defmodule Meld do
  @moduledoc """
    Meld is a command-line utility (and library) that makes it easy to provide a
    mix task as a global command, enabling __real__ CLIs.

    ## Usage
      Meld.link ".", "mix_task"
      Meld.unlink "mix_task"

    Where `File.cwd()` is a directory containing an Elixir app
    with a mix task that can be run. 'mix_task' is the mix task name, that means
    that it can be run with 'mix mix_task'.

    Meld will create a shell script in its directory at ~/.meld. This shell
    script will cd into the specified directory and run the mix task. By adding
    the Meld directory to the global PATH, a simulated global executable is
    achieved.
  """

  alias Meld.Util

  @doc """
    Links a mix task to a newly created shell script in `~/.meld`.

    ## Usage
      Meld.link ".", "mix_task", "script_name"

    ## Arguments
      * `dir` - A directory containing a mix project.
      * `mix_task` - The name of the mix task to link.
      * `script_name` - Custom name for the generated script.
  """
  def link(dir, mix_task, script_name) do
    Util.check_dir_not_exists "Please run 'meld setup' first, aborting."
    if !File.exists? dir do
      raise "The specified project directory does not exist, aborting."
    end

    content = "
    # Generated by Meld (http://github.com/conflate/meld)
    cd #{Path.expand(dir)}
    mix #{mix_task}
    "

    filename = Path.basename(Path.expand(dir))
    path = if script_name do
      Path.join([Util.path, script_name]) else
      Path.join([Util.path, "#{filename}_#{mix_task}"]) end
    File.write! path, content
    {_msg, _result} = System.cmd "chmod", ["755", path], cd: Util.path
  end

  @doc """
    Removes a script from the ~/.meld directory.

    ## Usage
      Meld.unlink "script_name"

    ## Arguments
      * `script_name` - The filename of the script to remove.
  """
  def unlink(script_name) do
    filepath = Path.join(Util.path, script_name)

    if !File.exists? filepath do
      raise "The specified script doesn't exist."
      exit ""
    end

    File.rm! filepath
  end
end