import Foundation
import Logging
import OrderedCollections
import Routes

public extension AtticVentilation.Request {
  private static let stackEffectCoefficient = 0.0188
  private static let windEffectCoefficient = 0.0299
  private static let minimumVentRatio = 1.0 / 300.0
  private static let recommendedVentRatio = 1.0 / 150
  private static let intakeToExhaustRatio = 1.5

  // swiftlint:disable function_body_length
  func respond(logger: Logger) async throws -> AtticVentilation.Response {
    try validate()

    var recommendations = [String]()
    var warnings = [String]()
    var ventilationStatus: AtticVentilation.VentilationStatus = .adequate

    let temperatureDifference = checkTemperatureDifferential(
      ventilationStatus: &ventilationStatus,
      warnings: &warnings
    )

    let dewpointDifference = atticDewpoint - outdoorDewpoint

    let stackEffect = Self.stackEffectCoefficient * atticFloorArea * sqrt(abs(temperatureDifference))
      * (temperatureDifference < 0 ? -1 : 1)

    let minimumVentArea = atticFloorArea * Self.minimumVentRatio
    let recommendVentArea = atticFloorArea * Self.recommendedVentRatio
    let requiredIntake = (recommendVentArea * Self.intakeToExhaustRatio) / (1 + Self.intakeToExhaustRatio)
    let requiredExhaust = recommendVentArea - requiredIntake

    if abs(pressureDifferential) > 2 {
      warnings.append(
        "High pressure differential - may indicate blocked or inadequate ventilation"
      )
      if ventilationStatus != .critical {
        ventilationStatus = .inadequate
      }
    }

    if abs(dewpointDifference) > 5 {
      warnings.append(
        "High moisture levels in the attic - increased ventilation is recommended"
      )
      if ventilationStatus != .critical {
        ventilationStatus = .inadequate
      }
    }

    // compare existing ventilation to requirements.
    checkExistingAreas(
      minimumVentArea: minimumVentArea,
      recommendVentArea: recommendVentArea,
      requiredIntake: requiredIntake,
      requiredExhaust: requiredExhaust,
      recommendations: &recommendations,
      ventilationStatus: &ventilationStatus,
      warnings: &warnings
    )

    // Pressure recommendations
    addPressureRecommendations(&recommendations)

    return .init(
      pressureDifferential: pressureDifferential,
      temperatureDifferential: temperatureDifference,
      dewpointDifferential: dewpointDifference,
      stackEffect: stackEffect,
      requiredVentilationArea: .init(intake: requiredIntake, exhaust: requiredExhaust),
      recommendations: recommendations,
      warnings: warnings,
      ventilationStatus: ventilationStatus
    )
  }

  // swiftlint:enable function_body_length

  private func checkTemperatureDifferential(
    ventilationStatus: inout AtticVentilation.VentilationStatus,
    warnings: inout [String]
  ) -> Double {
    let temperatureDifference = atticTemperature - outdoorTemperature
    let absTempDiff = abs(temperatureDifference)
    if absTempDiff > 20 {
      warnings.append(
        "High temperature differential - indicates insufficient ventilation."
      )
      ventilationStatus = .inadequate
    }
    if absTempDiff > 30 {
      warnings.append(
        "Critical temperature differential - immediate action recommended"
      )
      ventilationStatus = .critical
    }
    return temperatureDifference
  }

  // swiftlint:disable function_parameter_count
  private func checkExistingAreas(
    minimumVentArea: Double,
    recommendVentArea: Double,
    requiredIntake: Double,
    requiredExhaust: Double,
    recommendations: inout [String],
    ventilationStatus: inout AtticVentilation.VentilationStatus,
    warnings: inout [String]
  ) {
    if let existingIntakeArea, let existingExhaustArea {
      let totalExisting = existingIntakeArea + existingExhaustArea
      if totalExisting < minimumVentArea {
        warnings.append("Existing ventilation area below minimum requirement.")
        if ventilationStatus != .critical {
          ventilationStatus = .inadequate
        }
      } else if totalExisting < recommendVentArea {
        recommendations.append("Consider increasing ventilation area to meet recommended guidelines.")
      }

      if existingIntakeArea < requiredIntake {
        recommendations.append(
          "Add \(double: requiredIntake - existingIntakeArea, fractionDigits: 1) ft² of intake ventilation."
        )
      }
      if existingExhaustArea < requiredExhaust {
        recommendations.append(
          "Add \(double: requiredExhaust - existingExhaustArea, fractionDigits: 1) ft² of exhaust ventilation."
        )
      }
    } else {
      recommendations.append(
        "Add \(double: requiredIntake, fractionDigits: 1) ft² of intake ventilation."
      )
      recommendations.append(
        "Add \(double: requiredExhaust, fractionDigits: 1) ft² of exhaust ventilation."
      )
    }
  }

  // swiftlint:enable function_parameter_count

  private func addPressureRecommendations(_ recommendations: inout [String]) {
    if pressureDifferential > 0 {
      recommendations.append("Consider adding more exhaust ventilation to balance pressure.")
    } else if pressureDifferential < 0 {
      recommendations.append("Consider adding more intake ventilation to balance pressure.")
    }
  }

  private func validate() throws {
    guard atticFloorArea > 0 else {
      throw ValidationError(message: "Attic floor area should be greater than 0.")
    }
    if let existingIntakeArea, existingIntakeArea < 0 {
      throw ValidationError(message: "Existing intake area should be greater than 0.")
    }
    if let existingExhaustArea, existingExhaustArea < 0 {
      throw ValidationError(message: "Existing exhaust area should be greater than 0.")
    }
  }
}