feat: Finishes economic balance point.

Sources/ViewController/Views/HeatingBalancePoint.swift

@@ -41,11 +41,7 @@ struct HeatingBalancePointForm: HTML, Sendable {
         case .thermal:
           ThermalFields(heatLossMode: heatLossMode)
         case .economic:
-          div {
-            // FIX:
-            WarningBox("This is still under development and may not be fully functional.")
-              .attributes(.class("mb-6"))
-          }
+          EconomicFields()
         }
 
         div {
@@ -61,6 +57,29 @@ struct HeatingBalancePointForm: HTML, Sendable {
     }
   }
 
+  struct EconomicFields: HTML, Sendable {
+    var content: some HTML {
+      div(.class("grid grid-cols-1 lg:grid-cols-2 gap-4")) {
+        div {
+          InputLabel(for: "fuelType") { "Fuel Type" }
+          Select(for: HeatingBalancePoint.FuelType.self, id: "fuelType") { $0.label }
+        }
+        LabeledContent(label: "AFUE (%)") {
+          Input(id: "fuelAFUE", placeholder: "AFUE")
+            .attributes(.type(.number), .min("1"), .max("100"), .step("0.5"), .value("90"), .required)
+        }
+        LabeledContent(label: "Fuel Cost (gallon or therm)") {
+          Input(id: "fuelCostPerUnit", placeholder: "Fuel cost per unit")
+            .attributes(.type(.number), .min("0.1"), .step("0.01"), .value("1.33"), .required)
+        }
+        LabeledContent(label: "Electric Cost (kw/h)") {
+          Input(id: "costPerKW", placeholder: "Electric cost per kw/h")
+            .attributes(.type(.number), .min("0.01"), .step("0.01"), .value("0.13"), .required)
+        }
+      }
+    }
+  }
+
   struct ThermalFields: HTML, Sendable {
     let heatLossMode: HeatingBalancePoint.HeatLoss.Mode
 
@@ -175,6 +194,8 @@ struct HeatingBalancePointResponse: HTML, Sendable {
           }
         }
         switch response {
+        case let .economic(result):
+          economicResult(result)
         case let .thermal(result):
           thermalResult(result)
         }
@@ -184,6 +205,40 @@ struct HeatingBalancePointResponse: HTML, Sendable {
     }
   }
 
+  func economicResult(_ result: HeatingBalancePoint.Response.Economic) -> some HTML {
+    div {
+      VerticalGroup(
+        label: "Balance Point",
+        value: "\(double: result.balancePointTemperature, fractionDigits: 1)",
+        valueLabel: "°F"
+      )
+      .attributes(.class("mb-8"))
+
+      div(.class("grid grid-cols-2 space-y-6")) {
+        div {
+          VerticalGroup(
+            label: "Electric Cost",
+            value: "$\(double: result.electricCostPerMMBTU, fractionDigits: 2)",
+            valueLabel: "/ MMBTU"
+          )
+        }
+        div {
+          VerticalGroup(
+            label: "Fuel Cost",
+            value: "$\(double: result.fuelCostPerMMBTU, fractionDigits: 2)",
+            valueLabel: "/ MMBTU"
+          )
+        }
+      }
+      div {
+        VerticalGroup(
+          label: "COP at Balance Point",
+          value: "\(double: result.copAtBalancePoint, fractionDigits: 2)"
+        )
+      }
+    }
+  }
+
   func thermalResult(_ result: HeatingBalancePoint.Response.Thermal) -> some HTML {
     div {
       VerticalGroup(
@@ -239,12 +294,14 @@ private extension HeatingBalancePoint.HeatLoss.Mode {
 private extension HeatingBalancePoint.Response {
   var mode: HeatingBalancePoint.Mode {
     switch self {
+    case .economic: return .economic
     case .thermal: return .thermal
     }
   }
 
   var warnings: [String] {
     switch self {
+    case .economic: return []
     case let .thermal(result): return result.warnings
     }
   }