WIP: Html view that prints to pdf ok.

Sources/ManualDCore/FrictionRate.swift

@@ -3,6 +3,7 @@
 public struct FrictionRate: Codable, Equatable, Sendable {
   public let availableStaticPressure: Double
   public let value: Double
+  public var hasErrors: Bool { error != nil }
 
   public init(
     availableStaticPressure: Double,
@@ -11,4 +12,40 @@ public struct FrictionRate: Codable, Equatable, Sendable {
     self.availableStaticPressure = availableStaticPressure
     self.value = value
   }
+
+  public var error: FrictionRateError? {
+    if value >= 0.18 {
+      return .init(
+        "Friction rate should be lower than 0.18",
+        resolutions: [
+          "Decrease the blower speed",
+          "Decrease the blower size",
+          "Increase the Total Equivalent Length",
+        ]
+      )
+    } else if value <= 0.02 {
+      return .init(
+        "Friction rate should be higher than 0.02",
+        resolutions: [
+          "Increase the blower speed",
+          "Increase the blower size",
+          "Decrease the Total Equivalent Length",
+        ]
+      )
+    }
+    return nil
+  }
+}
+
+public struct FrictionRateError: Error, Equatable, Sendable {
+  public let reason: String
+  public let resolutions: [String]
+
+  public init(
+    _ reason: String,
+    resolutions: [String]
+  ) {
+    self.reason = reason
+    self.resolutions = resolutions
+  }
 }