take_a_number_deluxe

elixir/take-a-number-deluxe/lib/take_a_number_deluxe/queue.ex

@@ -0,0 +1,42 @@
+defmodule TakeANumberDeluxe.Queue do
+  # You don't need to read this module to solve this exercise.
+
+  # We would have used Erlang's queue module instead
+  # (https://www.erlang.org/doc/man/queue.html),
+  # but it lacks a `delete` function before OTP 24,
+  # and we want this exercise to work on older versions too.
+
+  defstruct in: [], out: []
+  @type t :: %__MODULE__{}
+
+  @spec new() :: t()
+  def new(), do: %__MODULE__{}
+
+  @spec push(t(), any()) :: t()
+  def push(%__MODULE__{in: in_q} = q, a), do: %__MODULE__{q | in: [a | in_q]}
+
+  @spec out(t()) :: {{:value, any()}, t()} | {:empty, t()}
+  def out(%__MODULE__{in: [], out: []} = q), do: {:empty, q}
+  def out(%__MODULE__{out: [head | tail]} = q), do: {{:value, head}, %__MODULE__{q | out: tail}}
+  def out(%__MODULE__{in: in_q}), do: out(%__MODULE__{out: Enum.reverse(in_q)})
+
+  @spec empty?(t()) :: boolean()
+  def empty?(%__MODULE__{in: [], out: []}), do: true
+  def empty?(%__MODULE__{}), do: false
+
+  @spec member?(t(), any()) :: boolean()
+  def member?(%__MODULE__{in: in_q, out: out}, a), do: a in in_q or a in out
+
+  @spec delete(t(), any()) :: t()
+  def delete(%__MODULE__{in: in_q, out: out}, a) do
+    out = out ++ Enum.reverse(in_q)
+    out = List.delete(out, a)
+    %__MODULE__{out: out}
+  end
+
+  @spec from_list([any()]) :: t()
+  def from_list(list), do: %__MODULE__{out: list}
+
+  @spec to_list(t()) :: [any()]
+  def to_list(%__MODULE__{in: in_q, out: out}), do: out ++ Enum.reverse(in_q)
+end

elixir/take-a-number-deluxe/lib/take_a_number_deluxe/state.ex

@@ -0,0 +1,87 @@
+defmodule TakeANumberDeluxe.State do
+  defstruct min_number: 1, max_number: 999, queue: nil, auto_shutdown_timeout: :infinity
+  @type t :: %__MODULE__{}
+
+  alias TakeANumberDeluxe.Queue
+
+  @spec new(integer, integer, timeout) :: {:ok, TakeANumberDeluxe.State.t()} | {:error, atom()}
+  def new(min_number, max_number, auto_shutdown_timeout \\ :infinity) do
+    if min_and_max_numbers_valid?(min_number, max_number) and
+         timeout_valid?(auto_shutdown_timeout) do
+      {:ok,
+       %__MODULE__{
+         min_number: min_number,
+         max_number: max_number,
+         queue: Queue.new(),
+         auto_shutdown_timeout: auto_shutdown_timeout
+       }}
+    else
+      {:error, :invalid_configuration}
+    end
+  end
+
+  @spec queue_new_number(TakeANumberDeluxe.State.t()) ::
+          {:ok, integer(), TakeANumberDeluxe.State.t()} | {:error, atom()}
+  def queue_new_number(%__MODULE__{} = state) do
+    case find_next_available_number(state) do
+      {:ok, next_available_number} ->
+        {:ok, next_available_number,
+         %{state | queue: Queue.push(state.queue, next_available_number)}}
+
+      {:error, error} ->
+        {:error, error}
+    end
+  end
+
+  @spec serve_next_queued_number(TakeANumberDeluxe.State.t(), integer() | nil) ::
+          {:ok, integer(), TakeANumberDeluxe.State.t()} | {:error, atom()}
+  def serve_next_queued_number(%__MODULE__{} = state, priority_number) do
+    cond do
+      Queue.empty?(state.queue) ->
+        {:error, :empty_queue}
+
+      is_nil(priority_number) ->
+        {{:value, next_number}, new_queue} = Queue.out(state.queue)
+        {:ok, next_number, %{state | queue: new_queue}}
+
+      Queue.member?(state.queue, priority_number) ->
+        {:ok, priority_number, %{state | queue: Queue.delete(state.queue, priority_number)}}
+
+      true ->
+        {:error, :priority_number_not_found}
+    end
+  end
+
+  defp min_and_max_numbers_valid?(min_number, max_number) do
+    is_integer(min_number) and is_integer(max_number) and min_number < max_number
+  end
+
+  defp timeout_valid?(timeout) do
+    timeout == :infinity || (is_integer(timeout) && timeout >= 0)
+  end
+
+  defp find_next_available_number(state) do
+    all_numbers_in_use = Queue.to_list(state.queue)
+    all_numbers = Enum.to_list(state.min_number..state.max_number)
+
+    case all_numbers_in_use do
+      [] ->
+        {:ok, state.min_number}
+
+      list when length(list) == length(all_numbers) ->
+        {:error, :all_possible_numbers_are_in_use}
+
+      _ ->
+        current_highest_number = Enum.max(all_numbers_in_use)
+
+        next_available_number =
+          if current_highest_number < state.max_number do
+            current_highest_number + 1
+          else
+            Enum.min(all_numbers -- all_numbers_in_use)
+          end
+
+        {:ok, next_available_number}
+    end
+  end
+end