package storage

import (
	"net/http"
	"time"

	"github.com/docker/distribution"
	"github.com/docker/distribution/context"
	"github.com/docker/distribution/digest"
	"github.com/docker/distribution/registry/storage/driver"
	"github.com/docker/distribution/uuid"
)

// linkPathFunc describes a function that can resolve a link based on the
// repository name and digest.
type linkPathFunc func(name string, dgst digest.Digest) (string, error)

// linkedBlobStore provides a full BlobService that namespaces the blobs to a
// given repository. Effectively, it manages the links in a given repository
// that grant access to the global blob store.
type linkedBlobStore struct {
	*blobStore
	blobServer             distribution.BlobServer
	blobAccessController   distribution.BlobDescriptorService
	repository             distribution.Repository
	ctx                    context.Context // only to be used where context can't come through method args
	deleteEnabled          bool
	resumableDigestEnabled bool

	// linkPathFns specifies one or more path functions allowing one to
	// control the repository blob link set to which the blob store
	// dispatches. This is required because manifest and layer blobs have not
	// yet been fully merged. At some point, this functionality should be
	// removed an the blob links folder should be merged. The first entry is
	// treated as the "canonical" link location and will be used for writes.
	linkPathFns []linkPathFunc
}

var _ distribution.BlobStore = &linkedBlobStore{}

func (lbs *linkedBlobStore) Stat(ctx context.Context, dgst digest.Digest) (distribution.Descriptor, error) {
	return lbs.blobAccessController.Stat(ctx, dgst)
}

func (lbs *linkedBlobStore) Get(ctx context.Context, dgst digest.Digest) ([]byte, error) {
	canonical, err := lbs.Stat(ctx, dgst) // access check
	if err != nil {
		return nil, err
	}

	return lbs.blobStore.Get(ctx, canonical.Digest)
}

func (lbs *linkedBlobStore) Open(ctx context.Context, dgst digest.Digest) (distribution.ReadSeekCloser, error) {
	canonical, err := lbs.Stat(ctx, dgst) // access check
	if err != nil {
		return nil, err
	}

	return lbs.blobStore.Open(ctx, canonical.Digest)
}

func (lbs *linkedBlobStore) ServeBlob(ctx context.Context, w http.ResponseWriter, r *http.Request, dgst digest.Digest) error {
	canonical, err := lbs.Stat(ctx, dgst) // access check
	if err != nil {
		return err
	}

	if canonical.MediaType != "" {
		// Set the repository local content type.
		w.Header().Set("Content-Type", canonical.MediaType)
	}

	return lbs.blobServer.ServeBlob(ctx, w, r, canonical.Digest)
}

func (lbs *linkedBlobStore) Put(ctx context.Context, mediaType string, p []byte) (distribution.Descriptor, error) {
	dgst := digest.FromBytes(p)
	// Place the data in the blob store first.
	desc, err := lbs.blobStore.Put(ctx, mediaType, p)
	if err != nil {
		context.GetLogger(ctx).Errorf("error putting into main store: %v", err)
		return distribution.Descriptor{}, err
	}

	if err := lbs.blobAccessController.SetDescriptor(ctx, dgst, desc); err != nil {
		return distribution.Descriptor{}, err
	}

	// TODO(stevvooe): Write out mediatype if incoming differs from what is
	// returned by Put above. Note that we should allow updates for a given
	// repository.

	return desc, lbs.linkBlob(ctx, desc)
}

// Writer begins a blob write session, returning a handle.
func (lbs *linkedBlobStore) Create(ctx context.Context) (distribution.BlobWriter, error) {
	context.GetLogger(ctx).Debug("(*linkedBlobStore).Writer")

	uuid := uuid.Generate().String()
	startedAt := time.Now().UTC()

	path, err := pathFor(uploadDataPathSpec{
		name: lbs.repository.Name(),
		id:   uuid,
	})

	if err != nil {
		return nil, err
	}

	startedAtPath, err := pathFor(uploadStartedAtPathSpec{
		name: lbs.repository.Name(),
		id:   uuid,
	})

	if err != nil {
		return nil, err
	}

	// Write a startedat file for this upload
	if err := lbs.blobStore.driver.PutContent(ctx, startedAtPath, []byte(startedAt.Format(time.RFC3339))); err != nil {
		return nil, err
	}

	return lbs.newBlobUpload(ctx, uuid, path, startedAt)
}

func (lbs *linkedBlobStore) Resume(ctx context.Context, id string) (distribution.BlobWriter, error) {
	context.GetLogger(ctx).Debug("(*linkedBlobStore).Resume")

	startedAtPath, err := pathFor(uploadStartedAtPathSpec{
		name: lbs.repository.Name(),
		id:   id,
	})

	if err != nil {
		return nil, err
	}

	startedAtBytes, err := lbs.blobStore.driver.GetContent(ctx, startedAtPath)
	if err != nil {
		switch err := err.(type) {
		case driver.PathNotFoundError:
			return nil, distribution.ErrBlobUploadUnknown
		default:
			return nil, err
		}
	}

	startedAt, err := time.Parse(time.RFC3339, string(startedAtBytes))
	if err != nil {
		return nil, err
	}

	path, err := pathFor(uploadDataPathSpec{
		name: lbs.repository.Name(),
		id:   id,
	})

	if err != nil {
		return nil, err
	}

	return lbs.newBlobUpload(ctx, id, path, startedAt)
}

func (lbs *linkedBlobStore) Delete(ctx context.Context, dgst digest.Digest) error {
	if !lbs.deleteEnabled {
		return distribution.ErrUnsupported
	}

	// Ensure the blob is available for deletion
	_, err := lbs.blobAccessController.Stat(ctx, dgst)
	if err != nil {
		return err
	}

	err = lbs.blobAccessController.Clear(ctx, dgst)
	if err != nil {
		return err
	}

	return nil
}

// newBlobUpload allocates a new upload controller with the given state.
func (lbs *linkedBlobStore) newBlobUpload(ctx context.Context, uuid, path string, startedAt time.Time) (distribution.BlobWriter, error) {
	fw, err := newFileWriter(ctx, lbs.driver, path)
	if err != nil {
		return nil, err
	}

	bw := &blobWriter{
		blobStore:              lbs,
		id:                     uuid,
		startedAt:              startedAt,
		digester:               digest.Canonical.New(),
		bufferedFileWriter:     *fw,
		resumableDigestEnabled: lbs.resumableDigestEnabled,
	}

	return bw, nil
}

// linkBlob links a valid, written blob into the registry under the named
// repository for the upload controller.
func (lbs *linkedBlobStore) linkBlob(ctx context.Context, canonical distribution.Descriptor, aliases ...digest.Digest) error {
	dgsts := append([]digest.Digest{canonical.Digest}, aliases...)

	// TODO(stevvooe): Need to write out mediatype for only canonical hash
	// since we don't care about the aliases. They are generally unused except
	// for tarsum but those versions don't care about mediatype.

	// Don't make duplicate links.
	seenDigests := make(map[digest.Digest]struct{}, len(dgsts))

	// only use the first link
	linkPathFn := lbs.linkPathFns[0]

	for _, dgst := range dgsts {
		if _, seen := seenDigests[dgst]; seen {
			continue
		}
		seenDigests[dgst] = struct{}{}

		blobLinkPath, err := linkPathFn(lbs.repository.Name(), dgst)
		if err != nil {
			return err
		}

		if err := lbs.blobStore.link(ctx, blobLinkPath, canonical.Digest); err != nil {
			return err
		}
	}

	return nil
}

type linkedBlobStatter struct {
	*blobStore
	repository distribution.Repository

	// linkPathFns specifies one or more path functions allowing one to
	// control the repository blob link set to which the blob store
	// dispatches. This is required because manifest and layer blobs have not
	// yet been fully merged. At some point, this functionality should be
	// removed an the blob links folder should be merged. The first entry is
	// treated as the "canonical" link location and will be used for writes.
	linkPathFns []linkPathFunc
}

var _ distribution.BlobDescriptorService = &linkedBlobStatter{}

func (lbs *linkedBlobStatter) Stat(ctx context.Context, dgst digest.Digest) (distribution.Descriptor, error) {
	var (
		resolveErr error
		target     digest.Digest
	)

	// try the many link path functions until we get success or an error that
	// is not PathNotFoundError.
	for _, linkPathFn := range lbs.linkPathFns {
		var err error
		target, err = lbs.resolveWithLinkFunc(ctx, dgst, linkPathFn)

		if err == nil {
			break // success!
		}

		switch err := err.(type) {
		case driver.PathNotFoundError:
			resolveErr = distribution.ErrBlobUnknown // move to the next linkPathFn, saving the error
		default:
			return distribution.Descriptor{}, err
		}
	}

	if resolveErr != nil {
		return distribution.Descriptor{}, resolveErr
	}

	if target != dgst {
		// Track when we are doing cross-digest domain lookups. ie, tarsum to sha256.
		context.GetLogger(ctx).Warnf("looking up blob with canonical target: %v -> %v", dgst, target)
	}

	// TODO(stevvooe): Look up repository local mediatype and replace that on
	// the returned descriptor.

	return lbs.blobStore.statter.Stat(ctx, target)
}

func (lbs *linkedBlobStatter) Clear(ctx context.Context, dgst digest.Digest) (err error) {
	// clear any possible existence of a link described in linkPathFns
	for _, linkPathFn := range lbs.linkPathFns {
		blobLinkPath, err := linkPathFn(lbs.repository.Name(), dgst)
		if err != nil {
			return err
		}

		err = lbs.blobStore.driver.Delete(ctx, blobLinkPath)
		if err != nil {
			switch err := err.(type) {
			case driver.PathNotFoundError:
				continue // just ignore this error and continue
			default:
				return err
			}
		}
	}

	return nil
}

// resolveTargetWithFunc allows us to read a link to a resource with different
// linkPathFuncs to let us try a few different paths before returning not
// found.
func (lbs *linkedBlobStatter) resolveWithLinkFunc(ctx context.Context, dgst digest.Digest, linkPathFn linkPathFunc) (digest.Digest, error) {
	blobLinkPath, err := linkPathFn(lbs.repository.Name(), dgst)
	if err != nil {
		return "", err
	}

	return lbs.blobStore.readlink(ctx, blobLinkPath)
}

func (lbs *linkedBlobStatter) SetDescriptor(ctx context.Context, dgst digest.Digest, desc distribution.Descriptor) error {
	// The canonical descriptor for a blob is set at the commit phase of upload
	return nil
}

// blobLinkPath provides the path to the blob link, also known as layers.
func blobLinkPath(name string, dgst digest.Digest) (string, error) {
	return pathFor(layerLinkPathSpec{name: name, digest: dgst})
}

// manifestRevisionLinkPath provides the path to the manifest revision link.
func manifestRevisionLinkPath(name string, dgst digest.Digest) (string, error) {
	return pathFor(manifestRevisionLinkPathSpec{name: name, revision: dgst})
}