import Dependencies
import Logging
import PsychrometricClient
import Routes

public extension FeetOfHead.Request {

  private static let specificGravity = 1.02

  func respond(logger: Logger) async throws -> FeetOfHead.Response {
    @Dependency(\.psychrometricClient) var psychrometricClient

    try validate()
    let waterTemperature = DryBulb.fahrenheit(self.waterTemperature ?? 60)
    let density = try await psychrometricClient.density.water(waterTemperature)
    let feetOfHead = pressure / ((density.value / 144) * Self.specificGravity)
    var warnings = [String]()

    if self.waterTemperature == nil {
      warnings.append(
        "Calculations are based on 60°F water temperature."
      )
    }

    return .init(feetOfHead: feetOfHead, density: density, warnings: warnings)
  }

  private func validate() throws {
    guard pressure > 0 else {
      throw ValidationError(message: "Pressure should be greater than 0.")
    }
    if let waterTemperature {
      guard waterTemperature > 32 else {
        throw ValidationError(message: "Water temperature should be above freezing.")
      }
    }
  }
}