#!/bin/sh

REMOTE_HOST="$1"
IMAP_COMMAND="${2:-MAIL=\$HOME/.maildir /usr/lib/dovecot/imap 2>/dev/null}"

SSH_KEY="$HOME/.offlineimap/${REMOTE_HOST}.ssh-seckey"
SSH_OPTIONS="command=\"$IMAP_COMMAND\",no-agent-forwarding,no-X11-forwarding,no-port-forwarding,no-pty"

if [ ! -f "$SSH_KEY" ]; then
  ssh-keygen -f "$SSH_KEY" -C "OfflineIMAP from $(hostname --fqdn)" -N '' -t ed25519
  COMMAND="echo '$SSH_OPTIONS $(cat "$SSH_KEY.pub")' >> .ssh/authorized_keys"
  ssh -F ~/.offlineimap/ssh_config -o ControlPath=none -o IdentityAgent=SSH_AUTH_SOCK \
    ${REMOTE_HOST} "$COMMAND"
fi

exec ssh -F ~/.offlineimap/ssh_config -i "$SSH_KEY" ${1} \
  echo "You need to configure a password-less SSH keypair and have the public key in the remote\'s" \
    "\~/.ssh/authorized_keys file, prefixed by \'$SSH_OPTIONS\'. You can try to invoke \'$0 $REMOTE_HOST\'"\
    "from an interactive shell and it will attempt to set this up for you."

# This relies on the IMAP command being specified on the server side, i.e. in
# ~/.ssh/authorized_keys, put a line like the following
#
#   command="MAIL=$HOME/.maildir /usr/lib/dovecot/imap 2>/dev/null",no-agent-forwarding,no-X11-forwarding,no-port-forwarding,no-pty ssh-ed25519 AAA…
#
# When a command is specified like this, it overrides the instructions being
# passed in the command above. So, when you invoke this script directly, you
# should see the IMAP server greet you:
#
# % ~/.offlineimap/preauthtunnel.sh madduck-net.imap.madduck.net
# * PREAUTH [CAPABILITY IMAP4rev1 […]] Logged in as madduck

# vim:tw=0