defmodule Credo.Code.Strings do
  @moduledoc """
  This module lets you strip strings from source code.
  """

  alias Credo.Code.InterpolationHelper

  @sigil_delimiters [
    {"(", ")"},
    {"[", "]"},
    {"{", "}"},
    {"<", ">"},
    {"|", "|"},
    {"\"", "\""},
    {"'", "'"}
  ]
  @all_string_sigils Enum.flat_map(@sigil_delimiters, fn {b, e} ->
                       [{"~s#{b}", e}, {"~S#{b}", e}]
                     end)

  # TODO v1.0: this should not remove heredocs, since
  #             there is a separate module for that

  @doc """
  Replaces all characters inside string literals and string sigils
  with the equivalent amount of white-space.
  """
  def replace_with_spaces(source, replacement \\ " ", interpolation_replacement \\ " ") do
    source
    |> InterpolationHelper.replace_interpolations(interpolation_replacement)
    |> parse_code("", replacement)
  end

  defp parse_code("", acc, _replacement) do
    acc
  end

  for {sigil_start, sigil_end} <- @all_string_sigils do
    defp parse_code(<<unquote(sigil_start)::utf8, t::binary>>, acc, replacement) do
      parse_string_sigil(
        t,
        acc <> unquote(sigil_start),
        unquote(sigil_end),
        replacement
      )
    end
  end

  defp parse_code(<<"\\\""::utf8, t::binary>>, acc, replacement) do
    parse_code(t, acc <> "\\\"", replacement)
  end

  defp parse_code(<<"?\""::utf8, t::binary>>, acc, replacement) do
    parse_code(t, acc <> "?\"", replacement)
  end

  defp parse_code(<<"#"::utf8, t::binary>>, acc, replacement) do
    parse_comment(t, acc <> "#", replacement)
  end

  defp parse_code(<<"\"\"\""::utf8, t::binary>>, acc, replacement) do
    parse_heredoc(t, acc <> ~s("""), replacement)
  end

  defp parse_code(<<"\'\'\'"::utf8, t::binary>>, acc, replacement) do
    parse_heredoc(t, acc <> ~s("""), replacement)
  end

  defp parse_code(<<"\""::utf8, t::binary>>, acc, replacement) do
    parse_string_literal(t, acc <> "\"", replacement)
  end

  defp parse_code(<<h::utf8, t::binary>>, acc, replacement) do
    parse_code(t, acc <> <<h::utf8>>, replacement)
  end

  defp parse_code(str, acc, replacement) when is_binary(str) do
    {h, t} = String.next_codepoint(str)

    parse_code(t, acc <> h, replacement)
  end

  defp parse_comment("", acc, _replacement) do
    acc
  end

  defp parse_comment(<<"\n"::utf8, t::binary>>, acc, replacement) do
    parse_code(t, acc <> "\n", replacement)
  end

  defp parse_comment(str, acc, replacement) when is_binary(str) do
    {h, t} = String.next_codepoint(str)

    parse_comment(t, acc <> h, replacement)
  end

  defp parse_string_literal("", acc, _replacement) do
    acc
  end

  defp parse_string_literal(<<"\\\\"::utf8, t::binary>>, acc, replacement) do
    parse_string_literal(t, acc, replacement)
  end

  defp parse_string_literal(<<"\\\""::utf8, t::binary>>, acc, replacement) do
    parse_string_literal(t, acc, replacement)
  end

  defp parse_string_literal(<<"\""::utf8, t::binary>>, acc, replacement) do
    parse_code(t, acc <> ~s("), replacement)
  end

  defp parse_string_literal(<<"\n"::utf8, t::binary>>, acc, replacement) do
    parse_string_literal(t, acc <> "\n", replacement)
  end

  defp parse_string_literal(<<_::utf8, t::binary>>, acc, replacement) do
    parse_string_literal(t, acc <> replacement, replacement)
  end

  for {_sigil_start, sigil_end} <- @all_string_sigils do
    defp parse_string_sigil("", acc, unquote(sigil_end), _replacement) do
      acc
    end

    defp parse_string_sigil(
           <<"\\\\"::utf8, t::binary>>,
           acc,
           unquote(sigil_end),
           replacement
         ) do
      parse_string_sigil(t, acc, unquote(sigil_end), replacement)
    end

    defp parse_string_sigil(
           <<"\\\""::utf8, t::binary>>,
           acc,
           unquote(sigil_end),
           replacement
         ) do
      parse_string_sigil(t, acc, unquote(sigil_end), replacement)
    end

    defp parse_string_sigil(
           <<unquote(sigil_end)::utf8, t::binary>>,
           acc,
           unquote(sigil_end),
           replacement
         ) do
      parse_code(t, acc <> unquote(sigil_end), replacement)
    end

    defp parse_string_sigil(
           <<"\n"::utf8, t::binary>>,
           acc,
           unquote(sigil_end),
           replacement
         ) do
      parse_string_sigil(t, acc <> "\n", unquote(sigil_end), replacement)
    end

    defp parse_string_sigil(
           <<_::utf8, t::binary>>,
           acc,
           unquote(sigil_end),
           replacement
         ) do
      parse_string_sigil(t, acc <> replacement, unquote(sigil_end), replacement)
    end
  end

  defp parse_heredoc("", acc, _replacement) do
    acc
  end

  defp parse_heredoc(<<"\\\\"::utf8, t::binary>>, acc, replacement) do
    parse_heredoc(t, acc, replacement)
  end

  defp parse_heredoc(<<"\\\""::utf8, t::binary>>, acc, replacement) do
    parse_heredoc(t, acc, replacement)
  end

  defp parse_heredoc(<<"\"\"\""::utf8, t::binary>>, acc, replacement) do
    parse_code(t, acc <> ~s("""), replacement)
  end

  defp parse_heredoc(<<"\n"::utf8, t::binary>>, acc, replacement) do
    parse_heredoc(t, acc <> "\n", replacement)
  end

  defp parse_heredoc(<<_::utf8, t::binary>>, acc, replacement) do
    parse_heredoc(t, acc <> replacement, replacement)
  end
end