/*
Copyright 2018 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 transformers

import (
	"fmt"
	"log"

	"sigs.k8s.io/kustomize/pkg/gvk"
	"sigs.k8s.io/kustomize/pkg/resid"
	"sigs.k8s.io/kustomize/pkg/resmap"
	"sigs.k8s.io/kustomize/pkg/transformers/config"
)

type nameReferenceTransformer struct {
	backRefs []config.NameBackReferences
}

var _ Transformer = &nameReferenceTransformer{}

// NewNameReferenceTransformer constructs a nameReferenceTransformer
// with a given slice of NameBackReferences.
func NewNameReferenceTransformer(br []config.NameBackReferences) Transformer {
	if br == nil {
		log.Fatal("backrefs not expected to be nil")
	}
	return &nameReferenceTransformer{backRefs: br}
}

// Transform updates name references in resource A that
// refer to resource B, given that B's name may have
// changed.
//
// For example, a HorizontalPodAutoscaler (HPA)
// necessarily refers to a Deployment, the thing that
// the HPA scales. The Deployment name might change
// (e.g. prefix added), and the reference in the HPA
// has to be fixed.
//
// In the outer loop over the ResMap below, say we
// encounter a specific HPA. Then, in scanning backrefs,
// we encounter an entry like
//
//   - kind: Deployment
//     fieldSpecs:
//     - path: spec/scaleTargetRef/name
//       kind: HorizontalPodAutoscaler
//
// saying that an HPA, via its 'spec/scaleTargetRef/name'
// field, may refer to a Deployment.  This match to HPA
// means we may need to modify the value in its
// 'spec/scaleTargetRef/name' field, by searching for
// the thing it refers to, and getting its new name.
//
// As a filter, and search optimization, we compute a
// subset of all resources that the HPA could refer to,
// by excluding objects from other namespaces, and
// excluding objects that don't have the same prefix-
// suffix mods as the HPA.
//
// We look in this subset for all Deployment objects
// with a resId that has a Name matching the field value
// present in the HPA.  If no match do nothing; if more
// than one match, it's an error.
//
// We overwrite the HPA name field with the value found
// in the Deployment's name field (the name in the raw
// object - the modified name - not the unmodified name
// in the Deployment's resId).
//
// This process assumes that the name stored in a ResId
// (the ResMap key) isn't modified by name transformers.
// Name transformers should only modify the name in the
// body of the resource object (the value in the ResMap).
//
func (o *nameReferenceTransformer) Transform(m resmap.ResMap) error {
	// TODO: Too much looping, here and in transitive calls.
	for referrer, res := range m.AsMap() {
		var candidates resmap.ResMap
		for _, target := range o.backRefs {
			for _, fSpec := range target.FieldSpecs {
				if referrer.Gvk().IsSelected(&fSpec.Gvk) {
					if candidates == nil {
						candidates = m.SubsetThatCouldBeReferencedBy(referrer)
					}
					err := mutateField(
						res.Map(),
						fSpec.PathSlice(),
						fSpec.CreateIfNotPresent,
						o.getNewName(
							referrer, target.Gvk, candidates))
					if err != nil {
						return err
					}
				}
			}
		}
	}
	return nil
}

func (o *nameReferenceTransformer) getNewName(
	referrer resid.ResId,
	target gvk.Gvk,
	referralCandidates resmap.ResMap) func(in interface{}) (interface{}, error) {
	return func(in interface{}) (interface{}, error) {
		switch in.(type) {
		case string:
			oldName, _ := in.(string)
			for id, res := range referralCandidates.AsMap() {
				if id.Gvk().IsSelected(&target) && id.Name() == oldName {
					matchedIds := referralCandidates.GetMatchingIds(id.GvknEquals)
					// If there's more than one match, there's no way
					// to know which one to pick, so emit error.
					if len(matchedIds) > 1 {
						return nil, fmt.Errorf(
							"Multiple matches for name %s:\n  %v", id, matchedIds)
					}
					// In the resource, note that it is referenced
					// by the referrer.
					res.AppendRefBy(referrer)
					// Return transformed name of the object,
					// complete with prefixes, hashes, etc.
					return res.GetName(), nil
				}
			}
			return in, nil
		case []interface{}:
			l, _ := in.([]interface{})
			var names []string
			for _, item := range l {
				name, ok := item.(string)
				if !ok {
					return nil, fmt.Errorf(
						"%#v is expected to be %T", item, name)
				}
				names = append(names, name)
			}
			for id, res := range referralCandidates.AsMap() {
				indexes := indexOf(id.Name(), names)
				if id.Gvk().IsSelected(&target) && len(indexes) > 0 {
					matchedIds := referralCandidates.GetMatchingIds(id.GvknEquals)
					if len(matchedIds) > 1 {
						return nil, fmt.Errorf(
							"Multiple matches for name %s:\n %v", id, matchedIds)
					}
					for _, index := range indexes {
						l[index] = res.GetName()
					}
					res.AppendRefBy(referrer)
					return l, nil
				}
			}
			return in, nil
		default:
			return nil, fmt.Errorf(
				"%#v is expected to be either a string or a []interface{}", in)
		}
	}
}

func indexOf(s string, slice []string) []int {
	var index []int
	for i, item := range slice {
		if item == s {
			index = append(index, i)
		}
	}
	return index
}