defmodule OddJob do
  @external_resource readme = Path.join([__DIR__, "../README.md"])

  @moduledoc readme
             |> File.read!()
             |> String.split("<!-- MDOC -->")
             |> Enum.fetch!(1)

  @moduledoc since: "0.1.0"

  alias OddJob.{Async, Job, Pool, Scheduler}

  @type job :: Job.t()
  @type pool :: Pool.t()
  @type child_spec :: %{
          id: atom,
          start: {OddJob.Supervisor, :start_link, [atom]},
          type: :supervisor
        }

  @doc """
  A macro for creating jobs with an expressive DSL.

  `perform_this/2` works like `perform/2` except it accepts a `do` block instead of an anonymous function.

  ## Examples

  You must `import` or `require` `OddJob` to use macros:

      import OddJob

      perform_this :work do
        some_work()
        some_other_work()
      end

      perform_this :work, do: something_hard()
  """
  defmacro perform_this(pool, contents)

  defmacro perform_this(pool, do: block) do
    quote do
      OddJob.perform(unquote(pool), fn -> unquote(block) end)
    end
  end

  defmacro perform_this(pool, [{key, val}, {:do, block}]) do
    quote do
      perform_this(unquote(pool), [{unquote(key), unquote(val)}], do: unquote(block))
    end
  end

  @doc """
  A macro for creating jobs with an expressive DSL.

  `perform_this/3` accepts a single configuration option as the second argument that will control execution of
  the job. The available options prvode the functionality of `async_perform/2`, `perform_at/3`,
  and `perform_after/3`.

  ## Options

    * `:async` - Passing the atom `:async` as the second argument before the `do` block creates an async
    job that can be awaited on. See `async_perform/2`.
    * `at: time` - Use this option to schedule the job for a specific `time` in the future. `time` must be
    a valid `Time` or `DateTime` struct. See `perform_at/3`.
    * `after: timer` - Use this option to schedule the job to perform after the given `timer` has elapsed. `timer`
    must be in milliseconds. See `perform_after/3`.

  ## Examples

      import OddJob

      time = ~T[03:00:00.000000]
      perform_this :work, at: time do
        scheduled_work()
      end

      perform_this :work, after: 5000, do: something_important()

      perform_this :work, :async do
        get_data()
      end
      |> await()

      iex> (perform_this :work, :async, do: 10 ** 2) |> await()
      100
  """
  defmacro perform_this(pool, option, contents)

  defmacro perform_this(pool, [{key, val}], do: block) do
    quote do
      OddJob.unquote(:"perform_#{key}")(unquote(val), unquote(pool), fn -> unquote(block) end)
    end
  end

  defmacro perform_this(pool, :async, do: block) do
    quote do
      OddJob.async_perform(unquote(pool), fn -> unquote(block) end)
    end
  end

  @doc false
  @spec child_spec(atom) :: child_spec
  defdelegate child_spec(name), to: OddJob.Supervisor

  @doc """
  Performs a fire and forget job.

  ## Examples

      iex> parent = self()
      iex> :ok = OddJob.perform(:job, fn -> send(parent, :hello) end)
      iex> receive do
      ...>   msg -> msg
      ...> end
      :hello
  """
  @spec perform(atom, function) :: :ok
  def perform(pool, fun) when is_atom(pool) and is_function(fun) do
    job = %Job{function: fun, owner: self()}
    GenServer.call(pool_id(pool), {:perform, job})
  end

  @doc """
  Performs an async job that can be awaited on for the result.

  Functions like `Task.async/1` and `Task.await/2`.

  ## Examples

      iex> job = OddJob.async_perform(:job, fn -> :math.exp(100) end)
      iex> OddJob.await(job)
      2.6881171418161356e43
  """
  @spec async_perform(atom, function) :: job
  def async_perform(pool, fun) when is_atom(pool) and is_function(fun) do
    Async.perform(pool, fun)
  end

  @doc """
  Awaits on an async job and returns the results.

  ## Examples

      iex> OddJob.async_perform(:job, fn -> :math.log(2.6881171418161356e43) end)
      ...> |> OddJob.await()
      100.0
  """
  @spec await(job, timeout) :: any
  def await(job, timeout \\ 5000) when is_struct(job, Job) do
    Async.await(job, timeout)
  end

  @doc """
  Awaits replies form multiple async jobs and returns them in a list.

  This function receives a list of jobs and waits for their replies in the given time interval.
  It returns a list of the results, in the same order as the jobs supplied in the `jobs` input argument.

  If any of the job worker processes dies, the caller process will exit with the same reason as that worker.

  A timeout, in milliseconds or `:infinity`, can be given with a default value of `5000`. If the timeout
  is exceeded, then the caller process will exit. Any worker processes that are linked to the caller process
  (which is the case when a job is started with `async_perform/2`) will also exit.

  This function assumes the jobs' monitors are still active or the monitor's :DOWN message is in the
  message queue. If any jobs have been demonitored, or the message already received, this function will
  wait for the duration of the timeout.

  ## Examples

      iex> job1 = OddJob.async_perform(:job, fn -> 2 ** 2 end)
      iex> job2 = OddJob.async_perform(:job, fn -> 3 ** 2 end)
      iex> [job1, job2] |> OddJob.await_many()
      [4, 9]
  """
  @spec await_many([job], timeout) :: [any]
  def await_many(jobs, timeout \\ 5000) when is_list(jobs) do
    Async.await_many(jobs, timeout)
  end

  @doc """
  Sends a job to the `pool` after the given `timer` has elapsed.

  `timer` is an integer that indicates the number of milliseconds that should elapse before
  the job is sent to the pool. The timed message is executed under a separate supervised process,
  so if the caller crashes the job will still be performed. A timer reference is returned,
  which can be read with `Process.read_timer/1` or cancelled with `OddJob.cancel_timer/1`.

  ## Examples

      timer_ref = OddJob.perform_after(5000, :job, fn -> deferred_job() end)
      Process.read_timer(timer_ref)
      #=> 2836 # time remaining before job is sent to the pool
      OddJob.cancel_timer(timer_ref)
      #=> 1175 # job has been cancelled

      timer_ref = OddJob.perform_after(5000, :job, fn -> deferred_job() end)
      Process.sleep(6000)
      OddJob.cancel_timer(timer_ref)
      #=> false # too much time has passed to cancel the job
  """
  @spec perform_after(integer, atom, function) :: reference
  def perform_after(timer, pool, fun)
      when is_integer(timer) and is_atom(pool) and is_function(fun) do
    Scheduler.perform_after(timer, pool, fun)
  end

  @doc """
  Sends a job to the `pool` at the given `time`.

  `time` can be a `Time` or a `DateTime` struct. If a `Time` struct is received, then
  the job will be done the next time the clock strikes the given time. The timer is executed
  under a separate supervised process, so if the caller crashes the job will still be performed.
  A timer reference is returned, which can be read with `Process.read_timer/1` or canceled with
  `OddJob.cancel_timer/1`.

  ## Examples

      time = Time.utc_now() |> Time.add(600, :second)
      OddJob.perform_at(time, :job, fn -> scheduled_job() end)
  """
  @spec perform_at(Time.t() | DateTime.t(), atom, function) :: reference
  def perform_at(time, pool, fun)
      when (is_struct(time, Time) or is_struct(time, DateTime)) and
             is_atom(pool) and is_function(fun) do
    Scheduler.perform_at(time, pool, fun)
  end

  @doc """
  Cancels a scheduled job.

  `timer_ref` is the unique reference returned by `perform_at/3` or `perform_after/3`. This function
  returns the number of milliseconds left in the timer when cancelled, or `false` if the timer already
  expired. If the return is `false` you can assume that the job has already been sent to the pool
  for execution.

  NOTE: Cancelling the timer with this function ensures that the job is never executed *and* that
  the scheduler process is exited and not left "hanging". Using `Process.cancel_timer/1` will also
  cancel execution, but may leave hanging processes. A hanging scheduler process will eventually
  timeout, but not until one second after the expiration of the original timer.

  ## Examples

      iex> ref = OddJob.perform_after(500, :work, fn -> :never end)
      iex> time = OddJob.cancel_timer(ref)
      iex> is_integer(time)
      true

      iex> ref = OddJob.perform_after(10, :work, fn -> :never end)
      iex> Process.sleep(11)
      iex> OddJob.cancel_timer(ref)
      false
  """
  @spec cancel_timer(reference) :: non_neg_integer | false
  def cancel_timer(timer_ref) when is_reference(timer_ref) do
    Scheduler.cancel_timer(timer_ref)
  end

  @doc """
  Returns the pid and state of the job `pool`.

  ## Examples

      iex> {pid, %OddJob.Pool{id: id}} = OddJob.pool(:job)
      iex> is_pid(pid)
      true
      iex> id
      :job_pool
  """
  @spec pool(atom) :: {pid, pool}
  def pool(pool) when is_atom(pool) do
    pool_id = pool_id(pool)
    state = pool_id |> Pool.state()
    pid = pool_id |> GenServer.whereis()
    {pid, state}
  end

  @doc """
  Returns the ID of the job `pool`.

  ## Examples

      iex> OddJob.pool_id(:job)
      :job_pool
  """
  @spec pool_id(atom) :: atom
  defdelegate pool_id(pool), to: OddJob.Supervisor

  @doc """
  Returns the pid of the job `pool`'s supervisor.

  There is no guarantee that the process will still be alive after the results are returned,
  as it could exit or be killed or restarted at any time. Use `supervisor_id/1` to obtain
  the persistent ID of the supervisor.

  ## Examples

      OddJob.supervisor(:job)
      #=> #PID<0.239.0>
  """
  @spec supervisor(atom) :: pid
  def supervisor(pool) when is_atom(pool) do
    pool
    |> supervisor_id()
    |> GenServer.whereis()
  end

  @doc """
  Returns the ID of the job `pool`'s supervisor.

  ## Examples

      iex> OddJob.supervisor_id(:job)
      :job_pool_sup
  """
  @spec supervisor_id(atom) :: atom
  defdelegate supervisor_id(pool), to: OddJob.Pool.Supervisor, as: :id

  @doc """
  Returns a list of `pid`s for the specified worker pool.

  There is no guarantee that the processes will still be alive after the results are returned,
  as they could exit or be killed at any time.

  ## Examples

      OddJob.workers(:job)
      #=> [#PID<0.105.0>, #PID<0.106.0>, #PID<0.107.0>, #PID<0.108.0>, #PID<0.109.0>]
  """
  @spec workers(atom) :: [pid]
  def workers(pool) when is_atom(pool) do
    {_, %{workers: workers}} = pool(pool)
    workers
  end
end