/*
Copyright 2016 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 registry

import (
	"context"
	"net/http"

	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apimachinery/pkg/watch"
)

type decoratedWatcher struct {
	w         watch.Interface
	decorator ObjectFunc
	cancel    context.CancelFunc
	resultCh  chan watch.Event
}

func newDecoratedWatcher(ctx context.Context, w watch.Interface, decorator ObjectFunc) *decoratedWatcher {
	ctx, cancel := context.WithCancel(ctx)
	d := &decoratedWatcher{
		w:         w,
		decorator: decorator,
		cancel:    cancel,
		resultCh:  make(chan watch.Event),
	}
	go d.run(ctx)
	return d
}

// run decorates watch events from the underlying watcher until its result channel
// is closed or the passed in context is done.
// When run() returns, decoratedWatcher#resultCh is closed.
func (d *decoratedWatcher) run(ctx context.Context) {
	var recv, send watch.Event
	var ok bool
	defer close(d.resultCh)
	for {
		select {
		case recv, ok = <-d.w.ResultChan():
			if !ok {
				// The underlying channel was closed, cancel our context
				d.cancel()
				return
			}
			switch recv.Type {
			case watch.Added, watch.Modified, watch.Deleted, watch.Bookmark:
				err := d.decorator(recv.Object)
				if err != nil {
					send = makeStatusErrorEvent(err)
					break
				}
				send = recv
			case watch.Error:
				send = recv
			}
			select {
			case d.resultCh <- send:
				// propagated event successfully
			case <-ctx.Done():
				// context timed out or was cancelled, stop the underlying watcher
				d.w.Stop()
				return
			}
		case <-ctx.Done():
			// context timed out or was cancelled, stop the underlying watcher
			d.w.Stop()
			return
		}
	}
}

func (d *decoratedWatcher) Stop() {
	// stop the underlying watcher
	d.w.Stop()
	// cancel our context
	d.cancel()
}

func (d *decoratedWatcher) ResultChan() <-chan watch.Event {
	return d.resultCh
}

func makeStatusErrorEvent(err error) watch.Event {
	status := &metav1.Status{
		Status:  metav1.StatusFailure,
		Message: err.Error(),
		Code:    http.StatusInternalServerError,
		Reason:  metav1.StatusReasonInternalError,
	}
	return watch.Event{
		Type:   watch.Error,
		Object: status,
	}
}
