/*
Copyright 2021 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 managedfields

import (
	"bytes"
	"fmt"

	"sigs.k8s.io/structured-merge-diff/v4/fieldpath"
	"sigs.k8s.io/structured-merge-diff/v4/typed"

	"k8s.io/apimachinery/pkg/api/meta"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
	"k8s.io/apimachinery/pkg/runtime"
)

// ExtractInto extracts the applied configuration state from object for fieldManager
// into applyConfiguration. If no managed fields are found for the given fieldManager,
// no error is returned, but applyConfiguration is left unpopulated. It is possible
// that no managed fields were found for the fieldManager because other field managers
// have taken ownership of all the fields previously owned by the fieldManager. It is
// also possible the fieldManager never owned fields.
func ExtractInto(object runtime.Object, objectType typed.ParseableType, fieldManager string, applyConfiguration interface{}) error {
	typedObj, err := toTyped(object, objectType)
	if err != nil {
		return fmt.Errorf("error converting obj to typed: %w", err)
	}

	accessor, err := meta.Accessor(object)
	if err != nil {
		return fmt.Errorf("error accessing metadata: %w", err)
	}
	fieldsEntry, ok := findManagedFields(accessor, fieldManager)
	if !ok {
		return nil
	}
	fieldset := &fieldpath.Set{}
	err = fieldset.FromJSON(bytes.NewReader(fieldsEntry.FieldsV1.Raw))
	if err != nil {
		return fmt.Errorf("error marshalling FieldsV1 to JSON: %w", err)
	}

	u := typedObj.ExtractItems(fieldset.Leaves()).AsValue().Unstructured()
	m, ok := u.(map[string]interface{})
	if !ok {
		return fmt.Errorf("unable to convert managed fields for %s to unstructured, expected map, got %T", fieldManager, u)
	}
	if err := runtime.DefaultUnstructuredConverter.FromUnstructured(m, applyConfiguration); err != nil {
		return fmt.Errorf("error extracting into obj from unstructured: %w", err)
	}
	return nil
}

func findManagedFields(accessor metav1.Object, fieldManager string) (metav1.ManagedFieldsEntry, bool) {
	objManagedFields := accessor.GetManagedFields()
	for _, mf := range objManagedFields {
		if mf.Manager == fieldManager && mf.Operation == metav1.ManagedFieldsOperationApply {
			return mf, true
		}
	}
	return metav1.ManagedFieldsEntry{}, false
}

func toTyped(obj runtime.Object, objectType typed.ParseableType) (*typed.TypedValue, error) {
	switch o := obj.(type) {
	case *unstructured.Unstructured:
		return objectType.FromUnstructured(o.Object)
	default:
		return objectType.FromStructured(o)
	}
}