From 69c97839552f9126e51e1e0ba216c76110001d37 Mon Sep 17 00:00:00 2001
From: Ricardo Guilherme Schmidt <3esmit@gmail.com>
Date: Fri, 17 Jul 2026 20:45:42 -0300
Subject: [PATCH] fix(amm): prevent swaps with identical tokens

---
 apps/amm/qml/components/swap/SwapCard.qml | 25 +++++++++++++++---
 apps/amm/tests/qml/tst_SwapPage.qml       | 31 +++++++++++++++++++++++
 2 files changed, 53 insertions(+), 3 deletions(-)

diff --git a/apps/amm/qml/components/swap/SwapCard.qml b/apps/amm/qml/components/swap/SwapCard.qml
index f27434e..5bcbcc6 100644
--- a/apps/amm/qml/components/swap/SwapCard.qml
+++ b/apps/amm/qml/components/swap/SwapCard.qml
@@ -24,9 +24,26 @@ Rectangle {
     signal requestTokenSelect(string side)
     signal previewRequested(var snapshot)
 
+    function isSameToken(left, right) {
+        if (!left || !right)
+            return false
+        if (left.address && right.address)
+            return String(left.address) === String(right.address)
+        return left === right
+    }
+
     function setToken(side, token) {
-        if (side === "sell") root.sellToken = token
-        else root.buyToken = token
+        if (side === "sell") {
+            const previousSellToken = root.sellToken
+            if (root.isSameToken(token, root.buyToken))
+                root.buyToken = previousSellToken
+            root.sellToken = token
+        } else {
+            const previousBuyToken = root.buyToken
+            if (root.isSameToken(token, root.sellToken))
+                root.sellToken = previousBuyToken
+            root.buyToken = token
+        }
     }
 
     readonly property real sellReserve: sellToken ? (sellToken.reserve || 0) : 0
@@ -65,11 +82,13 @@ Rectangle {
 
     readonly property bool hasAmount: editingSide === "sell" ? parsedSellInput > 0 : parsedBuyInput > 0
     readonly property bool tokensSelected: sellToken !== null && buyToken !== null
+    readonly property bool sameTokenSelected: isSameToken(sellToken, buyToken)
     readonly property bool insufficientBalance: hasAmount && sellToken !== null && parsedSellAmount > (sellToken.balance || 0)
     readonly property bool insufficientLiquidity: hasAmount && buyToken !== null && parsedBuyAmount > (buyToken.reserve || 0)
-    readonly property bool canSubmit: tokensSelected && hasAmount && parsedSellAmount > 0 && parsedBuyAmount > 0 && !insufficientBalance && !insufficientLiquidity
+    readonly property bool canSubmit: tokensSelected && !sameTokenSelected && hasAmount && parsedSellAmount > 0 && parsedBuyAmount > 0 && !insufficientBalance && !insufficientLiquidity
 
     readonly property string submitButtonText: {
+        if (sameTokenSelected) return qsTr("Select different tokens")
         if (!hasAmount || !tokensSelected) return qsTr("Enter an amount")
         if (insufficientBalance) return qsTr("Insufficient balance")
         if (insufficientLiquidity) return qsTr("Insufficient liquidity")
diff --git a/apps/amm/tests/qml/tst_SwapPage.qml b/apps/amm/tests/qml/tst_SwapPage.qml
index 1675e77..101072d 100644
--- a/apps/amm/tests/qml/tst_SwapPage.qml
+++ b/apps/amm/tests/qml/tst_SwapPage.qml
@@ -107,5 +107,36 @@ Item {
             verify(snapshot.minReceived.length > 0)
             verify(Number(snapshot.minReceived) < Number(snapshot.buyAmount))
         }
+
+        function test_reselectingOppositeTokenSwapsPair() {
+            const page = createTemporaryObject(pageComponent, root)
+            verify(page)
+
+            const card = findChild(page, "swapCard")
+            verify(card)
+            card.setToken("sell", page.tokens[0])
+            card.setToken("buy", page.tokens[1])
+            card.setToken("buy", page.tokens[0])
+
+            compare(card.sellToken.address, page.tokens[1].address)
+            compare(card.buyToken.address, page.tokens[0].address)
+            verify(!card.sameTokenSelected)
+        }
+
+        function test_sameTokenPairCannotBePreviewed() {
+            const page = createTemporaryObject(pageComponent, root)
+            verify(page)
+
+            const card = findChild(page, "swapCard")
+            verify(card)
+            card.sellToken = page.tokens[0]
+            card.buyToken = page.tokens[0]
+            card.sellInput = "1"
+            card.editingSide = "sell"
+
+            verify(card.sameTokenSelected)
+            verify(!card.canSubmit)
+            compare(card.submitButtonText, "Select different tokens")
+        }
     }
 }