defmodule RNS.DestinationStore do
  @moduledoc """
  Manages an ets table that holds the paths to destinations(including local ones).
  """

  require Record

  def child_spec(_args) do
    %{
      id: __MODULE__,
      start: {__MODULE__, :start_link, []}
    }
  end

  def start_link() do
    pid = spawn_link(__MODULE__, :init, [])
    {:ok, pid}
  end

  # Client
  @doc "Find a destination in the store using its hash."
  @spec fetch(RNS.Destination.hash()) :: {:ok, RNS.Destination.t()} | {:error, :not_found}
  def fetch(destination_hash) do
    case :ets.lookup(:destinations, destination_hash) do
      [result] ->
        if RNS.Destination.expired?(result) do
          delete(destination_hash)
          {:error, :not_found}
        else
          {:ok, result}
        end

      [] ->
        {:error, :not_found}
    end
  end

  @doc "Put a destination into the store."
  @spec put(RNS.Destination.t()) :: true
  def put(destination) do
    :ets.insert(:destinations, destination)
  end

  @doc "Delete a destination from the store using its hash."
  @spec delete(RNS.Destination.hash()) :: true
  def delete(destination_hash) do
    :ets.delete(:destinations, destination_hash)
  end

  @doc "Put a ratchet into the store."
  @spec put_ratchet(RNS.Identity.ratchet(), RNS.Destination.hash()) :: true
  def put_ratchet(ratchet, destination_hash) do
    :ets.insert(
      :ratchets,
      {destination_hash, ratchet, NaiveDateTime.add(NaiveDateTime.utc_now(), 30, :day)}
    )
  end

  @doc "Fetch all ratchets from the store."
  @spec fetch_ratchets(RNS.Destination.hash()) :: [RNS.Identity.ratchet()]
  def fetch_ratchets(destination_hash) do
    ratchets = :ets.lookup(:ratchets, destination_hash)

    Enum.reduce(ratchets, [], fn ratchet, ratchets ->
      if RNS.Destination.ratchet_expired?(ratchet) do
        delete_ratchet(elem(ratchet, 1))
        ratchets
      else
        [elem(ratchet, 1) | ratchets]
      end
    end)
  end

  @doc "Fetch the most recent ratchet from the store."
  @spec fetch_recent_ratchet(RNS.Destination.hash()) ::
          {:ok, RNS.Identity.ratchet()} | {:error, :not_found}
  def fetch_recent_ratchet(destination_hash) do
    ratchets = :ets.lookup(:ratchets, destination_hash)

    most_recent_ratchet =
      Enum.reduce(ratchets, nil, fn ratchet, most_recent_ratchet ->
        if RNS.Destination.ratchet_expired?(ratchet) do
          delete_ratchet(elem(ratchet, 1))
          most_recent_ratchet
        else
          if most_recent_ratchet == nil or
               NaiveDateTime.after?(elem(ratchet, 2), elem(most_recent_ratchet, 2)) do
            ratchet
          else
            most_recent_ratchet
          end
        end
      end)

    case most_recent_ratchet do
      nil ->
        {:error, :not_found}

      _ ->
        {:ok, elem(most_recent_ratchet, 1)}
    end
  end

  @doc "Delete a ratchet from the store."
  @spec delete_ratchet(RNS.Identity.ratchet()) :: true
  def delete_ratchet(ratchet) do
    :ets.match_delete(:ratchets, {:_, ratchet, :_})
  end

  # Callbacks
  @spec init() :: :ok
  def init() do
    :ets.new(:destinations, [
      {:read_concurrency, true},
      {:write_concurrency, true},
      {:keypos, RNS.Destination.hash_position() + 1},
      :public,
      :named_table
    ])

    :ets.new(:ratchets, [
      {:read_concurrency, true},
      {:write_concurrency, true},
      :bag,
      :public,
      :named_table
    ])

    Process.sleep(:infinity)
  end
end