new message on login

internal/domain/welcome_message.go

@@ -0,0 +1,40 @@
+package domain
+
+import (
+	"fmt"
+	"math"
+	"strings"
+)
+
+const officialWelcomeMessageTemplate = "👋 Welcome to OwpenGram!\n\nYou just signed in via %s.\n\nIf this wasn't you, revoke this session from Settings → Devices immediately."
+
+// OfficialWelcomeMessage builds the account-visible incoming message sent
+// from the official system account on every completed sign-in (SignUp and
+// every subsequent SignIn/SignInWithEmail), regardless of delivery channel.
+// Unlike OfficialLoginCodeMessage this never embeds a secret, so it is safe
+// to send unconditionally — it exists to give the account owner (and, on a
+// self-hosted single-admin server, that's usually also "the admin") a
+// visible record of every session start.
+func OfficialWelcomeMessage(userID int64, method string, date int) (Message, error) {
+	method = strings.TrimSpace(method)
+	if userID <= 0 || IsSystemUserID(userID) || method == "" || date < 0 || date > math.MaxInt32 {
+		return Message{}, fmt.Errorf("%w: user=%d method=%q date=%d", ErrLoginCodeDeliveryInvalid, userID, method, date)
+	}
+	return Message{
+		OwnerUserID: userID,
+		Peer:        Peer{Type: PeerTypeUser, ID: OfficialSystemUserID},
+		From:        Peer{Type: PeerTypeUser, ID: OfficialSystemUserID},
+		Date:        date,
+		Body:        fmt.Sprintf(officialWelcomeMessageTemplate, method),
+	}, nil
+}
+
+// SignInMethodLabel returns the human-readable method name embedded in
+// OfficialWelcomeMessage, derived from whether phone is an email-signup
+// synthetic number (see EncodeEmailPhone) or a real phone number.
+func SignInMethodLabel(phone string) string {
+	if IsEmailSignupPhone(phone) {
+		return "email"
+	}
+	return "phone number"
+}