From 23fc2ccdf99a714b9bbfbb16d72da5ece61a776d Mon Sep 17 00:00:00 2001
From: "ev.lekht" <ev.lekht@gmail.com>
Date: Tue, 17 Sep 2024 16:03:12 +0400
Subject: [PATCH] cheque verification

---
 pkg/cheques/cheques.go | 27 +++++++++++++++++++++++++++
 pkg/matrix/types.go    | 11 +++++++++++
 2 files changed, 38 insertions(+)

diff --git a/pkg/cheques/cheques.go b/pkg/cheques/cheques.go
index 57033e0d..7701a131 100644
--- a/pkg/cheques/cheques.go
+++ b/pkg/cheques/cheques.go
@@ -3,6 +3,7 @@ package cheques
 import (
 	"encoding/hex"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"math/big"
 
@@ -10,6 +11,13 @@ import (
 	"github.com/ethereum/go-ethereum/common/hexutil"
 )
 
+var (
+	ErrChequeAlreadyExpired                = errors.New("cheque already expired")
+	ErrChequeExpiresTooSoon                = errors.New("cheque expires too soon")
+	ErrChequeAmountLessThanPrevious        = errors.New("new cheque amount less than previous cheque amount")
+	ErrChequeCounterNotGreaterThanPrevious = errors.New("new cheque counter not greater than previous cheque counter")
+)
+
 type SignedCheque struct {
 	Cheque    `json:"cheque"`
 	Signature []byte `json:"signature"`
@@ -87,3 +95,22 @@ func (sc *SignedCheque) UnmarshalJSON(data []byte) error {
 
 	return nil
 }
+
+func VerifyCheque(previousCheque, newCheque *SignedCheque, timestamp, minDurationUntilExpiration *big.Int) error {
+	if newCheque.ExpiresAt.Cmp(timestamp) < 1 { // cheque.ExpiresAt <= timestamp
+		return fmt.Errorf("cheque expired at %s; %w", newCheque.ExpiresAt, ErrChequeAlreadyExpired)
+	}
+	durationUntilExpiration := big.NewInt(0).Sub(newCheque.ExpiresAt, timestamp)
+	if durationUntilExpiration.Cmp(minDurationUntilExpiration) < 0 { // durationUntilExpiration < minDurationUntilExpiration
+		return fmt.Errorf("duration until expiration less than min (%s < %s): %w", durationUntilExpiration, minDurationUntilExpiration, ErrChequeExpiresTooSoon)
+	}
+	switch {
+	case previousCheque == nil:
+		return nil
+	case previousCheque.Amount.Cmp(newCheque.Amount) > 0: // previous.Amount > new.Amount
+		return fmt.Errorf("new cheque amount (%s) < (%s) previous cheque amount: %w", newCheque.Amount, previousCheque.Amount, ErrChequeAmountLessThanPrevious)
+	case previousCheque.Counter.Cmp(newCheque.Counter) > -1: // previous.Counter >= new.Counter
+		return fmt.Errorf("new cheque counter (%s) <= (%s) previous cheque counter: %w", newCheque.Counter, previousCheque.Counter, ErrChequeCounterNotGreaterThanPrevious)
+	}
+	return nil
+}
diff --git a/pkg/matrix/types.go b/pkg/matrix/types.go
index 2cdc1f82..0752aacb 100644
--- a/pkg/matrix/types.go
+++ b/pkg/matrix/types.go
@@ -14,6 +14,8 @@ import (
 	transportv1 "buf.build/gen/go/chain4travel/camino-messenger-protocol/protocolbuffers/go/cmp/services/transport/v1"
 	"github.com/chain4travel/camino-messenger-bot/internal/messaging"
 	"github.com/chain4travel/camino-messenger-bot/internal/metadata"
+	"github.com/chain4travel/camino-messenger-bot/pkg/cheques"
+	"github.com/ethereum/go-ethereum/common"
 	"google.golang.org/protobuf/proto"
 	"maunium.net/go/mautrix/event"
 )
@@ -136,3 +138,12 @@ func (m *CaminoMatrixMessage) UnmarshalContent(src []byte) error {
 		return messaging.ErrUnknownMessageType
 	}
 }
+
+func (m *CaminoMatrixMessage) GetChequeFor(addr common.Address) *cheques.SignedCheque {
+	for _, cheque := range m.Metadata.Cheques {
+		if cheque.Cheque.ToCMAccount == addr {
+			return &cheque
+		}
+	}
+	return nil
+}