#!/bin/bash

error() {
    >&2 printf '\033[1;31mERROR:\033[0m \033[1m%s\033[0m\n' "$error"
    return "$1"
}

error_null_arg() {
    local error
    error="Variable \"${1}\" can't be null"
    error 1
}

parse_variable() {
    ! :
}

# Parser les variables
trap error_null_arg EXIT
set -e

ssh_host="$1"
shift

parse_variable ssh_host "$1" 'SSH host'
parse_variable local_port 'local port'
parse_variable distant_port 'distant port'

trap - EXIT
set +e

# Lancer la redirection SSH
start_forwarding() {
    ssh \
        -f -N \
        -L "${local_port}:${target}:${distant_port}" \
        "$@" \
        "$ssh_host"
}

# Supprimer la redirection SSH
stop_forwarding() {
    start_forwarding -O cancel
}

# Retourner 0 si le port de la redirection est déjà utilisé par SSH
is_forwarding_active() {
    lsof -i -P -n \
        | awk '($1 == "ssh" && $10 == "(LISTEN)") { print $9 }' \
        | cut -d : -f 2 \
        | grep -q "$local_port"
}

# Branchement principal
if ! is_forwarding_active; then
    start_forwarding
else
    stop_forwarding
fi