import Foundation

@dynamicMemberLookup
public struct Flagged: Equatable {
  
  public var checkValue: CheckHandler
  public var wrappedValue: Double
  
  public init(
    wrappedValue: Double,
    _ handler: CheckHandler
  ) {
    self.checkValue = handler
    self.wrappedValue = wrappedValue
  }
  
  public init(
    wrappedValue: Double,
    _ checkValue: @escaping (Double) -> CheckResult
  ) {
    self.checkValue = .init(checkValue)
    self.wrappedValue = wrappedValue
  }
  
  public static func error(_ wrappedValue: Double? = nil, message: String) -> Self {
    self.init(wrappedValue: wrappedValue ?? 0) { _ in
      return .error(message)
    }
  }
 
  public var projectedValue: CheckResult {
    checkValue(wrappedValue)
  }
  
  public struct GoodMessageHandler {
    let message: (Double) -> String?
    
    public init(message: @escaping (Double) -> String?) {
      self.message = message
    }
    
    public func callAsFunction(_ double: Double) -> String? {
      self.message(double)
    }
    
    public static var none: Self {
      .init { _ in nil }
    }
  }
  
  public struct CheckHandler {
    
    let checkValue: (Double) -> CheckResult
    
    public init(_ checkValue: @escaping (Double) -> CheckResult) {
      self.checkValue = checkValue
    }
    
    public func callAsFunction(_ value: Double) -> CheckResult {
      self.checkValue(value)
    }
  }
  
  public enum CheckResult: Equatable {
    
    case aboveMaximum(Double)
    case belowMinimum(Double)
    case betweenRange(minimum: Double, maximum: Double)
    case betweenRatedAndMaximum(rated: Double, maximum: Double)
    case good(String? = nil)
    case error(String)
    
    public var status: Status {
      switch self {
      case .aboveMaximum(_):
        return .error
      case .belowMinimum(_):
        return .error
      case .betweenRange:
        return .warning
      case .betweenRatedAndMaximum:
        return .warning
      case .good(_):
        return .good
      case .error(_):
        return .error
      }
    }

    public var message: String? {
      switch self {
      case let .aboveMaximum(max):
        return "Above maximum: \(doubleString(max))"

      case let .belowMinimum(min):
        return "Below minimum: \(doubleString(min))"

      case .betweenRange(minimum: let minimum, maximum: let maximum):
        return "Between: \(minimum) and \(maximum)"

      case .betweenRatedAndMaximum(rated: let rated, maximum: let maximum):
        return "Between rated: \(doubleString(rated)) and maximum: \(doubleString(maximum))"

      case let .good(goodMessage):
        return goodMessage

      case let .error(errorMessage):
        return errorMessage

      }
    }

    public enum Status: String, Equatable, CaseIterable {
      case good, warning, error

      public var title: String {
        self.rawValue.capitalized
      }
    }

  }
  
  public static func == (lhs: Flagged, rhs: Flagged) -> Bool {
    lhs.wrappedValue == rhs.wrappedValue
  }
  
  public subscript<T>(dynamicMember keyPath: KeyPath<CheckResult, T>) -> T {
    self.projectedValue[keyPath: keyPath]
  }
}

// MARK: - Check Handlers
extension Flagged.CheckHandler {
  public static func using(
    maximum: Double,
    minimum: Double,
    rated: Double,
    goodMessage: Flagged.GoodMessageHandler = .none
  ) -> Self {
    .init { value in
      if value < minimum {
        return .belowMinimum(minimum)
      } else if value > maximum {
        return .aboveMaximum(maximum)
      } else if value > rated {
        return .betweenRatedAndMaximum(rated: rated, maximum: maximum)
      } else {
        return .good(goodMessage(value))
      }
    }
  }
  
  public static func airflow(
    tons: CoolingCapacity,
    ratings: RatedAirflowPerTon = .init(),
    goodMessage: Flagged.GoodMessageHandler? = nil
  ) -> Self {
    .rated(RatedAirflowLimits(tons: tons, using: ratings), goodMessage: goodMessage)
  }

  public static func percent(
    goodMessage: Flagged.GoodMessageHandler = .none
  ) -> Self {
    .using(maximum: 100, minimum: 100, rated: 100)
  }

  public static func rated<T>(
    _ ratings: RatedEnvelope<T>,
    goodMessage: Flagged.GoodMessageHandler? = nil
  ) -> Self {
    .using(
      maximum: ratings.maximum,
      minimum: ratings.minimum,
      rated: ratings.rated,
      goodMessage: goodMessage ?? .none
    )
  }
  
  public static func result(_ result: Flagged.CheckResult) -> Self {
    self.init { _ in result }
  }
  
  public static func velocity(
    goodMessage: Flagged.GoodMessageHandler = .none
  ) -> Self {
    .init { value in
      if value <= 700 {
        return .good(goodMessage(value))
      } else if value < 900 {
        return .betweenRange(minimum: 700, maximum: 900)
      } else {
        return .error("Velocity greater than 900 FPM")
      }
    }
  }
}

// MARK: - Helpers
fileprivate let formatter: NumberFormatter = {
  let formatter = NumberFormatter()
  formatter.numberStyle = .decimal
  formatter.maximumFractionDigits = 2
  return formatter
}()

fileprivate func doubleString(_ double: Double) -> String {
  return formatter.string(for: double) ?? "\(double)"
}