<?php
declare(strict_types=1);

/**
 * Feuerwerk API.
 *
 * Routing uses the `r` query parameter (e.g. `index.php?r=projects/abc123`) because the
 * site's nginx configuration does not pass PATH_INFO to PHP.
 *
 *   GET    ?r=auth/session      → {user, role}                  (both null while nobody is signed in)
 *   POST   ?r=auth/login        {username,password}  → {user, role} | 401 | 429
 *   POST   ?r=auth/logout       → 204
 *   POST   ?r=auth/password     {currentPassword,newPassword} → 204 | 401 | 422 | 429
 *                               (the only auth route that needs a session; ends the account's
 *                                other logins, keeps the one asking)
 *
 * Five wrong passwords from one address within 15 minutes, and it gets 429 with `Retry-After` for
 * the next 15 (see LoginThrottle, #427). Wrong agent tokens count alike.
 *
 * The MCP relay (#429, tools/mcp/) asks two routes of its own, with the key both sides read from
 * `data/mcp-relay.key` in `X-Relay-Key`; without it they answer 404 like a route that is not there:
 *
 *   POST   ?r=agent/verify      {token,address} → {user, role} | 401 | 429
 *                               (`address` is the agent's, which the relay saw; the brake counts it)
 *   POST   ?r=agent/redeem      {ticket}        → {user, role} | 401
 *
 * A request that changes something (anything but GET) is refused with 403 when the browser says it
 * comes from another site, `Sec-Fetch-Site` being `cross-site` or `same-site`: the session cookie is
 * SameSite=Lax, and every subdomain of the site counts as the same site to it. Tools send no such
 * header and their own cookie.
 *
 * An account takes up at most 1 GB with its uploads, projects and snapshots (see Quota); a write that
 * would make it larger is refused with 413. Administrators have no limit.
 *
 * Everything below needs a signed-in user (401 otherwise), and projects belong to one: a project
 * of somebody else answers like one that is not there – unless the one asking is an administrator
 * (#179), who reads and saves it like their own; a save keeps its owner. Deleting a project is
 * its owner's alone (#272).
 *
 * Administrators only (403 for everybody else, #180):
 *
 *   GET    ?r=users             → [{username,role,createdAt,projects:[{id,name,revision,updatedAt}]}]
 *   POST   ?r=users             {username,password,role}           → 201 {username,role,createdAt} | 409 | 422
 *   PATCH  ?r=users/{name}      {username?,role?,password?}        → {username,role,createdAt} | 404 | 409 | 422
 *   DELETE ?r=users/{name}      → 204 | 404 | 409 (still owns projects) | 422
 *                               (renaming or deleting signs the account out everywhere; a new
 *                                password ends its other sessions)
 *
 * Agent tokens (#429) open the relay for an agent of the account and nothing else; a ticket gets a
 * tab onto it (see AgentTokens). Neither is for a guest:
 *
 *   GET    ?r=agent-tokens      → [{id,name,createdAt,expiresAt,usedAt}], oldest first
 *   POST   ?r=agent-tokens      {name,days?}  → 201 {id,name,createdAt,expiresAt,usedAt,token} | 409 | 422
 *                               (the one answer the token is in; `days` 1–365, 90 without)
 *   DELETE ?r=agent-tokens/{id} → 204 | 404
 *   POST   ?r=agent/ticket      → {ticket, expiresIn}
 *
 *   GET    ?r=projects          → [{id,name,revision,updatedAt}]
 *   POST   ?r=projects          {name}               → {id,name,revision,updatedAt,project}
 *   GET    ?r=projects/{id}     → {id,name,revision,updatedAt,project}
 *   PUT    ?r=projects/{id}     {revision, project}  → {revision,updatedAt} | 409 {error,revision}
 *   DELETE ?r=projects/{id}     → 204 | 403 | 404    (its snapshots and its release go with it;
 *                                                     403 for an administrator who is not the owner)
 *
 *   GET    ?r=projects/{id}/snapshots             → [{id,name,revision,createdAt}], newest first
 *   POST   ?r=projects/{id}/snapshots             {name?}    → 201 {id,name,revision,createdAt}
 *   DELETE ?r=projects/{id}/snapshots/{sid}       → 204
 *   POST   ?r=projects/{id}/snapshots/{sid}/restore {revision} → {revision,updatedAt,before} | 409
 *                               (a snapshot copies the project as stored; restoring keeps the
 *                                stand it replaces as the snapshot `before`, #231)
 *
 *   GET    ?r=projects/{id}/release    → {token,revision,publishedAt} | null
 *   POST   ?r=projects/{id}/release    → {token,revision,publishedAt}   (publishes the stored project)
 *   DELETE ?r=projects/{id}/release    → 204 | 404
 *                               (one link per project, kept when publishing again, #266)
 *
 * Released games are open to everybody, the token being the key:
 *
 *   GET    ?r=releases/{token}         → {name,publishedAt,project} | 404
 *
 * So are the demo copies a guest opens in the editor (#428), frozen copies like a release that an
 * administrator makes and updates per project:
 *
 *   GET    ?r=demos                    → [{token,name,publishedAt}], by name
 *   GET    ?r=demos/{token}            → {name,publishedAt,project} | 404
 *   GET    ?r=projects/{id}/demo       → {token,revision,publishedAt} | null    (administrators only)
 *   POST   ?r=projects/{id}/demo       → {token,revision,publishedAt}           (administrators only)
 *   DELETE ?r=projects/{id}/demo       → 204 | 404                             (administrators only)
 *
 *   GET    ?r=textures            → [{file,name,width,height,bytes,updatedAt,owner,deletable}]
 *   POST   ?r=textures&name=x.png raw image bytes    → {file,name,width,height,bytes}
 *   DELETE ?r=textures/{file}     → 204 | 403 | 404 | 409 (still used)
 *
 *   GET    ?r=fonts               → [{file,name,bytes,updatedAt,owner,deletable}]
 *   POST   ?r=fonts&name=x.ttf    raw font bytes     → {file,name,bytes}
 *   DELETE ?r=fonts/{file}        → 204 | 403 | 404 | 409
 *
 *   GET    ?r=sounds              → [{file,name,bytes,updatedAt,owner,deletable}]
 *   POST   ?r=sounds&name=x.wav   raw sound bytes    → {file,name,bytes}
 *   DELETE ?r=sounds/{file}       → 204 | 403 | 404 | 409
 *
 *   GET    ?r=videos              → [{file,name,status,…,original,owner,deletable}]
 *   POST   ?r=videos&name=x.mov[&convert=0]  raw video bytes → {file,name,status,…}
 *   POST   ?r=videos/{file}/convert          → {file,name,status,…} | 403 | 404
 *   DELETE ?r=videos/{file}       → 204 | 403 | 404 | 409
 *                               (an upload is converted by the worker in `feuerwerk-video` (#402):
 *                                `status` is queued, converting with `progress`, failed with `error`,
 *                                or ready with width, height, duration, fps, audio and `poster`;
 *                                with `convert=0` it is only kept, `unconverted`, until it is asked
 *                                to be. `original` is the upload as it came, null for a video
 *                                uploaded before uploads were kept)
 *
 * Uploads land in the uploader's own folder, and `file` carries it: `{folder}/{sha256}.{ext}`
 * (#344). A `file` without a folder belongs to nobody. A list shows the files of the one asking and
 * nobody's, an administrator's every file; `owner` is the account a file belongs to (null for
 * nobody, '' for a deleted account). A file goes only at its owner's or an administrator's hand,
 * and only while no project, snapshot, release or demo copy uses it.
 *
 * An administrator offers a file to everybody as demo material (#428); every list carries those
 * files too, with `demo: true`, and without a session a list holds nothing else. Only an
 * administrator deletes one while it is offered.
 *
 *   PATCH  ?r=textures/{file}     {demo} → 204 | 403 | 404 | 422   (administrators only)
 *   PATCH  ?r=fonts/{file}        {demo} → the same
 *   PATCH  ?r=sounds/{file}       {demo} → the same
 *   PATCH  ?r=videos/{file}       {demo} → the same
 *
 *   POST   ?r=pixels              raw cel bytes      → {file,bytes}   (pixel art, #130)
 *
 *   GET    ?r=plugins             → [{file,bytes,updatedAt}], sorted by file name
 *   GET    ?r=plugins/{file}      → the module source as text/javascript
 *                               (both without a session as well: a guest's demo may switch one on, #428)
 *
 * `name` is the file's original name, kept beside it as `{file}.json` (see OriginalName) and
 * empty when none is known. It is a caption, never a path: the stored file is always `{hash}.{ext}`
 * in a folder.
 *
 * Stored images, fonts, sounds, videos and cels are served straight from `data/textures/`, `data/fonts/`,
 * `data/sounds/`, `data/videos/` and `data/pixels/` as static files; the API only writes them.
 */

require __DIR__ . '/lib/AccountRules.php';
require __DIR__ . '/lib/AgentTokens.php';
require __DIR__ . '/lib/AtomicFile.php';
require __DIR__ . '/lib/Auth.php';
require __DIR__ . '/lib/DemoFiles.php';
require __DIR__ . '/lib/FileUsage.php';
require __DIR__ . '/lib/HashedFileStore.php'; // before the font, sound and texture stores built on it
require __DIR__ . '/lib/FontStore.php';
require __DIR__ . '/lib/LoginThrottle.php';
require __DIR__ . '/lib/OriginalName.php';
require __DIR__ . '/lib/PixelStore.php';
require __DIR__ . '/lib/PluginStore.php';
require __DIR__ . '/lib/Quota.php';
require __DIR__ . '/lib/ReleaseStore.php';
require __DIR__ . '/lib/Response.php';
require __DIR__ . '/lib/SessionStore.php';
require __DIR__ . '/lib/SnapshotStore.php';
require __DIR__ . '/lib/SoundStore.php';
require __DIR__ . '/lib/Store.php';
require __DIR__ . '/lib/TextureStore.php';
require __DIR__ . '/lib/UserStore.php';
require __DIR__ . '/lib/VideoQueue.php';
require __DIR__ . '/lib/VideoStore.php';

/**
 * Has to clear the largest upload held in memory, which is a sound; a video is streamed to disk and
 * has its own ceiling. The web server and the proxy in front of it have their own say.
 */
const MAX_BODY_BYTES = 256 * 1024 * 1024;

/** Upload ceiling for a single image. The editor downscales larger pictures before sending. */
const MAX_TEXTURE_BYTES = 4 * 1024 * 1024;

/** Upload ceiling for a single font. A font cannot be shrunk on the way, so this is a plain limit. */
const MAX_FONT_BYTES = 4 * 1024 * 1024;

/** The same for a sound, far higher: a recorded take is plain WAV, about 46 minutes in mono. */
const MAX_SOUND_BYTES = 256 * 1024 * 1024;

/**
 * A video goes up as it was recorded and is made smaller by the worker, not on the way. It is
 * streamed to disk, so memory is no limit; nginx and the Brandmauer let 2 GB through (#402).
 */
const MAX_VIDEO_BYTES = 2048 * 1024 * 1024;

/**
 * Where everything the API keeps lies, and how much of it an account may fill. The rights test
 * (tests/php/rights.test.php) runs the API under `php -S` on a scratch directory with a small quota;
 * behind nginx neither can be moved.
 */
define('DATA_DIR', testSetting('FEUERWERK_DATA') ?? dirname(__DIR__) . '/data');
define('QUOTA_BYTES', (int) (testSetting('FEUERWERK_QUOTA_BYTES') ?? Quota::BYTES));

function testSetting(string $name): ?string
{
    $value = PHP_SAPI === 'cli-server' ? getenv($name) : false;
    return is_string($value) && $value !== '' ? $value : null;
}

set_error_handler(static function (int $severity, string $message, string $file, int $line): bool {
    // PHP calls the handler for a call silenced with `@` as well, only with less reported: that
    // warning was expected and is answered where it happens (an unreadable image is a 422).
    if ((error_reporting() & $severity) === 0) {
        return false;
    }
    throw new ErrorException($message, 0, $severity, $file, $line);
});

/** @param list<string> $parts */
function routeAuth(array $parts, string $method, Auth $auth): never
{
    $what = $parts[1] ?? '';
    $throttle = new LoginThrottle(DATA_DIR . '/sign-ins');

    if ($what === 'session') {
        if ($method !== 'GET') {
            Response::error('Method not allowed', 405);
        }
        // Always 200, never 401: "nobody is signed in" is an answer, not a failure, and the
        // login screen asks this before it can know either way.
        $user = $auth->user();
        Response::json(['user' => $user, 'role' => $user === null ? null : $auth->role($user)]);
    }

    if ($what === 'login') {
        if ($method !== 'POST') {
            Response::error('Method not allowed', 405);
        }
        $body = Response::body();
        refuseWhileThrottled($throttle);
        $user = $auth->logIn((string) ($body['username'] ?? ''), (string) ($body['password'] ?? ''));
        if ($user === null) {
            countFailure($throttle);
            // One message for both halves: which of the two was wrong is the attacker's question.
            Response::error('Wrong user name or password', 401);
        }
        Response::json(['user' => $user, 'role' => $auth->role($user)]);
    }

    if ($what === 'password') {
        if ($method !== 'POST') {
            Response::error('Method not allowed', 405);
        }
        // The one route under `auth/` that needs a session: it changes the password of whoever is
        // signed in, so there has to be somebody.
        $user = $auth->require();
        $body = Response::body();
        $new = (string) ($body['newPassword'] ?? '');
        if (!UserStore::isValidPassword($new)) {
            Response::error('The new password needs at least ' . UserStore::MIN_PASSWORD_LENGTH . ' characters', 422);
        }
        // Guessing the current password from an open tab is guessing all the same.
        refuseWhileThrottled($throttle);
        if (!$auth->changePassword($user, (string) ($body['currentPassword'] ?? ''), $new)) {
            countFailure($throttle);
            Response::error('Wrong password', 401);
        }
        agentTokens()->endAllOf($user);
        Response::noContent();
    }

    if ($what === 'logout') {
        if ($method !== 'POST') {
            Response::error('Method not allowed', 405);
        }
        $auth->logOut();
        Response::noContent();
    }

    Response::error('Not found', 404);
}

/** The address a request came from: nginx puts the one the Brandmauer saw there (#427). */
function clientAddress(): string
{
    return (string) ($_SERVER['REMOTE_ADDR'] ?? '');
}

function countFailure(LoginThrottle $throttle, ?string $address = null): void
{
    $throttle->fail($address ?? clientAddress());
    // Now and then, so the folder holds the addresses of the last quarter of an hour and no more.
    if (random_int(1, 20) === 1) {
        $throttle->prune();
    }
}

function refuseWhileThrottled(LoginThrottle $throttle, ?string $address = null): void
{
    $wait = $throttle->waitFor($address ?? clientAddress());
    if ($wait === 0) {
        return;
    }
    header('Retry-After: ' . $wait);
    Response::error('Too many failed sign-ins. Try again in ' . (int) ceil($wait / 60) . ' minutes', 429);
}

/**
 * Bytes a project takes up as stored, 0 for one that is not there.
 */
function projectBytes(string $id): int
{
    $path = DATA_DIR . "/projects/{$id}.json";
    return is_file($path) ? (int) filesize($path) : 0;
}

/**
 * @param list<string> $parts
 * @param Closure(int):void $fits answers 413 when that many more bytes do not fit the quota
 */
function routeProjects(array $parts, string $method, string $owner, bool $seesAll, Closure $fits): never
{
    $store = new Store(DATA_DIR . '/projects', $owner, $seesAll);

    if (count($parts) === 1) {
        if ($method === 'GET') {
            Response::json($store->list());
        }
        if ($method === 'POST') {
            $body = Response::body();
            $name = trim((string) ($body['name'] ?? ''));
            if ($name === '' || mb_strlen($name) > 120) {
                Response::error('Project name must be 1–120 characters', 422);
            }
            // What an empty project takes up, give or take its name.
            $fits(1024);
            Response::json($store->create($name), 201);
        }
        Response::error('Method not allowed', 405);
    }

    $id = $parts[1];
    if (!Store::isValidId($id)) {
        Response::error('Invalid project id', 400);
    }

    $snapshots = new SnapshotStore(DATA_DIR . '/snapshots');
    if (($parts[2] ?? null) === 'snapshots') {
        routeSnapshots($parts, $method, $store, $snapshots, $id, $fits);
    }
    $releases = new ReleaseStore(DATA_DIR . '/releases');
    if (($parts[2] ?? null) === 'release' && count($parts) === 3) {
        routeRelease($method, $store, $releases, $id);
    }
    $demos = new ReleaseStore(DATA_DIR . '/demos');
    if (($parts[2] ?? null) === 'demo' && count($parts) === 3) {
        // What guests get to see is the administrators' call (#428).
        if (!$seesAll) {
            Response::error('Administrators only', 403);
        }
        routeRelease($method, $store, $demos, $id, 'Project has no demo copy');
    }
    if (count($parts) > 2) {
        Response::error('Not found', 404);
    }

    if ($method === 'GET') {
        $doc = $store->load($id);
        if ($doc === null) {
            Response::error('Project not found', 404);
        }
        Response::json($doc);
    }

    if ($method === 'PUT') {
        $body = Response::body();
        if (!isset($body['revision']) || !is_int($body['revision']) || !is_array($body['project'] ?? null)) {
            Response::error('Body must contain integer "revision" and object "project"', 422);
        }
        // Asked after whether the project is there for them: a 413 would tell a stranger it is.
        if ($store->load($id) === null) {
            Response::error('Project not found', 404);
        }
        $fits((int) ($_SERVER['CONTENT_LENGTH'] ?? 0) - projectBytes($id));
        try {
            $result = $store->save($id, $body['revision'], $body['project']);
        } catch (StaleRevisionException $e) {
            Response::error('Project was modified elsewhere', 409, ['revision' => $e->currentRevision]);
        }
        if ($result === null) {
            Response::error('Project not found', 404);
        }
        Response::json(['revision' => $result['revision'], 'updatedAt' => $result['updatedAt']]);
    }

    if ($method === 'DELETE') {
        try {
            $deleted = $store->delete($id);
        } catch (NotOwnerException $e) {
            Response::error($e->getMessage(), 403);
        }
        if (!$deleted) {
            Response::error('Project not found', 404);
        }
        $snapshots->deleteAll($id);
        $releases->takeDown($id);
        $demos->takeDown($id);
        Response::noContent();
    }

    Response::error('Method not allowed', 405);
}

/**
 * The snapshots of one project (#231). Whoever may load the project may see, make, restore and
 * delete its snapshots; for everybody else the project, and with it this route, is not there.
 *
 * A snapshot copies the project, and so does restoring one (the stand it replaces is kept), so both
 * count against the quota with the project's size.
 *
 * @param list<string> $parts
 * @param Closure(int):void $fits
 */
function routeSnapshots(array $parts, string $method, Store $store, SnapshotStore $snapshots, string $id, Closure $fits): never
{
    $doc = $store->load($id);
    if ($doc === null) {
        Response::error('Project not found', 404);
    }

    if (count($parts) === 3) {
        if ($method === 'GET') {
            Response::json($snapshots->list($id));
        }
        if ($method === 'POST') {
            $name = snapshotName(Response::body());
            $fits(projectBytes($id));
            Response::json($snapshots->create($id, $doc, $name === '' ? gmdate('Y-m-d H:i') . ' UTC' : $name), 201);
        }
        Response::error('Method not allowed', 405);
    }

    $snapshotId = $parts[3];
    if (!Store::isValidId($snapshotId) || count($parts) > 5) {
        Response::error('Not found', 404);
    }
    $snapshot = $snapshots->load($id, $snapshotId);
    if ($snapshot === null) {
        Response::error('Snapshot not found', 404);
    }

    if (count($parts) === 4) {
        if ($method !== 'DELETE') {
            Response::error('Method not allowed', 405);
        }
        $snapshots->delete($id, $snapshotId);
        Response::noContent();
    }

    if ($parts[4] !== 'restore') {
        Response::error('Not found', 404);
    }
    if ($method !== 'POST') {
        Response::error('Method not allowed', 405);
    }
    $body = Response::body();
    if (!isset($body['revision']) || !is_int($body['revision'])) {
        Response::error('Body must contain integer "revision"', 422);
    }
    $fits(projectBytes($id));
    // The same guard a save has: a tab that is behind must not throw away what another one saved.
    if ($body['revision'] !== $doc['revision']) {
        Response::error('Project was modified elsewhere', 409, ['revision' => $doc['revision']]);
    }
    // The stand being replaced is kept first, so a restore can itself be taken back.
    $before = $snapshots->create($id, $doc, mb_substr('Before restoring ' . $snapshot['name'], 0, 120));
    try {
        $result = $store->save($id, $doc['revision'], $snapshot['project']);
    } catch (StaleRevisionException $e) {
        $snapshots->delete($id, $before['id']);
        Response::error('Project was modified elsewhere', 409, ['revision' => $e->currentRevision]);
    }
    if ($result === null) {
        $snapshots->delete($id, $before['id']);
        Response::error('Project not found', 404);
    }
    Response::json(['revision' => $result['revision'], 'updatedAt' => $result['updatedAt'], 'before' => $before]);
}

/**
 * The released copy of one project (#266), or its demo copy (#428). Whoever may load the project may
 * publish it, update it and take it down; publishing copies the project as stored, not what a tab
 * has not saved yet.
 */
function routeRelease(
    string $method,
    Store $store,
    ReleaseStore $releases,
    string $id,
    string $none = 'Project is not released',
): never {
    $doc = $store->load($id);
    if ($doc === null) {
        Response::error('Project not found', 404);
    }
    if ($method === 'GET') {
        Response::json($releases->of($id));
    }
    if ($method === 'POST') {
        Response::json($releases->publish($doc));
    }
    if ($method === 'DELETE') {
        if (!$releases->takeDown($id)) {
            Response::error($none, 404);
        }
        Response::noContent();
    }
    Response::error('Method not allowed', 405);
}

/**
 * What is open without a sign-in: a released game (#266) and a demo copy (#428), each found by its
 * token. The demos are listed as well, for a guest to pick one.
 */
function routeCopies(array $parts, string $method, ReleaseStore $copies, string $missing, bool $listed): never
{
    if ($method !== 'GET' || count($parts) > 2 || (count($parts) === 1 && !$listed)) {
        Response::error('Not found', 404);
    }
    if (count($parts) === 1) {
        Response::json($copies->list());
    }
    $copy = $copies->load($parts[1]);
    if ($copy === null) {
        Response::error($missing, 404);
    }
    // The copy goes out under the token, not the project's own id: that one is nobody's business.
    $project = ['id' => $copy['token']] + $copy['project'];
    Response::json(['name' => $copy['name'], 'publishedAt' => $copy['publishedAt'], 'project' => $project]);
}

function snapshotName(array $body): string
{
    $name = trim((string) ($body['name'] ?? ''));
    if (mb_strlen($name) > 120) {
        Response::error('Snapshot name must be at most 120 characters', 422);
    }
    return $name;
}

function agentTokens(): AgentTokens
{
    return new AgentTokens(DATA_DIR . '/agent-tokens', DATA_DIR . '/agent-tickets');
}

/**
 * Whether the request is the MCP relay's (#429): it carries the key that lies in `data/` for both
 * sides. Nobody else can read that folder, nginx serves none of it.
 */
function fromRelay(): bool
{
    $path = DATA_DIR . '/mcp-relay.key';
    $key = is_file($path) ? trim((string) file_get_contents($path)) : '';
    $given = (string) ($_SERVER['HTTP_X_RELAY_KEY'] ?? '');
    return strlen($key) >= 32 && hash_equals($key, $given);
}

/**
 * The relay asks who is behind an agent's token or a tab's ticket. A wrong token is a wrong password
 * to the brake, counted against the agent's address, not the relay's.
 *
 * @param list<string> $parts
 */
function routeRelay(array $parts, string $method, Auth $auth): never
{
    if (!fromRelay() || count($parts) !== 2) {
        Response::error('Not found', 404);
    }
    if ($method !== 'POST') {
        Response::error('Method not allowed', 405);
    }
    $body = Response::body();
    $tokens = agentTokens();
    if ($parts[1] === 'verify') {
        $throttle = new LoginThrottle(DATA_DIR . '/sign-ins');
        $address = (string) ($body['address'] ?? '');
        refuseWhileThrottled($throttle, $address);
        $user = $tokens->verify((string) ($body['token'] ?? ''));
        if ($user === null) {
            countFailure($throttle, $address);
            Response::error('Unknown or expired agent token', 401);
        }
        Response::json(['user' => $user, 'role' => $auth->role($user)]);
    }
    if ($parts[1] === 'redeem') {
        $user = $tokens->redeemTicket((string) ($body['ticket'] ?? ''));
        if ($user === null) {
            Response::error('Unknown or used ticket', 401);
        }
        Response::json(['user' => $user, 'role' => $auth->role($user)]);
    }
    Response::error('Not found', 404);
}

/** @param list<string> $parts */
function routeAgentTokens(array $parts, string $method, string $user): never
{
    $tokens = agentTokens();
    if (count($parts) === 1) {
        if ($method === 'GET') {
            Response::json($tokens->listOf($user));
        }
        if ($method === 'POST') {
            $body = Response::body();
            $name = (string) ($body['name'] ?? '');
            $days = $body['days'] ?? AgentTokens::DEFAULT_DAYS;
            if (!AgentTokens::isValidName($name)) {
                Response::error('A token name is 1–60 characters', 422);
            }
            if (!is_int($days) || $days < 1 || $days > AgentTokens::MAX_DAYS) {
                Response::error('A token lasts 1–' . AgentTokens::MAX_DAYS . ' days', 422);
            }
            try {
                Response::json($tokens->create($user, $name, $days), 201);
            } catch (TooManyAgentTokensException $e) {
                Response::error($e->getMessage(), 409);
            }
        }
        Response::error('Method not allowed', 405);
    }
    if ($method !== 'DELETE') {
        Response::error('Method not allowed', 405);
    }
    if (!$tokens->revoke($user, $parts[1])) {
        Response::error('Agent token not found', 404);
    }
    Response::noContent();
}

/** @param list<string> $parts */
function routeAgent(array $parts, string $method, string $user): never
{
    if (($parts[1] ?? '') !== 'ticket' || count($parts) !== 2) {
        Response::error('Not found', 404);
    }
    if ($method !== 'POST') {
        Response::error('Method not allowed', 405);
    }
    Response::json(['ticket' => agentTokens()->issueTicket($user), 'expiresIn' => AgentTokens::TICKET_SECONDS]);
}

/** @param list<string> $parts */
function routeUsers(array $parts, string $method, Auth $auth, UserStore $users): never
{
    $actor = $auth->requireAdmin();
    $projects = new Store(DATA_DIR . '/projects', $actor, true);
    $shown = static function (string $name) use ($users): array {
        foreach ($users->accounts() as $account) {
            if (strcasecmp($account['username'], $name) === 0) {
                return $account;
            }
        }
        throw new RuntimeException("Account {$name} vanished");
    };

    if (count($parts) === 1) {
        if ($method === 'GET') {
            Response::json(array_map(
                static fn(array $a): array => $a + ['projects' => $projects->listOf($a['username'])],
                $users->accounts(),
            ));
        }
        if ($method === 'POST') {
            $body = Response::body();
            $name = (string) ($body['username'] ?? '');
            $password = (string) ($body['password'] ?? '');
            $role = (string) ($body['role'] ?? 'user');
            if (!UserStore::isValidName($name)) {
                Response::error('A user name is 2–32 letters, digits, dots, dashes or underscores', 422);
            }
            if (!UserStore::isValidPassword($password)) {
                Response::error('The password needs at least ' . UserStore::MIN_PASSWORD_LENGTH . ' characters', 422);
            }
            if (!UserStore::isValidRole($role)) {
                Response::error('Unknown role', 422);
            }
            if ($users->exists($name)) {
                Response::error("The name {$name} is taken", 409);
            }
            $users->put($name, $password, $role);
            Response::json($shown($name), 201);
        }
        Response::error('Method not allowed', 405);
    }

    $target = $parts[1];
    if (!$users->exists($target)) {
        Response::error('User not found', 404);
    }
    $role = $users->role($target);

    if ($method === 'PATCH') {
        $body = Response::body();
        $newName = array_key_exists('username', $body) ? (string) $body['username'] : null;
        $newRole = array_key_exists('role', $body) ? (string) $body['role'] : null;
        $password = array_key_exists('password', $body) ? (string) $body['password'] : null;
        // Everything is checked before anything is written: half an edit is worse than none.
        if ($newName !== null && $newName !== $target) {
            $refusal = AccountRules::renameRefusal($actor, $target);
            if ($refusal !== null) {
                Response::error($refusal, 422);
            }
            if (!UserStore::isValidName($newName)) {
                Response::error('A user name is 2–32 letters, digits, dots, dashes or underscores', 422);
            }
            if (strcasecmp($newName, $target) !== 0 && $users->exists($newName)) {
                Response::error("The name {$newName} is taken", 409);
            }
        }
        if ($newRole !== null) {
            if (!UserStore::isValidRole($newRole)) {
                Response::error('Unknown role', 422);
            }
            $refusal = AccountRules::roleRefusal($actor, $target, $role, $newRole, $users->adminCount());
            if ($refusal !== null) {
                Response::error($refusal, 422);
            }
        }
        if ($password !== null && !UserStore::isValidPassword($password)) {
            Response::error('The password needs at least ' . UserStore::MIN_PASSWORD_LENGTH . ' characters', 422);
        }

        if ($password !== null) {
            $auth->resetPassword($target, $password);
            agentTokens()->endAllOf($target);
        }
        if ($newRole !== null && $newRole !== $role) {
            $users->setRole($target, $newRole);
        }
        $name = $shown($target)['username'];
        if ($newName !== null && $newName !== $name) {
            $users->rename($name, $newName);
            $projects->transfer($name, $newName);
            $auth->endSessionsOf($name);
            agentTokens()->endAllOf($name);
            $name = $newName;
        }
        Response::json($shown($name));
    }

    if ($method === 'DELETE') {
        $refusal = AccountRules::deleteRefusal($actor, $target, $role, $users->adminCount());
        if ($refusal !== null) {
            Response::error($refusal, 422);
        }
        $refusal = AccountRules::ownerRefusal($target, count($projects->listOf($shown($target)['username'])));
        if ($refusal !== null) {
            Response::error($refusal, 409);
        }
        $users->remove($target);
        $auth->endSessionsOf($target);
        agentTokens()->endAllOf($target);
        Response::noContent();
    }

    Response::error('Method not allowed', 405);
}

/**
 * Images, fonts and sounds, stored under the hash of their bytes in a folder per account (#344).
 * Everybody signed in uploads into their own folder and lists their own files and nobody's; an
 * administrator lists every file. Deleting one is for its owner or an administrator, and refused
 * while a project of any account still uses it. What an administrator offers as demo material
 * (#428) is in every list.
 *
 * @param list<string> $parts
 * @param class-string<RuntimeException> $invalid what the store throws for bytes it cannot take
 * @param Closure(int):void $fits
 */
function routeFiles(
    array $parts,
    string $method,
    string $user,
    bool $isAdmin,
    UserStore $users,
    HashedFileStore $store,
    int $maxBytes,
    string $noun,
    string $invalid,
    Closure $fits,
): never {
    $kind = $parts[0];
    $demos = new DemoFiles(DATA_DIR . '/demo-files.json');
    if (count($parts) === 1) {
        if ($method === 'GET') {
            Response::json(filesOffered($store, $kind, $user, $isAdmin, $users));
        }
        if ($method === 'POST') {
            $tooLarge = "{$noun} must be at most " . ($maxBytes / 1024 / 1024) . ' MB';
            $name = (string) ($_GET['name'] ?? '');
            $fits((int) ($_SERVER['CONTENT_LENGTH'] ?? 0));
            try {
                // A video is too big for memory and goes from the request straight to disk.
                if ($store instanceof VideoStore) {
                    $in = fopen('php://input', 'rb');
                    $convert = ($_GET['convert'] ?? '1') !== '0';
                    Response::json($store->storeStream($in, $maxBytes, $name, $users->folderOf($user, true), $convert), 201);
                }
                $bytes = Response::rawBody();
                if (strlen($bytes) > $maxBytes) {
                    Response::error($tooLarge, 413);
                }
                Response::json($store->store($bytes, $name, $users->folderOf($user, true)), 201);
            } catch (VideoTooLargeException) {
                Response::error($tooLarge, 413);
            } catch (RuntimeException $e) {
                if (!$e instanceof $invalid) {
                    throw $e;
                }
                Response::error($e->getMessage(), 422);
            }
        }
        Response::error('Method not allowed', 405);
    }

    // A video kept without being converted is converted later, at its owner's word.
    if ($store instanceof VideoStore && $method === 'POST' && end($parts) === 'convert') {
        $file = implode('/', array_slice($parts, 1, -1));
        $folder = HashedFileStore::folderOf($file);
        if (!$isAdmin && ($folder === '' || $folder !== $users->folderOf($user))) {
            Response::error('Only its owner may convert this video', 403);
        }
        $record = $store->convert($file);
        if ($record === null) {
            Response::error("{$noun} not found", 404);
        }
        Response::json($record);
    }

    if ($method === 'PATCH') {
        $file = implode('/', array_slice($parts, 1));
        if (!$isAdmin) {
            Response::error('Administrators only', 403);
        }
        if (!$store->exists($file)) {
            Response::error("{$noun} not found", 404);
        }
        $body = Response::body();
        if (!is_bool($body['demo'] ?? null)) {
            Response::error('Body must contain boolean "demo"', 422);
        }
        $demos->set($kind, $file, $body['demo']);
        Response::noContent();
    }

    if ($method === 'DELETE') {
        $file = implode('/', array_slice($parts, 1));
        // Asked before whether there is one: somebody else's folder tells a stranger nothing.
        $folder = HashedFileStore::folderOf($file);
        if (!$isAdmin && ($folder === '' || $folder !== $users->folderOf($user))) {
            Response::error('Only its owner may delete this file', 403);
        }
        if (!$store->exists($file)) {
            Response::error("{$noun} not found", 404);
        }
        // Everybody may have it in a project by now; whether that ends is the administrators' call.
        if (!$isAdmin && $demos->has($kind, $file)) {
            Response::error('Offered to everybody as demo material: only an administrator can take that back', 409);
        }
        $uses = (new FileUsage(DATA_DIR))->of($file);
        if ($uses !== []) {
            Response::error(FileUsage::refusal($uses, $user, $isAdmin), 409);
        }
        $store->delete($file);
        $demos->set($kind, $file, false);
        Response::noContent();
    }

    Response::error('Method not allowed', 405);
}

/**
 * What a picker of `$kind` lists: the files of the one asking and nobody's, an administrator's every
 * file (#344), and everything offered as demo material (#428), with `demo` saying which those are.
 * Signed out (`$user` null) it is the demo material alone, without who uploaded it.
 *
 * @return list<array<string,mixed>>
 */
function filesOffered(HashedFileStore $store, string $kind, ?string $user, bool $isAdmin, UserStore $users): array
{
    $demo = (new DemoFiles(DATA_DIR . '/demo-files.json'))->of($kind);
    $owners = $users->folderOwners();
    $items = $user === null ? [] : $store->list($users->folderOf($user), $isAdmin, $owners);
    if ($demo !== [] && !$isAdmin) {
        $listed = array_column($items, 'file');
        $hidden = $user === null ? ['owner' => null] : [];
        foreach ($store->list('', true, $owners) as $item) {
            if (in_array($item['file'], $demo, true) && !in_array($item['file'], $listed, true)) {
                $items[] = ['deletable' => false, ...$hidden] + $item;
            }
        }
    }
    return array_map(static fn(array $item): array => $item + ['demo' => in_array($item['file'], $demo, true)], $items);
}

function fileStore(string $kind): HashedFileStore
{
    return match ($kind) {
        'textures' => new TextureStore(DATA_DIR . '/textures'),
        'fonts' => new FontStore(DATA_DIR . '/fonts'),
        'sounds' => new SoundStore(DATA_DIR . '/sounds'),
        'videos' => new VideoStore(DATA_DIR . '/videos'),
    };
}

/** @param list<string> $parts */
function routePixels(array $parts, string $method): never
{
    if (count($parts) !== 1 || $method !== 'POST') {
        Response::error('Method not allowed', 405);
    }
    $store = new PixelStore(DATA_DIR . '/pixels');
    $bytes = Response::rawBody();
    if (strlen($bytes) > PixelStore::MAX_BYTES) {
        Response::error('A cel is at most ' . PixelStore::MAX_BYTES . ' bytes', 413);
    }
    try {
        Response::json($store->store($bytes), 201);
    } catch (InvalidPixelsException $e) {
        Response::error($e->getMessage(), 422);
    }
}

/** @param list<string> $parts */
function routePlugins(array $parts, string $method): never
{
    $store = new PluginStore(DATA_DIR . '/plugins');

    if (count($parts) === 1) {
        if ($method !== 'GET') {
            Response::error('Method not allowed', 405);
        }
        Response::json($store->list());
    }

    if ($method !== 'GET') {
        Response::error('Method not allowed', 405);
    }

    $source = $store->read($parts[1]);
    if ($source === null) {
        Response::error('Plugin not found', 404);
    }
    // Every plugin file is handed out: the project says which of them the editor runs (#119),
    // and the server has no way of knowing which project the asking tab has open.
    header('Content-Type: text/javascript; charset=utf-8');
    header('X-Content-Type-Options: nosniff');
    // A replaced file has to be the one the next editor start runs.
    header('Cache-Control: no-cache');
    echo $source;
    exit;
}

try {
    $method = $_SERVER['REQUEST_METHOD'] ?? 'GET';
    $route = trim((string) ($_GET['r'] ?? ''), '/');
    $parts = $route === '' ? [] : explode('/', $route);

    $site = (string) ($_SERVER['HTTP_SEC_FETCH_SITE'] ?? '');
    if ($method !== 'GET' && $method !== 'HEAD' && ($site === 'cross-site' || $site === 'same-site')) {
        Response::error('Requests from other sites are refused', 403);
    }

    $maxBody = ($parts[0] ?? '') === 'videos' ? MAX_VIDEO_BYTES : MAX_BODY_BYTES;
    if ((int) ($_SERVER['CONTENT_LENGTH'] ?? 0) > $maxBody) {
        Response::error('Request body too large', 413);
    }

    // A project reaches deepest, `projects/{id}/snapshots/{snapshotId}/restore`; a stored file is
    // `textures/{folder}/{file}`, a video to convert `videos/{folder}/{file}/convert`; everything
    // else stops at two parts.
    $depth = match ($parts[0] ?? '') {
        'projects' => 5,
        'videos' => 4,
        'textures', 'fonts', 'sounds' => 3,
        default => 2,
    };
    if (count($parts) < 1 || count($parts) > $depth) {
        Response::error('Not found', 404);
    }

    $users = new UserStore(DATA_DIR . '/users.json');
    $auth = new Auth($users, new SessionStore(DATA_DIR . '/sessions'));
    if ($parts[0] === 'auth') {
        routeAuth($parts, $method, $auth);
    }
    if ($parts[0] === 'users') {
        routeUsers($parts, $method, $auth, $users);
    }
    if ($parts[0] === 'releases') {
        routeCopies($parts, $method, new ReleaseStore(DATA_DIR . '/releases'), 'Game not found', false);
    }
    if ($parts[0] === 'demos') {
        routeCopies($parts, $method, new ReleaseStore(DATA_DIR . '/demos'), 'Demo not found', true);
    }
    if ($parts[0] === 'agent' && in_array($parts[1] ?? '', ['verify', 'redeem'], true)) {
        routeRelay($parts, $method, $auth);
    }
    // A guest's editor runs the plugins a demo switches on (#428); they are the server's own code,
    // put there by its administrator, and only to be read.
    if ($parts[0] === 'plugins' && $method === 'GET') {
        routePlugins($parts, $method);
    }
    // A guest's pickers list the demo material without a session (#428), and nothing else.
    if (in_array($parts[0], DemoFiles::KINDS, true) && count($parts) === 1 && $method === 'GET' && $auth->user() === null) {
        Response::json(filesOffered(fileStore($parts[0]), $parts[0], null, false, $users));
    }
    // Being signed in is the price of admission for everything below, so an uploaded file cannot be
    // dropped in by a stranger.
    $user = $auth->require();
    $isAdmin = $auth->role($user) === 'admin';
    $fits = static function (int $adding) use ($user, $isAdmin, $users): void {
        if ($isAdmin) {
            return;
        }
        $refusal = (new Quota(DATA_DIR, QUOTA_BYTES))->refusal($user, $users->folderOf($user), $adding);
        if ($refusal !== null) {
            Response::error($refusal, 413);
        }
    };

    match ($parts[0]) {
        'projects' => routeProjects($parts, $method, $user, $isAdmin, $fits),
        'textures' => routeFiles(
            $parts,
            $method,
            $user,
            $isAdmin,
            $users,
            fileStore('textures'),
            MAX_TEXTURE_BYTES,
            'Image',
            InvalidImageException::class,
            $fits,
        ),
        'fonts' => routeFiles(
            $parts,
            $method,
            $user,
            $isAdmin,
            $users,
            fileStore('fonts'),
            MAX_FONT_BYTES,
            'Font',
            InvalidFontException::class,
            $fits,
        ),
        'sounds' => routeFiles(
            $parts,
            $method,
            $user,
            $isAdmin,
            $users,
            fileStore('sounds'),
            MAX_SOUND_BYTES,
            'Sound',
            InvalidSoundException::class,
            $fits,
        ),
        'videos' => routeFiles(
            $parts,
            $method,
            $user,
            $isAdmin,
            $users,
            fileStore('videos'),
            MAX_VIDEO_BYTES,
            'Video',
            InvalidVideoException::class,
            $fits,
        ),
        'pixels' => routePixels($parts, $method),
        'plugins' => routePlugins($parts, $method),
        'agent-tokens' => routeAgentTokens($parts, $method, $user),
        'agent' => routeAgent($parts, $method, $user),
        default => Response::error('Not found', 404),
    };
} catch (Throwable $e) {
    error_log('[feuerwerk api] ' . $e->getMessage());
    Response::error('Internal server error', 500);
}