Update withdraw mechanism

Withdraw operation works a bit different with neo:morph.
User calls "Deposit" and "Withdraw" methods that produce
notifications for the inner ring nodes.

"Deposit" method does not produce feedback, but "Withdraw"
does. Inner ring nodes check if user eligible to withdraw
assets. If so, nodes invoke "Cheque" method. This method
collects invocations from inner ring nods. When there are
2/3n + 1 invocations, smart-contract transfers assets back
to the user and produces notifications.

neofs_contract.go

@@ -20,7 +20,6 @@ type (
 
 	check struct {
 		id []byte
-		height []byte
 	}
 )
 
@@ -148,39 +147,74 @@ func Main(op string, args []interface{}) interface{} {
 
 		runtime.Log("funds have been transferred")
 
+		var rcv = []byte{}
+		if len(args) == 3 {
+			rcv = args[2].([]byte) // todo: check if rcv value is valid
+		}
+
+		runtime.Notify("Deposit", pk, amount, rcv)
+
 		return true
 	case "Withdraw":
-		from := engine.GetExecutingScriptHash()
-		data := args[0].([]byte)
-		message := data[0:66]
-		uuid := data[0:25]
-		owner := data[25:50]
-		value := data[50:58]
-		height := data[58:66]
-		offset := 68
-		usedList := getSerialized(ctx, "UsedVerifCheckList").([]check)
-
-		c := check{
-			id:     uuid,
-			height: height,
-		}
-		if containsCheck(usedList, c) {
-			panic("verification check has already been used")
+		if len(args) != 2 {
+			panic("withdraw: bad arguments")
 		}
 
+		user := args[0].([]byte)
+		if !runtime.CheckWitness(user) {
+			// todo: consider something different with neoID
+			panic("withdraw: you should be the owner of the account")
+		}
+
+		amount := args[1].(int)
+		if amount > 0 {
+			amount = amount * 100000000
+		}
+
+		runtime.Notify("Withdraw", user, amount)
+
+		return true
+	case "Cheque":
+		if len(args) != 4 {
+			panic("cheque: bad arguments")
+		}
+
+		id := args[0].([]byte)      // unique cheque id
+		user := args[1].([]byte)    // GAS receiver
+		amount := args[2].(int)     // amount of GAS
+		lockAcc := args[3].([]byte) // lock account from internal banking that must be cashed out
+
+		ctx := storage.GetContext()
+
+		hashID := crypto.Hash256(id)
 		irList := getSerialized(ctx, "InnerRingList").([]node)
-		if !verifySignatures(irList, data, message, offset) {
-			panic("can't verify signatures")
+		usedList := getSerialized(ctx, "UsedVerifCheckList").([]check)
+		threshold := len(irList)/3*2 + 1
+
+		if !isInnerRingRequest(irList) {
+			panic("cheque: invoked by non inner ring node")
 		}
 
-		h := owner[1:21]
-		params := []interface{}{from, h, value}
+		c := check{id: id} // todo: use different cheque id for inner ring update and withdraw
+		if containsCheck(usedList, c) {
+			panic("cheque: non unique id")
+		}
+
+		n := vote(ctx, hashID)
+		if n >= threshold {
+			removeVotes(ctx, hashID)
+
+			from := engine.GetExecutingScriptHash()
+			params := []interface{}{from, user, amount}
+
 			transferred := engine.AppCall([]byte(tokenHash), "transfer", params).(bool)
 			if !transferred {
-			panic("failed to transfer funds, aborting")
+				panic("cheque: failed to transfer funds, aborting")
 			}
 
 			putSerialized(ctx, "UsedVerifCheckList", c)
+			runtime.Notify("Cheque", id, user, amount, lockAcc)
+		}
 
 		return true
 	case "InnerRingUpdate":
@@ -387,41 +421,6 @@ func delSerializedIR(ctx storage.Context, key string, value []byte) bool {
 	runtime.Log("target element has not been removed")
 	return false
 }
-func verifySignatures(irList []node, data []byte, message []byte, offset int) bool {
-	n := len(irList)
-	f := (n - 1) / 3
-	s := n - f
-	if s < 3 {
-		runtime.Log("not enough inner ring nodes for consensus")
-		return false
-	}
-
-	used := [][]byte{}
-	count := 0
-	for count < s && offset < len(data) {
-		pubkey := data[offset : offset+33]
-		signature := data[offset+33 : offset+97]
-		if containsPub(irList, pubkey) {
-			if crypto.VerifySignature(message, signature, pubkey) {
-				count++
-				for i := 0; i < len(used); i++ {
-					if util.Equals(used[i], pubkey) {
-						panic("duplicate public keys")
-					}
-				}
-				used = append(used, pubkey)
-			}
-		}
-		offset += 97
-	}
-
-	if count >= s {
-		return true
-	}
-
-	runtime.Log("not enough verified signatures")
-	return false
-}
 
 // isInnerRingRequest returns true if contract was invoked by inner ring node.
 func isInnerRingRequest(irList []node) bool {