keygen

#!/usr/bin/env elixir

defmodule Keygen do
  @defaults %{
    keyFilePath: Path.expand("./keyfile"),
    keySizeBytes: "32",
    fileMode: 0o400
  }

  def main(["-h"]), do: usage()
  def main(["-help"]), do: usage()
  def main(["--help"]), do: usage()

  def main([]) do
    main([@defaults.keyFilePath, @defaults.keySizeBytes])
  end

  def main([keyFilePath]) do
    main([keyFilePath, @defaults.keySizeBytes])
  end

  def main([keyFilePath, keySizeBytes]) do
    case File.stat(keyFilePath) do
      {:error, _reason} ->
        case Integer.parse(keySizeBytes) do
          {keySizeInt, ""} ->
            key = :crypto.strong_rand_bytes(keySizeInt)
            case File.write(keyFilePath, key, [:raw]) do
              :ok ->
                File.chmod!(keyFilePath, @defaults.fileMode)
                keyHash = :crypto.hash(:sha256, key) |> :binary.encode_hex() |> :string.lowercase()
                IO.puts("** Generated #{keySizeInt} bytes of key material with SHA256 checksum #{keyHash}\n")
                IO.puts("** Wrote raw key to #{keyFilePath}\n\n")
                IO.puts("** Copy/paste the following hexadecimal version into the browser extension:\n")
                IO.puts(:binary.encode_hex(key) |> :string.lowercase())
                IO.puts("\n** IMPORTANT: The above will *not be shown again*!")

              {:error, reason} ->
                IO.puts("failed to write #{keyFilePath}: '#{reason}'")
            end

          _ ->
            IO.puts("cannot parse keySizeBytes '#{inspect(keySizeBytes)}'")
          end

      {:ok, _stat} ->
        IO.puts("keyfile already exists, will not overwrite")
    end
  end

  def main(_), do: usage()

  defp usage() do
    IO.puts("Usage: keygen [keyFilePath] [keySizeBytes]\n\n" <>
      "Defaults when not specified:" <>
      "\n\tkeyFilePath:  #{@defaults.keyFilePath}" <>
      "\n\tkeySizeBytes: #{@defaults.keySizeBytes}")
  end
end

Keygen.main(System.argv())