var (
	// ErrLayerExists returned when layer already exists
	ErrLayerExists = fmt.Errorf("layer exists")

	// ErrLayerTarSumVersionUnsupported when tarsum is unsupported version.
	ErrLayerTarSumVersionUnsupported = fmt.Errorf("unsupported tarsum version")

	// ErrLayerUploadUnknown returned when upload is not found.
	ErrLayerUploadUnknown = fmt.Errorf("layer upload unknown")

	// ErrLayerClosed returned when an operation is attempted on a closed
	// Layer or LayerUpload.
	ErrLayerClosed = fmt.Errorf("layer closed")
)

var GlobalScope = Scope(fullScope{})

type Descriptor struct {
	// MediaType describe the type of the content. All text based formats are
	// encoded as utf-8.
	MediaType string `json:"mediaType,omitempty"`

	// Length in bytes of content.
	Length int64 `json:"length,omitempty"`

	// Digest uniquely identifies the content. A byte stream can be verified
	// against against this digest.
	Digest digest.Digest `json:"digest,omitempty"`
}

type ErrLayerInvalidDigest struct {
	Digest digest.Digest
	Reason error
}

type ErrManifestUnknown struct {
	Name string
	Tag  string
}

type ErrManifestUnverified struct{}

type ErrManifestVerification []error

type ErrRepositoryNameInvalid struct {
	Name   string
	Reason error
}

type ErrRepositoryUnknown struct {
	Name string
}

type ErrUnknownLayer struct {
	FSLayer manifest.FSLayer
}

type ErrUnknownManifestRevision struct {
	Name     string
	Revision digest.Digest
}

type Layer interface {
	// http.ServeContent requires an efficient implementation of
	// ReadSeeker.Seek(0, os.SEEK_END).
	io.ReadSeeker
	io.Closer

	// Digest returns the unique digest of the blob.
	Digest() digest.Digest

	// Length returns the length in bytes of the blob.
	Length() int64

	// CreatedAt returns the time this layer was created.
	CreatedAt() time.Time

	// Handler returns an HTTP handler which serves the layer content, whether
	// by providing a redirect directly to the content, or by serving the
	// content itself.
	Handler(r *http.Request) (http.Handler, error)
}

type LayerService interface {
	// Exists returns true if the layer exists.
	Exists(digest digest.Digest) (bool, error)

	// Fetch the layer identifed by TarSum.
	Fetch(digest digest.Digest) (Layer, error)

	// Upload begins a layer upload to repository identified by name,
	// returning a handle.
	Upload() (LayerUpload, error)

	// Resume continues an in progress layer upload, returning a handle to the
	// upload. The caller should seek to the latest desired upload location
	// before proceeding.
	Resume(uuid string) (LayerUpload, error)
}

type LayerUpload interface {
	io.WriteSeeker
	io.ReaderFrom
	io.Closer

	// UUID returns the identifier for this upload.
	UUID() string

	// StartedAt returns the time this layer upload was started.
	StartedAt() time.Time

	// Finish marks the upload as completed, returning a valid handle to the
	// uploaded layer. The digest is validated against the contents of the
	// uploaded layer.
	Finish(digest digest.Digest) (Layer, error)

	// Cancel the layer upload process.
	Cancel() error
}

type ManifestService interface {
	// Exists returns true if the manifest exists.
	Exists(dgst digest.Digest) (bool, error)

	// Get retrieves the identified by the digest, if it exists.
	Get(dgst digest.Digest) (*manifest.SignedManifest, error)

	// Delete removes the manifest, if it exists.
	Delete(dgst digest.Digest) error

	// Put creates or updates the manifest.
	Put(manifest *manifest.SignedManifest) error

	// Tags lists the tags under the named repository.
	Tags() ([]string, error)

	// ExistsByTag returns true if the manifest exists.
	ExistsByTag(tag string) (bool, error)

	// GetByTag retrieves the named manifest, if it exists.
	GetByTag(tag string) (*manifest.SignedManifest, error)
}

type Namespace interface {
	// Scope describes the names that can be used with this Namespace. The
	// global namespace will have a scope that matches all names. The scope
	// effectively provides an identity for the namespace.
	Scope() Scope

	// Repository should return a reference to the named repository. The
	// registry may or may not have the repository but should always return a
	// reference.
	Repository(ctx context.Context, name string) (Repository, error)
}

type Repository interface {
	// Name returns the name of the repository.
	Name() string

	// Manifests returns a reference to this repository's manifest service.
	Manifests() ManifestService

	// Layers returns a reference to this repository's layers service.
	Layers() LayerService

	// Signatures returns a reference to this repository's signatures service.
	Signatures() SignatureService
}

type Scope interface {
	// Contains returns true if the name belongs to the namespace.
	Contains(name string) bool
}

type SignatureService interface {
	// Get retrieves all of the signature blobs for the specified digest.
	Get(dgst digest.Digest) ([][]byte, error)

	// Put stores the signature for the provided digest.
	Put(dgst digest.Digest, signatures ...[]byte) error
}