func (c Client) verifyRoot(role string, s *data.Signed, minVersion int) error {
	// this will confirm that the root has been signed by the old root role
	// as c.keysDB contains the root keys we bootstrapped with.
	// Still need to determine if there has been a root key update and
	// confirm signature with new root key
	logrus.Debug("verifying root with existing keys")
	err := signed.Verify(s, role, minVersion, c.keysDB)
	if err != nil {
		logrus.Debug("root did not verify with existing keys")
		return err
	}

	// This will cause keyDB to get updated, overwriting any keyIDs associated
	// with the roles in root.json
	logrus.Debug("updating known root roles and keys")
	err = c.local.SetRoot(s)
	if err != nil {
		logrus.Error(err.Error())
		return err
	}
	// verify again now that the old keys have been replaced with the new keys.
	// TODO(endophage): be more intelligent and only re-verify if we detect
	//                  there has been a change in root keys
	logrus.Debug("verifying root with updated keys")
	err = signed.Verify(s, role, minVersion, c.keysDB)
	if err != nil {
		logrus.Debug("root did not verify with new keys")
		return err
	}
	logrus.Debug("successfully verified root")
	return nil
}

func validateSnapshot(role string, oldSnap *data.SignedSnapshot, snapUpdate storage.MetaUpdate, roles map[string]storage.MetaUpdate, kdb *keys.KeyDB) error {
	s := &data.Signed{}
	err := json.Unmarshal(snapUpdate.Data, s)
	if err != nil {
		return errors.New("could not parse snapshot")
	}
	// version specifically gets validated when writing to store to
	// better handle race conditions there.
	if err := signed.Verify(s, role, 0, kdb); err != nil {
		return err
	}

	snap, err := data.SnapshotFromSigned(s)
	if err != nil {
		return errors.New("could not parse snapshot")
	}
	if !data.ValidTUFType(snap.Signed.Type, data.CanonicalSnapshotRole) {
		return errors.New("snapshot has wrong type")
	}
	err = checkSnapshotEntries(role, oldSnap, snap, roles)
	if err != nil {
		return err
	}
	return nil
}

// downloadTimestamp is responsible for downloading the timestamp.json
func (c *Client) downloadTimestamp() error {
	logrus.Debug("downloadTimestamp")
	role := data.RoleName("timestamp")

	// We may not have a cached timestamp if this is the first time
	// we're interacting with the repo. This will result in the
	// version being 0
	var download bool
	old := &data.Signed{}
	version := 0
	cachedTS, err := c.cache.GetMeta(role, maxSize)
	if err == nil {
		err := json.Unmarshal(cachedTS, old)
		if err == nil {
			ts, err := data.TimestampFromSigned(old)
			if err == nil {
				version = ts.Signed.Version
			}
		} else {
			old = nil
		}
	}
	// unlike root, targets and snapshot, always try and download timestamps
	// from remote, only using the cache one if we couldn't reach remote.
	logrus.Debug("Downloading timestamp")
	raw, err := c.remote.GetMeta(role, maxSize)
	var s *data.Signed
	if err != nil || len(raw) == 0 {
		if err, ok := err.(store.ErrMetaNotFound); ok {
			return err
		}
		if old == nil {
			if err == nil {
				// couldn't retrieve data from server and don't have valid
				// data in cache.
				return store.ErrMetaNotFound{}
			}
			return err
		}
		s = old
	} else {
		download = true
		s = &data.Signed{}
		err = json.Unmarshal(raw, s)
		if err != nil {
			return err
		}
	}
	err = signed.Verify(s, role, version, c.keysDB)
	if err != nil {
		return err
	}
	logrus.Debug("successfully verified timestamp")
	if download {
		c.cache.SetMeta(role, raw)
	}
	c.local.SetTimestamp(s)
	return nil
}

// downloadTimestamp is responsible for downloading the timestamp.json
func (c *Client) downloadTimestamp() error {
	role := data.RoleName("timestamp")
	raw, err := c.remote.GetMeta(role, 5<<20)
	if err != nil {
		return err
	}
	s := &data.Signed{}
	err = json.Unmarshal(raw, s)
	if err != nil {
		return err
	}
	err = signed.Verify(s, role, 0, c.keysDB)
	if err != nil {
		return err
	}
	c.local.SetTimestamp(s)
	return nil
}

// downloadSnapshot is responsible for downloading the snapshot.json
func (c *Client) downloadSnapshot() error {
	role := data.RoleName("snapshot")
	size := c.local.Timestamp.Signed.Meta[role].Length
	raw, err := c.remote.GetMeta(role, size)
	if err != nil {
		return err
	}
	s := &data.Signed{}
	err = json.Unmarshal(raw, s)
	if err != nil {
		return err
	}
	err = signed.Verify(s, role, 0, c.keysDB)
	if err != nil {
		return err
	}
	c.local.SetSnapshot(s)
	return nil
}

func (c Client) GetTargetsFile(roleName string, keyIDs []string, snapshotMeta data.Files, consistent bool, threshold int) (*data.Signed, error) {
	rolePath, err := c.RoleTargetsPath(roleName, snapshotMeta, consistent)
	if err != nil {
		return nil, err
	}
	r, err := c.remote.GetMeta(rolePath, snapshotMeta[roleName].Length)
	if err != nil {
		return nil, err
	}
	s := &data.Signed{}
	err = json.Unmarshal(r, s)
	if err != nil {
		logrus.Error("Error unmarshalling targets file:", err)
		return nil, err
	}
	err = signed.Verify(s, roleName, 0, c.keysDB)
	if err != nil {
		return nil, err
	}
	return s, nil
}

func validateTargets(role string, roles map[string]storage.MetaUpdate, kdb *keys.KeyDB) (*data.SignedTargets, error) {
	// TODO: when delegations are being validated, validate parent
	//       role exists for any delegation
	s := &data.Signed{}
	err := json.Unmarshal(roles[role].Data, s)
	if err != nil {
		return nil, fmt.Errorf("could not parse %s", role)
	}
	// version specifically gets validated when writing to store to
	// better handle race conditions there.
	if err := signed.Verify(s, role, 0, kdb); err != nil {
		return nil, err
	}
	t, err := data.TargetsFromSigned(s)
	if err != nil {
		return nil, err
	}
	if !data.ValidTUFType(t.Signed.Type, data.CanonicalTargetsRole) {
		return nil, fmt.Errorf("%s has wrong type", role)
	}
	return t, nil
}

func (c Client) getTargetsFile(role string, keyIDs []string, snapshotMeta data.Files, consistent bool, threshold int) (*data.Signed, error) {
	// require role exists in snapshots
	roleMeta, ok := snapshotMeta[role]
	if !ok {
		return nil, ErrMissingMeta{role: role}
	}
	expectedSha256, ok := snapshotMeta[role].Hashes["sha256"]
	if !ok {
		return nil, ErrMissingMeta{role: role}
	}

	// try to get meta file from content addressed cache
	var download bool
	old := &data.Signed{}
	version := 0
	raw, err := c.cache.GetMeta(role, roleMeta.Length)
	if err != nil || raw == nil {
		logrus.Debugf("Couldn't not find cached %s, must download", role)
		download = true
	} else {
		// file may have been tampered with on disk. Always check the hash!
		genHash := sha256.Sum256(raw)
		if !bytes.Equal(genHash[:], expectedSha256) {
			download = true
		}
		err := json.Unmarshal(raw, old)
		if err == nil {
			targ, err := data.TargetsFromSigned(old)
			if err == nil {
				version = targ.Signed.Version
			} else {
				download = true
			}
		} else {
			download = true
		}
	}

	size := snapshotMeta[role].Length
	var s *data.Signed
	if download {
		rolePath, err := c.RoleTargetsPath(role, hex.EncodeToString(expectedSha256), consistent)
		if err != nil {
			return nil, err
		}
		raw, s, err = c.downloadSigned(rolePath, size, expectedSha256)
		if err != nil {
			return nil, err
		}
	} else {
		logrus.Debug("using cached ", role)
		s = old
	}

	err = signed.Verify(s, role, version, c.keysDB)
	if err != nil {
		return nil, err
	}
	logrus.Debugf("successfully verified %s", role)
	if download {
		// if we error when setting meta, we should continue.
		err = c.cache.SetMeta(role, raw)
		if err != nil {
			logrus.Errorf("Failed to write snapshot to local cache: %s", err.Error())
		}
	}
	return s, nil
}

// downloadSnapshot is responsible for downloading the snapshot.json
func (c *Client) downloadSnapshot() error {
	logrus.Debug("downloadSnapshot")
	role := data.RoleName("snapshot")
	if c.local.Timestamp == nil {
		return ErrMissingMeta{role: "snapshot"}
	}
	size := c.local.Timestamp.Signed.Meta[role].Length
	expectedSha256, ok := c.local.Timestamp.Signed.Meta[role].Hashes["sha256"]
	if !ok {
		return ErrMissingMeta{role: "snapshot"}
	}

	var download bool
	old := &data.Signed{}
	version := 0
	raw, err := c.cache.GetMeta(role, size)
	if raw == nil || err != nil {
		logrus.Debug("no snapshot in cache, must download")
		download = true
	} else {
		// file may have been tampered with on disk. Always check the hash!
		genHash := sha256.Sum256(raw)
		if !bytes.Equal(genHash[:], expectedSha256) {
			logrus.Debug("hash of snapshot in cache did not match expected hash, must download")
			download = true
		}
		err := json.Unmarshal(raw, old)
		if err == nil {
			snap, err := data.TimestampFromSigned(old)
			if err == nil {
				version = snap.Signed.Version
			} else {
				logrus.Debug("Could not parse Signed part of snapshot, must download")
				download = true
			}
		} else {
			logrus.Debug("Could not parse snapshot, must download")
			download = true
		}
	}
	var s *data.Signed
	if download {
		raw, s, err = c.downloadSigned(role, size, expectedSha256)
		if err != nil {
			return err
		}
	} else {
		logrus.Debug("using cached snapshot")
		s = old
	}

	err = signed.Verify(s, role, version, c.keysDB)
	if err != nil {
		return err
	}
	logrus.Debug("successfully verified snapshot")
	snap, err := data.SnapshotFromSigned(s)
	if err != nil {
		return err
	}
	c.local.SetSnapshot(snap)
	if download {
		err = c.cache.SetMeta(role, raw)
		if err != nil {
			logrus.Errorf("Failed to write snapshot to local cache: %s", err.Error())
		}
	}
	return nil
}

// downloadSnapshot is responsible for downloading the snapshot.json
func (c *Client) downloadSnapshot() error {
	logrus.Debug("downloadSnapshot")
	role := data.RoleName("snapshot")
	size := c.local.Timestamp.Signed.Meta[role].Length
	expectedSha256, ok := c.local.Timestamp.Signed.Meta[role].Hashes["sha256"]
	if !ok {
		return fmt.Errorf("Sha256 is currently the only hash supported by this client. No Sha256 found for snapshot")
	}

	var download bool
	old := &data.Signed{}
	version := 0
	raw, err := c.cache.GetMeta(role, size)
	if raw == nil || err != nil {
		logrus.Debug("no snapshot in cache, must download")
		download = true
	} else {
		// file may have been tampered with on disk. Always check the hash!
		genHash := sha256.Sum256(raw)
		if !bytes.Equal(genHash[:], expectedSha256) {
			logrus.Debug("hash of snapshot in cache did not match expected hash, must download")
			download = true
		}
		err := json.Unmarshal(raw, old)
		if err == nil {
			snap, err := data.TimestampFromSigned(old)
			if err == nil {
				version = snap.Signed.Version
			} else {
				logrus.Debug("Could not parse Signed part of snapshot, must download")
				download = true
			}
		} else {
			logrus.Debug("Could not parse snapshot, must download")
			download = true
		}
	}
	var s *data.Signed
	if download {
		logrus.Debug("downloading new snapshot")
		raw, err = c.remote.GetMeta(role, size)
		if err != nil {
			return err
		}
		genHash := sha256.Sum256(raw)
		if !bytes.Equal(genHash[:], expectedSha256) {
			return fmt.Errorf("Retrieved snapshot did not verify against hash in timestamp.")
		}
		s = &data.Signed{}
		err = json.Unmarshal(raw, s)
		if err != nil {
			return err
		}
	} else {
		logrus.Debug("using cached snapshot")
		s = old
	}

	err = signed.Verify(s, role, version, c.keysDB)
	if err != nil {
		return err
	}
	logrus.Debug("successfully verified snapshot")
	c.local.SetSnapshot(s)
	if download {
		err = c.cache.SetMeta(role, raw)
		if err != nil {
			logrus.Errorf("Failed to write snapshot to local cache: %s", err.Error())
		}
	}
	return nil
}