// Copyright 2017-2018 DERO Project. All rights reserved.
// Use of this source code in any form is governed by RESEARCH license.
// license can be found in the LICENSE file.
// GPG: 0F39 E425 8C65 3947 702A  8234 08B2 0360 A03A 9DE8
//
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

package ringct

import "io"
import "fmt"

import "github.com/arnaucode/derosuite/crypto"

// enable debuggin mode within ringct
// if true debugging mode enabled
const DEBUGGING_MODE = false

// TODO this package need serious love of atleast few weeks
// but atleast the parser and serdes works
// we neeed to expand everthing so as chances of a bug slippping in becomes very low
// NOTE:DO NOT waste time implmenting pre-RCT code

const (
	RCTTypeNull = iota
	RCTTypeFull
	RCTTypeSimple
)

// Pedersen Commitment is generated from this struct
// C = aG + bH where a = mask and b = amount
// senderPk is the one-time public key for ECDH exchange
type ECdhTuple struct {
	Mask   Key `msgpack:"M"`
	Amount Key `msgpack:"A"`
	//	senderPk Key
}

// Range proof commitments
type Key64 [64]Key

// Range Signature
// Essentially data for a Borromean Signature
type RangeSig struct {
	asig BoroSig
	ci   Key64
}

// Borromean Signature
type BoroSig struct {
	s0 Key64
	s1 Key64
	ee Key
}

// MLSAG (Multilayered Linkable Spontaneous Anonymous Group) Signature
type MlsagSig struct {
	ss [][]Key
	cc Key   // this stores the starting point
	II []Key // this stores the keyimage, but is taken from the tx,it is NOT serialized
}

// Confidential Transaction Keys, mask is Pedersen Commitment
// most of the time, it holds public keys, except (transaction making ) where it holds private keys
type CtKey struct {
	Destination Key `msgpack:"D"` // this is the destination and needs to expanded from blockchain
	Mask        Key `msgpack:"M"` // this is the public key amount/commitment homomorphic mask
}

// Ring Confidential Signature parts that we have to keep
type RctSigBase struct {
	sigType    uint8
	Message    Key       // transaction prefix hash
	MixRing    [][]CtKey // this is not serialized
	pseudoOuts []Key
	ECdhInfo   []ECdhTuple
	OutPk      []CtKey // only mask amount is serialized
	txFee      uint64

	Txid crypto.Hash // this field is extra and only used for logging purposes to track which txid was at fault
}

// Ring Confidential Signature parts that we can just prune later
type RctSigPrunable struct {
	rangeSigs []RangeSig
	MlsagSigs []MlsagSig // there can be as many mlsagsigs as many vins
}

// Ring Confidential Signature struct that can verify everything
type RctSig struct {
	RctSigBase
	RctSigPrunable
}

func (k *Key64) Serialize() (result []byte) {
	for _, key := range k {
		result = append(result, key[:]...)
	}
	return
}

func (b *BoroSig) Serialize() (result []byte) {
	result = append(b.s0.Serialize(), b.s1.Serialize()...)
	result = append(result, b.ee[:]...)
	return
}

func (r *RangeSig) Serialize() (result []byte) {
	result = append(r.asig.Serialize(), r.ci.Serialize()...)
	return
}

func (m *MlsagSig) Serialize() (result []byte) {
	for i := 0; i < len(m.ss); i++ {
		for j := 0; j < len(m.ss[i]); j++ {
			result = append(result, m.ss[i][j][:]...)
		}
	}
	result = append(result, m.cc[:]...)
	return
}

func (r *RctSigBase) SerializeBase() (result []byte) {
	result = []byte{r.sigType}
	// Null type returns right away
	if r.sigType == RCTTypeNull {
		return
	}
	result = append(result, Uint64ToBytes(r.txFee)...)
	if r.sigType == RCTTypeSimple {
		for _, input := range r.pseudoOuts {
			result = append(result, input[:]...)
		}
	}
	for _, ecdh := range r.ECdhInfo {
		result = append(result, ecdh.Mask[:]...)
		result = append(result, ecdh.Amount[:]...)
	}
	for _, ctKey := range r.OutPk {
		result = append(result, ctKey.Mask[:]...)
	}
	return
}

func (r *RctSigBase) BaseHash() (result crypto.Hash) {
	result = crypto.Keccak256(r.SerializeBase())
	return
}

func (r *RctSig) SerializePrunable() (result []byte) {
	if r.sigType == RCTTypeNull {
		return
	}
	for _, rangeSig := range r.rangeSigs {
		result = append(result, rangeSig.Serialize()...)
	}
	for _, mlsagSig := range r.MlsagSigs {
		result = append(result, mlsagSig.Serialize()...)
	}
	return
}

func (r *RctSig) Get_Sig_Type() byte {
	return r.sigType
}

func (r *RctSig) Get_TX_Fee() (result uint64) {
	if r.sigType == RCTTypeNull {
		panic("RCTTypeNull cannot have TX fee")
	}
	return r.txFee
}

func (r *RctSig) PrunableHash() (result crypto.Hash) {
	if r.sigType == RCTTypeNull {
		return
	}
	result = crypto.Keccak256(r.SerializePrunable())
	return
}

// this is the function which should be used by external world
// if any exceptions occur while handling, we simply return false
// transaction must be expanded before verification
// coinbase transactions are always success, since they are tied to PoW of block
func (r *RctSig) Verify() (result bool) {

	result = false
	defer func() { // safety so if anything wrong happens, verification fails
		if r := recover(); r != nil {
			//connection.logger.Fatalf("Recovered while Verify transaction", r)
			fmt.Printf("Recovered while Verify transaction")
			result = false
		}
	}()

	switch r.sigType {
	case RCTTypeNull:
		return true /// this is only possible for miner tx
	case RCTTypeFull:
		return r.VerifyRctFull()
	case RCTTypeSimple:
		return r.VerifyRctSimple()

	default:
		return false
	}

	// can never reach here
	// return false
}

// Verify a RCTTypeSimple RingCT Signature
func (r *RctSig) VerifyRctSimple() bool {
	sumOutPks := identity()
	for _, ctKey := range r.OutPk {
		AddKeys(sumOutPks, sumOutPks, &ctKey.Mask)
	}
	//txFeeKey := ScalarMultH(d2h(r.txFee))
	txFeeKey := Commitment_From_Amount(r.txFee)
	AddKeys(sumOutPks, sumOutPks, &txFeeKey)
	sumPseudoOuts := identity()
	for _, pseudoOut := range r.pseudoOuts {
		AddKeys(sumPseudoOuts, sumPseudoOuts, &pseudoOut)
	}
	if *sumPseudoOuts != *sumOutPks {
		return false
	}
	for i, ctKey := range r.OutPk {
		if !VerifyRange(&ctKey.Mask, r.rangeSigs[i]) {
			return false
		}
	}

	return r.VerifyRCTSimple_Core()
}

func (r *RctSig) VerifyRctFull() bool {
	for i, ctKey := range r.OutPk {
		if !VerifyRange(&ctKey.Mask, r.rangeSigs[i]) {
			return false
		}
	}
	return r.VerifyRCTFull_Core()
}

func ParseCtKey(buf io.Reader) (result CtKey, err error) {
	if result.Mask, err = ParseKey(buf); err != nil {
		return
	}
	return
}

func ParseKey64(buf io.Reader) (result Key64, err error) {
	for i := 0; i < 64; i++ {
		if result[i], err = ParseKey(buf); err != nil {
			return
		}
	}
	return
}

// parse Borromean signature
func ParseBoroSig(buf io.Reader) (result BoroSig, err error) {
	if result.s0, err = ParseKey64(buf); err != nil {
		return
	}
	if result.s1, err = ParseKey64(buf); err != nil {
		return
	}
	if result.ee, err = ParseKey(buf); err != nil {
		return
	}
	return
}

// range data consists of Single Borromean sig and 64 keys for 64 bits
func ParseRangeSig(buf io.Reader) (result RangeSig, err error) {
	if result.asig, err = ParseBoroSig(buf); err != nil {
		return
	}
	if result.ci, err = ParseKey64(buf); err != nil {
		return
	}
	return
}

// parser for ringct signature
// we need to be extra cautious as almost anything cam come as input
func ParseRingCtSignature(buf io.Reader, nInputs, nOutputs, nMixin int) (result *RctSig, err error) {
	r := new(RctSig)
	sigType := make([]byte, 1)
	_, err = buf.Read(sigType)
	if err != nil {
		return
	}
	r.sigType = uint8(sigType[0])
	if r.sigType == RCTTypeNull {
		result = r
		return
	}

	/* This triggers go vet saying suspect OR
	         if (r.sigType != RCTTypeFull) || (r.sigType != RCTTypeSimple) {
			err = fmt.Errorf("Bad signature Type %d", r.sigType)
	                return
		}*/

	switch r.sigType {
	case RCTTypeFull:
	case RCTTypeSimple:
	default:
		err = fmt.Errorf("Bad signature Type %d", r.sigType)
		return

	}

	r.txFee, err = ReadVarInt(buf)
	if err != nil {
		return
	}
	var nMg, nSS int
	if r.sigType == RCTTypeSimple {
		nMg = nInputs
		nSS = 2
		r.pseudoOuts = make([]Key, nInputs)
		for i := 0; i < nInputs; i++ {
			if r.pseudoOuts[i], err = ParseKey(buf); err != nil {
				return
			}
		}
	} else {
		nMg = 1
		nSS = nInputs + 1
	}
	r.ECdhInfo = make([]ECdhTuple, nOutputs)
	for i := 0; i < nOutputs; i++ {
		if r.ECdhInfo[i].Mask, err = ParseKey(buf); err != nil {
			return
		}
		if r.ECdhInfo[i].Amount, err = ParseKey(buf); err != nil {
			return
		}
	}
	r.OutPk = make([]CtKey, nOutputs)
	for i := 0; i < nOutputs; i++ {
		if r.OutPk[i], err = ParseCtKey(buf); err != nil {
			return
		}
	}
	r.rangeSigs = make([]RangeSig, nOutputs)
	for i := 0; i < nOutputs; i++ {
		if r.rangeSigs[i], err = ParseRangeSig(buf); err != nil {
			return
		}
	}
	r.MlsagSigs = make([]MlsagSig, nMg)
	for i := 0; i < nMg; i++ {
		r.MlsagSigs[i].ss = make([][]Key, nMixin+1)
		for j := 0; j < nMixin+1; j++ {
			r.MlsagSigs[i].ss[j] = make([]Key, nSS)
			for k := 0; k < nSS; k++ {
				if r.MlsagSigs[i].ss[j][k], err = ParseKey(buf); err != nil {
					return
				}
			}
		}
		if r.MlsagSigs[i].cc, err = ParseKey(buf); err != nil {
			return
		}
	}
	result = r
	return
}

/*
   //Elliptic Curve Diffie Helman: encodes and decodes the amount b and mask a
   // where C= aG + bH
   void ecdhEncode(ecdhTuple & unmasked, const key & sharedSec) {
       key sharedSec1 = hash_to_scalar(sharedSec);
       key sharedSec2 = hash_to_scalar(sharedSec1);
       //encode
       sc_add(unmasked.mask.bytes, unmasked.mask.bytes, sharedSec1.bytes);
       sc_add(unmasked.amount.bytes, unmasked.amount.bytes, sharedSec2.bytes);
   }
   void ecdhDecode(ecdhTuple & masked, const key & sharedSec) {
       key sharedSec1 = hash_to_scalar(sharedSec);
       key sharedSec2 = hash_to_scalar(sharedSec1);
       //decode
       sc_sub(masked.mask.bytes, masked.mask.bytes, sharedSec1.bytes);
       sc_sub(masked.amount.bytes, masked.amount.bytes, sharedSec2.bytes);
   }
*/
func ecdhEncode(tuple *ECdhTuple, shared_secret Key) {
	shared_secret1 := HashToScalar(shared_secret[:])
	shared_secret2 := HashToScalar(shared_secret1[:])

	// encode
	ScAdd(&tuple.Mask, &tuple.Mask, shared_secret1)
	ScAdd(&tuple.Amount, &tuple.Amount, shared_secret2)
}

func ecdhDecode(tuple *ECdhTuple, shared_secret Key) {
	shared_secret1 := HashToScalar(shared_secret[:])
	shared_secret2 := HashToScalar(shared_secret1[:])

	// encode
	ScSub(&tuple.Mask, &tuple.Mask, shared_secret1)
	ScSub(&tuple.Amount, &tuple.Amount, shared_secret2)
}

// decode and verify a previously encrypted tuple
// the keys come in from the wallet
// tuple is the encoded data
// skey is the secret scalar key
// outpk is public key used to verify whether the decode was sucessfull
func Decode_Amount(tuple ECdhTuple, skey Key, outpk Key) (amount uint64, mask Key, result bool) {
	var Ctmp Key

	ecdhDecode(&tuple, skey) // decode the amounts

	// saniity check similiar to  original one
	// addKeys2(Ctmp, mask, amount, H);
	AddKeys2(&Ctmp, &tuple.Mask, &tuple.Amount, &H)

	if Ctmp != outpk {
		fmt.Printf("warning, amount decoded incorrectly, will be unable to spend")
		result = false
		return
	}
	amount = h2d(tuple.Amount)
	mask = tuple.Mask

	result = true
	return
}