Fix calculator swap button

hdyc-svelte/src/lib/components/Calculator.svelte

@@ -14,6 +14,7 @@
   let val2 = '';
   let val3 = '';
   let activeField: 1 | 2 | 3 = 1;
+  let swapState: { originalField: 1 | 2; originalValue: string } | null = null;
 
   $: has3 = ['3col', '3col-mul'].includes(config.type) || !!config.labels.in3;
   $: isTextInput = ['base', 'text-bin', 'bin-text', 'dec-frac', 'dms-dd', 'dd-dms'].includes(config.type);
@@ -25,7 +26,10 @@
 
   let paramsInitializing = true;
 
-  function handleInput(source: 1 | 2 | 3) {
+  function handleInput(source: 1 | 2 | 3, options?: { preserveSwap?: boolean }) {
+    if (!options?.preserveSwap) {
+      swapState = null;
+    }
     activeField = source;
     const result = solve(config, source, val1, val2, val3);
     if (source !== 1) val1 = result.val1;
@@ -34,14 +38,30 @@
   }
 
   function swap() {
-    const nextSource: 1 | 2 = activeField === 1 ? 2 : 1;
-    handleInput(nextSource);
+    if (!swapState) {
+      const manualField: 1 | 2 = activeField === 1 ? 1 : 2;
+      const manualValue = manualField === 1 ? val1 : val2;
+      const targetField: 1 | 2 = manualField === 1 ? 2 : 1;
+      swapState = { originalField: manualField, originalValue: manualValue };
+      if (targetField === 1) val1 = manualValue;
+      else val2 = manualValue;
+      handleInput(targetField, { preserveSwap: true });
+      return;
+    }
+
+    const manualField = swapState.originalField;
+    const manualValue = swapState.originalValue;
+    if (manualField === 1) val1 = manualValue;
+    else val2 = manualValue;
+    swapState = null;
+    handleInput(manualField, { preserveSwap: true });
   }
 
   function clear() {
     val1 = '';
     val2 = '';
     val3 = '';
+    swapState = null;
   }
 
   onMount(() => {