#!/bin/bash

function get_ssh_param () {
    local session_name ssh_param
    session_name="${1:?}"
    ssh_param="${2:?}"

    # SSHtunnelUser     -> ssh_user
    # SSHtunnelHost     -> ssh_target_server
    # SSHtunnelHostPort -> ssh_target_port
    # SSHtunnelPort     -> ssh_local_port
    # Host              -> tunneled_target_host
    # Port              -> tunneled_target_port

    local value
    value="$(grep -Pio -- '(?<=^Servers\\'"${session_name}"'\\'"${ssh_param}"'<\|\|\|>[[:digit:]]<\|\|\|>)[^\r\n\f]+' "${settings_file}")"
    if [[ ! "${value}" ]]; then
        case "${ssh_param}" in
            SSHtunnelUser)
                value="${USER}"
                ;;
            SSHtunnelHostPort)
                value='22'
                ;;
            Host)
                value='127.0.0.1'
                ;;
            *)
                return 1
                ;;
        esac
    fi
    printf -- '%s' "${value}"
}

function local_port_is_free () {
    local local_port local_listeners
    local_port="${1:?}"
    local_listeners="$(ss --no-header -tln 'sport :'"${local_port}")"
    if [[ "${local_listeners}" ]]; then
        return 1
    fi
    return 0
}

function prep_tunnel () {
    local session_name
    session_name="${1:?}"

    local ssh_user ssh_target_server ssh_target_port ssh_local_port tunneled_target_host tunneled_target_port
    
    ssh_user="$(get_ssh_param "${session_name}" 'SSHtunnelUser')"
    ssh_target_server="$(get_ssh_param "${session_name}" 'SSHtunnelHost')"
    ssh_target_port="$(get_ssh_param "${session_name}" 'SSHtunnelHostPort')"
    ssh_local_port="$(get_ssh_param "${session_name}" 'SSHtunnelPort')"
    tunneled_target_host="$(get_ssh_param "${session_name}" 'Host')"
    tunneled_target_port="$(get_ssh_param "${session_name}" 'Port')"

    if [[ ! "${ssh_user}" ]] || \
        [[ ! "${ssh_target_server}" ]] || \
        [[ ! "${ssh_target_port}" ]] || \
        [[ ! "${ssh_local_port}" ]] || \
        [[ ! "${tunneled_target_host}" ]] || \
        [[ ! "${tunneled_target_port}" ]]; then
        printf 'Session name\n\n    %s\n\nUnable to set all necessary SSH vars, exiting 256 ...\n' "'${session_name}'"
        exit 256
    fi

    printf '%s\n' 'Starting SSH tunnel ...'

    if local_port_is_free "${ssh_local_port}"; then
        set -xv
        ssh "${ssh_user}"'@'"${ssh_target_server}" \
            -o 'ExitOnForwardFailure=yes' \
            -o 'ConnectTimeout=2' \
            -f \
            -p "${ssh_target_port}" \
            -N \
            -L "${ssh_local_port}"':'"${tunneled_target_host}"':'"${tunneled_target_port}" && {
            set +xv
            printf -- 'Done!'
            local_port_is_free "${ssh_local_port}"
        }
        set +xv
    else
        printf -- '%s\n' \
            'Failed! Something is listening on local TCP port '"${ssh_local_port}"'.' \
            'Try ss --no-header -tlpn '"'"'sport :'"${ssh_local_port}"''"'"' to ID processes.' \
            'Exiting 256 ...'
        exit 256
    fi
}

function main () {
    settings_file=~/'.heidisql/portable_settings.txt'
    if [[ ! -r "${settings_file}" ]]; then
        COMPREPLY="$(printf -- '%s' '<File '"${settings_file}"' not readable, nothing to auto-complete>')"
        return 1
    fi
    prep_tunnel "${@}"
}

main "${@}"