject: Test\r\nContent-Type: "+contentType+"\r\n\r\nbody\r\n"),
			}

			body, err := email.Body()
			require.Error(t, err)
			require.ErrorIs(t, err, errMalformedMessage,
				"an unparseable header is permanent, so the sender must not be told to retry")
			require.Empty(t, body)
		})
	}
}

func TestBodyReadsMessageWithoutContentType(t *testing.T) {
	email := ReceivedEmail{Msg: readMessage(t, "Subject: Test\r\n\r\nplain body\r\n")}

	body, err := email.Body()
	require.NoError(t, err)
	require.Equal(t, "plain body\r\n", body)
}

func TestBodyPrefersPlainTextPartOverHTML(t *testing.T) {
	email := ReceivedEmail{Msg: readMessage(t, strings.Join([]string{
		"Subject: Test",
		`Content-Type: multipart/alternative; boundary="b"`,
		"",
		"--b",
		"Content-Type: text/html; charset=utf-8",
		"",
		"<p>html body</p>",
		"--b",
		"Content-Type: text/plain; charset=utf-8",
		"",
		"plain body",
		"--b--",
		"",
	}, "\r\n"))}

	body, err := email.Body()
	require.NoError(t, err)
	require.Equal(t, "plain body", body)
}

func TestBodyFallsBackToHTMLPart(t *testing.T) {
	email := ReceivedEmail{Msg: readMessage(t, strings.Join([]string{
		"Subject: Test",
		`Content-Type: multipart/alternative; boundary="b"`,
		"",
		"--b",
		"Content-Type: text/html; charset=utf-8",
		"",
		"<p>html body</p>",
		"--b--",
		"",
	}, "\r\n"))}

	body, err := email.Body()
	require.NoError(t, err)
	require.Equal(t, "<p>html body</p>", body)
}

func TestBodyDecodesQuotedPrintable(t *testing.T) {
	email := ReceivedEmail{Msg: readMessage(t, strings.Join([]string{
		"Subject: Test",
		"Content-Type: text/plain; charset=utf-8",
		"Content-Transfer-Encoding: quoted-printable",
		"",
		"caf=C3=A9 =E2=80=94 a very long line that the sender wrapped =",
		"here",
		"",
	}, "\r\n"))}

	body, err := email.Body()
	require.NoError(t, err)
	require.Equal(t, "café — a very long line that the sender wrapped here\r\n", body)
}

func TestBodyDecodesBase64(t *testing.T) {
	email := ReceivedEmail{Msg: readMessage(t, strings.Join([]string{
		"Subject: Test",
		"Content-Type: text/plain; charset=utf-8",
		"Content-Transfer-Encoding: base64",
		"",
		base64.StdEncoding.EncodeToString([]byte("café — encoded")),
		"",
	}, "\r\n"))}

	body, err := email.Body()
	require.NoError(t, err)
	require.Equal(t, "café — encoded", body)
}

// Windows-1252 and Latin-1 are still what a good deal of automated mail is
// written in, and their bytes are not valid UTF-8.
func TestBodyDecodesNonUTF8Charset(t *testing.T) {
	email := ReceivedEmail{Msg: readMessage(t,
		"Subject: Test\r\nContent-Type: text/plain; charset=iso-8859-1\r\n\r\ncaf\xe9\r\n")}

	body, err := email.Body()
	require.NoError(t, err)
	require.Equal(t, "café\r\n", body)
	require.True(t, utf8.ValidString(body))
}

func TestBodyUnknownCharsetIsForwardedUndecoded(t *testing.T) {
	email := ReceivedEmail{Msg: readMessage(t,
		"Subject: Test\r\nContent-Type: text/plain; charset=not-a-charset\r\n\r\nbody\r\n")}

	body, err := email.Body()
	require.NoError(t, err)
	require.Equal(t, "body\r\n", body)
}

// A forwarded message is a multipart/mixed wrapping the multipart/alternative
// that holds what the sender actually wrote. Stopping at the outer container
// left the notification empty.
func TestBodyDescendsIntoNestedMultipart(t *testing.T) {
	email := ReceivedEmail{Msg: readMessage(t, strings.Join([]string{
		"Subject: Test",
		`Content-Type: multipart/mixed; boundary="outer"`,
		"",
		"--outer",
		`Content-Type: multipart/alternative; boundary="inner"`,
		"",
		"--inner",
		"Content-Type: text/html; charset=utf-8",
		"",
		"<p>html body</p>",
		"--inner",
		"Content-Type: text/plain; charset=utf-8",
		"",
		"plain body",
		"--inner--",
		"--outer--",
		"",
	}, "\r\n"))}

	body, err := email.Body()
	require.NoError(t, err)
	require.Equal(t, "plain body", body)
}

func TestBodySkipsAttachments(t *testing.T) {
	email := ReceivedEmail{Msg: readMessage(t, strings.Join([]string{
		"Subject: Test",
		`Content-Type: multipart/mixed; boundary="b"`,
		"",
		"--b",
		"Content-Type: text/plain; charset=utf-8",
		`Content-Disposition: attachment; filename="notes.txt"`,
		"",
		"an enclosed file, not the message",
		"--b",
		"Content-Type: text/plain; charset=utf-8",
		"",
		"the message itself",
		"--b--",
		"",
	}, "\r\n"))}

	body, err := email.Body()
	require.NoError(t, err)
	require.Equal(t, "the message itself", body)
}

// Senders that build the HTML alternative from a template routinely emit an
// empty text/plain beside it.
func TestBodyPrefersHTMLOverAnEmptyPlainTextPart(t *testing.T) {
	email := ReceivedEmail{Msg: readMessage(t, strings.Join([]string{
		"Subject: Test",
		`Content-Type: multipart/alternative; boundary="b"`,
		"",
		"--b",
		"Content-Type: text/plain; charset=utf-8",
		"",
		"   ",
		"--b",
		"Content-Type: text/html; charset=utf-8",
		"",
		"<p>html body</p>",
		"--b--",
		"",
	}, "\r\n"))}

	body, err := email.Body()
	require.NoError(t, err)
	require.Equal(t, "<p>html body</p>", body)
}

func TestBodyRejectsMultipartWithoutBoundary(t *testing.T) {
	email := ReceivedEmail{Msg: readMessage(t,
		"Subject: Test\r\nContent-Type: multipart/alternative\r\n\r\nbody\r\n")}

	_, err := email.Body()
	require.ErrorIs(t, err, errMalformedMessage)
}

func TestFormattedBodyConvertsHTML(t *testing.T) {
	raw := strings.Join([]string{
		"Subject: Test",
		"Content-Type: text/html; charset=utf-8",
		"Content-Transfer-Encoding: quoted-printable",
		"",
		"<p>Build <b>failed</b>: <a href=3D\"https://ci.example.com/42\">run 42</a></p>",
		"",
	}, "\r\n")

	for format, want := range map[BodyFormat]string{
		FormatMarkdown: "Build **failed**: [run 42](https://ci.example.com/42)",
		FormatRaw:      "<p>Build <b>failed</b>: <a href=\"https://ci.example.com/42\">run 42</a></p>\r\n",
	} {
		t.Run(string(format), func(t *testing.T) {
			email := ReceivedEmail{Msg: readMessage(t, raw)}

			body, err := email.FormattedBody(format)
			require.NoError(t, err)
			require.Equal(t, want, body)
		})
	}
}

// A recipient asking for Markdown is asking for HTML to stop reaching it, not
// for the plain text a sender wrote to be run through a renderer.
func TestFormattedBodyLeavesPlainTextAlone(t *testing.T) {
	raw := "Subject: Test\r\nContent-Type: text/plain; charset=utf-8\r\n\r\n2 * 3 = 6 <see notes>\r\n"

	for _, format := range []BodyFormat{FormatRaw, FormatMarkdown} {
		t.Run(string(format), func(t *testing.T) {
			email := ReceivedEmail{Msg: readMessage(t, raw)}

			body, err := email.FormattedBody(format)
			require.NoError(t, err)
			require.Equal(t, "2 * 3 = 6 <see notes>\r\n", body)
		})
	}
}

// The zero value of the option means the same as raw, so a recipient built in
// code rather than loaded from a file still forwards what it received.
func TestFormattedBodyTreatsUnsetFormatAsRaw(t *testing.T) {
	email := ReceivedEmail{Msg: readMessage(t,
		"Subject: Test\r\nContent-Type: text/html\r\n\r\n<p>html body</p>\r\n")}

	body, err := email.FormattedBody("")
	require.NoError(t, err)
	require.Equal(t, "<p>html body</p>\r\n", body)
}

// Reformatting is a courtesy, so a body the renderer cannot use is still
// forwarded rather than costing the reader the notification.
func TestFormattedBodyFallsBackToTheRawHTML(t *testing.T) {
	// The parser refuses a document with more than 512 elements open at once.
	tooDeep := strings.Repeat("<div>", 600) + "deep" + strings.Repeat("</div>", 600)

	for name, source := range map[string]string{
		"a body the parser refuses": tooDeep,
		// Otherwise shoutrrr is handed "", which Mattermost and Discord
		// reject, so every target fails and the sender retries the same
		// message forever.
		"a body that renders to nothing": `<img src="https://x.example/pixel.gif">`,
	} {
		t.Run(name, func(t *testing.T) {
			email := ReceivedEmail{Msg: readMessage(t,
				"Subject: Test\r\nContent-Type: text/html\r\n\r\n"+source)}

			body, err := email.FormattedBody(FormatMarkdown)
			require.NoError(t, err)
			require.Equal(t, source, body)
		})
	}
}

func TestBodyIsReadOnlyOnce(t *testing.T) {
	email := ReceivedEmail{Msg: readMessage(t,
		"Subject: Test\r\nContent-Type: text/html\r\n\r\n<p>body</p>\r\n")}

	first, err := email.FormattedBody(FormatMarkdown)
	require.NoError(t, err)

	second, err := email.FormattedBody(FormatMarkdown)
	require.NoError(t, err)

	require.Equal(t, "body", first)
	require.Equal(t, first, second, "the message body is consumed as it is read")
}

// Regression: an unreadable transfer encoding used to be reported as a
// permanent 550, which tells the sender to stop retrying and loses a
// notification that main delivered. Real mailers emit unpadded base64.
func TestBodyToleratesAnUndecodableTransferEncoding(t *testing.T) {
	for name, tc := range map[string]struct{ raw, want string }{
		"unpadded base64": {
			raw:  base64.RawStdEncoding.EncodeToString([]byte("hello world")),
			want: "hello world",
		},
		"base64 that is not base64 at all": {
			raw:  "!!!! not base64 !!!!",
			want: "!!!! not base64 !!!!",
		},
	} {
		t.Run(name, func(t *testing.T) {
			email := ReceivedEmail{Msg: readMessage(t,
				"Subject: Test\r\nContent-Type: text/plain\r\n"+
					"Content-Transfer-Encoding: base64\r\n\r\n"+tc.raw+"\r\n")}

			body, err := email.Body()
			require.NoError(t, err)
			require.Equal(t, tc.want, strings.TrimSpace(body))
		})
	}
}

// Regression: one part that would not decode used to fail the whole message,
// even with a perfectly good alternative already in hand.
func TestBodyKeepsAGoodPartBesideAnUnreadableOne(t *testing.T) {
	email := ReceivedEmail{Msg: readMessage(t, strings.Join([]string{
		"Subject: Test",
		`Content-Type: multipart/alternative; boundary="b"`,
		"",
		"--b",
		"Content-Type: text/html",
		"Content-Transfer-Encoding: base64",
		"",
		"!!!!not base64!!!!",
		"--b",
		"Content-Type: text/plain",
		"",
		"the real body",
		"--b--",
		"",
	}, "\r\n"))}

	body, err := email.Body()
	require.NoError(t, err)
	require.Equal(t, "the real body", body)
}

// Regression: mime.ParseMediaType returns a usable media type alongside the
// error it reports for a malformed parameter. Discarding both dropped the part
// that held the message and delivered an empty notification with a 250.
func TestBodyReadsPartsWithAMalformedContentType(t *testing.T) {
	email := ReceivedEmail{Msg: readMessage(t, strings.Join([]string{
		"Subject: Test",
		`Content-Type: multipart/alternative; boundary="b"`,
		"",
		"--b",
		"Content-Type: text/plain; charset=",
		"",
		"still text",
		"--b--",
		"",
	}, "\r\n"))}

	body, err := email.Body()
	require.NoError(t, err)
	require.Equal(t, "still text", body)
}

// The same fault the other way round: the attachment guard used to fail open
// on the unquoted file names older mailers emit, so the enclosure won.
func TestBodySkipsAttachmentsWithAMalformedDisposition(t *testing.T) {
	email := ReceivedEmail{Msg: readMessage(t, strings.Join([]string{
		"Subject: Test",
		`Content-Type: multipart/mixed; boundary="b"`,
		"",
		"--b",
		"Content-Type: text/plain",
		"Content-Disposition: attachment; filename=log file.txt",
		"",
		"an enclosed file, not the message",
		"--b",
		"Content-Type: text/plain",
		"",
		"the message itself",
		"--b--",
		"",
	}, "\r\n"))}

	body, err := email.Body()
	require.NoError(t, err)
	require.Equal(t, "the message itself", body)
}

// RFC 2046 §5.1.3: the parts of a multipart/mixed are cumulative, so the first
// one carrying a body is the message and the rest are footers and enclosures.
// Applying "plain beats HTML" across them handed list mail its unsubscribe
// footer as the notification.
func TestBodyPrefersTheFirstPartOfACumulativeMultipart(t *testing.T) {
	email := ReceivedEmail{Msg: readMessage(t, strings.Join([]string{
		"Subject: Test",
		`Content-Type: multipart/mixed; boundary="b"`,
		"",
		"--b",
		"Content-Type: text/html",
		"",
		"<p>the newsletter</p>",
		"--b",
		"Content-Type: text/plain",
		"",
		"You are receiving this because you subscribed.",
		"--b--",
		"",
	}, "\r\n"))}

	body, err := email.FormattedBody(FormatMarkdown)
	require.NoError(t, err)
	require.Equal(t, "the newsletter", body,
		"the HTML body is the message, and asking for Markdown must reach it")
}

func TestBodyPassesOverAnEmptyHTMLAlternative(t *testing.T) {
	email := ReceivedEmail{Msg: readMessage(t, strings.Join([]string{
		"Subject: Test",
		`Content-Type: multipart/alternative; boundary="b"`,
		"",
		"--b",
		"Content-Type: text/html",
		"",
		"  ",
		"--b",
		"Content-Type: text/html",
		"",
		"<p>the real one</p>",
		"--b--",
		"",
	}, "\r\n"))}

	body, err := email.Body()
	require.NoError(t, err)
	require.Equal(t, "<p>the real one</p>", body)
}

// A container this server cannot finish reading still hands over the parts it
// read. Only a message that yielded nothing at all is refused, since there is
// then nothing left to notify with and the same bytes fail the same way on
// every redelivery.
func TestBodyKeepsWhatItReadFromABrokenContainer(t *testing.T) {
	t.Run("a good part before the break is delivered", func(t *testing.T) {
		email := ReceivedEmail{Msg: readMessage(t, strings.Join([]string{
			"Subject: Test",
			`Content-Type: multipart/mixed; boundary="b"`,
			"",
			"--b",
			"Content-Type: text/plain",
			"",
			"good body",
			"--b",
			"this is not a header",
			"",
			"x",
			"--b--",
			"",
		}, "\r\n"))}

		body, err := email.Body()
		require.NoError(t, err)
		require.Equal(t, "good body", body)
	})

	t.Run("a break before anything readable is permanent", func(t *testing.T) {
		email := ReceivedEmail{Msg: readMessage(t, strings.Join([]string{
			"Subject: Test",
			`Content-Type: multipart/alternative; boundary="b"`,
			"",
			"--b",
			"this is not a header",
			"",
			"body",
			"--b--",
			"",
		}, "\r\n"))}

		_, err := email.Body()
		require.ErrorIs(t, err, errMalformedMessage)
	})
}