refactor: move CEL checker to its own package

Signed-off-by: Xe Iaso <me@xeiaso.net>

lib/checker/expression/factory.go

@@ -0,0 +1,43 @@
+package expression
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+
+	"github.com/TecharoHQ/anubis/lib/checker"
+)
+
+func init() {
+	checker.Register("expression", Factory{})
+}
+
+type Factory struct{}
+
+func (f Factory) Build(ctx context.Context, data json.RawMessage) (checker.Interface, error) {
+	var fc = &Config{}
+
+	if err := json.Unmarshal([]byte(data), fc); err != nil {
+		return nil, errors.Join(checker.ErrUnparseableConfig, err)
+	}
+
+	if err := fc.Valid(); err != nil {
+		return nil, errors.Join(checker.ErrInvalidConfig, err)
+	}
+
+	return New(fc)
+}
+
+func (f Factory) Valid(ctx context.Context, data json.RawMessage) error {
+	var fc = &Config{}
+
+	if err := json.Unmarshal([]byte(data), fc); err != nil {
+		return err
+	}
+
+	if err := fc.Valid(); err != nil {
+		return err
+	}
+
+	return nil
+}