defmodule Filterable do
  @default_options [allow_blank: false, allow_nil: false, trim: true, default: nil, cast: nil]

  defmacro __using__(_) do
    quote do
      import unquote(__MODULE__), only: [filterable: 2, filterable: 1]

      @before_compile unquote(__MODULE__)
      @filters_module __MODULE__
      @filter_options []
    end
  end

  defmacro __before_compile__(_) do
    quote do
      def apply_filters!(queryable, params, opts \\ []) do
        Filterable.apply_filters!(queryable, params, @filters_module, filter_options(opts))
      end

      def apply_filters(queryable, params, opts \\ []) do
        Filterable.apply_filters(queryable, params, @filters_module, filter_options(opts))
      end

      def filter_values(params, opts \\ []) do
        Filterable.filter_values(params, @filters_module, filter_options(opts))
      end

      def filter_options(opts \\ []) do
        Keyword.merge(opts, @filter_options)
      end

      defoverridable [apply_filters!: 3, apply_filters!: 2,
                      apply_filters: 3, apply_filters: 2,
                      filter_values: 2, filter_values: 1,
                      filter_options: 1, filter_options: 0]
    end
  end

  defmacro filterable(arg, opts \\ [])
  defmacro filterable([do: block], opts),
    do: filterable(nil, block, opts)
  defmacro filterable(arg, do: block),
    do: filterable(nil, block, arg)
  defmacro filterable(arg, opts),
    do: filterable(arg, nil, opts)

  def apply_filters!(queryable, params, module, opts \\ []) do
    case apply_filters(queryable, params, module, opts) do
      {:ok, result, values} -> {result, values}
      {:error, message}     -> raise Filterable.FilterError, message
    end
  end

  def apply_filters(queryable, params, module, opts \\ []) do
    with {:ok, values} <- filter_values(params, module, opts),
         {:ok, result} <- module.defined_filters
           |> Enum.reduce_while({:ok, queryable}, fn ({filter_name, filter_opts}, {:ok, queryable}) ->
             options = Keyword.merge(opts, filter_opts)
             value   = Map.get(values, filter_name)

             case apply_filter(queryable, module, filter_name, value, options) do
               error = {:error, _} -> {:halt, error}
               queryable           -> {:cont, {:ok, queryable}}
             end
           end),
     do: {:ok, result, values}
  end

  def filter_values(params, module, opts \\ []) do
    Enum.reduce_while module.defined_filters, {:ok, %{}}, fn ({filter_name, filter_opts}, {:ok, acc}) ->
      options =
        [param: filter_name]
        |> Keyword.merge(@default_options)
        |> Keyword.merge(filter_opts)
        |> Keyword.merge(opts)

      case Filterable.Params.filter_value(params, options) do
        {:ok, nil}          -> {:cont, {:ok, acc}}
        {:ok, val}          -> {:cont, {:ok, Map.put(acc, filter_name, val)}}
        error = {:error, _} -> {:halt, error}
      end
    end
  end

  defp apply_filter(queryable, module, filter_name, value, opts) do
    share     = Keyword.get(opts, :share)
    allow_nil = Keyword.get(opts, :allow_nil)

    try do
      cond do
        (allow_nil || value) && share ->
          apply(module, filter_name, [queryable, value, share])
        allow_nil || value ->
          apply(module, filter_name, [queryable, value])
        true -> queryable
      end
    rescue
      FunctionClauseError -> queryable
    end
  end

  defp filterable(module, block, opts) do
    quote do
      @filter_options unquote(opts)
      @filters_module unquote(module) || Module.concat([__MODULE__, Filterable])

      if unquote(is_tuple(block)) do
        defmodule @filters_module do
          use Filterable.DSL
          unquote(block)
        end
      end
    end
  end
end