swift-hvac-toolbox/Sources/ApiController/Extensions/RoomPressure.swift

import Foundation
import Logging
import OrderedCollections
import Routes

public extension RoomPressure.Request {

  static let pascalToIWCMultiplier = 0.004014
  static let targetVelocity = 400.0
  static let maxVelocity = 600.0
  static let minGrilleFreeArea = 0.7
  static let standardDuctSizes = OrderedSet([4, 5, 6, 7, 8, 9, 10, 12, 14, 16, 18, 20])
  static let standardGrilleHeights = OrderedSet([4, 6, 8, 10, 12, 14, 20])
  static let standardGrilleSizes = [
    4: OrderedSet([8, 10, 12, 14]),
    6: OrderedSet([8, 10, 12, 14]),
    8: OrderedSet([10, 12, 14]),
    10: OrderedSet([10]),
    12: OrderedSet([12]),
    14: OrderedSet([14])
  ]

  // OrderedSet([
  //   (width: 8, height: 4),
  //   (width: 10, height: 4),
  //   (width: 12, height: 4),
  //   (width: 14, height: 4),
  //   (width: 8, height: 6),
  //   (width: 10, height: 6),
  //   (width: 12, height: 6),
  //   (width: 14, height: 6),
  //   (width: 10, height: 8),
  //   (width: 12, height: 8),
  //   (width: 14, height: 8),
  //   (width: 10, height: 10),
  //   (width: 12, height: 12),
  //   (width: 14, height: 14)
  // ])

  func respond(logger: Logger) async throws -> RoomPressure.Response {
    switch self {
    case let .knownAirflow(request):
      return try await calculateKnownAirflow(request, logger)
    case let .measuredPressure(request):
      return try await calculateMeasuredPressure(request, logger)
    }
  }

  private func calculateKnownAirflow(
    _ request: RoomPressure.Request.KnownAirflow,
    _ logger: Logger
  ) async throws -> RoomPressure.Response {
    try request.validate()

    let totalLeakageArea = calculateDoorLeakageArea(
      doorWidth: request.doorWidth,
      doorHeight: request.doorHeight,
      doorUndercut: request.doorUndercut
    )

    // Net free area (in^2)
    let netFreeArea = (request.supplyAirflow / Self.targetVelocity) * 144.0
    let grilleDimensions = try getStandardGrilleSize(
      requiredArea: netFreeArea,
      selectedHeight: request.preferredGrilleHeight.rawValue
    )
    let (standardDuctSize, actualVelocity) = calculateDuctMetrics(for: request.supplyAirflow)

    return .init(
      grilleSize: .init(width: grilleDimensions.width, height: grilleDimensions.height, area: netFreeArea / 144),
      ductSize: .init(diameter: standardDuctSize, velocity: actualVelocity),
      warnings: generateWarnings(
        roomPressure: request.targetRoomPressure,
        actualVelocity: actualVelocity,
        totalLeakageArea: totalLeakageArea,
        netFreeArea: netFreeArea
      )
    )
  }

  private func calculateMeasuredPressure(
    _ request: RoomPressure.Request.MeasuredPressure,
    _ logger: Logger
  ) async throws -> RoomPressure.Response {
    try request.validate()

    let totalLeakageArea = calculateDoorLeakageArea(
      doorWidth: request.doorWidth,
      doorHeight: request.doorHeight,
      doorUndercut: request.doorUndercut
    )

    let pressureInchesWaterColumn = request.measuredRoomPressure * Self.pascalToIWCMultiplier
    let calculatedAirflow = totalLeakageArea * 4005 * sqrt(pressureInchesWaterColumn)
    // in^2
    let netFreeArea = (calculatedAirflow / Self.targetVelocity) * 144
    let grilleDimensions = try getStandardGrilleSize(
      requiredArea: netFreeArea,
      selectedHeight: request.preferredGrilleHeight.rawValue
    )
    let (standardDuctSize, actualVelocity) = calculateDuctMetrics(for: calculatedAirflow)

    return .init(
      grilleSize: .init(width: grilleDimensions.width, height: grilleDimensions.height, area: netFreeArea / 144),
      ductSize: .init(diameter: standardDuctSize, velocity: actualVelocity),
      calculatedAirflow: calculatedAirflow,
      warnings: generateWarnings(
        roomPressure: request.measuredRoomPressure,
        actualVelocity: actualVelocity,
        totalLeakageArea: totalLeakageArea,
        netFreeArea: netFreeArea
      )
    )
  }

  private func calculateDuctMetrics(for airflow: Double) -> (diameter: Int, velocity: Double) {
    let ductArea = airflow / Self.targetVelocity
    let ductDiameter = sqrt((4 * ductArea) / Double.pi) * 12
    let standardDuctSize = getStandardDuctSize(for: Int(ductDiameter))
    let actualVelocity = airflow / (Double.pi * pow(Double(standardDuctSize) / 24, 2))

    return (standardDuctSize, actualVelocity)
  }

  private func generateWarnings(
    roomPressure: Double,
    actualVelocity: Double,
    totalLeakageArea: Double,
    netFreeArea: Double
  ) -> [String] {
    var warnings = [String]()

    if roomPressure > 3 {
      warnings.append(
        "Room pressure exceeds 3 Pascals - consider reducing pressure differntial."
      )
    }

    if totalLeakageArea > netFreeArea / 144 * 0.5 {
      warnings.append(
        "Door leakage area is significant - consider reducing gaps or increasing grille size."
      )
    }

    if actualVelocity > Self.maxVelocity {
      warnings.append(
        "Return air velocity exceeds maximum recommended velocity - consider next size up duct."
      )
    }
    return []
  }

  private func getStandardDuctSize(for calculatedSize: Int) -> Int {
    Self.standardDuctSizes.sorted()
      .first { $0 >= calculatedSize }
      ?? 20
  }

  private func getStandardGrilleSize(requiredArea: Double, selectedHeight: Int) throws -> (width: Int, height: Int) {
    guard let availableSizes = Self.standardGrilleSizes[selectedHeight] else {
      throw RoomPressureError.invalidPreferredHeight
    }

    if let width = availableSizes.first(where: {
      Double($0) * Double(selectedHeight) * Self.minGrilleFreeArea >= (requiredArea / Self.minGrilleFreeArea)
    }) {
      return (width, selectedHeight)
    }

    // If no width matches return largest for the selectedHeight.
    if let largestSize = availableSizes.last { return (largestSize, selectedHeight) }
    return (14, selectedHeight)
  }

  // Calculate door leakage area in sq. ft.
  private func calculateDoorLeakageArea(doorWidth: Double, doorHeight: Double, doorUndercut: Double) -> Double {
    let doorLeakageArea = (doorWidth * doorUndercut) / 144.0
    let doorPerimiterLeakage = ((2 * doorHeight + doorWidth) * 0.125) / 144.0
    return doorLeakageArea + doorPerimiterLeakage
  }

  enum RoomPressureError: Error {
    case invalidPreferredHeight
  }
}

extension RoomPressure.Request.KnownAirflow {
  func validate() throws {
    guard targetRoomPressure > 0 else {
      throw ValidationError(message: "Target room pressure should be greater than 0.")
    }
    guard doorWidth > 0 else {
      throw ValidationError(message: "Door width should be greater than 0.")
    }
    guard doorHeight > 0 else {
      throw ValidationError(message: "Door height should be greater than 0.")
    }
    guard doorUndercut > 0 else {
      throw ValidationError(message: "Door undercut should be greater than 0.")
    }
    guard supplyAirflow > 0 else {
      throw ValidationError(message: "Supply airflow should be greater than 0.")
    }
  }
}

extension RoomPressure.Request.MeasuredPressure {
  func validate() throws {
    guard measuredRoomPressure > 0 else {
      throw ValidationError(message: "MeasuredPressure room pressure should be greater than 0.")
    }
    guard doorWidth > 0 else {
      throw ValidationError(message: "Door width should be greater than 0.")
    }
    guard doorHeight > 0 else {
      throw ValidationError(message: "Door height should be greater than 0.")
    }
    guard doorUndercut > 0 else {
      throw ValidationError(message: "Door undercut should be greater than 0.")
    }
  }
}