From fdb6e9fa8b1b2597a02f5a06215f9322ebc5acfe Mon Sep 17 00:00:00 2001
From: Vladimir Domnich <v.domnich@yadro.com>
Date: Mon, 20 Nov 2023 16:05:27 +0400
Subject: [PATCH] Fix buying items from merchants

Signed-off-by: Vladimir Domnich <v.domnich@yadro.com>
---
 l6/README.md                     |  4 ++++
 l6/merchant/config.yml           |  2 +-
 l6/merchant/merchant_contract.go | 15 ++++++++++++++-
 l6/player/player_contract.go     | 17 ++++++++++++++++-
 4 files changed, 35 insertions(+), 3 deletions(-)

diff --git a/l6/README.md b/l6/README.md
index e93b5b0..1bb0f78 100644
--- a/l6/README.md
+++ b/l6/README.md
@@ -99,3 +99,7 @@ To create a new player, invoke `newPlayer` function on the player contract and s
 neo-go contract invokefunction -r http://localhost:30333 -w ../../wallet.json e7e4910b3a83ce0eff180a3f5462030391fde830 newPlayer string:demo
 ```
 
+```sh
+neo-go contract invokefunction -r http://localhost:30333 -w ../../wallet.json 8d099cb315c03c1f040d8912f1f2a84e569ca50c buyItem string:demo string:Shortbow -- 'NP8wjGz3Wvxe4gUAkTbK2McR95Y4LM2jMW:None'
+```
+
diff --git a/l6/merchant/config.yml b/l6/merchant/config.yml
index b032344..ed61056 100644
--- a/l6/merchant/config.yml
+++ b/l6/merchant/config.yml
@@ -1,6 +1,6 @@
 name: "Merchant"
 supportedstandards: []
 events:
-safemethods: ["getItemName"]
+safemethods: ["getItemName", "getLotsForSale"]
 permissions:
   - methods: ["onNEP17Payment", "transfer"]
diff --git a/l6/merchant/merchant_contract.go b/l6/merchant/merchant_contract.go
index d952168..76e6b95 100644
--- a/l6/merchant/merchant_contract.go
+++ b/l6/merchant/merchant_contract.go
@@ -2,6 +2,7 @@ package player
 
 import (
 	"github.com/nspcc-dev/neo-go/pkg/interop"
+	"github.com/nspcc-dev/neo-go/pkg/interop/iterator"
 	"github.com/nspcc-dev/neo-go/pkg/interop/native/gas"
 	"github.com/nspcc-dev/neo-go/pkg/interop/native/std"
 	"github.com/nspcc-dev/neo-go/pkg/interop/runtime"
@@ -47,6 +48,18 @@ func GetItemName(lotID int) string {
 	return getLot(storage.GetReadOnlyContext(), lotID).itemName
 }
 
+func GetLotsForSale() []Lot {
+	lots := make([]Lot, 0)
+
+	ctx := storage.GetReadOnlyContext()
+	it := storage.Find(ctx, lotsPrefix, storage.ValuesOnly|storage.DeserializeValues)
+	for iterator.Next(it) {
+		lot := iterator.Value(it).(Lot)
+		lots = append(lots, lot)
+	}
+	return lots
+}
+
 func Sell(itemName string, price int) {
 	ctx := storage.GetContext()
 	playerHash := storage.Get(ctx, playerHashKey).(interop.Hash160)
@@ -63,7 +76,7 @@ func Sell(itemName string, price int) {
 		gasAmount := price * gasDecimals
 		success := gas.Transfer(runtime.GetExecutingScriptHash(), runtime.GetScriptContainer().Sender, gasAmount, nil)
 		if !success {
-			panic("failed to transfer gas")
+			panic("failed to transfer gas to seller")
 		}
 	}
 
diff --git a/l6/player/player_contract.go b/l6/player/player_contract.go
index 7c2fee5..0f36e34 100644
--- a/l6/player/player_contract.go
+++ b/l6/player/player_contract.go
@@ -7,8 +7,11 @@ import (
 	"github.com/nspcc-dev/neo-go/pkg/interop/native/std"
 	"github.com/nspcc-dev/neo-go/pkg/interop/runtime"
 	"github.com/nspcc-dev/neo-go/pkg/interop/storage"
+	"github.com/nspcc-dev/neo-go/pkg/interop/util"
 )
 
+const gasDecimals = 1_0000_0000
+
 var itemPrices = map[string]int{
 	"Sword":    100,
 	"Shortbow": 50,
@@ -94,7 +97,11 @@ func BuyItemForGas(playerName string, lotID int, itemPrice int, merchantHash int
 
 	itemName := contract.Call(merchantHash, "getItemName", contract.ReadOnly, lotID).(string)
 
-	gas.Transfer(runtime.GetScriptContainer().Sender, merchantHash, itemPrice, lotID)
+	gasPrice := itemPrice * gasDecimals
+	success := gas.Transfer(runtime.GetScriptContainer().Sender, merchantHash, gasPrice, lotID)
+	if !success {
+		panic("failed to transfer gas to merchant")
+	}
 
 	addItemToInventory(player, itemName)
 	savePlayer(ctx, playerName, player)
@@ -112,7 +119,15 @@ func SellItemForGas(playerName string, itemName string, itemPrice int, merchantH
 	}
 	removeItemFromInventory(player, itemName)
 
+	balanceBefore := gas.BalanceOf(runtime.GetScriptContainer().Sender)
 	contract.Call(merchantHash, "sell", contract.All, itemName, itemPrice)
+	balanceAfter := gas.BalanceOf(runtime.GetScriptContainer().Sender)
+
+	gasProfit := (balanceAfter - balanceBefore)
+	if gasProfit < itemPrice*gasDecimals {
+		runtime.Log("merchant payment does not cover item price: " + std.Itoa10(gasProfit) + " < " + std.Itoa10(itemPrice*gasDecimals))
+		util.Abort()
+	}
 
 	savePlayer(ctx, playerName, player)
 }