internal/system: relocate from system

These packages are highly specific to hakurei and are difficult to use safely from other pieces of code.

Their exported symbols are made available until v0.4.0 where they will be removed for #24.

Signed-off-by: Ophestra <cat@gensokyo.uk>

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())
+			}
+		}
+	}
+}