changes for email signup

internal/domain/emailphone.go

@@ -0,0 +1,74 @@
+package domain
+
+import (
+	"math/big"
+	"strings"
+)
+
+// EmailPhonePrefix marks a "phone number" as a synthetic identity encoding an
+// email address, not a real phone. It reuses Telegram's own +888 "Anonymous
+// Number" range (already declared in this server's help.getAppConfig
+// fragment_prefixes), so patched clients that already special-case 888
+// numbers have a head start, and the range is guaranteed to never collide
+// with a real assigned country code.
+const EmailPhonePrefix = "888"
+
+// MaxEmailSignupPhoneLen mirrors the users.phone column width (see migration
+// 0087) and ValidPhone's upper bound.
+const MaxEmailSignupPhoneLen = 200
+
+// EncodeEmailPhone deterministically and reversibly encodes an email address
+// into a synthetic "888"-prefixed all-digit phone number: the email's
+// lowercased/trimmed UTF-8 bytes, read as a big-endian unsigned integer, then
+// printed in decimal. This lets the existing phone-based sendCode/signUp/
+// signIn/changePhone flow carry an email address end to end unchanged — no
+// new TL constructors, no server-side reverse-lookup table required.
+//
+// ok is false if email is empty/invalid or the encoded result would not fit
+// the users.phone column (MaxEmailSignupPhoneLen) — this comfortably covers
+// realistic email addresses (roughly up to 80 bytes).
+func EncodeEmailPhone(email string) (phone string, ok bool) {
+	normalized := NormalizeEmailForPhone(email)
+	if normalized == "" || !strings.Contains(normalized, "@") {
+		return "", false
+	}
+	n := new(big.Int).SetBytes([]byte(normalized))
+	digits := n.String()
+	phone = EmailPhonePrefix + digits
+	if len(phone) > MaxEmailSignupPhoneLen {
+		return "", false
+	}
+	return phone, true
+}
+
+// DecodeEmailPhone reverses EncodeEmailPhone. ok is false if phone does not
+// carry the "888" prefix or does not decode to a plausible email address.
+func DecodeEmailPhone(phone string) (email string, ok bool) {
+	phone = NormalizePhone(strings.TrimSpace(phone))
+	digits, found := strings.CutPrefix(phone, EmailPhonePrefix)
+	if !found || digits == "" {
+		return "", false
+	}
+	n, valid := new(big.Int).SetString(digits, 10)
+	if !valid {
+		return "", false
+	}
+	decoded := string(n.Bytes())
+	if decoded == "" || !strings.Contains(decoded, "@") {
+		return "", false
+	}
+	return decoded, true
+}
+
+// NormalizeEmailForPhone lowercases and trims an email so the same address
+// always encodes to the same synthetic phone number regardless of how the
+// user typed it (e.g. on a different device).
+func NormalizeEmailForPhone(email string) string {
+	return strings.ToLower(strings.TrimSpace(email))
+}
+
+// IsEmailSignupPhone reports whether phone was produced by EncodeEmailPhone
+// (i.e. carries the synthetic "888" prefix), without decoding it.
+func IsEmailSignupPhone(phone string) bool {
+	return strings.HasPrefix(NormalizePhone(strings.TrimSpace(phone)), EmailPhonePrefix)
+}