midas

// Names mixed/Team/Group/Individual/myriad/motly
import process/process
import process/process.{From, Pid, BarePid, ExitReason, Normal, Kill, Infinity, Milliseconds, TrapExit}

pub type ChildSpecs(a, b, c) {
  One(fn() -> Pid(a))
  Two(fn() -> Pid(a), fn(Pid(a)) -> Pid(b))
  Three(fn() -> Pid(a), fn(Pid(a)) -> Pid(b), fn(Pid(a), Pid(b)) -> Pid(c))
}

type ChildState(a) {
  Running(Pid(a))
  Stopping(Pid(a))
  Stopped
}

// Finished
fn do_stop(pid) {
  process.exit(pid, Kill)
  Stopping(pid)
}

fn stop3(children) {
  let tuple(child1, child2, child3) = children

  case child3 {
    Running(pid) -> tuple(child1, child2, do_stop(pid))
    Stopping(_pid) -> tuple(child1, child2, child3)
    Stopped -> tuple(child1, child2, child3)
  }
}

fn stop2(children) {
  let tuple(child1, child2, child3) = children

  case child2 {
    Running(pid) -> tuple(child1, do_stop(pid), child3)
    Stopping(_pid) -> tuple(child1, child2, child3)
    Stopped -> stop3(tuple(child1, child2, child3))
  }
}

fn stop1(children) {
  let tuple(child1, child2, child3) = children

  case child1 {
    Running(pid) -> tuple(do_stop(pid), child2, child3)
    Stopping(_pid) -> tuple(child1, child2, child3)
    Stopped -> stop2(tuple(child1, child2, child3))
  }
}

fn start3(pid1, pid2, specs) {
  let tuple(_, _, fn3) = specs
  let pid3 = fn3(pid1, pid2)
  tuple(Running(pid1), Running(pid2), Running(pid3))
}

fn start2(pid1, specs) {
  let tuple(_, fn2, _) = specs
  let pid2 = fn2(pid1)
  start3(pid1, pid2, specs)
}

fn start1(specs) {
  let tuple(fn1, _, _) = specs
  let pid1 = fn1()
  start2(pid1, specs)
}

fn maybe_restart(specs, children) {
  case children {
    // All running
    tuple(Running(_), Running(_), Running(_)) -> children
    // Pid1 already running
    tuple(Running(pid1), Running(pid2), Stopped) -> start3(pid1, pid2, specs)
    tuple(Running(_), Running(_), _) -> stop3(children)
    // Pid2 already running
    tuple(Running(pid1), Stopped, Stopped) -> start2(pid1, specs)
    tuple(Running(_), _, _) -> stop2(children)
    // Pid3 already running
    tuple(Stopped, Stopped, Stopped) -> start1(specs)
    tuple(_, _, _) -> stop1(children)
  }
}

// This would be a much simpler statement for all_for_one, If all running do nothing, if none running start, in all other cases start killing from one.
fn child_pid(child) {
  case child {
    Running(pid) | Stopping(pid) -> Ok(process.bare(pid))
    Stopped -> Error(Nil)
  }
}

pub type Messages(m) {
  WhichChildren(From(List(Pid(m))))
  EXIT(BarePid, ExitReason)
}

fn loop(receive, specs, children) {
  case receive(Infinity) {
    Ok(EXIT(pid, _reason)) -> {
      let tuple(child1, child2, child3) = children

      let pid1 = child_pid(child1)
      let pid2 = child_pid(child2)
      let pid3 = child_pid(child3)

      let children = case Ok(pid) {
        p if p == pid1 -> tuple(Stopped, child2, child3)
        p if p == pid2 -> tuple(child1, Stopped, child3)
        p if p == pid3 -> tuple(child1, child2, Stopped)
      }

      // p -> {
      //     // TODO handle parent pid, for the moment parents are simply killed.
      //     tuple(child1, child2, child3)
      // }
      let children = maybe_restart(specs, children)
      loop(receive, specs, children)
    }
  }
}

// Theres probably an more efficient no op pid that doesnt need to start a real process
fn spawn_dummy1(_) {
  process.spawn_link(
    fn(receive) {
      let _ = receive(Infinity)
      Normal
    },
  )
}

fn spawn_dummy2(_, _) {
  process.spawn_link(
    fn(receive) {
      let _ = receive(Infinity)
      Normal
    },
  )
}

pub fn spawn_link(init: fn() -> ChildSpecs(a, b, c)) {
  process.spawn_link(
    fn(receive) {
      process.process_flag(TrapExit(True))
      let specs = case init() {
        One(fn1) -> tuple(fn1, spawn_dummy1, spawn_dummy2)
        Two(fn1, fn2) -> tuple(fn1, fn2, spawn_dummy2)
        Three(fn1, fn2, fn3) -> tuple(fn1, fn2, fn3)
      }

      let children = tuple(Stopped, Stopped, Stopped)
      let children = maybe_restart(specs, children)
      loop(receive, specs, children)
    },
  )
}