DebugPrinter

DebugPrinter.swift

final class DebugPrinter {
  private var address2Name: [UnsafeMutableRawPointer: String] = [:]
  private var typeIndex: [String: Int] = [:]
  private let marker: String

  private let formatter: DateFormatter = {
    let formatter = DateFormatter()
    formatter.dateFormat = "HH:mm:ss.SSS"
    return formatter
  }()

  private var now: String {
    formatter.string(from: Date())
  }

  init(marker: String = "[T]") {
    self.marker = marker
  }

  func add<Instance>(_ object: Instance?, name: String? = nil) {
    guard let object = object else { return }

    let pointer = Unmanaged.passUnretained(object as AnyObject).toOpaque()
    guard address2Name[pointer] == nil else { return }

    let name = name ?? String(describing: type(of: object))

    typeIndex[name, default: 0] += 1
    let index = typeIndex[name]!

    address2Name[pointer] = "<\(name) #\(index)>"
  }

  func print<Instance>(
    _ object: Instance?,
    function: String = #function,
    _ extra: String = ""
  ) {
    Swift.print(marker, now, "\(name(object)).\(function)", extra)
  }

  func name<Instance>(_ object: Instance?) -> String {
    let typeName = String(describing: type(of: object))
    guard let object = object else { return "\(typeName).nil" }
    add(object)
    let pointer = Unmanaged.passUnretained(object as AnyObject).toOpaque()
    return address2Name[pointer]!
  }
}

let debugPrinter = DebugPrinter()

[T] 17:31:22.241 <CoreVideoPlayer #7>.integrate(onView:) view: <VideoPlayerView #3>
[T] 17:31:22.241 <CoreVideoPlayer #7>.rebindLayer() Optional<AVPlayer>.nil <VideoPlayerLayer #5>
[T] 17:31:22.242 <VideoPlayerLayer #5>.player Optional<AVPlayer>.nil

debugPrinter.print(self, "\(debugPrinter.name(oldValue)) -> \(debugPrinter.name(owner))")