#!/bin/sh
usage() {
  echo "usage: $0 [-w] [-h]"
  echo "   -w   use OpenSSH for Windows instead of WSL ssh-agent"
  echo "   -h   show help and exit"
}

error() {
  printf "ERROR: %s\n" "$1" >&2
  exit 1
}

require() {
  command -v "$@" >/dev/null 2>&1 || error "'$1' not found"
}

start_wsl_agent() {
  if [ "$#" -gt 0 ]; then
    SHLVL=0 exec ssh-agent "$SHELL" -c "$@"
  else
    SHLVL=0 exec ssh-agent "$SHELL"
  fi
}

start_windows_agent() {
  require socat
  require npiperelay

  # Forward SSH Agent requests from withitn WSL to OpenSSH for Windows, based on:
  # https://stuartleeks.com/posts/wsl-ssh-key-forward-to-windows/
  export SSH_AUTH_SOCK="$HOME/.ssh/agent.sock"
  [ -S "$SSH_AUTH_SOCK" ] && rm "$SSH_AUTH_SOCK"
  socat \
    UNIX-LISTEN:$SSH_AUTH_SOCK,fork \
    EXEC:"npiperelay -ei -s //./pipe/openssh-ssh-agent",nofork \
    &

  if [ "$#" -gt 0 ]; then
    SHLVL=0 exec "$SHELL" -c "$@"
  else
    SHLVL=0 exec "$SHELL"
  fi
}

main() {
  WSL_SSH_AGENT=yes
  while getopts ":wh" arg; do
    case "$arg" in
      w)  WSL_SSH_AGENT=no;;
      h)  usage; exit 0;;
      ?)  usage >&2; error "unknown option -$OPTARG";;
    esac
    shift
  done

  if [ "$WSL_SSH_AGENT" = "yes" ]; then
    start_wsl_agent "$@"
  else
    start_windows_agent "$@"
  fi
}

main "$@"