defmodule TermTable do

  def build(data, _options \\ :empty) do

    max_lengths_by_index = max_lengths_by_index(data)

    { table_base, last_row_cell_lengths, _ } = do_build(data, max_lengths_by_index)

    table_bottom = do_separator(last_row_cell_lengths)
    result = table_base <> table_bottom <> "\n"
    result
  end

  defp do_build(rows, max_lengths_by_index) do
    rows
    |> Enum.with_index
    |> Enum.reduce({"", [], false}, fn({cols, row_idx}, acc) ->
      { previous_row_output, previous_row_cell_lengths, sep_preceding } = acc

      if cols == [:separator] do
        { previous_row_output, previous_row_cell_lengths, true }
      else
        { row_output, row_cell_lengths } =
          cols
          |> Enum.with_index
          |> Enum.reduce({ "|", []}, fn({i, col_idx}, acc) ->

            { output, cell_lengths } = acc

            { i, opts } = if is_tuple(i), do: i, else: { i, [] }

            colspan = Keyword.get(opts, :colspan, 1)
            align   = Keyword.get(opts, :align, :left)

            cell = adjust(max_lengths_by_index, i, col_idx, align, colspan)
            cell_length = String.length(cell)
            new_cell_lengths = cell_lengths ++ [ cell_length ]

            output = output <> cell <> "|"

            { output, new_cell_lengths }
          end)

        if sep_preceding || row_idx == 0  do
          separator = separator(previous_row_cell_lengths, row_cell_lengths)
          { previous_row_output <> separator <> "\n" <> row_output <> "\n", row_cell_lengths, false }
        else
          { previous_row_output <> row_output <> "\n", row_cell_lengths, false }
        end
      end

    end)
  end

  defp lengths_by_index(cols) do
    cols
    |> Enum.with_index
    |> Enum.reduce(%{}, &length_for_element/2)
  end

  defp length_for_element({{i, opts}, col_idx}, acc) do
    width = Keyword.get(opts, :width)

    unless width do
      width = String.length(to_string(i))
    end

    Map.put acc, col_idx, width
  end

  defp length_for_element({i, col_idx}, acc) do
    Map.put acc, col_idx, String.length(to_string(i))
  end

  defp separator(prev_lengths, curr_lengths) do
    { a, b } = { length(prev_lengths), length(curr_lengths) }

    lengths = if a > b, do: prev_lengths, else: curr_lengths
    do_separator(lengths)
  end

  defp do_separator(lengths) do
    fun = fn(x, acc) ->
      acc <> String.ljust("", x, ?-) <> "+"
    end
    lengths |> Enum.reduce("+", fun)
  end

  defp adjust(max_lengths_by_index, content, col_idx, align, colspan) do
    range = col_idx..(col_idx + colspan - 1)

    required_length = Enum.reduce range, 0, fn(idx, acc) ->
      acc + max_lengths_by_index[idx]
    end

    # correction by length of spaces between cols
    required_length = required_length + (colspan - 1) * 3
    content = to_string(content)

    case align do
      :left   ->
        " " <> String.ljust(content, required_length) <> " "

      :right  ->
        " " <> String.rjust(content, required_length) <> " "

      :center ->
        right_adjust   = div(required_length + String.length(content), 2)
        right_adjusted = String.rjust(content, right_adjust)

        " " <> String.ljust(right_adjusted, required_length) <> " "
    end
  end

  defp max_lengths_by_index(cols) do
    fun = fn(el, acc) ->

      lengths_by_index = lengths_by_index(el)

      Enum.reduce lengths_by_index, acc, fn({k, v}, acc) ->
        if acc[k] == nil || lengths_by_index[k] > acc[k] do
          Map.put(acc, k, v)
        else
          acc
        end
      end
    end

    cols |> Enum.reduce(%{}, fun)
  end

  def render(rows, options \\ :empty) do
    build(rows, options)
  end

end