defmodule IO.ANSI.Sequence do
  @moduledoc false

  defmacro defsequence(name, code \\ "", terminator \\ "m") do
    quote bind_quoted: [name: name, code: code, terminator: terminator] do
      def unquote(name)() do
        "\e[#{unquote(code)}#{unquote(terminator)}"
      end

      defp format_sequence(unquote(name)) do
        unquote(name)()
      end
    end
  end
end

defmodule IO.ANSI do
  @moduledoc """
  Functionality to render ANSI escape sequences
  (http://en.wikipedia.org/wiki/ANSI_escape_code) —  characters embedded
  in text used to control formatting, color, and other output options
  on video text terminals.
  """

  import IO.ANSI.Sequence

  @typep ansicode :: atom()
  @typep ansilist :: maybe_improper_list(char() | ansicode() | binary() | ansilist(), binary() | ansicode() | [])
  @type  ansidata :: ansilist() | ansicode() | binary()

  @doc """
  Checks if ANSI coloring is supported and enabled on this machine.

  This function simply reads the configuration value for
  `:ansi_enabled` in the `:elixir` application. The value is by
  default false unless Elixir can detect during startup that
  both `stdout` and `stderr` are terminals.
  """
  @spec enabled? :: boolean
  def enabled? do
    Application.get_env(:elixir, :ansi_enabled, false)
  end

  @doc "Resets all attributes"
  defsequence :reset, 0

  @doc "Bright (increased intensity) or Bold"
  defsequence :bright, 1

  @doc "Faint (decreased intensity), not widely supported"
  defsequence :faint, 2

  @doc "Italic: on. Not widely supported. Sometimes treated as inverse."
  defsequence :italic, 3

  @doc "Underline: Single"
  defsequence :underline, 4

  @doc "Blink: Slow. Less than 150 per minute"
  defsequence :blink_slow, 5

  @doc "Blink: Rapid. MS-DOS ANSI.SYS; 150 per minute or more; not widely supported"
  defsequence :blink_rapid, 6

  @doc "Image: Negative. Swap foreground and background"
  defsequence :inverse, 7

  @doc "Image: Negative. Swap foreground and background"
  defsequence :reverse, 7

  @doc "Conceal. Not widely supported"
  defsequence :conceal, 8

  @doc "Crossed-out. Characters legible, but marked for deletion. Not widely supported."
  defsequence :crossed_out, 9

  @doc "Sets primary (default) font"
  defsequence :primary_font, 10

  for font_n <- [1, 2, 3, 4, 5, 6, 7, 8, 9] do
    @doc "Sets alternative font #{font_n}"
    defsequence :"font_#{font_n}", font_n + 10
  end

  @doc "Normal color or intensity"
  defsequence :normal, 22

  @doc "Not italic"
  defsequence :not_italic, 23

  @doc "Underline: None"
  defsequence :no_underline, 24

  @doc "Blink: off"
  defsequence :blink_off, 25

  colors = [:black, :red, :green, :yellow, :blue, :magenta, :cyan, :white]
  colors = Enum.zip(0..(length(colors)-1), colors)

  for {code, color} <- colors do
    @doc "Sets foreground color to #{color}"
    defsequence color, code + 30

    @doc "Sets background color to #{color}"
    defsequence :"#{color}_background", code + 40
  end

  @doc "Default text color"
  defsequence :default_color, 39

  @doc "Default background color"
  defsequence :default_background, 49

  @doc "Framed"
  defsequence :framed, 51

  @doc "Encircled"
  defsequence :encircled, 52

  @doc "Overlined"
  defsequence :overlined, 53

  @doc "Not framed or encircled"
  defsequence :not_framed_encircled, 54

  @doc "Not overlined"
  defsequence :not_overlined, 55

  @doc "Send cursor home"
  defsequence :home, "", "H"

  @doc "Clear screen"
  defsequence :clear, "2", "J"

  defp format_sequence(other) do
    raise ArgumentError, "invalid ANSI sequence specification: #{other}"
  end

  @doc ~S"""
  Formats a chardata-like argument by converting named ANSI sequences into actual
  ANSI codes.

  The named sequences are represented by atoms.

  It will also append an `IO.ANSI.reset` to the chardata when a conversion is
  performed. If you don't want this behaviour, use `format_fragment/2`.

  An optional boolean parameter can be passed to enable or disable
  emitting actual ANSI codes. When `false`, no ANSI codes will emitted.
  By default checks if ANSI is enabled using the `enabled?/0` function.

  ## Examples

      iex> IO.ANSI.format(["Hello, ", :red, :bright, "world!"], true)
      [[[[[[], "Hello, "] | "\e[31m"] | "\e[1m"], "world!"] | "\e[0m"]

  """
  def format(chardata, emit \\ enabled?) when is_boolean(emit) do
    do_format(chardata, [], [], emit, :maybe)
  end

  @doc ~S"""
  Formats a chardata-like argument by converting named ANSI sequences into actual
  ANSI codes.

  The named sequences are represented by atoms.

  An optional boolean parameter can be passed to enable or disable
  emitting actual ANSI codes. When `false`, no ANSI codes will emitted.
  By default checks if ANSI is enabled using the `enabled?/0` function.

  ## Examples

      iex> IO.ANSI.format_fragment([:bright, 'Word'], true)
      [[[[[[] | "\e[1m"], 87], 111], 114], 100]

  """
  def format_fragment(chardata, emit \\ enabled?) when is_boolean(emit) do
    do_format(chardata, [], [], emit, false)
  end

  defp do_format([term | rest], rem, acc, emit, append_reset) do
    do_format(term, [rest | rem], acc, emit, append_reset)
  end

  defp do_format(term, rem, acc, true, append_reset) when is_atom(term) do
    do_format([], rem, [acc | format_sequence(term)], true, !!append_reset)
  end

  defp do_format(term, rem, acc, false, append_reset) when is_atom(term) do
    do_format([], rem, acc, false, append_reset)
  end

  defp do_format(term, rem, acc, emit, append_reset) when not is_list(term) do
    do_format([], rem, [acc | [term]], emit, append_reset)
  end

  defp do_format([], [next | rest], acc, emit, append_reset) do
    do_format(next, rest, acc, emit, append_reset)
  end

  defp do_format([], [], acc, true, true) do
    [acc | IO.ANSI.reset]
  end

  defp do_format([], [], acc, _emit, _append_reset) do
    acc
  end
end
