#! /bin/sh

set -e
usage="Usage: $0 [-bc] [COMMAND [ARGS...]]"

### Parse options
case "${SHELL-/bin/sh}" in
  *csh*) style=csh;;
  *) style=sh;;
esac
force=nil chosen= commands=
while [ $# -gt 0 ]; do
  case "$1" in
    -h | --help) echo "$usage"; exit 0 ;;
    -c | --cshell | --tcsh) style=csh chosen=t ;;
    -b | --bourne | --bash | --zsh) style=sh chosen=t ;;
    -f | --force) force=t ;;
    --) shift; break ;;
    -*) echo >&2 "$usage"; exit 1 ;;
    *) break ;;
  esac
  shift
done
[ $# -gt 0 ] && style=commands
case $chosen,$style in
  t,commands)
    echo >&2 "$0: output style and commands? you're odd"
    exit 1
    ;;
esac

## Check that this stands a chance of working.
if ! type >/dev/null 2>&1 ssh-agent || ! type >/dev/null >&1 ssh-add; then
  echo >&2 "$0: ssh not installed; chickening out"
  exit 1
fi

## Some useful variables.
hostname=${HOST-$(hostname)}
user=${USER-${LOGNAME-$(id -un)}} uid=${UID-$(id -u)}
dir=$TMPDIR/.ssh-agent.$hostname.$user
socket=$dir/sock; pid=$dir/pid
export SSH_AUTH_SOCK

## Should I start a new agent?
foundp=nil
case $force in
  nil)
    case ${SSH_AUTH_SOCK+t} in
      t)
	set +e; ssh-add -l >/dev/null 2>&1; rc=$?; set -e
	if [ $rc -lt 2 ]; then foundp=t; fi
	;;
    esac
    case $foundp in
      t) ;;
      *)
	for i in \
	  "$HOME/.cache/keyring-"*"/ssh" \
	  "/run/user/$uid/keyring/ssh" \
	  "$socket"
	do
	  SSH_AUTH_SOCK=$i
	  set +e; ssh-add -l >/dev/null 2>&1; rc=$?; set -e
	  if [ $rc -lt 2 ]; then foundp=t; break; fi
	done
	;;
    esac
    ;;
esac

### If so, do that
case $foundp in
  nil)
    mkdir -p -m700 "$dir"
    SSH_AUTH_SOCK=$socket
    p=$PATH
    runes=
    while :; do
      case $p in *:*) d=${p%%:*} p=${p#*:} ;; *) d=$p p= ;; esac
      if [ -x "${d+$d/}setsid" ]; then runes="$runes setsid"; break; fi
      case $p in "") break ;; esac
    done
    set +e; ssh-add -l >/dev/null 2>&1; rc=$?; set -e
    if [ $rc -ge 2 ]; then
      if [ -f "$pid" ]; then
	kill $(cat "$pid") >/dev/null 2>&1 || :
      fi
      rm -f "$socket" "$pid"
      (cd /; exec $runes ssh-agent -d -a "$socket" </dev/null >/dev/null 2>&1)&
      echo $! >"$pid"
      SSH_AUTH_SOCK=$socket
    fi
    ;;
esac

### Run a program, or export the details
case $style in
  sh) echo "SSH_AUTH_SOCK='$SSH_AUTH_SOCK'; export SSH_AUTH_SOCK" ;;
  csh) echo "setenv SSH_AUTH_SOCK '$SSH_AUTH_SOCK'" ;;
  commands) exec "$@" ;;
esac