defmodule Membrane.Pipeline.Action do
  @moduledoc """
  This module contains type specifications of actions that can be returned
  from pipeline callbacks.

  Returning actions is a way of pipeline interaction with
  other components and parts of framework. Each action may be returned by any
  callback (except for `c:Membrane.Pipeline.handle_shutdown/2`, as it
  does not support returning any actions) unless explicitly stated otherwise.
  """

  alias Membrane.{Child, ParentSpec}

  @typedoc """
  Action that sends a message to a child identified by name.
  """
  @type forward_t :: {:forward, {Child.name_t(), any} | [{Child.name_t(), any}]}

  @typedoc """
  Action that instantiates children and links them according to `Membrane.ParentSpec`.

  Children's playback state is changed to the current pipeline state.
  `c:Membrane.Pipeline.handle_spec_started/3` callback is executed once it happens.
  """
  @type spec_t :: {:spec, ParentSpec.t()}

  @typedoc """
  Action that stops, unlinks and removes specified child/children from the pipeline.
  """
  @type remove_child_t ::
          {:remove_child, Child.name_t() | [Child.name_t()]}

  @typedoc """
  Action that sets `Logger` metadata for the pipeline and all its descendants.

  Uses `Logger.metadata/1` underneath.
  """
  @type log_metadata_t :: {:log_metadata, Keyword.t()}

  @typedoc """
  Starts a timer that will invoke `c:Membrane.Pipeline.handle_tick/3` callback
  every `interval` according to the given `clock`.

  The timer's `id` is passed to the `c:Membrane.Pipeline.handle_tick/3`
  callback and can be used for changing its interval via `t:timer_interval_t/0`
  or stopping it via `t:stop_timer_t/0`.

  If `interval` is set to `:no_interval`, the timer won't issue any ticks until
  the interval is set with `t:timer_interval_t/0` action.

  If no `clock` is passed, pipeline clock is chosen.

  Timers use `Process.send_after/3` under the hood.
  """
  @type start_timer_t ::
          {:start_timer,
           {timer_id :: any, interval :: Ratio.t() | non_neg_integer | :no_interval}
           | {timer_id :: any, interval :: Ratio.t() | non_neg_integer | :no_interval,
              clock :: Membrane.Clock.t()}}

  @typedoc """
  Changes interval of a timer started with `t:start_timer_t/0`.

  Permitted only from `c:Membrane.Pipeline.handle_tick/3`, unless the interval
  was previously set to `:no_interval`.

  If the `interval` is `:no_interval`, the timer won't issue any ticks until
  another `t:timer_interval_t/0` action. Otherwise, the timer will issue ticks every
  new `interval`. The next tick after interval change is scheduled at
  `new_interval + previous_time`, where previous_time is the time of the latest
  tick or the time of returning `t:start_timer_t/0` action if no tick has been
  sent yet. Note that if `current_time - previous_time > new_interval`, a burst
  of `div(current_time - previous_time, new_interval)` ticks is issued immediately.
  """
  @type timer_interval_t ::
          {:timer_interval,
           {timer_id :: any, interval :: Ratio.t() | non_neg_integer | :no_interval}}

  @typedoc """
  Stops a timer started with `t:start_timer_t/0` action.

  This action is atomic: stopping timer guarantees that no ticks will arrive from it.
  """
  @type stop_timer_t :: {:stop_timer, timer_id :: any}

  @typedoc """
  Type describing actions that can be returned from pipeline callbacks.

  Returning actions is a way of pipeline interaction with its children and
  other parts of framework.
  """
  @type t ::
          forward_t
          | spec_t
          | remove_child_t
          | log_metadata_t
          | start_timer_t
          | timer_interval_t
          | stop_timer_t
end