defmodule GithubIssues.TableFormatter do
  import Enum, only: [each: 2, map: 2, map_join: 3, max: 1]
  @doc """
  Takes a list of row data, where each row is Map, and a list of
  headers. Prints a table to STDOUT of the data from each row
  identified by each header. That is, each header identifies a column,
  and those columns are extracted and printed from the rows.
  We calculate the width of each column to fit the longest element
  in that column.
  """
  def print_table_for_columns(rows, headers) do
    data_by_columns = split_into_columns(rows, headers)
    column_widths = widths_of(data_by_columns)
    format = format_for(column_widths)
    puts_one_line_in_columns(headers, format)
    IO.puts separator(column_widths)
    puts_in_columns(data_by_columns, format)
  end

  @doc """
  Given a list of rows, where each row contains a keyed list 
  of columns, return a list containing lists of the data in each column.
  The `headers` parameter contains the list of columns to extract.
  ## Examples
      iex> list = [Enum.into([{"a", "1"}, {"b", "2"}, {"c", "3"}], Map.new),
      ...> Enum.into([{"a", "4"}, {"b", "5"}, {"c", "6"}], Map.new)]
      iex> GithubIssues.TableFormatter.split_into_columns(list, ["a", "b", "c"])
      [["1", "4"], ["2", "5"], ["3", "6"]]
  """
  def split_into_columns(rows, headers) do
    for header <- headers do
      for row <- rows, do: printable(row[header])
    end
  end

  @doc """
  Returns a binary (string) version of our parameter.
  ## Examples
      iex> GithubIssues.TableFormatter.printable("a")
      "a"
      iex> GithubIssues.TableFormatter.printable(99)
      "99"
  """
  def printable(str) when is_binary(str), do: str
  def printable(str), do: to_string(str)

  @doc """
  Given a list containg sublists, where each sublist contains the data
  for a column, return a list containing the maximum width of each column
  ## Examples
      iex> data = [["cat", "wombat", "dog"], ["elephant", "ant", "rhino"]]
      iex> GithubIssues.TableFormatter.widths_of(data)
      [6, 8]
  """
  def widths_of(columns) do
    for column <- columns, do: column |> map(&String.length/1) |> max
  end


  @doc """
  Return a format string that hard codes the widths of a set of columns.
  We put `"|"` between each column.
  ## Examples
      iex> widths = [5, 6, 99]
      iex> GithubIssues.TableFormatter.format_for(widths)
      "~-5s|~-6s|~-99s~n"
  """
  def format_for(column_widths) do
    map_join(column_widths, "|", fn width -> "~-#{width}s" end) <> "~n"
  end

  @doc """
  Generate the line that goes below the column headings. It is a string of 
  hyphens, with + signs where the vertical bar between columns goes.
  ## Examples
      iex> widths = [5, 6, 9]
      iex> GithubIssues.TableFormatter.separator(widths)
      "------+--------+----------"
  """
  def separator(column_widths) do
    map_join(column_widths, "-+-", fn width -> List.duplicate("-", width) end)
  end

  @doc """
  Given a list containing rows of data, a list containing the header
  selectors, and a format string, write the extracted data under control
  of the format string.
  """
  def puts_in_columns(data_by_columns, format) do
    data_by_columns
    |> List.zip
    |> map(&Tuple.to_list/1)
    |> each(&puts_one_line_in_columns(&1, format))
  end

  def puts_one_line_in_columns(fields, format) do
    :io.format(format, fields)
  end
end