defmodule CTE.Adapter.Memory do
  @moduledoc """
  Basic implementation of the CTE, using the memory for persisting the models. Adapter provided as a convenient way of using CTE in tests or during the development
  """
  use CTE.Adapter

  @doc false
  def descendants(pid, ancestor, opts) do
    GenServer.call(pid, {:descendants, ancestor, opts})
  end

  @doc false
  def ancestors(pid, descendant, opts) do
    GenServer.call(pid, {:ancestors, descendant, opts})
  end

  @doc false
  def insert(pid, leaf, ancestor, opts) do
    GenServer.call(pid, {:insert, leaf, ancestor, opts})
  end

  @doc false
  def delete(pid, leaf, opts) do
    leaf? = Keyword.get(opts, :limit, 0) == 1
    GenServer.call(pid, {:delete, leaf, leaf?, opts})
  end

  @doc false
  def move(pid, leaf, ancestor, opts) do
    GenServer.call(pid, {:move, leaf, ancestor, opts})
  end

  @doc false
  def tree(pid, leaf, opts) do
    GenServer.call(pid, {:tree, leaf, opts})
  end

  @doc false
  def handle_call({:tree, leaf, opts}, _from, config) do
    %CTE{paths: paths, nodes: nodes} = config

    descendants_opts = [itself: true] ++ Keyword.take(opts, [:depth])
    descendants = _descendants(leaf, descendants_opts, config)

    subtree =
      paths
      |> Enum.filter(fn [ancestor, descendant, _] ->
        ancestor in descendants && descendant in descendants
      end)

    nodes =
      subtree
      |> Enum.reduce(%{}, fn [ancestor, descendant, _depth], acc ->
        Map.merge(acc, %{
          ancestor => Map.get(nodes, ancestor),
          descendant => Map.get(nodes, descendant)
        })
      end)

    {:reply, {:ok, %{paths: subtree, nodes: nodes}}, config}
  end

  @doc false
  def handle_call({:delete, leaf, true, _opts}, _from, config) do
    %CTE{paths: paths} = config
    paths = Enum.filter(paths, fn [_ancestor, descendant, _] -> descendant != leaf end)
    {:reply, :ok, %{config | paths: paths}}
  end

  @doc false
  def handle_call({:delete, leaf, _subtree, opts}, _from, config) do
    opts = Keyword.put(opts, :itself, true)

    descendants = _descendants(leaf, opts, config)

    paths = Enum.filter(descendants, &(&1 != leaf))
    {:reply, :ok, %{config | paths: paths}}
  end

  @doc false
  def handle_call({:move, leaf, ancestor, _opts}, _from, config) do
    %CTE{paths: paths} = config
    ex_ancestors = _ancestors(leaf, [itself: true], config)

    {descendants_paths, _} = descendants_collector(leaf, [itself: true], config)
    descendants = Enum.map(descendants_paths, fn [_, descendant, _] -> descendant end)

    paths_with_leaf =
      paths
      |> Enum.filter(fn [ancestor, descendant, _] ->
        ancestor in ex_ancestors and descendant in descendants and ancestor != descendant
      end)

    paths_without_leaf = Enum.filter(paths, &(&1 not in paths_with_leaf))

    {new_ancestors_paths, _} =
      ancestors_collector(ancestor, [itself: true], %{config | paths: paths_without_leaf})

    new_paths =
      for [ancestor, _, super_tree_depth] <- [[leaf, leaf, -1] | new_ancestors_paths],
          [_, descendant, subtree_depth] <- descendants_paths,
          into: [] do
        [ancestor, descendant, super_tree_depth + subtree_depth + 1]
      end
      |> Enum.reverse()

    {:reply, :ok, %{config | paths: paths_without_leaf ++ new_paths}}
  end

  @doc false
  def handle_call({:insert, leaf, ancestor, opts}, _from, config) do
    case _insert(leaf, ancestor, opts, config) do
      {:ok, new_paths, config} -> {:reply, {:ok, new_paths}, config}
      err -> {:reply, {:error, err}, config}
    end
  end

  @doc false
  def handle_call({:ancestors, descendant, opts}, _from, config) do
    result =
      _ancestors(descendant, opts, config)
      |> Enum.reverse()

    {:reply, {:ok, result}, config}
  end

  @doc false
  def handle_call({:descendants, ancestor, opts}, _from, config) do
    result =
      _descendants(ancestor, opts, config)
      |> Enum.reverse()

    {:reply, {:ok, result}, config}
  end

  @doc false
  defp _descendants(ancestor, opts, config) do
    descendants_collector(ancestor, opts, config)
    |> depth(opts, config)
    |> selected(opts, config)
  end

  @doc false
  defp descendants_collector(ancestor, opts, config) do
    mapper = fn paths -> Enum.map(paths, fn [_, descendant, _] -> descendant end) end

    fn path, {acc_paths, _mapper, size} = acc, itself? ->
      case path do
        [^ancestor, ^ancestor, _] when not itself? ->
          acc

        [^ancestor, _descendant, _depth] = descendants ->
          {[descendants | acc_paths], mapper, size + 1}

        _ ->
          acc
      end
    end
    |> _find_leaves(opts, config)
  end

  @doc false
  defp _ancestors(descendant, opts, config) do
    ancestors_collector(descendant, opts, config)
    |> depth(opts, config)
    |> selected(opts, config)
  end

  @doc false
  defp ancestors_collector(descendant, opts, config) do
    mapper = fn paths -> Enum.map(paths, fn [ancestor, _, _] -> ancestor end) end

    fn path, {acc_paths, _mapper, size} = acc, itself? ->
      case path do
        [^descendant, ^descendant, _] when not itself? ->
          acc

        [_ancestor, ^descendant, _depth] = ancestors ->
          {[ancestors | acc_paths], mapper, size + 1}

        _ ->
          acc
      end
    end
    |> _find_leaves(opts, config)
  end

  @doc false
  defp _insert(leaf, ancestor, _opts, config) do
    %CTE{nodes: nodes, paths: paths} = config

    case Map.has_key?(nodes, ancestor) do
      true ->
        {leaf_new_ancestors, _} = ancestors_collector(ancestor, [itself: true], config)

        new_paths =
          leaf_new_ancestors
          |> Enum.reduce([[leaf, leaf, 0]], fn [ancestor, _, depth], acc ->
            [[ancestor, leaf, depth + 1] | acc]
          end)

        acc_paths = paths ++ new_paths
        config = %{config | paths: acc_paths}

        {:ok, new_paths, config}

      _ ->
        {:error, :no_ancestor, config}
    end
  end

  @doc false
  defp _find_leaves(fun, opts, %CTE{paths: paths}) do
    itself? = Keyword.get(opts, :itself, false)
    limit = Keyword.get(opts, :limit, 0)

    {leaves_paths, mapper, _size} =
      paths
      |> Enum.reduce_while({[], & &1, 0}, fn path, acc ->
        {_, _, sz} = dsz = fun.(path, acc, itself?)

        if limit == 0 or sz < limit, do: {:cont, dsz}, else: {:halt, dsz}
      end)

    {leaves_paths, mapper}
  end

  @doc false
  defp depth({leaves_paths, mapper}, opts, _config) do
    leaves_paths =
      if depth = Keyword.get(opts, :depth) do
        leaves_paths
        |> Enum.filter(fn [_, _, depth_] -> depth_ <= max(depth, 0) end)
      else
        leaves_paths
      end

    {leaves_paths, mapper}
  end

  @doc false
  defp selected({leaves_paths, mapper}, opts, %CTE{nodes: nodes}) do
    leaves = mapper.(leaves_paths)

    if Keyword.get(opts, :nodes, false) do
      Enum.map(leaves, &Map.get(nodes, &1))
    else
      leaves
    end
  end
end