feat: backend service

backend/internal/admin/errors.go

@@ -0,0 +1,21 @@
+package admin
+
+import "errors"
+
+// Sentinel errors emitted by Service methods. Handlers translate them
+// into HTTP responses; callers in tests can match on them with
+// errors.Is.
+var (
+	// ErrNotFound is returned when a lookup against `backend.admin_accounts`
+	// matches no row. Handlers map it to HTTP 404.
+	ErrNotFound = errors.New("admin: account not found")
+
+	// ErrUsernameTaken is returned by Create when the supplied username
+	// already exists. Handlers map it to HTTP 409 with code "conflict".
+	ErrUsernameTaken = errors.New("admin: username already in use")
+
+	// ErrInvalidInput is returned when a request is syntactically valid
+	// but semantically rejected (empty username, empty password). Handlers
+	// map it to HTTP 400.
+	ErrInvalidInput = errors.New("admin: invalid input")
+)