doti3/bin/i3_switch_focus_container.php

#!/usr/bin/php
<?php

function getTree()
{
    return json_decode(shell_exec('i3-msg -t get_tree'));
}

function getFocusedWindowContainer($tree)
{
    if (empty($tree->nodes)) {
        return null;
    }

    foreach ($tree->nodes as $k => $container) {
        if (true === $container->focused) {
            return $tree->nodes;
        }

        if (null !== $container = getFocusedWindowContainer($container)) {
            return $container;
        }
    }

    return null;
}

function getFocusWindowNumber($default, $max)
{
    global $argv;

    if (!isset($argv[1])) {
        $argv[1] = $default;
    }

    return min($max, max(1, $argv[1])) - 1;
}

function getDefaultFocusWindowNumber($container)
{
    foreach ($container as $k => $v) {
        if ($v->focused) {
            return $k + 1;
        }
    }
}

function setFocusToWindow($window)
{
    shell_exec(sprintf("i3-msg '[con_id=\"%s\"] focus'", $window->id));
}

$container = getFocusedWindowContainer(getTree());

if (null !== $container) {
    $number = getFocusWindowNumber(getDefaultFocusWindowNumber($container), count($container));

    foreach ($container as $k => $window) {
        if ($k == $number) {
            setFocusToWindow($window);
        }
    }
}