Address PR review: graceful shutdown, Role/NewUser, drop SQLite.

internal/store/db.go

@@ -8,15 +8,30 @@ import (
 // ErrLastAdmin is returned when demoting the only remaining admin.
 var ErrLastAdmin = errors.New("cannot demote the last admin")
 
+// Role is a user privilege level stored in users.role.
+type Role string
+
+const (
+	RoleUser  Role = "user"
+	RoleAdmin Role = "admin"
+)
+
+// NewUser is the input for CreateUser.
+type NewUser struct {
+	Username     string
+	PasswordHash string
+	Role         Role
+}
+
 // DB is the persistence API used by the web layer.
 // Named DB to avoid colliding with scs.Store.
 type DB interface {
-	CreateUser(ctx context.Context, username, passwordHash string, asAdmin bool) (*User, error)
+	CreateUser(ctx context.Context, user NewUser) (*User, error)
 	UserByID(ctx context.Context, id string) (*User, error)
 	UserByUsername(ctx context.Context, username string) (*User, error)
 	CountAdmins(ctx context.Context) (int, error)
 	ListUsers(ctx context.Context) ([]User, error)
-	SetRole(ctx context.Context, userID, role string) error
+	SetRole(ctx context.Context, userID string, role Role) error
 	CreateQuestion(ctx context.Context, authorID, title, body, city string) (*RankedQuestion, error)
 	ListHunt(ctx context.Context, huntDate, viewerID string) ([]RankedQuestion, error)
 	GetQuestion(ctx context.Context, id, viewerID string) (*RankedQuestion, error)