1 files changed, 88 insertions, 0 deletions
diff --git a/internal/system/output.go b/internal/system/output.go
new file mode 100644
index 00000000..71acace4
--- /dev/null
+++ b/internal/system/output.go
@@ -0,0 +1,88 @@
+package system
+
+import (
+	"errors"
+	"net"
+	"os"
+
+	"hakurei.app/container"
+	"hakurei.app/message"
+)
+
+// OpError is returned by [I.Commit] and [I.Revert].
+type OpError struct {
+	Op     string
+	Err    error
+	Msg    string
+	Revert bool
+}
+
+func (e *OpError) Unwrap() error { return e.Err }
+func (e *OpError) Error() string {
+	if e.Msg != "" {
+		return e.Msg
+	}
+
+	switch {
+	case errors.As(e.Err, new(*os.PathError)),
+		errors.As(e.Err, new(*os.LinkError)),
+		errors.As(e.Err, new(*net.OpError)),
+		errors.As(e.Err, new(*container.StartError)):
+		return e.Err.Error()
+
+	default:
+		if !e.Revert {
+			return "apply " + e.Op + ": " + e.Err.Error()
+		} else {
+			return "revert " + e.Op + ": " + e.Err.Error()
+		}
+	}
+}
+
+func (e *OpError) Message() string {
+	switch {
+	case e.Msg != "":
+		return e.Error()
+
+	default:
+		return "cannot " + e.Error()
+	}
+}
+
+// newOpError returns an [OpError] without a message string.
+func newOpError(op string, err error, revert bool) error {
+	if err == nil {
+		return nil
+	}
+	return &OpError{op, err, "", revert}
+}
+
+// newOpErrorMessage returns an [OpError] with an overriding message string.
+func newOpErrorMessage(op string, err error, message string, revert bool) error {
+	if err == nil {
+		return nil
+	}
+	return &OpError{op, err, message, revert}
+}
+
+func printJoinedError(println func(v ...any), fallback string, err error) {
+	var joinErr interface {
+		Unwrap() []error
+		error
+	}
+	if !errors.As(err, &joinErr) {
+		if m, ok := message.GetMessage(err); ok {
+			println(m)
+		} else {
+			println(fallback, err)
+		}
+	} else {
+		for _, err = range joinErr.Unwrap() {
+			if m, ok := message.GetMessage(err); ok {
+				println(m)
+			} else {
+				println(err.Error())
+			}
+		}
+	}
+}