package session_test

import (
	"context"
	"crypto/hmac"
	"crypto/sha256"
	"encoding/base64"
	"fmt"
	"net/http"
	"net/http/httptest"
	"strings"
	"testing"
	"time"

	"github.com/gorilla/sessions"
	"github.com/stretchr/testify/assert"
	"github.com/stretchr/testify/require"
	"sneak.berlin/go/webhooker/internal/session"
)

// The tests below exercise the securecookie codecs underneath the
// store and nothing else: Session.Get only decodes, so no server-side
// expiry check takes part in the result. They exist because
// NewCookieStore gives its codecs a 30-day max age that assigning
// store.Options does not override, which would let the codec accept a
// cookie weeks past the cap the cookie attribute advertises.

// issuedCookie returns a session cookie the store itself wrote.
func issuedCookie(t *testing.T, s *session.Session) string {
	t.Helper()

	req := httptest.NewRequestWithContext(
		context.Background(), http.MethodGet, "/", nil)
	w := httptest.NewRecorder()

	sess, err := s.Get(req)
	require.NoError(t, err)

	sess.Values["probe"] = "value"
	require.NoError(t, s.Save(req, w, sess))

	cookies := w.Result().Cookies()
	require.Len(t, cookies, 1)

	return cookies[0].Value
}

// restamp rewrites the timestamp inside an encoded session cookie and
// re-signs it, yielding the cookie the store would have written at
// that instant. securecookie stamps the encoding time itself and
// exposes no seam to move it, so its wire format is reproduced here:
// the base64url payload is "date|value|mac", where mac is HMAC-SHA256
// of "name|date|value" under the store's key.
func restamp(
	t *testing.T,
	encoded string,
	at time.Time,
) string {
	t.Helper()

	raw, err := base64.URLEncoding.DecodeString(encoded)
	require.NoError(t, err)

	parts := strings.SplitN(string(raw), "|", 3)
	require.Len(t, parts, 3)

	stamped := fmt.Sprintf("%d|%s", at.Unix(), parts[1])

	mac := hmac.New(sha256.New, testKey())
	_, err = mac.Write([]byte(session.SessionName + "|" + stamped))
	require.NoError(t, err)

	payload := append([]byte(stamped+"|"), mac.Sum(nil)...)

	return base64.URLEncoding.EncodeToString(payload)
}

// decodeCookie feeds value back through the store's decode path.
func decodeCookie(
	t *testing.T,
	s *session.Session,
	value string,
) (*sessions.Session, error) {
	t.Helper()

	req := httptest.NewRequestWithContext(
		context.Background(), http.MethodGet, "/", nil)
	req.AddCookie(&http.Cookie{
		Name:     session.SessionName,
		Value:    value,
		Path:     "/",
		HttpOnly: true,
		Secure:   true,
		SameSite: http.SameSiteLaxMode,
	})

	sess, err := s.Get(req)
	require.NotNil(t, sess)

	return sess, err
}

func TestCodec_AcceptsCookieInsideAbsoluteCap(t *testing.T) {
	t.Parallel()

	s := testSession(t)

	sess, err := decodeCookie(t, s, restamp(
		t,
		issuedCookie(t, s),
		time.Now().Add(-(testAbsoluteMaxAge-time.Hour)),
	))
	require.NoError(t, err)
	assert.False(
		t, sess.IsNew,
		"a cookie inside the cap must still decode",
	)
	assert.Equal(
		t, "value", sess.Values["probe"],
		"decoding must yield the values that were saved",
	)
}

func TestCodec_RejectsCookiePastAbsoluteCap(t *testing.T) {
	t.Parallel()

	s := testSession(t)

	sess, err := decodeCookie(t, s, restamp(
		t,
		issuedCookie(t, s),
		time.Now().Add(-(testAbsoluteMaxAge+time.Hour)),
	))
	require.Error(
		t, err,
		"the codec must refuse a cookie older than the cap",
	)
	assert.Contains(
		t, err.Error(), "expired timestamp",
		"rejection must come from the codec's age check",
	)
	assert.True(
		t, sess.IsNew,
		"a cookie past the cap must not populate a session",
	)
	assert.Nil(
		t, sess.Values["probe"],
		"a cookie past the cap must not yield its values",
	)
}