package distribution

import (
	"context"
	"encoding/json"
	"fmt"
	"io"
	"strings"

	"github.com/containerd/containerd/content"
	cerrdefs "github.com/containerd/containerd/errdefs"
	"github.com/containerd/containerd/remotes"
	"github.com/containerd/log"
	"github.com/distribution/reference"
	"github.com/docker/distribution"
	"github.com/docker/distribution/manifest/manifestlist"
	"github.com/docker/distribution/manifest/schema1"
	"github.com/docker/distribution/manifest/schema2"
	"github.com/docker/docker/registry"
	"github.com/opencontainers/go-digest"
	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
	"github.com/pkg/errors"
)

// labelDistributionSource describes the source blob comes from.
const labelDistributionSource = "containerd.io/distribution.source"

// This is used by manifestStore to pare down the requirements to implement a
// full distribution.ManifestService, since `Get` is all we use here.
type manifestGetter interface {
	Get(ctx context.Context, dgst digest.Digest, options ...distribution.ManifestServiceOption) (distribution.Manifest, error)
	Exists(ctx context.Context, dgst digest.Digest) (bool, error)
}

type manifestStore struct {
	local  ContentStore
	remote manifestGetter
}

// ContentStore is the interface used to persist registry blobs
//
// Currently this is only used to persist manifests and manifest lists.
// It is exported because `distribution.Pull` takes one as an argument.
type ContentStore interface {
	content.Ingester
	content.Provider
	Info(ctx context.Context, dgst digest.Digest) (content.Info, error)
	Abort(ctx context.Context, ref string) error
	Update(ctx context.Context, info content.Info, fieldpaths ...string) (content.Info, error)
}

func makeDistributionSourceLabel(ref reference.Named) (string, string) {
	domain := reference.Domain(ref)
	if domain == "" {
		domain = registry.DefaultNamespace
	}
	repo := reference.Path(ref)

	return fmt.Sprintf("%s.%s", labelDistributionSource, domain), repo
}

// Taken from https://github.com/containerd/containerd/blob/e079e4a155c86f07bbd602fe6753ecacc78198c2/remotes/docker/handler.go#L84-L108
func appendDistributionSourceLabel(originLabel, repo string) string {
	repos := []string{}
	if originLabel != "" {
		repos = strings.Split(originLabel, ",")
	}
	repos = append(repos, repo)

	// use empty string to present duplicate items
	for i := 1; i < len(repos); i++ {
		tmp, j := repos[i], i-1
		for ; j >= 0 && repos[j] >= tmp; j-- {
			if repos[j] == tmp {
				tmp = ""
			}
			repos[j+1] = repos[j]
		}
		repos[j+1] = tmp
	}

	i := 0
	for ; i < len(repos) && repos[i] == ""; i++ {
	}

	return strings.Join(repos[i:], ",")
}

func hasDistributionSource(label, repo string) bool {
	sources := strings.Split(label, ",")
	for _, s := range sources {
		if s == repo {
			return true
		}
	}
	return false
}

func (m *manifestStore) getLocal(ctx context.Context, desc ocispec.Descriptor, ref reference.Named) (distribution.Manifest, error) {
	ra, err := m.local.ReaderAt(ctx, desc)
	if err != nil {
		return nil, errors.Wrap(err, "error getting content store reader")
	}
	defer ra.Close()

	distKey, distRepo := makeDistributionSourceLabel(ref)
	info, err := m.local.Info(ctx, desc.Digest)
	if err != nil {
		return nil, errors.Wrap(err, "error getting content info")
	}

	if _, ok := ref.(reference.Canonical); ok {
		// Since this is specified by digest...
		// We know we have the content locally, we need to check if we've seen this content at the specified repository before.
		// If we have, we can just return the manifest from the local content store.
		// If we haven't, we need to check the remote repository to see if it has the content, otherwise we can end up returning
		// a manifest that has never even existed in the remote before.
		if !hasDistributionSource(info.Labels[distKey], distRepo) {
			log.G(ctx).WithField("ref", ref).Debug("found manifest but no mataching source repo is listed, checking with remote")
			exists, err := m.remote.Exists(ctx, desc.Digest)
			if err != nil {
				return nil, errors.Wrap(err, "error checking if remote exists")
			}

			if !exists {
				return nil, errors.Wrapf(cerrdefs.ErrNotFound, "manifest %v not found", desc.Digest)
			}

		}
	}

	// Update the distribution sources since we now know the content exists in the remote.
	if info.Labels == nil {
		info.Labels = map[string]string{}
	}
	info.Labels[distKey] = appendDistributionSourceLabel(info.Labels[distKey], distRepo)
	if _, err := m.local.Update(ctx, info, "labels."+distKey); err != nil {
		log.G(ctx).WithError(err).WithField("ref", ref).Warn("Could not update content distribution source")
	}

	r := io.NewSectionReader(ra, 0, ra.Size())
	data, err := io.ReadAll(r)
	if err != nil {
		return nil, errors.Wrap(err, "error reading manifest from content store")
	}

	manifest, _, err := distribution.UnmarshalManifest(desc.MediaType, data)
	if err != nil {
		return nil, errors.Wrap(err, "error unmarshaling manifest from content store")
	}

	return manifest, nil
}

func (m *manifestStore) getMediaType(ctx context.Context, desc ocispec.Descriptor) (string, error) {
	ra, err := m.local.ReaderAt(ctx, desc)
	if err != nil {
		return "", errors.Wrap(err, "error getting reader to detect media type")
	}
	defer ra.Close()

	mt, err := detectManifestMediaType(ra)
	if err != nil {
		return "", errors.Wrap(err, "error detecting media type")
	}
	return mt, nil
}

func (m *manifestStore) Get(ctx context.Context, desc ocispec.Descriptor, ref reference.Named) (distribution.Manifest, error) {
	l := log.G(ctx)

	if desc.MediaType == "" {
		// When pulling by digest we will not have the media type on the
		// descriptor since we have not made a request to the registry yet
		//
		// We already have the digest, so we only lookup locally... by digest.
		//
		// Let's try to detect the media type so we can have a good ref key
		// here. We may not even have the content locally, and this is fine, but
		// if we do we should determine that.
		mt, err := m.getMediaType(ctx, desc)
		if err != nil && !cerrdefs.IsNotFound(err) {
			l.WithError(err).Warn("Error looking up media type of content")
		}
		desc.MediaType = mt
	}

	key := remotes.MakeRefKey(ctx, desc)

	// Here we open a writer to the requested content. This both gives us a
	// reference to write to if indeed we need to persist it and increments the
	// ref count on the content.
	w, err := m.local.Writer(ctx, content.WithDescriptor(desc), content.WithRef(key))
	if err != nil {
		if cerrdefs.IsAlreadyExists(err) {
			var manifest distribution.Manifest
			if manifest, err = m.getLocal(ctx, desc, ref); err == nil {
				return manifest, nil
			}
		}
		// always fallback to the remote if there is an error with the local store
	}
	if w != nil {
		defer w.Close()
	}

	l.WithError(err).Debug("Fetching manifest from remote")

	manifest, err := m.remote.Get(ctx, desc.Digest)
	if err != nil {
		if err := m.local.Abort(ctx, key); err != nil {
			l.WithError(err).Warn("Error while attempting to abort content ingest")
		}
		return nil, err
	}

	if w != nil {
		// if `w` is nil here, something happened with the content store, so don't bother trying to persist.
		if err := m.Put(ctx, manifest, desc, w, ref); err != nil {
			if err := m.local.Abort(ctx, key); err != nil {
				l.WithError(err).Warn("error aborting content ingest")
			}
			l.WithError(err).Warn("Error persisting manifest")
		}
	}
	return manifest, nil
}

func (m *manifestStore) Put(ctx context.Context, manifest distribution.Manifest, desc ocispec.Descriptor, w content.Writer, ref reference.Named) error {
	mt, payload, err := manifest.Payload()
	if err != nil {
		return err
	}
	desc.Size = int64(len(payload))
	desc.MediaType = mt

	if _, err = w.Write(payload); err != nil {
		return errors.Wrap(err, "error writing manifest to content store")
	}

	distKey, distSource := makeDistributionSourceLabel(ref)
	if err := w.Commit(ctx, desc.Size, desc.Digest, content.WithLabels(map[string]string{
		distKey: distSource,
	})); err != nil {
		return errors.Wrap(err, "error committing manifest to content store")
	}
	return nil
}

func detectManifestMediaType(ra content.ReaderAt) (string, error) {
	dt := make([]byte, ra.Size())
	if _, err := ra.ReadAt(dt, 0); err != nil {
		return "", err
	}

	return detectManifestBlobMediaType(dt)
}

// This is used when the manifest store does not know the media type of a sha it
// was told to get. This would currently only happen when pulling by digest.
// The media type is needed so the blob can be unmarshalled properly.
func detectManifestBlobMediaType(dt []byte) (string, error) {
	var mfst struct {
		MediaType string          `json:"mediaType"`
		Manifests json.RawMessage `json:"manifests"` // oci index, manifest list
		Config    json.RawMessage `json:"config"`    // schema2 Manifest
		Layers    json.RawMessage `json:"layers"`    // schema2 Manifest
		FSLayers  json.RawMessage `json:"fsLayers"`  // schema1 Manifest
	}

	if err := json.Unmarshal(dt, &mfst); err != nil {
		return "", err
	}

	// We may have a media type specified in the json, in which case that should be used.
	// Docker types should generally have a media type set.
	// OCI (golang) types do not have a `mediaType` defined, and it is optional in the spec.
	//
	// `distribution.UnmarshalManifest`, which is used to unmarshal this for real, checks these media type values.
	// If the specified media type does not match it will error, and in some cases (docker media types) it is required.
	// So pretty much if we don't have a media type we can fall back to OCI.
	// This does have a special fallback for schema1 manifests just because it is easy to detect.
	switch mfst.MediaType {
	case schema2.MediaTypeManifest, ocispec.MediaTypeImageManifest:
		if mfst.Manifests != nil || mfst.FSLayers != nil {
			return "", fmt.Errorf(`media-type: %q should not have "manifests" or "fsLayers"`, mfst.MediaType)
		}
		return mfst.MediaType, nil
	case manifestlist.MediaTypeManifestList, ocispec.MediaTypeImageIndex:
		if mfst.Config != nil || mfst.Layers != nil || mfst.FSLayers != nil {
			return "", fmt.Errorf(`media-type: %q should not have "config", "layers", or "fsLayers"`, mfst.MediaType)
		}
		return mfst.MediaType, nil
	case schema1.MediaTypeManifest:
		if mfst.Manifests != nil || mfst.Layers != nil {
			return "", fmt.Errorf(`media-type: %q should not have "manifests" or "layers"`, mfst.MediaType)
		}
		return mfst.MediaType, nil
	default:
		if mfst.MediaType != "" {
			return mfst.MediaType, nil
		}
	}
	switch {
	case mfst.FSLayers != nil && mfst.Manifests == nil && mfst.Layers == nil && mfst.Config == nil:
		return schema1.MediaTypeManifest, nil
	case mfst.Config != nil && mfst.Manifests == nil && mfst.FSLayers == nil,
		mfst.Layers != nil && mfst.Manifests == nil && mfst.FSLayers == nil:
		return ocispec.MediaTypeImageManifest, nil
	case mfst.Config == nil && mfst.Layers == nil && mfst.FSLayers == nil:
		// fallback to index
		return ocispec.MediaTypeImageIndex, nil
	}
	return "", errors.New("media-type: cannot determine")
}
