add min d price

fuel-calc.html

@@ -48,7 +48,8 @@
 
     <div class="result-box">
         To offset the tax difference at <span id="displayKm">17500</span> km/year, 
-        a petrol car would need to consume at least <b id="breakEvenCons">0.00</b> L/100km.
+        a petrol car would need to consume at least <b id="breakEvenCons">0.00</b> L/100km, 
+        or the diesel price should be at least <b id="minDieselPrice">0.00</b> €/L.
     </div>
 
     <table id="comparisonTable">

script.js

@@ -18,7 +18,22 @@ function calculate() {
     document.getElementById('displayKm').innerText = annualKm.toLocaleString();
     document.getElementById('breakEvenCons').innerText = isFinite(breakEven) ? breakEven.toFixed(2) : "0.00";
 
-    // 2. Generate Table
+    // 2. Calculate Minimum Diesel Price where user's pCons equals break-even consumption
+    // We want to solve for dPrice such that: pCons = (100 * taxDiff / (annualKm * pPrice)) + (dCons * dPrice / pPrice)
+    // Rearranging for dPrice:
+    // pCons - (100 * taxDiff / (annualKm * pPrice)) = (dCons * dPrice / pPrice)
+    // dPrice = (pCons - (100 * taxDiff / (annualKm * pPrice))) * pPrice / dCons
+    
+    let minDieselPrice = 0;
+    if (dCons > 0 && annualKm > 0 && pPrice > 0) {
+        const firstTerm = 100 * taxDiff / (annualKm * pPrice);
+        const secondTerm = pCons - firstTerm;
+        minDieselPrice = secondTerm * pPrice / dCons;
+    }
+    
+    document.getElementById('minDieselPrice').innerText = isFinite(minDieselPrice) ? minDieselPrice.toFixed(2) : "0.00";
+
+    // 3. Generate Table
     const distances = [5000, 10000, 15000, 20000, 25000, 30000];
     const tbody = document.querySelector('#comparisonTable tbody');
     tbody.innerHTML = '';