v2/pkg/genruntime/convertible_spec.go

/*
 * Copyright (c) Microsoft Corporation.
 * Licensed under the MIT license.
 */

package genruntime

import (
	"github.com/rotisserie/eris"
	"k8s.io/apimachinery/pkg/runtime"
	"k8s.io/apimachinery/pkg/runtime/schema"
)

// ConvertibleSpec is implemented by Spec types to allow conversion among the different versions of a given spec
//
// Why do we need both directions of conversion?
//
// Each version of a resource is in a different package, so the implementations of this interface will necessarily be
// referencing types from other packages. If we tried to use an interface with a single method, we'd inevitably end up
// with circular package references:
//
//	+----------------+                    +----------------+
//	|       v1       |                    |       v2       |
//	|   PersonSpec   | --- import v2 ---> |   PersonSpec   |
//	|                |                    |                |
//	| ConvertTo()    | <--- import v1 --- | ConvertTo()    |
//	+----------------+                    +----------------+
//
// Instead, we have to have support for both directions, so that we can always operate from one side of the package
// reference chain:
//
//	+----------------+                    +----------------+
//	|       v1       |                    |       v2       |
//	|   PersonSpec   |                    |   PersonSpec   |
//	|                |                    |                |
//	| ConvertTo()    | --- import v2 ---> |                |
//	| ConvertFrom()  |                    |                |
//	+----------------+                    +----------------+
type ConvertibleSpec interface {
	// ConvertSpecTo will populate the passed Spec by copying over all available information from this one
	ConvertSpecTo(destination ConvertibleSpec) error

	// ConvertSpecFrom will populate this spec by copying over all available information from the passed one
	ConvertSpecFrom(source ConvertibleSpec) error
}

// GetVersionedSpec returns a versioned spec for the provided resource; the original API version used when the
// resource was first created is used to identify the version to return
// TODO: This is currently unused
func GetVersionedSpec(metaObject ARMMetaObject, scheme *runtime.Scheme) (ConvertibleSpec, error) {
	return GetVersionedSpecFromGVK(metaObject, scheme, GetOriginalGVK(metaObject))
}

// GetVersionedSpecFromGVK returns a versioned spec for the provided resource; the original API version used when the
// resource was first created is used to identify the version to return
func GetVersionedSpecFromGVK(metaObject ARMMetaObject, scheme *runtime.Scheme, gvk schema.GroupVersionKind) (ConvertibleSpec, error) {
	rsrc, err := NewEmptyVersionedResourceFromGVK(scheme, gvk)
	if err != nil {
		return nil, eris.Wrap(err, "getting versioned spec")
	}

	if rsrc.GetObjectKind().GroupVersionKind() == metaObject.GetObjectKind().GroupVersionKind() {
		// No conversion needed, empty resource is the same GVK that we already have
		return metaObject.GetSpec(), nil
	}

	// Get a blank spec and populate it
	spec := rsrc.GetSpec()
	err = spec.ConvertSpecFrom(metaObject.GetSpec())
	if err != nil {
		return nil, eris.Wrap(err, "failed conversion of spec")
	}

	return spec, nil
}