Make new item swap reversible

GAME.md

@@ -130,7 +130,7 @@ The app models this with the New item comparison panel:
 - Enter the new roll's base stat and effects.
 - The app shows DPS and Regen change separately.
 - If `Pet` is selected, the app chooses the current worst pet by piece score as the replacement target.
-- Swapping in the new roll stores the replaced piece and prior New item fields so the user can swap back.
+- Pressing `Swap` exchanges the new roll with the current target. The replaced target becomes the New item candidate, so pressing `Swap` again restores the previous state.
 
 ## Profiles
 

README.md

@@ -26,7 +26,7 @@ For the game rules, stat caps, formulas, assumptions, and known limitations used
    - choose what it would replace,
    - enter the new roll's value and effects,
    - compare DPS and Regen changes before swapping.
-   - use **Swap in new item** to apply it, with **Swap back** available if you want to undo.
+   - press **Swap** to exchange the new roll with the current target; pressing **Swap** again exchanges them back.
 7. Use **Best sacrifice candidates** as a quick shortlist of low-value pieces.
 
 When comparing a new pet, choose `Pet`; the app automatically compares against your currently weakest pet.

app.js

@@ -68,10 +68,10 @@ function createDefaultState() {
 function createDefaultNewItem() {
   return {
     target: "item-0",
+    targetPieceId: null,
     baseDamage: 0,
     baseHealth: 0,
     effects: [{ type: "", value: 1 }, { type: "", value: 1 }],
-    lastSwap: null,
   };
 }
 
@@ -146,10 +146,10 @@ function normalizeNewItem(candidate) {
     ...fallback,
     ...candidate,
     target: getReplacementOptions().some((option) => option.value === candidate?.target) ? candidate.target : fallback.target,
+    targetPieceId: candidate?.targetPieceId || null,
     baseDamage: Math.max(0, Number(candidate?.baseDamage || 0)),
     baseHealth: Math.max(0, Number(candidate?.baseHealth || 0)),
     effects,
-    lastSwap: candidate?.lastSwap || null,
   };
 }
 
@@ -367,9 +367,7 @@ function updateNewItemImpactHints(replacementTotals, replacementDps) {
 }
 
 function updateSwapControls() {
-  const hasSwap = Boolean(state.newItem.lastSwap);
-  $("#swapBackNewItem").disabled = !hasSwap;
-  $("#swapStatus").textContent = hasSwap ? `Can swap back ${state.newItem.lastSwap.piece?.name || "previous item"}.` : "";
+  $("#swapStatus").textContent = "Press Swap again to exchange back.";
 }
 
 function calculateTotals() {
@@ -407,6 +405,10 @@ function getFixedReplacementTarget(target) {
 }
 
 function getReplacementTargetPiece(target, pieceScores) {
+  if (state.newItem.targetPieceId) {
+    const pinned = state.pieces.find((piece) => piece.id === state.newItem.targetPieceId);
+    if (pinned) return pinned;
+  }
   if (target === "mount") return state.pieces.find((piece) => piece.type === "mount") || null;
   if (target === "pet") {
     return [...pieceScores]
@@ -457,7 +459,6 @@ function cloneNewItem(newItem) {
   return {
     ...newItem,
     effects: newItem.effects.map((effect) => ({ ...effect })),
-    lastSwap: null,
   };
 }
 
@@ -472,25 +473,21 @@ function swapInNewItem() {
   const previousPiece = clonePiece(targetPiece);
   const previousNewItem = cloneNewItem(state.newItem);
   state.pieces[index] = createPieceFromCandidate(targetPiece, candidate);
-  state.newItem = {
-    ...previousNewItem,
-    lastSwap: {
-      index,
-      target: previousNewItem.target,
-      piece: previousPiece,
-      newItem: previousNewItem,
-      swappedAt: new Date().toISOString(),
-    },
-  };
+  state.newItem = createNewItemFromPiece(previousPiece, previousNewItem.target, targetPiece.id);
   render();
 }
 
-function swapBackNewItem() {
-  const lastSwap = state.newItem.lastSwap;
-  if (!lastSwap || !state.pieces[lastSwap.index]) return;
-  state.pieces[lastSwap.index] = clonePiece(lastSwap.piece);
-  state.newItem = cloneNewItem(lastSwap.newItem);
-  render();
+function createNewItemFromPiece(piece, target, targetPieceId = null) {
+  return {
+    target,
+    targetPieceId,
+    baseDamage: Number(piece.baseDamage || 0),
+    baseHealth: Number(piece.baseHealth || 0),
+    effects: [0, 1].map((index) => ({
+      type: piece.effects?.[index]?.type || "",
+      value: piece.effects?.[index]?.value || 1,
+    })),
+  };
 }
 
 function formatDelta(value, suffix = "") {
@@ -833,11 +830,11 @@ function bindEvents() {
   $("#importFile").addEventListener("change", importUploadedJson);
   $("#newItemTarget").addEventListener("change", (event) => {
     state.newItem.target = event.target.value;
+    state.newItem.targetPieceId = null;
     renderNewItemComparison();
     updateAnalysis();
   });
   $("#swapNewItem").addEventListener("click", swapInNewItem);
-  $("#swapBackNewItem").addEventListener("click", swapBackNewItem);
   $(".new-item-card").addEventListener("input", handleNewItemInput);
   $(".new-item-card").addEventListener("change", handleNewItemInput);
 }

index.html

@@ -105,8 +105,7 @@
           <div><span>Regen change</span><strong id="replacementRegenDelta">0</strong></div>
         </div>
         <div class="swap-actions">
-          <button id="swapNewItem" type="button">Swap in new item</button>
-          <button id="swapBackNewItem" type="button" class="secondary" disabled>Swap back</button>
+          <button id="swapNewItem" type="button">Swap</button>
           <span id="swapStatus" class="status"></span>
         </div>
       </section>