defmodule PhaseDB.Client.CLI do
  alias PhaseDB.Client.Session
  require PhaseDB.Client

  @moduledoc """
  Implements the command line interface for the `phase_db_cli` escript.
  """

  @switches [
    version: :boolean,
    help:    :boolean
  ]

  @aliases [
    v: :version,
    h: :help
  ]

  @valid_schemes ~w| ws wss |

  def go %{help: true} do
    IO.puts version
    IO.write """
      usage: phase_db_cli <uri> [options]

      uri:
        The URI of the phaseDB server you are connecting to.
        Defaults to "%{PhaseDB.Client.default_uri}".

      options:
        -v --version    Display the phaseDB CLI version and exit
        -h --help       This message
    """
  end

  def go %{version: true} do
    IO.puts version
  end

  def go %{uri: uri} do
    Session.create uri
  end

  def main(args) do
    args
    |> parse_args
    |> go
  end

  def parse_args args do
    case OptionParser.parse args, switches: @switches, aliases: @aliases do
      {opts, [], _} ->
        opts
        |> Dict.put(:uri, PhaseDB.Client.default_uri)
        |> Enum.into(%{})
      {opts, [uri], _} ->
        opts
        |> Dict.put(:uri, validate_uri(uri))
        |> Enum.into(%{})
      {_, uris, _} ->
        halt_with_error "Invalid arguments: #{inspect uris}"
    end
  end

  defp validate_uri(uri) when is_binary(uri) do
    validate_uri URI.parse(uri)
  end

  defp validate_uri(%{scheme: scheme, path: path}=uri) do
    errors = []

    errors = if Enum.member? @valid_schemes, scheme do
      errors
    else
      [ ~s|Invalid URI: Scheme must be one of #{inspect @valid_schemes}]| | errors ]
    end

    errors = case path do
      nil -> errors
      "/" -> errors
      _   -> [ ~s|Invalid URI: Path must be "/"| | errors ]
    end

    if Enum.any? errors do
      halt_with_error Enum.join(errors, "\n\t")
    else
      URI.to_string uri
    end
  end

  def version do
    {:ok, version} = :application.get_key :phasedb_client, :vsn
    "PhaseDB CLI version #{version}"
  end

  def halt_with_error message do
    IO.write :stderr, "Error: #{message}"
    System.halt 1
  end
end