<?php
/*
 * The zoo's robot: a real account, `zoo-robot`, visible in the directory like anyone, that the
 * self-check signs in as. Its passkey is a software key kept in $RC_DATA/robot.json (the zoo's
 * own data; nothing of root's or account's). It signs in exactly as a person does: a WebAuthn
 * assertion to account, then the silent upgrade into the zoo.
 *
 * Live and staging each have their own account, so each environment has its own robot.
 */

require_once __DIR__ . "/web.php";

const ROBOT_NAME = "zoo-robot";

function b64u(string $b): string { return rtrim(strtr(base64_encode($b), "+/", "-_"), "="); }

// CBOR, just enough for a COSE key and an attestation object.
function cbor(int $major, int $n): string {
    return $n < 24 ? chr(($major << 5) | $n) : ($n < 256 ? chr(($major << 5) | 24) . chr($n) : chr(($major << 5) | 25) . pack("n", $n));
}
function cbor_int(int $n): string { return $n >= 0 ? cbor(0, $n) : cbor(1, -1 - $n); }
function cbor_bytes(string $s): string { return cbor(2, strlen($s)) . $s; }
function cbor_text(string $s): string { return cbor(3, strlen($s)) . $s; }
function cbor_map(array $kv): string { $o = cbor(5, count($kv)); foreach ($kv as [$k, $v]) $o .= $k . $v; return $o; }

function robot_path(): string { return env("RC_DATA") . "/robot.json"; }
function rp_id(): string { return parse_url(env("RC_ACCOUNTS"), PHP_URL_HOST); }

function account_api(Browser $b, string $name, array $in = []): array {
    [$code, , $j] = $b->go("POST", env("RC_ACCOUNTS") . "/api/$name", $in, ["X-RC: 1"]);
    return [$code, is_array($j) ? $j : []];
}

// Make the robot's account (once per environment) and give it a picture.
function robot_register(Browser $b): array {
    $key = openssl_pkey_new(["private_key_type" => OPENSSL_KEYTYPE_EC, "curve_name" => "prime256v1"]);
    $credId = random_bytes(16);
    // If a previous robot.json was lost, its name is retired for good: take the next free one.
    for ($i = 0; $i < 5; $i++) {
        $name = ROBOT_NAME . ($i ? "-$i" : "");
        [$code, $o] = account_api($b, "register-start", ["username" => $name]);
        if ($code === 200) break;
    }
    if ($code !== 200) throw new RuntimeException("account would not register a robot: " . json_encode($o));
    $ec = openssl_pkey_get_details($key)["ec"];
    $cose = cbor_map([[cbor_int(1), cbor_int(2)], [cbor_int(3), cbor_int(-7)], [cbor_int(-1), cbor_int(1)],
        [cbor_int(-2), cbor_bytes(str_pad($ec["x"], 32, "\0", STR_PAD_LEFT))], [cbor_int(-3), cbor_bytes(str_pad($ec["y"], 32, "\0", STR_PAD_LEFT))]]);
    $ad = hash("sha256", rp_id(), true) . chr(0x45) . pack("N", 0) . str_repeat("\0", 16) . pack("n", 16) . $credId . $cose;
    $att = cbor_map([[cbor_text("fmt"), cbor_text("none")], [cbor_text("attStmt"), cbor_map([])], [cbor_text("authData"), cbor_bytes($ad)]]);
    $cdj = json_encode(["type" => "webauthn.create", "challenge" => $o["challenge"], "origin" => env("RC_ACCOUNTS"), "crossOrigin" => false]);
    [$code, $j] = account_api($b, "register-finish", ["clientDataJSON" => b64u($cdj), "attestationObject" => b64u($att)]);
    if ($code !== 200) throw new RuntimeException("robot registration failed: " . json_encode($j));
    openssl_pkey_export($key, $pem);
    $r = ["username" => $j["user"]["username"], "id" => $j["user"]["id"], "cred" => b64u($credId), "key" => $pem, "count" => 0];
    robot_save($r);
    account_api($b, "profile", ["name" => "Zoo Robot"]);
    account_api($b, "picture", ["image" => base64_encode(robot_picture())]);
    return $r;
}

// The robot's passkey and counter, written whole or not at all: a half-written file would read as
// "no robot", the next run would register zoo-robot-1, and the real robot's name would be stranded.
function robot_save(array $r): void {
    $tmp = robot_path() . "." . bin2hex(random_bytes(4));
    $old = umask(077);
    $ok = file_put_contents($tmp, json_encode($r)) === strlen(json_encode($r));
    umask($old);
    if (!$ok || !rename($tmp, robot_path())) { @unlink($tmp); throw new RuntimeException("could not save the robot's state"); }
}

// A little robot face, drawn here so the guestbook has a picture to show.
function robot_picture(): string {
    $im = imagecreatetruecolor(128, 128);
    imagefill($im, 0, 0, imagecolorallocate($im, 46, 125, 90));
    $w = imagecolorallocate($im, 240, 240, 230);
    imagefilledrectangle($im, 24, 34, 104, 100, $w);
    $k = imagecolorallocate($im, 30, 30, 30);
    imagefilledellipse($im, 48, 60, 16, 16, $k);
    imagefilledellipse($im, 80, 60, 16, 16, $k);
    imagefilledrectangle($im, 46, 82, 82, 88, $k);
    imagefilledrectangle($im, 61, 18, 67, 34, $w);
    ob_start(); imagepng($im); return ob_get_clean();
}

// A browser signed in as the robot at account, or an exception saying why not. One sign-in per
// process; it signs out again when the process ends, so robot sessions never pile up.
function robot(): Browser {
    static $b = null;
    if ($b) return $b;
    $lock = fopen(robot_path() . ".lock", "c");
    flock($lock, LOCK_EX);   // the cron check and a web check never sign in with one counter value
    try {
        $nb = new Browser();
        $r = json_decode((string)@file_get_contents(robot_path()), true) ?: robot_register($nb);
        account_api($nb, "signout");   // registering signed it in; start clean either way
        [$code, $o] = account_api($nb, "login-start");
        if ($code !== 200) throw new RuntimeException("account login-start answered $code");
        // The signature counter must go up every time. Time does, even after a restore from backup.
        $r["count"] = max($r["count"] + 1, time());
        $ad = hash("sha256", rp_id(), true) . chr(0x05) . pack("N", $r["count"]);
        $cdj = json_encode(["type" => "webauthn.get", "challenge" => $o["challenge"], "origin" => env("RC_ACCOUNTS")]);
        openssl_sign($ad . hash("sha256", $cdj, true), $sig, openssl_pkey_get_private($r["key"]), OPENSSL_ALGO_SHA256);
        robot_save($r);
        [$code, $j] = account_api($nb, "login-finish", ["id" => $r["cred"], "clientDataJSON" => b64u($cdj),
            "authenticatorData" => b64u($ad), "signature" => b64u($sig)]);
        if ($code !== 200) throw new RuntimeException("the robot could not sign in at account ($code): " . ($j["error"] ?? ""));
    } finally {
        flock($lock, LOCK_UN);
    }
    register_shutdown_function(fn() => account_api($nb, "signout"));
    return $b = $nb;
}

function robot_user(): array {
    $r = json_decode((string)@file_get_contents(robot_path()), true) ?: [];
    return ["id" => (int)($r["id"] ?? 0), "username" => (string)($r["username"] ?? "")];
}

// The robot's browser after a page load at the zoo, so it holds the zoo's own token.
function robot_at_zoo(): Browser {
    static $done = null;
    $b = robot();
    if (!$done) {
        [$code] = $b->visit("https://" . env("RC_HOST") . "/");
        if ($code !== 200) throw new RuntimeException("the zoo answered the robot with $code");
        $done = true;
    }
    return $b;
}