jsonc

defmodule JSONC.Combinators do
  @moduledoc false

  def parse(text, pos \\ 0) when is_binary(text) and is_integer(pos) do
    case data().(text, pos) do
      {_, _, ast} -> ast
    end
  end

  def data do
    node(:data, chain([line(), repeat(chain([literal("\n"), line()]))]))
  end

  def line do
    node(:line, chain([item(), repeat(chain([literal(","), item()]))]))
  end

  def item do
    node(
      :item,
      chain([
        ignore(literal(" ")),
        repeat(
          chain([
            negate(literal(",")),
            negate(literal("\n")),
            # &any/2,
            branch([chain([negate(literal(",")), negate(literal("\n"))]), literal(" "), &any/2])
          ])
        ),
        ignore(literal(" "))
      ])
    )
  end

  def node(type, pattern) when is_atom(type) and is_function(pattern) do
    fn text, pos when is_binary(text) and is_integer(pos) ->
      result = pattern.(text, pos)

      case result do
        nil ->
          nil

        {pattern_start, pattern_end, value} ->
          {pattern_start, pattern_end,
           %{type: type, value: value, start: pattern_start, end: pattern_end}}
      end
    end
  end

  def nothing(text, pos) when is_binary(text) and is_integer(pos) do
    case String.split_at(text, pos) |> elem(1) |> String.starts_with?("") do
      true ->
        {pos, pos, ""}

      false ->
        nil
    end
  end

  def any(text, pos) when is_binary(text) and is_integer(pos) do
    case pos < String.length(text) do
      true -> {pos, pos + 1, String.at(text, pos)}
      false -> nil
    end
  end

  def literal(pattern) when is_binary(pattern) do
    fn text, pos when is_binary(text) and is_integer(pos) ->
      case String.split_at(text, pos) |> elem(1) |> String.starts_with?(pattern) do
        true ->
          {pos, pos + String.length(pattern), pattern}

        false ->
          nil
      end
    end
  end

  def ignore(pattern) when is_function(pattern) do
    fn text, pos when is_binary(text) and is_integer(pos) ->
      case pattern.(text, pos) do
        nil -> nil
        {_, pattern_end, _} -> {pos, pattern_end, ""}
      end
    end
  end

  def chain(patterns) when is_list(patterns) do
    check_patterns(patterns)

    fn text, pos when is_binary(text) and is_integer(pos) ->
      start = pos

      case chain_check(patterns, text, pos) do
        nil ->
          nil

        results ->
          {_, chain_end, _} = results |> Enum.at(-1)

          case results |> Enum.all?(fn {_, _, child} -> is_binary(child) end) do
            true ->
              {start, chain_end,
               results |> Enum.map(fn {_, _, child} -> child end) |> Enum.join()}

            false ->
              {start, chain_end,
               results
               |> Enum.filter(fn {_, _, child} -> !is_binary(child) end)
               |> Enum.map(fn {_, _, child} -> child end)
               |> List.flatten()}
          end
      end
    end
  end

  def branch(patterns) when is_list(patterns) do
    check_patterns(patterns)

    fn text, pos when is_binary(text) and is_integer(pos) ->
      branch_check(patterns, text, pos)
    end
  end

  def repeat(pattern) when is_function(pattern) do
    repeat_internal(pattern)
  end

  def check_patterns(patterns) when is_list(patterns) do
    patterns
    |> Enum.each(fn p ->
      case is_function(p) do
        true -> nil
        false -> raise "#{p |> inspect()} is not a function"
      end
    end)
  end

  def negate(pattern) when is_function(pattern) do
    fn text, pos when is_binary(text) and is_integer(pos) ->
      result = pattern.(text, pos)

      case result do
        nil ->
          {pos, pos, ""}

        _ ->
          nil
      end
    end
  end

  def peek(pattern) when is_function(pattern) do
    fn text, pos when is_binary(text) and is_integer(pos) ->
      case pattern.(text, pos + 1) do
        nil -> nil
        _ -> {pos, pos, ""}
      end
    end
  end

  def chain_check(nil) do
    nil
  end

  def chain_check(patterns, text, pos, results \\ [])
      when is_list(patterns) and is_binary(text) and is_integer(pos) do
    case patterns do
      [] ->
        results

      [pattern | rest] ->
        case pattern.(text, pos) do
          nil ->
            chain_check(nil)

          {_pattern_start, pattern_end, _children} = result ->
            chain_check(
              rest,
              text,
              pattern_end,
              results ++ [result]
            )
        end
    end
  end

  def branch_check(patterns, text, pos) when is_list(patterns) do
    case patterns do
      [] ->
        nil

      [pattern | rest] ->
        case pattern.(text, pos) do
          nil -> branch_check(rest, text, pos)
          result -> result
        end
    end
  end

  def repeat_internal(pattern) when is_function(pattern) do
    fn text, pos when is_binary(text) and is_integer(pos) ->
      branch([
        chain([
          pattern,
          repeat_internal(pattern)
        ]),
        &nothing/2
      ]).(text, pos)
    end
  end
end