From 177f8eb03b19c3d50a8eaf7e1ad2bc507c1be897 Mon Sep 17 00:00:00 2001
From: "Nelo-T. Wallus" <nelo@wallus.de>
Date: Fri, 18 Jul 2025 19:51:24 +0200
Subject: [PATCH] Add chain provider

---
 providers/chain/provider.go | 76 +++++++++++++++++++++++++++++++++++++
 1 file changed, 76 insertions(+)
 create mode 100644 providers/chain/provider.go

diff --git a/providers/chain/provider.go b/providers/chain/provider.go
new file mode 100644
index 0000000..f7248a7
--- /dev/null
+++ b/providers/chain/provider.go
@@ -0,0 +1,76 @@
+/*
+Copyright 2025 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package chain
+
+import (
+	"context"
+	"errors"
+
+	"sigs.k8s.io/controller-runtime/pkg/client"
+	"sigs.k8s.io/controller-runtime/pkg/cluster"
+
+	"sigs.k8s.io/multicluster-runtime/pkg/multicluster"
+)
+
+var _ multicluster.Provider = &Provider{}
+
+// Provider is a multicluster.Provider that chains multiple providers
+// together.
+type Provider struct {
+	providers []multicluster.Provider
+}
+
+// New creates a new provider to chain multiple providers together.
+// The providers are expected to be started.
+func New(providers ...multicluster.Provider) *Provider {
+	return &Provider{
+		providers: providers,
+	}
+}
+
+// Add adds a new provider to the chain.
+func (p *Provider) Add(provider multicluster.Provider) {
+	p.providers = append(p.providers, provider)
+}
+
+// Get iterates over the chained providers and calls Get on each of them
+// in the order they were passed to New or added, returning the first
+// found cluster.
+// If any provider returns an unexpected error the error is returned
+// immediately.
+func (p *Provider) Get(ctx context.Context, clusterName string) (cluster.Cluster, error) {
+	for _, provider := range p.providers {
+		cluster, err := provider.Get(ctx, clusterName)
+		if err == nil {
+			return cluster, nil
+		}
+		if !errors.Is(err, multicluster.ErrClusterNotFound) {
+			return nil, err
+		}
+	}
+	return nil, multicluster.ErrClusterNotFound
+}
+
+// IndexField iterates over the chained providers and calls IndexField
+// on each of them. The errors are aggregated and returned.
+func (p *Provider) IndexField(ctx context.Context, obj client.Object, field string, indexer client.IndexerFunc) error {
+	var errs error
+	for _, provider := range p.providers {
+		errs = errors.Join(errs, provider.IndexField(ctx, obj, field, indexer))
+	}
+	return errs
+}