// Copyright 2019-2020 Google LLC
//
// 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
//
//     https://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 storage implements an interface that can be implemented by
// storage backends, such as Google Cloud Storage or the local
// filesystem.
package storage

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

type Persister = func(io.Writer) (string, int64, error)

type Backend interface {
	// Name returns the name of the storage backend, for use in
	// log messages and such.
	Name() string

	// Persist provides a user-supplied function with a writer
	// that stores data in the storage backend.
	//
	// It needs to return the SHA256 hash of the data written as
	// well as the total number of bytes, as those are required
	// for the image manifest.
	Persist(ctx context.Context, path, contentType string, f Persister) (string, int64, error)

	// Fetch retrieves data from the storage backend.
	Fetch(ctx context.Context, path string) (io.ReadCloser, error)

	// Move renames a path inside the storage backend. This is
	// used for staging uploads while calculating their hashes.
	Move(ctx context.Context, old, new string) error

	// Serve provides a handler function to serve HTTP requests
	// for objects in the storage backend.
	Serve(digest string, r *http.Request, w http.ResponseWriter) error
}