cli.ex

defmodule Issues.CLI do
  @moduledoc """
  Handle the command line parsing and the dispatch to the various functions
  that end up generating a table of the last _n_ issues in a GitHub project.
  """

  @default_count 4

  def run(argv) do
    argv
    |> parse_args
    |> process
  end

  @doc """
  `argv` can be -h or --help, which returns :help.

  Otherwise, it is a GitHub username, project name, and optionally the number
  of entries to format.

  Return a tuple of `{user, project, count}`, or `:help` if help was given.
  """
  def parse_args(argv) do
    parse = OptionParser.parse(argv, switches: [help: :booleaan],
                                     aliases: [h: :help])
    case parse do
      {[help: true], _, _ } ->
        :help
      {_, [user, project, count], _} ->
        {user, project, String.to_integer(count)}
      {_, [user, project], _} ->
        {user, project, @default_count}
      _ -> :help
    end
  end

  def process(:help) do
    IO.puts """
    usage: issues <user> <project> [ count | #{@default_count} ] ]
    """
    System.halt(0)
  end

  def ({user, project, _count}) do
    Issues.GitHubIssues.fetch(user, project)
  end
end