#!/usr/bin/php
<?php
function is_subnet_overlaps($subnet, $candidate)
{
    $parts = explode("/", $subnet);
    $prefix = $parts[1];
    $subnet_first = ip2long($parts[0]);
    $candidate_prefix = explode("/", $candidate)[1];
    $count = pow(2, 32 - (int)$prefix);
    $subnet_last = $subnet_first + $count - 1;
    $test_ip = ip2long(explode("/", $candidate)[0]);
    return $test_ip >= $subnet_first and $test_ip <= $subnet_last and $candidate_prefix > $prefix;
}

class RoutingTableReader
{
    private $routes = [];

    /**
     * @return array
     */
    public function getRoutes(): array
    {
        return $this->routes;
    }

    public function __construct()
    {
        $result = @shell_exec("ip --json route show");
        if (!$result) {
            throw new RuntimeException("Failed to read routing table");
        }
        $this->routes = @json_decode($result, true);
        if ($this->routes === null) {
            throw new RuntimeException("Failed to parse json output");
        }
        foreach ($this->routes as $key => &$route) {
            if ($route["dst"] === "default") {
                $route["dst"] = "0.0.0.0/0";
            } elseif (!str_contains($route["dst"], "/")) {
                $route["dst"] .= "/32";
            }
        }
    }
}

try {
    if (!isset($argv[1])) {
        throw new RuntimeException("Output config is not set");
    }
    $config = [];
    $reader = new RoutingTableReader();
    $routes = [];
    $overlapped = [];
    foreach ($reader->getRoutes() as $route) {
        if ($route["dst"] == "0.0.0.0/0") {
            continue;
        }
        $routes[] = $route;
    }
    foreach ($routes as $i => $master) {
        if (in_array($master, $overlapped)) {
            continue;
        }
        foreach ($routes as $j => $slave) {
            if ($i == $j or in_array($slave, $overlapped)) {
                continue;
            }
            if (is_subnet_overlaps($master["dst"], $slave["dst"])) {
                $overlapped[] = $slave;
            }
        }
    }
    $subnets = [];
    foreach ($routes as $i => $master) {
        if (in_array($master, $overlapped)) {
            continue;
        }
        $subnets[] = $master["dst"];
    }
    foreach ($subnets as $route) {
        $parts = explode("/", $route);
        $mask = long2ip(-1 << (32 - (int)$parts[1]));
        $dst = $parts[0];
        $config[] = "push \"route {$dst} {$mask}\"";
    }
    $outfile = $argv[1];
    file_put_contents($outfile, implode("\n", $config));
} catch (Exception $e) {
    echo "\nError:" . $e->getMessage() . "\n";
    exit(1);
}
exit(0);