package manifest

import (
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"

	"github.com/docker/libtrust"
	imgspecv1 "github.com/opencontainers/image-spec/specs-go/v1"
)

// FIXME: Should we just use docker/distribution and docker/docker implementations directly?

// FIXME(runcom, mitr): should we havea mediatype pkg??
const (
	// DockerV2Schema1MediaType MIME type represents Docker manifest schema 1
	DockerV2Schema1MediaType = "application/vnd.docker.distribution.manifest.v1+json"
	// DockerV2Schema1MediaType MIME type represents Docker manifest schema 1 with a JWS signature
	DockerV2Schema1SignedMediaType = "application/vnd.docker.distribution.manifest.v1+prettyjws"
	// DockerV2Schema2MediaType MIME type represents Docker manifest schema 2
	DockerV2Schema2MediaType = "application/vnd.docker.distribution.manifest.v2+json"
	// DockerV2ListMediaType MIME type represents Docker manifest schema 2 list
	DockerV2ListMediaType = "application/vnd.docker.distribution.manifest.list.v2+json"
)

// DefaultRequestedManifestMIMETypes is a list of MIME types a types.ImageSource
// should request from the backend unless directed otherwise.
var DefaultRequestedManifestMIMETypes = []string{
	imgspecv1.MediaTypeImageManifest,
	DockerV2Schema2MediaType,
	DockerV2Schema1SignedMediaType,
	DockerV2Schema1MediaType,
}

// GuessMIMEType guesses MIME type of a manifest and returns it _if it is recognized_, or "" if unknown or unrecognized.
// FIXME? We should, in general, prefer out-of-band MIME type instead of blindly parsing the manifest,
// but we may not have such metadata available (e.g. when the manifest is a local file).
func GuessMIMEType(manifest []byte) string {
	// A subset of manifest fields; the rest is silently ignored by json.Unmarshal.
	// Also docker/distribution/manifest.Versioned.
	meta := struct {
		MediaType     string      `json:"mediaType"`
		SchemaVersion int         `json:"schemaVersion"`
		Signatures    interface{} `json:"signatures"`
	}{}
	if err := json.Unmarshal(manifest, &meta); err != nil {
		return ""
	}

	switch meta.MediaType {
	case DockerV2Schema2MediaType, DockerV2ListMediaType, imgspecv1.MediaTypeImageManifest, imgspecv1.MediaTypeImageManifestList: // A recognized type.
		return meta.MediaType
	}
	// this is the only way the function can return DockerV2Schema1MediaType, and recognizing that is essential for stripping the JWS signatures = computing the correct manifest digest.
	switch meta.SchemaVersion {
	case 1:
		if meta.Signatures != nil {
			return DockerV2Schema1SignedMediaType
		}
		return DockerV2Schema1MediaType
	case 2: // Really should not happen, meta.MediaType should have been set. But given the data, this is our best guess.
		return DockerV2Schema2MediaType
	}
	return ""
}

// Digest returns the a digest of a docker manifest, with any necessary implied transformations like stripping v1s1 signatures.
func Digest(manifest []byte) (string, error) {
	if GuessMIMEType(manifest) == DockerV2Schema1SignedMediaType {
		sig, err := libtrust.ParsePrettySignature(manifest, "signatures")
		if err != nil {
			return "", err
		}
		manifest, err = sig.Payload()
		if err != nil {
			// Coverage: This should never happen, libtrust's Payload() can fail only if joseBase64UrlDecode() fails, on a string
			// that libtrust itself has josebase64UrlEncode()d
			return "", err
		}
	}

	hash := sha256.Sum256(manifest)
	return "sha256:" + hex.EncodeToString(hash[:]), nil
}

// MatchesDigest returns true iff the manifest matches expectedDigest.
// Error may be set if this returns false.
// Note that this is not doing ConstantTimeCompare; by the time we get here, the cryptographic signature must already have been verified,
// or we are not using a cryptographic channel and the attacker can modify the digest along with the manifest blob.
func MatchesDigest(manifest []byte, expectedDigest string) (bool, error) {
	// This should eventually support various digest types.
	actualDigest, err := Digest(manifest)
	if err != nil {
		return false, err
	}
	return expectedDigest == actualDigest, nil
}