defmodule Pageantry.Input do
  @moduledoc """
  User input for paging/sorting/filtering.

  ## Fields

  * `off`
  : Page offset start; `0` to start with the first item.
  * `max`
  : Maximum items per page, eg `10`.
  * `sort`
  : Keyword list of fields to sort by, eg `[asc: :name, desc: :created]`.
  * `filter`
  : Keyword list of fields to filter by, eg `[name: "foo", active: true]`.
    `ALL` is a special field that means filter across all fields, eg `[ALL: "today"]`.
  """

  alias Pageantry.{Cast, Prefs}

  defstruct off: 0, max: 10, sort: [], filter: []
  @type t :: %__MODULE__{off: integer, max: integer, sort: keyword(atom), filter: keyword(atom)}

  @doc """
  Creates new Input struct.

  ## Examples

      iex> import Pageantry.Input
      iex> new(100)
      %Pageantry.Input{off: 0, max: 100, sort: [], filter: []}
  """
  @spec new(integer) :: __MODULE__.t()
  def new(max \\ 10) do
    %__MODULE__{max: max}
  end

  @doc """
  Creates new Input struct.

  ## Examples

      iex> import Pageantry.Input
      iex> new(100, [desc: :created], [created: "today"])
      %Pageantry.Input{off: 0, max: 100, sort: [desc: :created], filter: [created: "today"]}
  """
  @spec new(integer, keyword, keyword) :: __MODULE__.t()
  def new(max, sort \\ [], filter) do
    %__MODULE__{max: max, sort: sort, filter: filter}
  end

  @doc """
  Parses request parameters into Input struct.

  ## Examples

      iex> import Pageantry.Input
      iex> parse(%{"off" => "100"})
      %Pageantry.Input{off: 100, max: 10, sort: [], filter: []}
      iex> parse(%{"sort" => "name-created", "q" => "today"})
      %Pageantry.Input{off: 0, max: 10, sort: [asc: :name, desc: :created], filter: [ALL: "today"]}
  """
  @spec parse(map, Prefs.t()) :: __MODULE__.t()
  def parse(params, prefs \\ %Prefs{}) do
    parse(%__MODULE__{}, params, prefs)
  end

  @doc """
  Parses request parameters into Input struct with defaults.

  ## Examples

      iex> import Pageantry.Input
      iex> parse(%Pageantry.Input{max: 20}, %{"off" => "100"}, %Pageantry.Prefs{})
      %Pageantry.Input{off: 100, max: 20, sort: [], filter: []}
      iex> input = %Pageantry.Input{max: 20, sort: [desc: :created]}
      iex> params = %{"max" => "100", "field" => "name", "q" => "foo"}
      iex> parse(input, params, %Pageantry.Prefs{})
      %Pageantry.Input{off: 0, max: 100, sort: [desc: :created], filter: [name: "foo"]}
  """
  @spec parse(__MODULE__.t(), map, Prefs.t()) :: __MODULE__.t()
  def parse(input, params, prefs) do
    %__MODULE__{
      off: parse_off(params, input.off, prefs),
      max: parse_max(params, input.max, prefs),
      sort: parse_sort(params, input.sort, prefs),
      filter: parse_filter(params, input.filter, prefs)
    }
  end

  @doc """
  Extracts "off" parameter as non-negative integer.

  ## Examples

      iex> import Pageantry.Input
      iex> parse_off(%{"off" => "100"})
      100
      iex> parse_off(%{"off" => ""})
      0
  """
  @spec parse_off(map, integer, Prefs.t()) :: integer
  def parse_off(params, default \\ 0, prefs \\ %Prefs{}) do
    case Cast.cast_to_integer(params["off"], prefs) do
      number when is_integer(number) and number >= 0 -> number
      _ -> default
    end
  end

  @doc """
  Extracts "max" parameter as positive integer.

  ## Examples

      iex> import Pageantry.Input
      iex> parse_max(%{"max" => "100"})
      100
      iex> parse_max(%{"max" => ""}, 10)
      10
  """
  @spec parse_max(map, integer, Prefs.t()) :: integer
  def parse_max(params, default \\ 10, prefs \\ %Prefs{}) do
    case Cast.cast_to_integer(params["max"], prefs) do
      number when is_integer(number) and number > 0 -> number
      _ -> default
    end
  end

  @doc """
  Extracts "sort" parameter as sort keyword list.

  ## Examples

      iex> import Pageantry.Input
      iex> parse_sort(%{"sort" => "name"})
      [asc: :name]
      iex> parse_sort(%{"sort" => "-name"})
      [desc: :name]
      iex> parse_sort(%{"sort" => ""})
      []
  """
  @spec parse_sort(map, keyword(atom), Prefs.t()) :: keyword(atom)
  def parse_sort(params, default \\ [], prefs \\ %Prefs{}) do
    case params["sort"] do
      nil -> default
      "" -> []
      x -> parse_sort_value(x, prefs)
    end
  end

  @spec parse_sort_value(String.t(), Prefs.t()) :: keyword(atom)
  defp parse_sort_value(x, _prefs) do
    Regex.scan(~r/([- ])?([^- ]+)/, x)
    |> Enum.map(fn
      [_, "-", field] -> {:desc, String.to_existing_atom(field)}
      [_, _, field] -> {:asc, String.to_existing_atom(field)}
    end)
  end

  @doc """
  Extracts "field" and "q" parameters as filter keyword list.

  ## Examples

      iex> import Pageantry.Input
      iex> parse_filter(%{"field" => "created", "q" => "today"})
      [created: "today"]
      iex> parse_filter(%{"q" => "today"})
      [ALL: "today"]
      iex> parse_filter(%{"q" => ""})
      []
  """
  @spec parse_filter(map, keyword(String.t()), Prefs.t()) :: keyword(String.t())
  def parse_filter(params, default \\ [], prefs \\ %Prefs{}) do
    case params["q"] do
      nil -> default
      "" -> []
      x -> parse_filter_value(x, params["field"], prefs)
    end
  end

  @spec parse_filter_value(String.t(), String.t(), Prefs.t()) :: keyword(String.t())
  defp parse_filter_value(x, nil, _prefs), do: [ALL: x]
  defp parse_filter_value(x, field, _prefs), do: [{String.to_existing_atom(field), x}]

  @doc """
  Builds URL with paging params in query string.

  ## Examples

      iex> import Pageantry.Input
      iex> alias Pageantry.Input
      iex> to_url(%Input{off: 10, max: 20, sort: [asc: :name], filter: [ALL: "today"]})
      "?max=20&off=10&q=today&sort=name"
      iex> to_url(%Input{})
      ""
  """
  @spec to_url(__MODULE__.t(), integer) :: String.t()
  def to_url(input, default_max \\ 10) do
    case to_params(input, default_max) do
      params when map_size(params) == 0 -> ""
      params -> "?#{URI.encode_query(params)}"
    end
  end

  @doc """
  Builds paging params map.

  ## Examples

      iex> import Pageantry.Input
      iex> alias Pageantry.Input
      iex> to_params(%Input{off: 10, max: 20, sort: [asc: :name], filter: [ALL: "today"]})
      %{"max" => "20", "off" => "10", "q" => "today", "sort" => "name"}
      iex> to_params(%Input{})
      %{}
  """
  @spec to_params(__MODULE__.t(), integer) :: map
  def to_params(input, default_max \\ 10) do
    add_params(%{}, input, default_max)
  end

  @doc """
  Adds paging to existing params map.

  ## Examples

      iex> import Pageantry.Input
      iex> alias Pageantry.Input
      iex> add_params(%{}, %Input{off: 10, max: 20, sort: [asc: :name], filter: [ALL: "today"]})
      %{"max" => "20", "off" => "10", "q" => "today", "sort" => "name"}
      iex> add_params(%{}, %Input{})
      %{}
  """
  @spec add_params(map, __MODULE__.t(), integer) :: map
  def add_params(params, input, default_max \\ 10) do
    params
    |> add_off_param(input)
    |> add_max_param(input, default_max)
    |> add_sort_param(input)
    |> add_filter_param(input)
  end

  @doc """
  Adds offset parameter to map of paging params.

  ## Examples

      iex> import Pageantry.Input
      iex> alias Pageantry.Input
      iex> add_off_param(%{}, %Input{off: 10})
      %{"off" => "10"}
      iex> add_off_param(%{}, %Input{off: 0})
      %{}
  """
  @spec add_off_param(map, __MODULE__.t()) :: map
  def add_off_param(params, %{off: 0}), do: Map.delete(params, "off")
  def add_off_param(params, %{off: off}), do: Map.put(params, "off", to_string(off))

  @doc """
  Adds items-per-page parameter to map of paging params.

  ## Examples

      iex> import Pageantry.Input
      iex> alias Pageantry.Input
      iex> add_max_param(%{}, %Input{max: 100}, 10)
      %{"max" => "100"}
      iex> add_max_param(%{}, %Input{max: 100}, 100)
      %{}
  """
  @spec add_max_param(map, __MODULE__.t(), integer) :: map
  def add_max_param(params, %{max: max}, default_max) when max == default_max do
    Map.delete(params, "max")
  end

  def add_max_param(params, %{max: max}, _), do: Map.put(params, "max", to_string(max))

  @doc """
  Adds sort parameter to map of paging params.

  ## Examples

      iex> import Pageantry.Input
      iex> alias Pageantry.Input
      iex> add_sort_param(%{}, %Input{sort: [asc: :name]})
      %{"sort" => "name"}
      iex> add_sort_param(%{}, %Input{sort: [desc: :name]})
      %{"sort" => "-name"}
      iex> add_sort_param(%{}, %Input{})
      %{}
  """
  @spec add_sort_param(map, __MODULE__.t()) :: map
  def add_sort_param(params, %{sort: []}), do: Map.delete(params, "sort")

  def add_sort_param(params, %{sort: sort}) do
    value = add_sort_param_value("", sort)
    Map.put(params, "sort", value)
  end

  @spec add_sort_param_value(String.t(), keyword) :: String.t()
  defp add_sort_param_value(value, []), do: value

  defp add_sort_param_value("", [{:asc, field} | rest]) do
    add_sort_param_value("#{field}", rest)
  end

  defp add_sort_param_value(value, [{:asc, field} | rest]) do
    add_sort_param_value("#{value} #{field}", rest)
  end

  defp add_sort_param_value(value, [{:desc, field} | rest]) do
    add_sort_param_value("#{value}-#{field}", rest)
  end

  @doc """
  Adds filter parameter to map of paging params.

  ## Examples

      iex> import Pageantry.Input
      iex> alias Pageantry.Input
      iex> add_filter_param(%{}, %Input{filter: [created: "today"]})
      %{"field" => "created", "q" => "today"}
      iex> add_filter_param(%{}, %Input{filter: [ALL: "today"]})
      %{"q" => "today"}
      iex> add_filter_param(%{}, %Input{})
      %{}
  """
  @spec add_filter_param(map, __MODULE__.t()) :: map
  def add_filter_param(params, %{filter: []}), do: Map.drop(params, ["field", "q"])

  def add_filter_param(params, %{filter: [ALL: value]}) do
    params |> Map.delete("field") |> Map.put("q", value)
  end

  def add_filter_param(params, %{filter: [{field, value}]}) do
    Map.merge(params, %{"field" => to_string(field), "q" => value})
  end
end