/*
Copyright 2014 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 rest

import (
	"context"
	"io"
	"net/http"
	"net/url"

	metainternalversion "k8s.io/apimachinery/pkg/apis/meta/internalversion"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apimachinery/pkg/runtime"
	"k8s.io/apimachinery/pkg/runtime/schema"
	"k8s.io/apimachinery/pkg/watch"
	"sigs.k8s.io/structured-merge-diff/v4/fieldpath"
)

//TODO:
// Storage interfaces need to be separated into two groups; those that operate
// on collections and those that operate on individually named items.
// Collection interfaces:
// (Method: Current -> Proposed)
//    GET: Lister -> CollectionGetter
//    WATCH: Watcher -> CollectionWatcher
//    CREATE: Creater -> CollectionCreater
//    DELETE: (n/a) -> CollectionDeleter
//    UPDATE: (n/a) -> CollectionUpdater
//
// Single item interfaces:
// (Method: Current -> Proposed)
//    GET: Getter -> NamedGetter
//    WATCH: (n/a) -> NamedWatcher
//    CREATE: (n/a) -> NamedCreater
//    DELETE: Deleter -> NamedDeleter
//    UPDATE: Update -> NamedUpdater

// Storage is a generic interface for RESTful storage services.
// Resources which are exported to the RESTful API of apiserver need to implement this interface. It is expected
// that objects may implement any of the below interfaces.
type Storage interface {
	// New returns an empty object that can be used with Create and Update after request data has been put into it.
	// This object must be a pointer type for use with Codec.DecodeInto([]byte, runtime.Object)
	New() runtime.Object

	// Destroy cleans up its resources on shutdown.
	// Destroy has to be implemented in thread-safe way and be prepared
	// for being called more than once.
	Destroy()
}

// Scoper indicates what scope the resource is at. It must be specified.
// It is usually provided automatically based on your strategy.
type Scoper interface {
	// NamespaceScoped returns true if the storage is namespaced
	NamespaceScoped() bool
}

// KindProvider specifies a different kind for its API than for its internal storage.  This is necessary for external
// objects that are not compiled into the api server.  For such objects, there is no in-memory representation for
// the object, so they must be represented as generic objects (e.g. runtime.Unknown), but when we present the object as part of
// API discovery we want to present the specific kind, not the generic internal representation.
type KindProvider interface {
	Kind() string
}

// ShortNamesProvider is an interface for RESTful storage services. Delivers a list of short names for a resource. The list is used by kubectl to have short names representation of resources.
type ShortNamesProvider interface {
	ShortNames() []string
}

// CategoriesProvider allows a resource to specify which groups of resources (categories) it's part of. Categories can
// be used by API clients to refer to a batch of resources by using a single name (e.g. "all" could translate to "pod,rc,svc,...").
type CategoriesProvider interface {
	Categories() []string
}

// SingularNameProvider returns singular name of resources. This is used by kubectl discovery to have singular
// name representation of resources. In case of shortcut conflicts(with CRD shortcuts) singular name should always map to this resource.
type SingularNameProvider interface {
	GetSingularName() string
}

// GroupVersionKindProvider is used to specify a particular GroupVersionKind to discovery.  This is used for polymorphic endpoints
// which generally point to foreign versions.  Scale refers to Scale.v1beta1.extensions for instance.
// This trumps KindProvider since it is capable of providing the information required.
// TODO KindProvider (only used by federation) should be removed and replaced with this, but that presents greater risk late in 1.8.
type GroupVersionKindProvider interface {
	GroupVersionKind(containingGV schema.GroupVersion) schema.GroupVersionKind
}

// GroupVersionAcceptor is used to determine if a particular GroupVersion is acceptable to send to an endpoint.
// This is used for endpoints which accept multiple versions (which is extremely rare).
// The only known instance is pods/evictions which accepts policy/v1, but also policy/v1beta1 for backwards compatibility.
type GroupVersionAcceptor interface {
	AcceptsGroupVersion(gv schema.GroupVersion) bool
}

// Lister is an object that can retrieve resources that match the provided field and label criteria.
type Lister interface {
	// NewList returns an empty object that can be used with the List call.
	// This object must be a pointer type for use with Codec.DecodeInto([]byte, runtime.Object)
	NewList() runtime.Object
	// List selects resources in the storage which match to the selector. 'options' can be nil.
	List(ctx context.Context, options *metainternalversion.ListOptions) (runtime.Object, error)
	// TableConvertor ensures all list implementers also implement table conversion
	TableConvertor
}

// Getter is an object that can retrieve a named RESTful resource.
type Getter interface {
	// Get finds a resource in the storage by name and returns it.
	// Although it can return an arbitrary error value, IsNotFound(err) is true for the
	// returned error value err when the specified resource is not found.
	Get(ctx context.Context, name string, options *metav1.GetOptions) (runtime.Object, error)
}

// GetterWithOptions is an object that retrieve a named RESTful resource and takes
// additional options on the get request. It allows a caller to also receive the
// subpath of the GET request.
type GetterWithOptions interface {
	// Get finds a resource in the storage by name and returns it.
	// Although it can return an arbitrary error value, IsNotFound(err) is true for the
	// returned error value err when the specified resource is not found.
	// The options object passed to it is of the same type returned by the NewGetOptions
	// method.
	// TODO: Pass metav1.GetOptions.
	Get(ctx context.Context, name string, options runtime.Object) (runtime.Object, error)

	// NewGetOptions returns an empty options object that will be used to pass
	// options to the Get method. It may return a bool and a string, if true, the
	// value of the request path below the object will be included as the named
	// string in the serialization of the runtime object. E.g., returning "path"
	// will convert the trailing request scheme value to "path" in the map[string][]string
	// passed to the converter.
	NewGetOptions() (runtime.Object, bool, string)
}

type TableConvertor interface {
	ConvertToTable(ctx context.Context, object runtime.Object, tableOptions runtime.Object) (*metav1.Table, error)
}

// GracefulDeleter knows how to pass deletion options to allow delayed deletion of a
// RESTful object.
type GracefulDeleter interface {
	// Delete finds a resource in the storage and deletes it.
	// The delete attempt is validated by the deleteValidation first.
	// If options are provided, the resource will attempt to honor them or return an invalid
	// request error.
	// Although it can return an arbitrary error value, IsNotFound(err) is true for the
	// returned error value err when the specified resource is not found.
	// Delete *may* return the object that was deleted, or a status object indicating additional
	// information about deletion.
	// It also returns a boolean which is set to true if the resource was instantly
	// deleted or false if it will be deleted asynchronously.
	Delete(ctx context.Context, name string, deleteValidation ValidateObjectFunc, options *metav1.DeleteOptions) (runtime.Object, bool, error)
}

// MayReturnFullObjectDeleter may return deleted object (instead of a simple status) on deletion.
type MayReturnFullObjectDeleter interface {
	DeleteReturnsDeletedObject() bool
}

// CollectionDeleter is an object that can delete a collection
// of RESTful resources.
type CollectionDeleter interface {
	// DeleteCollection selects all resources in the storage matching given 'listOptions'
	// and deletes them. The delete attempt is validated by the deleteValidation first.
	// If 'options' are provided, the resource will attempt to honor them or return an
	// invalid request error.
	// DeleteCollection may not be atomic - i.e. it may delete some objects and still
	// return an error after it. On success, returns a list of deleted objects.
	DeleteCollection(ctx context.Context, deleteValidation ValidateObjectFunc, options *metav1.DeleteOptions, listOptions *metainternalversion.ListOptions) (runtime.Object, error)
}

// Creater is an object that can create an instance of a RESTful object.
type Creater interface {
	// New returns an empty object that can be used with Create after request data has been put into it.
	// This object must be a pointer type for use with Codec.DecodeInto([]byte, runtime.Object)
	New() runtime.Object

	// Create creates a new version of a resource.
	Create(ctx context.Context, obj runtime.Object, createValidation ValidateObjectFunc, options *metav1.CreateOptions) (runtime.Object, error)
}

// NamedCreater is an object that can create an instance of a RESTful object using a name parameter.
type NamedCreater interface {
	// New returns an empty object that can be used with Create after request data has been put into it.
	// This object must be a pointer type for use with Codec.DecodeInto([]byte, runtime.Object)
	New() runtime.Object

	// Create creates a new version of a resource. It expects a name parameter from the path.
	// This is needed for create operations on subresources which include the name of the parent
	// resource in the path.
	Create(ctx context.Context, name string, obj runtime.Object, createValidation ValidateObjectFunc, options *metav1.CreateOptions) (runtime.Object, error)
}

// SubresourceObjectMetaPreserver adds configuration options to a Creater for subresources.
type SubresourceObjectMetaPreserver interface {
	// PreserveRequestObjectMetaSystemFieldsOnSubresourceCreate indicates that a
	// handler should preserve fields of ObjectMeta that are managed by the system.
	PreserveRequestObjectMetaSystemFieldsOnSubresourceCreate() bool
}

// UpdatedObjectInfo provides information about an updated object to an Updater.
// It requires access to the old object in order to return the newly updated object.
type UpdatedObjectInfo interface {
	// Returns preconditions built from the updated object, if applicable.
	// May return nil, or a preconditions object containing nil fields,
	// if no preconditions can be determined from the updated object.
	Preconditions() *metav1.Preconditions

	// UpdatedObject returns the updated object, given a context and old object.
	// The only time an empty oldObj should be passed in is if a "create on update" is occurring (there is no oldObj).
	UpdatedObject(ctx context.Context, oldObj runtime.Object) (newObj runtime.Object, err error)
}

// ValidateObjectFunc is a function to act on a given object. An error may be returned
// if the hook cannot be completed. A ValidateObjectFunc may NOT transform the provided
// object.
type ValidateObjectFunc func(ctx context.Context, obj runtime.Object) error

// ValidateAllObjectFunc is a "admit everything" instance of ValidateObjectFunc.
func ValidateAllObjectFunc(ctx context.Context, obj runtime.Object) error {
	return nil
}

// ValidateObjectUpdateFunc is a function to act on a given object and its predecessor.
// An error may be returned if the hook cannot be completed. An UpdateObjectFunc
// may NOT transform the provided object.
type ValidateObjectUpdateFunc func(ctx context.Context, obj, old runtime.Object) error

// ValidateAllObjectUpdateFunc is a "admit everything" instance of ValidateObjectUpdateFunc.
func ValidateAllObjectUpdateFunc(ctx context.Context, obj, old runtime.Object) error {
	return nil
}

// Updater is an object that can update an instance of a RESTful object.
type Updater interface {
	// New returns an empty object that can be used with Update after request data has been put into it.
	// This object must be a pointer type for use with Codec.DecodeInto([]byte, runtime.Object)
	New() runtime.Object

	// Update finds a resource in the storage and updates it. Some implementations
	// may allow updates creates the object - they should set the created boolean
	// to true.
	Update(ctx context.Context, name string, objInfo UpdatedObjectInfo, createValidation ValidateObjectFunc, updateValidation ValidateObjectUpdateFunc, forceAllowCreate bool, options *metav1.UpdateOptions) (runtime.Object, bool, error)
}

// CreaterUpdater is a storage object that must support both create and update.
// Go prevents embedded interfaces that implement the same method.
type CreaterUpdater interface {
	Creater
	Update(ctx context.Context, name string, objInfo UpdatedObjectInfo, createValidation ValidateObjectFunc, updateValidation ValidateObjectUpdateFunc, forceAllowCreate bool, options *metav1.UpdateOptions) (runtime.Object, bool, error)
}

// CreaterUpdater must satisfy the Updater interface.
var _ Updater = CreaterUpdater(nil)

// Patcher is a storage object that supports both get and update.
type Patcher interface {
	Getter
	Updater
}

// Watcher should be implemented by all Storage objects that
// want to offer the ability to watch for changes through the watch api.
type Watcher interface {
	// 'label' selects on labels; 'field' selects on the object's fields. Not all fields
	// are supported; an error should be returned if 'field' tries to select on a field that
	// isn't supported. 'resourceVersion' allows for continuing/starting a watch at a
	// particular version.
	Watch(ctx context.Context, options *metainternalversion.ListOptions) (watch.Interface, error)
}

// StandardStorage is an interface covering the common verbs. Provided for testing whether a
// resource satisfies the normal storage methods. Use Storage when passing opaque storage objects.
type StandardStorage interface {
	Getter
	Lister
	CreaterUpdater
	GracefulDeleter
	CollectionDeleter
	Watcher

	// Destroy cleans up its resources on shutdown.
	// Destroy has to be implemented in thread-safe way and be prepared
	// for being called more than once.
	Destroy()
}

// Redirector know how to return a remote resource's location.
type Redirector interface {
	// ResourceLocation should return the remote location of the given resource, and an optional transport to use to request it, or an error.
	ResourceLocation(ctx context.Context, id string) (remoteLocation *url.URL, transport http.RoundTripper, err error)
}

// Responder abstracts the normal response behavior for a REST method and is passed to callers that
// may wish to handle the response directly in some cases, but delegate to the normal error or object
// behavior in other cases.
type Responder interface {
	// Object writes the provided object to the response. Invoking this method multiple times is undefined.
	Object(statusCode int, obj runtime.Object)
	// Error writes the provided error to the response. This method may only be invoked once.
	Error(err error)
}

// Connecter is a storage object that responds to a connection request.
type Connecter interface {
	// Connect returns an http.Handler that will handle the request/response for a given API invocation.
	// The provided responder may be used for common API responses. The responder will write both status
	// code and body, so the ServeHTTP method should exit after invoking the responder. The Handler will
	// be used for a single API request and then discarded. The Responder is guaranteed to write to the
	// same http.ResponseWriter passed to ServeHTTP.
	Connect(ctx context.Context, id string, options runtime.Object, r Responder) (http.Handler, error)

	// NewConnectOptions returns an empty options object that will be used to pass
	// options to the Connect method. If nil, then a nil options object is passed to
	// Connect. It may return a bool and a string. If true, the value of the request
	// path below the object will be included as the named string in the serialization
	// of the runtime object.
	NewConnectOptions() (runtime.Object, bool, string)

	// ConnectMethods returns the list of HTTP methods handled by Connect
	ConnectMethods() []string
}

// ResourceStreamer is an interface implemented by objects that prefer to be streamed from the server
// instead of decoded directly.
type ResourceStreamer interface {
	// InputStream should return an io.ReadCloser if the provided object supports streaming. The desired
	// api version and an accept header (may be empty) are passed to the call. If no error occurs,
	// the caller may return a flag indicating whether the result should be flushed as writes occur
	// and a content type string that indicates the type of the stream.
	// If a null stream is returned, a StatusNoContent response wil be generated.
	InputStream(ctx context.Context, apiVersion, acceptHeader string) (stream io.ReadCloser, flush bool, mimeType string, err error)
}

// StorageMetadata is an optional interface that callers can implement to provide additional
// information about their Storage objects.
type StorageMetadata interface {
	// ProducesMIMETypes returns a list of the MIME types the specified HTTP verb (GET, POST, DELETE,
	// PATCH) can respond with.
	ProducesMIMETypes(verb string) []string

	// ProducesObject returns an object the specified HTTP verb respond with. It will overwrite storage object if
	// it is not nil. Only the type of the return object matters, the value will be ignored.
	ProducesObject(verb string) interface{}
}

// StorageVersionProvider is an optional interface that a storage object can
// implement if it wishes to disclose its storage version.
type StorageVersionProvider interface {
	// StorageVersion returns a group versioner, which will outputs the gvk
	// an object will be converted to before persisted in etcd, given a
	// list of kinds the object might belong to.
	StorageVersion() runtime.GroupVersioner
}

// ResetFieldsStrategy is an optional interface that a storage object can
// implement if it wishes to provide the fields reset by its strategies.
type ResetFieldsStrategy interface {
	GetResetFields() map[fieldpath.APIVersion]*fieldpath.Set
}

// CreateUpdateResetFieldsStrategy is a union of RESTCreateUpdateStrategy
// and ResetFieldsStrategy.
type CreateUpdateResetFieldsStrategy interface {
	RESTCreateUpdateStrategy
	ResetFieldsStrategy
}

// UpdateResetFieldsStrategy is a union of RESTUpdateStrategy
// and ResetFieldsStrategy.
type UpdateResetFieldsStrategy interface {
	RESTUpdateStrategy
	ResetFieldsStrategy
}
