/*
Copyright 2014 Google Inc. All rights reserved.

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 generic

import (
	"github.com/GoogleCloudPlatform/kubernetes/pkg/api"
	"github.com/GoogleCloudPlatform/kubernetes/pkg/labels"
	"github.com/GoogleCloudPlatform/kubernetes/pkg/runtime"
	"github.com/GoogleCloudPlatform/kubernetes/pkg/watch"
)

// AttrFunc returns label and field sets for List or Watch to compare against, or an error.
type AttrFunc func(obj runtime.Object) (label, field labels.Set, err error)

// SelectionPredicate implements a generic predicate that can be passed to
// GenericRegistry's List or Watch methods. Implements the Matcher interface.
type SelectionPredicate struct {
	Label    labels.Selector
	Field    labels.Selector
	GetAttrs AttrFunc
}

// Matches returns true if the given object's labels and fields (as
// returned by s.GetAttrs) match s.Label and s.Field. An error is
// returned if s.GetAttrs fails.
func (s *SelectionPredicate) Matches(obj runtime.Object) (bool, error) {
	if s.Label.Empty() && s.Field.Empty() {
		return true, nil
	}
	labels, fields, err := s.GetAttrs(obj)
	if err != nil {
		return false, err
	}
	return s.Label.Matches(labels) && s.Field.Matches(fields), nil
}

// Matcher can return true if an object matches the Matcher's selection
// criteria.
type Matcher interface {
	Matches(obj runtime.Object) (bool, error)
}

// MatcherFunc makes a matcher from the provided function. For easy definition
// of matchers for testing.
func MatcherFunc(f func(obj runtime.Object) (bool, error)) Matcher {
	return matcherFunc(f)
}

type matcherFunc func(obj runtime.Object) (bool, error)

// Matches calls the embedded function.
func (m matcherFunc) Matches(obj runtime.Object) (bool, error) {
	return m(obj)
}

// Registry knows how to store & list any runtime.Object. Can be used for
// any object types which don't require special features from the storage
// layer.
type Registry interface {
	List(api.Context, Matcher) (runtime.Object, error)
	Create(ctx api.Context, id string, obj runtime.Object) error
	Update(ctx api.Context, id string, obj runtime.Object) error
	Get(ctx api.Context, id string) (runtime.Object, error)
	Delete(ctx api.Context, id string) error
	Watch(ctx api.Context, m Matcher, resourceVersion string) (watch.Interface, error)
}

// FilterList filters any list object that conforms to the api conventions,
// provided that 'm' works with the concrete type of list.
func FilterList(list runtime.Object, m Matcher) (filtered runtime.Object, err error) {
	// TODO: push a matcher down into tools.EtcdHelper to avoid all this
	// nonsense. This is a lot of unnecessary copies.
	items, err := runtime.ExtractList(list)
	if err != nil {
		return nil, err
	}
	var filteredItems []runtime.Object
	for _, obj := range items {
		match, err := m.Matches(obj)
		if err != nil {
			return nil, err
		}
		if match {
			filteredItems = append(filteredItems, obj)
		}
	}
	err = runtime.SetList(list, filteredItems)
	if err != nil {
		return nil, err
	}
	return list, nil
}