#!/bin/bash

step() {
    printf '\033[1;32m*\033[0m \033[1m%s...\033[0m\n' "$*"
}

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

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

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

show_redirection_info() {
    lsof -i -P -n | awk '($1 == "ssh" && $10 == "(LISTEN)" && $9 ~ /.*:'"${local_port}"'/) { print }'
}

get_ssh_pid() {
    show_redirection_info | awk '{ print $2 }' | sort | uniq
}

# Supprimer la redirection SSH
stop_forwarding() {
    start_forwarding -O cancel
    if [ "$?" -eq 255 ]; then
        echo "Okay then, brutally killing SSH..."
        kill "$(get_ssh_pid)"
    fi
}

# Retourner 0 si le port de la redirection est déjà utilisé par SSH
is_forwarding_active() {
    [ -n "$(show_redirection_info)" ]
}

# Parser les variables
trap error_null_arg EXIT
set -e

arg_name='SSH host'    ; ssh_host="$1"    ; shift
arg_name='local port'  ; local_port="$1"  ; shift
arg_name='distant port'; distant_port="$1"; shift
trap - EXIT
unset arg_name

if [ -n "$1" ]
    then target="$1"
    else target=localhost
fi

set +e

# Branchement principal
if ! is_forwarding_active; then
    step "Starting the redirection"
    start_forwarding
else
    step "Stopping the redirection"
    stop_forwarding
fi