corsa

defmodule Corsa.Stack do
  @moduledoc false

  @typep id() :: {module(), atom(), non_neg_integer()}

  @spec new(id()) :: :ok
  defp new(function) do
    id = to_id(function)

    if :ets.info(id) == :undefined do
      :ets.new(id, [:ordered_set, :private, :named_table])
      :ets.insert(id, {"size", 0})
    end

    :ok
  end

  @spec push(id(), [any()]) :: :ok
  def push(function, args) do
    id = to_id(function)

    if :ets.info(id) == :undefined do
      new(function)
      push(function, args)
    else
      [{_, size}] = :ets.lookup(id, "size")
      :ets.insert(id, {size, args})
      :ets.insert(id, {"size", size + 1})
      :ok
    end
  end

  @spec peek(id) :: :empty | [any()]
  def peek(function) do
    id = to_id(function)
    info = :ets.info(id)

    cond do
      info == :undefined ->
        new(function)
        peek(function)

      Keyword.get(info, :size) == 1 ->
        :empty

      true ->
        [{_, size}] = :ets.lookup(id, "size")
        [{_, args}] = :ets.lookup(id, size - 1)
        args
    end
  end

  @spec pop(id) :: :empty | [any()]
  def pop(function) do
    id = to_id(function)
    info = :ets.info(id)

    cond do
      info == :undefined ->
        new(function)

      Keyword.get(info, :size) == 1 ->
        :empty

      true ->
        [{_, size}] = :ets.lookup(id, "size")
        [{_, args}] = :ets.lookup(id, size - 1)
        :ets.delete(id, size - 1)
        :ets.insert(id, {"size", size - 1})
        args
    end
  end

  @spec flush(id) :: :ok
  def flush(function) do
    id = to_id(function)
    info = :ets.info(id)

    if info == :undefined do
      :ok
    else
      :ets.delete(id)
    end
  end

  @spec empty?(id) :: boolean()
  def empty?(function), do: peek(function) == :empty

  @spec to_id(id) :: atom()
  defp to_id({m, f, a}), do: :"#{m}.#{f}/#{a}"
end