appnap.swift

import AppKit

// https://stackoverflow.com/a/48486247
func shell(_ launchPath: String, _ arguments: [String]) -> String {
  let task = Process()
  task.launchPath = launchPath
  task.arguments = arguments

  let pipe = Pipe()
  task.standardOutput = pipe
  task.launch()

  let data = pipe.fileHandleForReading.readDataToEndOfFile()
  let output = String(data: data, encoding: String.Encoding.utf8)!

  if output.count > 0 {
    // remove newline character.
    let lastIndex = output.index(before: output.endIndex)
    return String(output[output.startIndex ..< lastIndex])
  }
  return output
}


func main(pattern: String, stop_on_launch: Bool = false) throws {
  let workspace = NSWorkspace.shared

  let regex = try NSRegularExpression(pattern: "^\(pattern)$")
  let is_matching = { (app: NSRunningApplication) -> Bool in
    let x = app.bundleIdentifier ?? "[no name]"
    return regex.numberOfMatches(in: x, range: NSRange(x.startIndex..., in: x)) > 0
  }

  // Set of applications to stop
  var pids = Set(
    workspace.runningApplications
      .filter { is_matching($0) }
      .map { $0.processIdentifier }
  )

  let resume_app = { (pid: pid_t) in
    print("kill -CONT \(pid)")
    shell("/bin/kill", ["-CONT", "\(pid)"])
    pids.insert(pid)
  }

  let stop_apps = { () in
    pids.forEach { print("kill -STOP \($0)") }
    pids.forEach { shell("/bin/kill", ["-STOP", "\($0)"]) }
    pids.removeAll()
  }

  let token = workspace.observe(\.frontmostApplication) { workspace, _ in
    guard let app = workspace.frontmostApplication else {
      return
    }

    print("Switching to: \(app.bundleIdentifier ?? "") (pid: \(app.processIdentifier))")

    if is_matching(app) {
      resume_app(app.processIdentifier)
    } else if (!pids.isEmpty) {
      stop_apps()
    }
  }

  if stop_on_launch {
    stop_apps()
  }

  RunLoop.current.run(
    mode: RunLoopMode.defaultRunLoopMode,
    before: NSDate.distantFuture
  )
}

do {
  try main(pattern: CommandLine.arguments[1])
} catch {
  print("Invalid regexp pattern")
}