/*
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 merge

import (
	"fmt"

	"sigs.k8s.io/structured-merge-diff/fieldpath"
	"sigs.k8s.io/structured-merge-diff/typed"
)

// Converter is an interface to the conversion logic. The converter
// needs to be able to convert objects from one version to another.
type Converter interface {
	Convert(object typed.TypedValue, version fieldpath.APIVersion) (typed.TypedValue, error)
	IsMissingVersionError(error) bool
}

// Updater is the object used to compute updated FieldSets and also
// merge the object on Apply.
type Updater struct {
	Converter Converter
}

func (s *Updater) update(oldObject, newObject typed.TypedValue, version fieldpath.APIVersion, managers fieldpath.ManagedFields, workflow string, force bool) (fieldpath.ManagedFields, error) {
	conflicts := fieldpath.ManagedFields{}
	removed := fieldpath.ManagedFields{}
	type Versioned struct {
		oldObject typed.TypedValue
		newObject typed.TypedValue
	}
	versions := map[fieldpath.APIVersion]Versioned{
		version: Versioned{
			oldObject: oldObject,
			newObject: newObject,
		},
	}

	for manager, managerSet := range managers {
		if manager == workflow {
			continue
		}
		versioned, ok := versions[managerSet.APIVersion]
		if !ok {
			var err error
			versioned.oldObject, err = s.Converter.Convert(oldObject, managerSet.APIVersion)
			if err != nil {
				if s.Converter.IsMissingVersionError(err) {
					delete(managers, manager)
					continue
				}
				return nil, fmt.Errorf("failed to convert old object: %v", err)
			}
			versioned.newObject, err = s.Converter.Convert(newObject, managerSet.APIVersion)
			if err != nil {
				if s.Converter.IsMissingVersionError(err) {
					delete(managers, manager)
					continue
				}
				return nil, fmt.Errorf("failed to convert new object: %v", err)
			}
			versions[managerSet.APIVersion] = versioned
		}
		compare, err := versioned.oldObject.Compare(versioned.newObject)
		if err != nil {
			return nil, fmt.Errorf("failed to compare objects: %v", err)
		}

		conflictSet := managerSet.Intersection(compare.Modified.Union(compare.Added))
		if !conflictSet.Empty() {
			conflicts[manager] = &fieldpath.VersionedSet{
				Set:        conflictSet,
				APIVersion: managerSet.APIVersion,
			}
		}

		if !compare.Removed.Empty() {
			removed[manager] = &fieldpath.VersionedSet{
				Set:        compare.Removed,
				APIVersion: managerSet.APIVersion,
			}
		}
	}

	if !force && len(conflicts) != 0 {
		return nil, ConflictsFromManagers(conflicts)
	}

	for manager, conflictSet := range conflicts {
		managers[manager].Set = managers[manager].Set.Difference(conflictSet.Set)
	}

	for manager, removedSet := range removed {
		managers[manager].Set = managers[manager].Set.Difference(removedSet.Set)
	}

	for manager := range managers {
		if managers[manager].Set.Empty() {
			delete(managers, manager)
		}
	}

	return managers, nil
}

// Update is the method you should call once you've merged your final
// object on CREATE/UPDATE/PATCH verbs. newObject must be the object
// that you intend to persist (after applying the patch if this is for a
// PATCH call), and liveObject must be the original object (empty if
// this is a CREATE call).
func (s *Updater) Update(liveObject, newObject typed.TypedValue, version fieldpath.APIVersion, managers fieldpath.ManagedFields, manager string) (fieldpath.ManagedFields, error) {
	var err error
	managers = shallowCopyManagers(managers)
	managers, err = s.update(liveObject, newObject, version, managers, manager, true)
	if err != nil {
		return fieldpath.ManagedFields{}, err
	}
	compare, err := liveObject.Compare(newObject)
	if err != nil {
		return fieldpath.ManagedFields{}, fmt.Errorf("failed to compare live and new objects: %v", err)
	}
	if _, ok := managers[manager]; !ok {
		managers[manager] = &fieldpath.VersionedSet{
			Set: fieldpath.NewSet(),
		}
	}
	managers[manager].Set = managers[manager].Set.Union(compare.Modified).Union(compare.Added).Difference(compare.Removed)
	managers[manager].APIVersion = version
	if managers[manager].Set.Empty() {
		delete(managers, manager)
	}
	return managers, nil
}

// Apply should be called when Apply is run, given the current object as
// well as the configuration that is applied. This will merge the object
// and return it.
func (s *Updater) Apply(liveObject, configObject typed.TypedValue, version fieldpath.APIVersion, managers fieldpath.ManagedFields, manager string, force bool) (typed.TypedValue, fieldpath.ManagedFields, error) {
	managers = shallowCopyManagers(managers)
	newObject, err := liveObject.Merge(configObject)
	if err != nil {
		return nil, fieldpath.ManagedFields{}, fmt.Errorf("failed to merge config: %v", err)
	}
	lastSet := managers[manager]
	set, err := configObject.ToFieldSet()
	if err != nil {
		return nil, fieldpath.ManagedFields{}, fmt.Errorf("failed to get field set: %v", err)
	}
	managers[manager] = &fieldpath.VersionedSet{
		Set:        set,
		APIVersion: version,
		Applied:    true,
	}
	newObject, err = s.prune(newObject, managers, manager, lastSet)
	if err != nil {
		return nil, fieldpath.ManagedFields{}, fmt.Errorf("failed to prune fields: %v", err)
	}
	managers, err = s.update(liveObject, newObject, version, managers, manager, force)
	if err != nil {
		return nil, fieldpath.ManagedFields{}, err
	}
	return newObject, managers, nil
}

func shallowCopyManagers(managers fieldpath.ManagedFields) fieldpath.ManagedFields {
	newManagers := fieldpath.ManagedFields{}
	for manager, set := range managers {
		newManagers[manager] = set
	}
	return newManagers
}

// prune will remove a list or map item, iff:
// * applyingManager applied it last time
// * applyingManager didn't apply it this time
// * no other applier claims to manage it
func (s *Updater) prune(merged typed.TypedValue, managers fieldpath.ManagedFields, applyingManager string, lastSet *fieldpath.VersionedSet) (typed.TypedValue, error) {
	if lastSet == nil || lastSet.Set.Empty() {
		return merged, nil
	}
	convertedMerged, err := s.Converter.Convert(merged, lastSet.APIVersion)
	if err != nil {
		if s.Converter.IsMissingVersionError(err) {
			return merged, nil
		}
		return nil, fmt.Errorf("failed to convert merged object to last applied version: %v", err)
	}
	pruned := convertedMerged.RemoveItems(lastSet.Set)
	pruned, err = s.addBackOwnedItems(convertedMerged, pruned, managers, applyingManager)
	if err != nil {
		return nil, fmt.Errorf("failed add back owned items: %v", err)
	}
	pruned, err = s.addBackDanglingItems(convertedMerged, pruned, lastSet)
	if err != nil {
		return nil, fmt.Errorf("failed add back dangling items: %v", err)
	}
	return s.Converter.Convert(pruned, managers[applyingManager].APIVersion)
}

// addBackOwnedItems adds back any list and map items that were removed by prune,
// but other appliers (or the current applier's new config) claim to own.
func (s *Updater) addBackOwnedItems(merged, pruned typed.TypedValue, managedFields fieldpath.ManagedFields, applyingManager string) (typed.TypedValue, error) {
	var err error
	managedAtVersion := map[fieldpath.APIVersion]*fieldpath.Set{}
	for _, managerSet := range managedFields {
		if managerSet.Applied {
			if _, ok := managedAtVersion[managerSet.APIVersion]; !ok {
				managedAtVersion[managerSet.APIVersion] = fieldpath.NewSet()
			}
			managedAtVersion[managerSet.APIVersion] = managedAtVersion[managerSet.APIVersion].Union(managerSet.Set)
		}
	}
	for version, managed := range managedAtVersion {
		merged, err = s.Converter.Convert(merged, version)
		if err != nil {
			if s.Converter.IsMissingVersionError(err) {
				continue
			}
			return nil, fmt.Errorf("failed to convert merged object at version %v: %v", version, err)
		}
		pruned, err = s.Converter.Convert(pruned, version)
		if err != nil {
			if s.Converter.IsMissingVersionError(err) {
				continue
			}
			return nil, fmt.Errorf("failed to convert pruned object at version %v: %v", version, err)
		}
		mergedSet, err := merged.ToFieldSet()
		if err != nil {
			return nil, fmt.Errorf("failed to create field set from merged object at version %v: %v", version, err)
		}
		prunedSet, err := pruned.ToFieldSet()
		if err != nil {
			return nil, fmt.Errorf("failed to create field set from pruned object at version %v: %v", version, err)
		}
		pruned = merged.RemoveItems(mergedSet.Difference(prunedSet.Union(managed)))
	}
	return pruned, nil
}


// addBackDanglingItems makes sure that the only items removed by prune are items that were
// previously owned by the currently applying manager. This will add back unowned items and items
// which are owned by Updaters that shouldn't be removed.
func (s *Updater) addBackDanglingItems(merged, pruned typed.TypedValue, lastSet *fieldpath.VersionedSet) (typed.TypedValue, error) {
	convertedPruned, err := s.Converter.Convert(pruned, lastSet.APIVersion)
	if err != nil {
		if s.Converter.IsMissingVersionError(err) {
			return merged, nil
		}
		return nil, fmt.Errorf("failed to convert pruned object to last applied version: %v", err)
	}
	prunedSet, err := convertedPruned.ToFieldSet()
	if err != nil {
		return nil, fmt.Errorf("failed to create field set from pruned object in last applied version: %v", err)
	}
	mergedSet, err := merged.ToFieldSet()
	if err != nil {
		return nil, fmt.Errorf("failed to create field set from merged object in last applied version: %v", err)
	}
	return merged.RemoveItems(mergedSet.Difference(prunedSet).Intersection(lastSet.Set)), nil
}