use nix::errno::Errno;
use nix::sys::wait::{waitid, Id, WaitPidFlag, WaitStatus};
use nix::unistd::Pid;

pub struct DebugTarget<S: DebugState> {
	state: S,
}

pub trait DebugState {
	#[allow(dead_code)]
	fn pid(&self) -> Pid;
}

pub struct Stopped {
	pid: Pid,
}

impl DebugState for Stopped {
	fn pid(&self) -> Pid { self.pid }
}

impl DebugTarget<Stopped> {
	pub fn new(pid: Pid) -> Result<Self, Errno> {
		waitid(Id::Pid(pid), WaitPidFlag::WSTOPPED).and(Ok(DebugTarget { state: Stopped { pid } }))
	}

	pub fn cont(self) -> Result<DebugTarget<Running>, Errno> {
		nix::sys::ptrace::cont(self.state.pid, None).and(Ok(DebugTarget { state: Running { pid: self.state.pid } }))
	}
}

pub struct Running {
	pid: Pid,
}

impl DebugState for Running {
	fn pid(&self) -> Pid { self.pid }
}


impl DebugTarget<Running> {
	pub fn wait_for_exit(self) -> Result<i32, Errno> {
		waitid(Id::Pid(self.state.pid), WaitPidFlag::WEXITED).and_then(|status| match status {
			WaitStatus::Exited(_, exit_code) => Ok(exit_code),
			_ => Err(Errno::EINVAL), // TODO: custom error type?
		})
	}
}