Notify question authors via Resend when an admin posts the first answer.

Require email at registration (editable on profile), add a Resend mailer with idempotent first-answer sends, and keep answer saves independent of delivery.

internal/store/email.go

@@ -0,0 +1,52 @@
+package store
+
+import (
+	"fmt"
+	"net/mail"
+	"strings"
+	"unicode/utf8"
+)
+
+const (
+	minEmailLen = 3
+	maxEmailLen = 254
+)
+
+// NormalizeEmail trims and lowercases an address for storage/comparison.
+func NormalizeEmail(s string) string {
+	return strings.ToLower(strings.TrimSpace(s))
+}
+
+// ValidateEmail returns a normalized address or an error message suitable for UI.
+func ValidateEmail(raw string) (normalized string, errMsg string) {
+	normalized = NormalizeEmail(raw)
+	if normalized == "" {
+		return "", "Email is required."
+	}
+	n := utf8.RuneCountInString(normalized)
+	if n < minEmailLen || len(normalized) > maxEmailLen {
+		return "", "Enter a valid email address."
+	}
+	addr, err := mail.ParseAddress(normalized)
+	if err != nil || addr.Address != normalized {
+		return "", "Enter a valid email address."
+	}
+	at := strings.LastIndex(normalized, "@")
+	if at < 1 || at == len(normalized)-1 {
+		return "", "Enter a valid email address."
+	}
+	domain := normalized[at+1:]
+	if !strings.Contains(domain, ".") || strings.HasPrefix(domain, ".") || strings.HasSuffix(domain, ".") {
+		return "", "Enter a valid email address."
+	}
+	return normalized, ""
+}
+
+// MustValidateEmail is like ValidateEmail but returns a Go error.
+func MustValidateEmail(raw string) (string, error) {
+	n, msg := ValidateEmail(raw)
+	if msg != "" {
+		return "", fmt.Errorf("%s", msg)
+	}
+	return n, nil
+}

internal/store/email_test.go

@@ -0,0 +1,21 @@
+package store
+
+import "testing"
+
+func TestValidateEmail(t *testing.T) {
+	cases := []struct {
+		in, want, err string
+	}{
+		{"", "", "Email is required."},
+		{"  Alice@Example.COM ", "alice@example.com", ""},
+		{"not-an-email", "", "Enter a valid email address."},
+		{"a@b", "", "Enter a valid email address."},
+		{"ok@example.com", "ok@example.com", ""},
+	}
+	for _, tc := range cases {
+		got, msg := ValidateEmail(tc.in)
+		if got != tc.want || msg != tc.err {
+			t.Fatalf("%q: got (%q, %q) want (%q, %q)", tc.in, got, msg, tc.want, tc.err)
+		}
+	}
+}

internal/store/memory.go

@@ -42,9 +42,17 @@ func (m *Memory) CreateUser(_ context.Context, u *User) error {
 		return fmt.Errorf("invalid role")
 	}
 	u.Username = NormalizeUsername(u.Username)
+	u.Email = NormalizeEmail(u.Email)
 	if _, ok := m.byName[u.Username]; ok {
 		return ErrDuplicateUsername
 	}
+	if u.Email != "" {
+		for _, existing := range m.users {
+			if existing.Email == u.Email {
+				return ErrDuplicateEmail
+			}
+		}
+	}
 	if u.ID == "" {
 		u.ID = uuid.NewString()
 	}
@@ -179,11 +187,21 @@ func (m *Memory) SaveUserProfile(_ context.Context, u *User) error {
 	if !ok {
 		return sql.ErrNoRows
 	}
+	email := NormalizeEmail(u.Email)
+	if email != "" {
+		for id, existing := range m.users {
+			if id != u.ID && existing.Email == email {
+				return ErrDuplicateEmail
+			}
+		}
+	}
 	cur.State = strings.TrimSpace(u.State)
+	cur.Email = email
 	if u.AvatarURL != "" {
 		cur.AvatarURL = u.AvatarURL
 	}
 	u.State = cur.State
+	u.Email = cur.Email
 	u.AvatarURL = cur.AvatarURL
 	return nil
 }

internal/store/migrate.go

@@ -21,6 +21,20 @@ func migrateUserProfileColumns(ctx context.Context, exec execContext) error {
 	return nil
 }
 
+// migrateUserEmail adds email and a partial unique index on lower(email).
+func migrateUserEmail(ctx context.Context, exec execContext) error {
+	if _, err := exec.ExecContext(ctx, `ALTER TABLE users ADD COLUMN IF NOT EXISTS email TEXT NOT NULL DEFAULT ''`); err != nil {
+		return fmt.Errorf("add column email: %w", err)
+	}
+	if _, err := exec.ExecContext(ctx, `
+CREATE UNIQUE INDEX IF NOT EXISTS users_email_lower_uidx
+  ON users (lower(email))
+  WHERE email <> ''`); err != nil {
+		return fmt.Errorf("users_email_lower_uidx: %w", err)
+	}
+	return nil
+}
+
 type execContext interface {
 	ExecContext(ctx context.Context, query string, args ...any) (sql.Result, error)
 	QueryContext(ctx context.Context, query string, args ...any) (*sql.Rows, error)
@@ -66,6 +80,7 @@ CREATE TABLE IF NOT EXISTS schema_migrations (
 			return applySchema(ctx, exec, schemaSQL)
 		}},
 		{"002_user_profile_columns", migrateUserProfileColumns},
+		{"003_user_email", migrateUserEmail},
 	}
 	for _, m := range migrations {
 		if applied[m.version] {

internal/store/postgres_store.go

@@ -29,6 +29,7 @@ func (p *Postgres) CreateUser(ctx context.Context, u *User) error {
 		return fmt.Errorf("invalid role")
 	}
 	u.Username = NormalizeUsername(u.Username)
+	u.Email = NormalizeEmail(u.Email)
 	if u.ID == "" {
 		u.ID = uuid.NewString()
 	}
@@ -69,6 +70,7 @@ func (p *Postgres) CreateUser(ctx context.Context, u *User) error {
 		Name:         u.Name,
 		PasswordHash: u.PasswordHash,
 		Role:         string(role),
+		Email:        u.Email,
 		CreatedAt:    u.CreatedAt,
 	}); err != nil {
 		return mapUniqueViolation(err)

internal/store/sqlc/models.go

@@ -39,6 +39,7 @@ type User struct {
 	Name         string
 	PasswordHash string
 	Role         string
+	Email        string
 	AvatarUrl    string
 	State        string
 	CreatedAt    string

internal/store/sqlc/users.sql.go

@@ -24,8 +24,8 @@ func (q *Queries) CountAdmins(ctx context.Context, role string) (int64, error) {
 }
 
 const createUser = `-- name: CreateUser :exec
-INSERT INTO users (id, username, name, password_hash, role, avatar_url, state, created_at)
-VALUES ($1, $2, $3, $4, $5, '', '', $6)
+INSERT INTO users (id, username, name, password_hash, role, email, avatar_url, state, created_at)
+VALUES ($1, $2, $3, $4, $5, $6, '', '', $7)
 `
 
 type CreateUserParams struct {
@@ -34,6 +34,7 @@ type CreateUserParams struct {
 	Name         string
 	PasswordHash string
 	Role         string
+	Email        string
 	CreatedAt    string
 }
 
@@ -44,13 +45,14 @@ func (q *Queries) CreateUser(ctx context.Context, arg CreateUserParams) error {
 		arg.Name,
 		arg.PasswordHash,
 		arg.Role,
+		arg.Email,
 		arg.CreatedAt,
 	)
 	return err
 }
 
 const getUserByID = `-- name: GetUserByID :one
-SELECT id, username, name, role, avatar_url, state, created_at
+SELECT id, username, name, role, email, avatar_url, state, created_at
 FROM users
 WHERE id = $1
 `
@@ -60,6 +62,7 @@ type GetUserByIDRow struct {
 	Username  string
 	Name      string
 	Role      string
+	Email     string
 	AvatarUrl string
 	State     string
 	CreatedAt string
@@ -73,6 +76,7 @@ func (q *Queries) GetUserByID(ctx context.Context, id string) (GetUserByIDRow, e
 		&i.Username,
 		&i.Name,
 		&i.Role,
+		&i.Email,
 		&i.AvatarUrl,
 		&i.State,
 		&i.CreatedAt,
@@ -81,7 +85,7 @@ func (q *Queries) GetUserByID(ctx context.Context, id string) (GetUserByIDRow, e
 }
 
 const getUserByUsername = `-- name: GetUserByUsername :one
-SELECT id, username, name, role, avatar_url, state, created_at, password_hash
+SELECT id, username, name, role, email, avatar_url, state, created_at, password_hash
 FROM users
 WHERE username = $1
 `
@@ -91,6 +95,7 @@ type GetUserByUsernameRow struct {
 	Username     string
 	Name         string
 	Role         string
+	Email        string
 	AvatarUrl    string
 	State        string
 	CreatedAt    string
@@ -105,6 +110,7 @@ func (q *Queries) GetUserByUsername(ctx context.Context, username string) (GetUs
 		&i.Username,
 		&i.Name,
 		&i.Role,
+		&i.Email,
 		&i.AvatarUrl,
 		&i.State,
 		&i.CreatedAt,
@@ -127,12 +133,13 @@ func (q *Queries) GetUserRole(ctx context.Context, id string) (string, error) {
 }
 
 const listUsers = `-- name: ListUsers :many
-SELECT id, username, name, role, avatar_url, state, created_at
+SELECT id, username, name, role, email, avatar_url, state, created_at
 FROM users
 WHERE (
   $1 = ''
   OR username ILIKE '%' || $1 || '%'
   OR name ILIKE '%' || $1 || '%'
+  OR email ILIKE '%' || $1 || '%'
 )
 AND (
   $2 = ''
@@ -155,6 +162,7 @@ type ListUsersRow struct {
 	Username  string
 	Name      string
 	Role      string
+	Email     string
 	AvatarUrl string
 	State     string
 	CreatedAt string
@@ -179,6 +187,7 @@ func (q *Queries) ListUsers(ctx context.Context, arg ListUsersParams) ([]ListUse
 			&i.Username,
 			&i.Name,
 			&i.Role,
+			&i.Email,
 			&i.AvatarUrl,
 			&i.State,
 			&i.CreatedAt,
@@ -196,6 +205,46 @@ func (q *Queries) ListUsers(ctx context.Context, arg ListUsersParams) ([]ListUse
 	return items, nil
 }
 
+const updateUserProfile = `-- name: UpdateUserProfile :exec
+UPDATE users
+SET state = $1, email = $2
+WHERE id = $3
+`
+
+type UpdateUserProfileParams struct {
+	State string
+	Email string
+	ID    string
+}
+
+func (q *Queries) UpdateUserProfile(ctx context.Context, arg UpdateUserProfileParams) error {
+	_, err := q.db.ExecContext(ctx, updateUserProfile, arg.State, arg.Email, arg.ID)
+	return err
+}
+
+const updateUserProfileAndAvatar = `-- name: UpdateUserProfileAndAvatar :exec
+UPDATE users
+SET state = $1, email = $2, avatar_url = $3
+WHERE id = $4
+`
+
+type UpdateUserProfileAndAvatarParams struct {
+	State     string
+	Email     string
+	AvatarUrl string
+	ID        string
+}
+
+func (q *Queries) UpdateUserProfileAndAvatar(ctx context.Context, arg UpdateUserProfileAndAvatarParams) error {
+	_, err := q.db.ExecContext(ctx, updateUserProfileAndAvatar,
+		arg.State,
+		arg.Email,
+		arg.AvatarUrl,
+		arg.ID,
+	)
+	return err
+}
+
 const updateUserRole = `-- name: UpdateUserRole :execresult
 UPDATE users
 SET role = $1
@@ -210,36 +259,3 @@ type UpdateUserRoleParams struct {
 func (q *Queries) UpdateUserRole(ctx context.Context, arg UpdateUserRoleParams) (sql.Result, error) {
 	return q.db.ExecContext(ctx, updateUserRole, arg.Role, arg.ID)
 }
-
-const updateUserState = `-- name: UpdateUserState :exec
-UPDATE users
-SET state = $1
-WHERE id = $2
-`
-
-type UpdateUserStateParams struct {
-	State string
-	ID    string
-}
-
-func (q *Queries) UpdateUserState(ctx context.Context, arg UpdateUserStateParams) error {
-	_, err := q.db.ExecContext(ctx, updateUserState, arg.State, arg.ID)
-	return err
-}
-
-const updateUserStateAndAvatar = `-- name: UpdateUserStateAndAvatar :exec
-UPDATE users
-SET state = $1, avatar_url = $2
-WHERE id = $3
-`
-
-type UpdateUserStateAndAvatarParams struct {
-	State     string
-	AvatarUrl string
-	ID        string
-}
-
-func (q *Queries) UpdateUserStateAndAvatar(ctx context.Context, arg UpdateUserStateAndAvatarParams) error {
-	_, err := q.db.ExecContext(ctx, updateUserStateAndAvatar, arg.State, arg.AvatarUrl, arg.ID)
-	return err
-}

internal/store/user.go

@@ -30,6 +30,7 @@ type User struct {
 	Username     string
 	Name         string
 	Role         Role
+	Email        string
 	AvatarURL    string
 	State        string
 	CreatedAt    string
@@ -50,12 +51,13 @@ func NormalizeUsername(s string) string {
 	return strings.ToLower(strings.TrimSpace(s))
 }
 
-func toUser(db *sql.DB, id, username, name, role, avatarURL, state, createdAt, passwordHash string) *User {
+func toUser(db *sql.DB, id, username, name, role, email, avatarURL, state, createdAt, passwordHash string) *User {
 	return &User{
 		ID:           id,
 		Username:     username,
 		Name:         name,
 		Role:         Role(role),
+		Email:        email,
 		AvatarURL:    avatarURL,
 		State:        state,
 		CreatedAt:    createdAt,
@@ -73,6 +75,7 @@ func (u *User) Create(ctx context.Context) error {
 		return fmt.Errorf("invalid role")
 	}
 	u.Username = NormalizeUsername(u.Username)
+	u.Email = NormalizeEmail(u.Email)
 	if u.ID == "" {
 		u.ID = uuid.NewString()
 	}
@@ -88,6 +91,7 @@ func (u *User) Create(ctx context.Context) error {
 		Name:         u.Name,
 		PasswordHash: u.PasswordHash,
 		Role:         string(u.Role),
+		Email:        u.Email,
 		CreatedAt:    u.CreatedAt,
 	}))
 }
@@ -149,21 +153,27 @@ func (u *User) SetRole(ctx context.Context, role Role) error {
 	return nil
 }
 
-// SaveProfile writes State and optionally AvatarURL.
+// SaveProfile writes Email, State, and optionally AvatarURL.
 func (u *User) SaveProfile(ctx context.Context) error {
 	if u == nil || u.db == nil {
 		return fmt.Errorf("user: no database")
 	}
 	u.State = strings.TrimSpace(u.State)
+	u.Email = NormalizeEmail(u.Email)
 	q := sqlc.New(u.db)
 	if u.AvatarURL == "" {
-		return q.UpdateUserState(ctx, sqlc.UpdateUserStateParams{State: u.State, ID: u.ID})
+		return mapUniqueViolation(q.UpdateUserProfile(ctx, sqlc.UpdateUserProfileParams{
+			State: u.State,
+			Email: u.Email,
+			ID:    u.ID,
+		}))
 	}
-	return q.UpdateUserStateAndAvatar(ctx, sqlc.UpdateUserStateAndAvatarParams{
+	return mapUniqueViolation(q.UpdateUserProfileAndAvatar(ctx, sqlc.UpdateUserProfileAndAvatarParams{
 		State:     u.State,
+		Email:     u.Email,
 		AvatarUrl: u.AvatarURL,
 		ID:        u.ID,
-	})
+	}))
 }
 
 func CountAdmins(ctx context.Context, db *sql.DB) (int, error) {
@@ -187,7 +197,7 @@ func ListUsers(ctx context.Context, db *sql.DB, q ListUsersQuery) ([]User, strin
 	}
 	out := make([]User, 0, len(rows))
 	for _, r := range rows {
-		u := toUser(db, r.ID, r.Username, r.Name, r.Role, r.AvatarUrl, r.State, r.CreatedAt, "")
+		u := toUser(db, r.ID, r.Username, r.Name, r.Role, r.Email, r.AvatarUrl, r.State, r.CreatedAt, "")
 		out = append(out, *u)
 	}
 	var nextCreated, nextID string
@@ -204,7 +214,7 @@ func UserByID(ctx context.Context, db *sql.DB, id string) (*User, error) {
 	if err != nil {
 		return nil, err
 	}
-	return toUser(db, r.ID, r.Username, r.Name, r.Role, r.AvatarUrl, r.State, r.CreatedAt, ""), nil
+	return toUser(db, r.ID, r.Username, r.Name, r.Role, r.Email, r.AvatarUrl, r.State, r.CreatedAt, ""), nil
 }
 
 func UserByUsername(ctx context.Context, db *sql.DB, username string) (*User, error) {
@@ -212,5 +222,5 @@ func UserByUsername(ctx context.Context, db *sql.DB, username string) (*User, er
 	if err != nil {
 		return nil, err
 	}
-	return toUser(db, r.ID, r.Username, r.Name, r.Role, r.AvatarUrl, r.State, r.CreatedAt, r.PasswordHash), nil
+	return toUser(db, r.ID, r.Username, r.Name, r.Role, r.Email, r.AvatarUrl, r.State, r.CreatedAt, r.PasswordHash), nil
 }

internal/store/vote.go

@@ -5,6 +5,7 @@ import (
 	"database/sql"
 	"errors"
 	"fmt"
+	"strings"
 
 	"github.com/jackc/pgx/v5/pgconn"
 
@@ -14,6 +15,9 @@ import (
 // ErrDuplicateUsername is returned when inserting a username that already exists.
 var ErrDuplicateUsername = errors.New("username taken")
 
+// ErrDuplicateEmail is returned when inserting/updating an email that already exists.
+var ErrDuplicateEmail = errors.New("email taken")
+
 // ErrHiddenOrMissing is returned when voting on a hidden or unknown question.
 var ErrHiddenOrMissing = errors.New("question not votable")
 
@@ -58,6 +62,9 @@ func Vote(ctx context.Context, db *sql.DB, userID, questionID string, value int)
 func mapUniqueViolation(err error) error {
 	var pgErr *pgconn.PgError
 	if errors.As(err, &pgErr) && pgErr.Code == "23505" {
+		if strings.Contains(strings.ToLower(pgErr.ConstraintName), "email") {
+			return ErrDuplicateEmail
+		}
 		return ErrDuplicateUsername
 	}
 	return err