/*
Copyright 2014 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 generic

import (
	"k8s.io/kubernetes/pkg/api"
	"k8s.io/kubernetes/pkg/fields"
	"k8s.io/kubernetes/pkg/labels"
	"k8s.io/kubernetes/pkg/runtime"
	"k8s.io/kubernetes/pkg/storage"
)

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

// ObjectMetaFieldsSet returns a fields set that represents the ObjectMeta.
func ObjectMetaFieldsSet(objectMeta api.ObjectMeta, hasNamespaceField bool) fields.Set {
	if !hasNamespaceField {
		return fields.Set{
			"metadata.name": objectMeta.Name,
		}
	}
	return fields.Set{
		"metadata.name":      objectMeta.Name,
		"metadata.namespace": objectMeta.Namespace,
	}
}

// MergeFieldsSets merges a fields'set from fragment into the source.
func MergeFieldsSets(source fields.Set, fragment fields.Set) fields.Set {
	for k, value := range fragment {
		source[k] = value
	}
	return source
}

// 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       fields.Selector
	GetAttrs    AttrFunc
	IndexFields []string
}

// 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
}

// MatchesSingle will return (name, true) if and only if s.Field matches on the object's
// name.
func (s *SelectionPredicate) MatchesSingle() (string, bool) {
	// TODO: should be namespace.name
	if name, ok := s.Field.RequiresExactMatch("metadata.name"); ok {
		return name, true
	}
	return "", false
}

// For any index defined by IndexFields, if a matcher can match only (a subset)
// of objects that return <value> for a given index, a pair (<index name>, <value>)
// wil be returned.
// TODO: Consider supporting also labels.
func (s *SelectionPredicate) MatcherIndex() []storage.MatchValue {
	var result []storage.MatchValue
	for _, field := range s.IndexFields {
		if value, ok := s.Field.RequiresExactMatch(field); ok {
			result = append(result, storage.MatchValue{IndexName: field, Value: value})
		}
	}
	return result
}

// Matcher can return true if an object matches the Matcher's selection
// criteria. If it is known that the matcher will match only a single object
// then MatchesSingle should return the key of that object and true. This is an
// optimization only--Matches() should continue to work.
type Matcher interface {
	// Matches should return true if obj matches this matcher's requirements.
	Matches(obj runtime.Object) (matchesThisObject bool, err error)

	// If this matcher matches a single object, return the key for that
	// object and true here. This will greatly increase efficiency. You
	// must still implement Matches(). Note that key does NOT need to
	// include the object's namespace.
	MatchesSingle() (key string, matchesSingleObject bool)

	// For any known index, if a matcher can match only (a subset) of objects
	// that return <value> for a given index, a pair (<index name>, <value>)
	// will be returned.
	MatcherIndex() []storage.MatchValue
}

// MatcherFunc makes a matcher from the provided function. For easy definition
// of matchers for testing. Note: use SelectionPredicate above for real code!
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)
}

// MatchesSingle always returns "", false-- because this is a predicate
// implementation of Matcher.
func (m matcherFunc) MatchesSingle() (string, bool) {
	return "", false
}

// MatcherIndex always returns empty list.
func (m matcherFunc) MatcherIndex() []storage.MatchValue {
	return nil
}

// MatchOnKey returns a matcher that will send only the object matching key
// through the matching function f. For testing!
// Note: use SelectionPredicate above for real code!
func MatchOnKey(key string, f func(obj runtime.Object) (bool, error)) Matcher {
	return matchKey{key, f}
}

type matchKey struct {
	key string
	matcherFunc
}

// MatchesSingle always returns its key, true.
func (m matchKey) MatchesSingle() (string, bool) {
	return m.key, true
}

var (
	// Assert implementations match the interface.
	_ = Matcher(matchKey{})
	_ = Matcher(&SelectionPredicate{})
	_ = Matcher(matcherFunc(nil))
)