/*
Copyright IBM Corp. 2017 All Rights Reserved.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

		 http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package gossip

import (
	"bytes"
	"errors"
	"fmt"

	"github.com/hyperledger/fabric/bccsp"
	"github.com/hyperledger/fabric/bccsp/factory"
	"github.com/hyperledger/fabric/common/crypto"
	"github.com/hyperledger/fabric/common/flogging"
	"github.com/hyperledger/fabric/common/policies"
	"github.com/hyperledger/fabric/common/util"
	"github.com/hyperledger/fabric/gossip/api"
	"github.com/hyperledger/fabric/gossip/common"
	"github.com/hyperledger/fabric/msp"
	"github.com/hyperledger/fabric/msp/mgmt"
	pcommon "github.com/hyperledger/fabric/protos/common"
	"github.com/hyperledger/fabric/protos/utils"
)

var mcsLogger = flogging.MustGetLogger("peer/gossip/mcs")

// mspMessageCryptoService implements the MessageCryptoService interface
// using the peer MSPs (local and channel-related)
//
// In order for the system to be secure it is vital to have the
// MSPs to be up-to-date. Channels' MSPs are updated via
// configuration transactions distributed by the ordering service.
//
// A similar mechanism needs to be in place to update the local MSP, as well.
// This implementation assumes that these mechanisms are all in place and working.
type mspMessageCryptoService struct {
	channelPolicyManagerGetter policies.ChannelPolicyManagerGetter
	localSigner                crypto.LocalSigner
	deserializer               mgmt.DeserializersManager
}

// NewMCS creates a new instance of mspMessageCryptoService
// that implements MessageCryptoService.
// The method takes in input:
// 1. a policies.ChannelPolicyManagerGetter that gives access to the policy manager of a given channel via the Manager method.
// 2. an instance of crypto.LocalSigner
// 3. an identity deserializer manager
func NewMCS(channelPolicyManagerGetter policies.ChannelPolicyManagerGetter, localSigner crypto.LocalSigner, deserializer mgmt.DeserializersManager) api.MessageCryptoService {
	return &mspMessageCryptoService{channelPolicyManagerGetter: channelPolicyManagerGetter, localSigner: localSigner, deserializer: deserializer}
}

// ValidateIdentity validates the identity of a remote peer.
// If the identity is invalid, revoked, expired it returns an error.
// Else, returns nil
func (s *mspMessageCryptoService) ValidateIdentity(peerIdentity api.PeerIdentityType) error {
	// As prescibed by the contract of method,
	// here we check only that peerIdentity is not
	// invalid, revoked or expired.

	_, _, err := s.getValidatedIdentity(peerIdentity)
	return err
}

// GetPKIidOfCert returns the PKI-ID of a peer's identity
// If any error occurs, the method return nil
// The PKid of a peer is computed as the SHA2-256 of peerIdentity which
// is supposed to be the serialized version of MSP identity.
// This method does not validate peerIdentity.
// This validation is supposed to be done appropriately during the execution flow.
func (s *mspMessageCryptoService) GetPKIidOfCert(peerIdentity api.PeerIdentityType) common.PKIidType {
	// Validate arguments
	if len(peerIdentity) == 0 {
		mcsLogger.Error("Invalid Peer Identity. It must be different from nil.")

		return nil
	}

	sid, err := s.deserializer.Deserialize(peerIdentity)
	if err != nil {
		mcsLogger.Errorf("Failed getting validated identity from peer identity [% x]: [%s]", peerIdentity, err)

		return nil
	}

	// concatenate msp-id and idbytes
	// idbytes is the low-level representation of an identity.
	// it is supposed to be already in its minimal representation

	mspIdRaw := []byte(sid.Mspid)
	raw := append(mspIdRaw, sid.IdBytes...)

	// Hash
	digest, err := factory.GetDefault().Hash(raw, &bccsp.SHA256Opts{})
	if err != nil {
		mcsLogger.Errorf("Failed computing digest of serialized identity [% x]: [%s]", peerIdentity, err)

		return nil
	}

	return digest
}

// VerifyBlock returns nil if the block is properly signed, and the claimed seqNum is the
// sequence number that the block's header contains.
// else returns error
func (s *mspMessageCryptoService) VerifyBlock(chainID common.ChainID, seqNum uint64, signedBlock []byte) error {
	// - Convert signedBlock to common.Block.
	block, err := utils.GetBlockFromBlockBytes(signedBlock)
	if err != nil {
		return fmt.Errorf("Failed unmarshalling block bytes on channel [%s]: [%s]", chainID, err)
	}

	if block.Header == nil {
		return fmt.Errorf("Invalid Block on channel [%s]. Header must be different from nil.", chainID)
	}

	blockSeqNum := block.Header.Number
	if seqNum != blockSeqNum {
		return fmt.Errorf("Claimed seqNum is [%d] but actual seqNum inside block is [%d]", seqNum, blockSeqNum)
	}

	// - Extract channelID and compare with chainID
	channelID, err := utils.GetChainIDFromBlock(block)
	if err != nil {
		return fmt.Errorf("Failed getting channel id from block with id [%d] on channel [%s]: [%s]", block.Header.Number, chainID, err)
	}

	if channelID != string(chainID) {
		return fmt.Errorf("Invalid block's channel id. Expected [%s]. Given [%s]", chainID, channelID)
	}

	// - Unmarshal medatada
	if block.Metadata == nil || len(block.Metadata.Metadata) == 0 {
		return fmt.Errorf("Block with id [%d] on channel [%s] does not have metadata. Block not valid.", block.Header.Number, chainID)
	}

	metadata, err := utils.GetMetadataFromBlock(block, pcommon.BlockMetadataIndex_SIGNATURES)
	if err != nil {
		return fmt.Errorf("Failed unmarshalling medatata for signatures [%s]", err)
	}

	// - Verify that Header.DataHash is equal to the hash of block.Data
	// This is to ensure that the header is consistent with the data carried by this block
	if !bytes.Equal(block.Data.Hash(), block.Header.DataHash) {
		return fmt.Errorf("Header.DataHash is different from Hash(block.Data) for block with id [%d] on channel [%s]", block.Header.Number, chainID)
	}

	// - Get Policy for block validation

	// Get the policy manager for channelID
	cpm, ok := s.channelPolicyManagerGetter.Manager(channelID)
	if cpm == nil {
		return fmt.Errorf("Could not acquire policy manager for channel %s", channelID)
	}
	// ok is true if it was the manager requested, or false if it is the default manager
	mcsLogger.Debugf("Got policy manager for channel [%s] with flag [%s]", channelID, ok)

	// Get block validation policy
	policy, ok := cpm.GetPolicy(policies.BlockValidation)
	// ok is true if it was the policy requested, or false if it is the default policy
	mcsLogger.Debugf("Got block validation policy for channel [%s] with flag [%s]", channelID, ok)

	// - Prepare SignedData
	signatureSet := []*pcommon.SignedData{}
	for _, metadataSignature := range metadata.Signatures {
		shdr, err := utils.GetSignatureHeader(metadataSignature.SignatureHeader)
		if err != nil {
			return fmt.Errorf("Failed unmarshalling signature header for block with id [%d] on channel [%s]: [%s]", block.Header.Number, chainID, err)
		}
		signatureSet = append(
			signatureSet,
			&pcommon.SignedData{
				Identity:  shdr.Creator,
				Data:      util.ConcatenateBytes(metadata.Value, metadataSignature.SignatureHeader, block.Header.Bytes()),
				Signature: metadataSignature.Signature,
			},
		)
	}

	// - Evaluate policy
	return policy.Evaluate(signatureSet)
}

// Sign signs msg with this peer's signing key and outputs
// the signature if no error occurred.
func (s *mspMessageCryptoService) Sign(msg []byte) ([]byte, error) {
	return s.localSigner.Sign(msg)
}

// Verify checks that signature is a valid signature of message under a peer's verification key.
// If the verification succeeded, Verify returns nil meaning no error occurred.
// If peerIdentity is nil, then the verification fails.
func (s *mspMessageCryptoService) Verify(peerIdentity api.PeerIdentityType, signature, message []byte) error {
	identity, chainID, err := s.getValidatedIdentity(peerIdentity)
	if err != nil {
		mcsLogger.Errorf("Failed getting validated identity from peer identity [%s]", err)

		return err
	}

	if len(chainID) == 0 {
		// At this stage, this means that peerIdentity
		// belongs to this peer's LocalMSP.
		// The signature is validated directly
		return identity.Verify(message, signature)
	}

	// At this stage, the signature must be validated
	// against the reader policy of the channel
	// identified by chainID

	return s.VerifyByChannel(chainID, peerIdentity, signature, message)
}

// VerifyByChannel checks that signature is a valid signature of message
// under a peer's verification key, but also in the context of a specific channel.
// If the verification succeeded, Verify returns nil meaning no error occurred.
// If peerIdentity is nil, then the verification fails.
func (s *mspMessageCryptoService) VerifyByChannel(chainID common.ChainID, peerIdentity api.PeerIdentityType, signature, message []byte) error {
	// Validate arguments
	if len(peerIdentity) == 0 {
		return errors.New("Invalid Peer Identity. It must be different from nil.")
	}

	// Get the policy manager for channel chainID
	cpm, flag := s.channelPolicyManagerGetter.Manager(string(chainID))
	if cpm == nil {
		return fmt.Errorf("Could not acquire policy manager for channel %s", string(chainID))
	}
	mcsLogger.Debugf("Got policy manager for channel [%s] with flag [%s]", string(chainID), flag)

	// Get channel reader policy
	policy, flag := cpm.GetPolicy(policies.ChannelApplicationReaders)
	mcsLogger.Debugf("Got reader policy for channel [%s] with flag [%s]", string(chainID), flag)

	return policy.Evaluate(
		[]*pcommon.SignedData{{
			Data:      message,
			Identity:  []byte(peerIdentity),
			Signature: signature,
		}},
	)
}

func (s *mspMessageCryptoService) getValidatedIdentity(peerIdentity api.PeerIdentityType) (msp.Identity, common.ChainID, error) {
	// Validate arguments
	if len(peerIdentity) == 0 {
		return nil, nil, errors.New("Invalid Peer Identity. It must be different from nil.")
	}

	// Notice that peerIdentity is assumed to be the serialization of an identity.
	// So, first step is the identity deserialization and then verify it.

	// First check against the local MSP.
	// If the peerIdentity is in the same organization of this node then
	// the local MSP is required to take the final decision on the validity
	// of the signature.
	identity, err := s.deserializer.GetLocalDeserializer().DeserializeIdentity([]byte(peerIdentity))
	if err == nil {
		// No error means that the local MSP successfully deserialized the identity.
		// We now check additional properties.

		// TODO: The following check will be replaced by a check on the organizational units
		// when we allow the gossip network to have organization unit (MSP subdivisions)
		// scoped messages.
		// The following check is consistent with the SecurityAdvisor#OrgByPeerIdentity
		// implementation.
		// TODO: Notice that the following check saves us from the fact
		// that DeserializeIdentity does not yet enforce MSP-IDs consistency.
		// This check can be removed once DeserializeIdentity will be fixed.
		if identity.GetMSPIdentifier() == s.deserializer.GetLocalMSPIdentifier() {
			// Check identity validity

			// Notice that at this stage we don't have to check the identity
			// against any channel's policies.
			// This will be done by the caller function, if needed.
			return identity, nil, identity.Validate()
		}
	}

	// Check against managers
	for chainID, mspManager := range s.deserializer.GetChannelDeserializers() {
		// Deserialize identity
		identity, err := mspManager.DeserializeIdentity([]byte(peerIdentity))
		if err != nil {
			mcsLogger.Debugf("Failed deserialization identity [% x] on [%s]: [%s]", peerIdentity, chainID, err)
			continue
		}

		// Check identity validity
		// Notice that at this stage we don't have to check the identity
		// against any channel's policies.
		// This will be done by the caller function, if needed.

		if err := identity.Validate(); err != nil {
			mcsLogger.Debugf("Failed validating identity [% x] on [%s]: [%s]", peerIdentity, chainID, err)
			continue
		}

		mcsLogger.Debugf("Validation succeeded [% x] on [%s]", peerIdentity, chainID)

		return identity, common.ChainID(chainID), nil
	}

	return nil, nil, fmt.Errorf("Peer Identity [% x] cannot be validated. No MSP found able to do that.", peerIdentity)
}