<?php
declare(strict_types=1);

/** Thrown by Store::save when the client's revision is older than the stored one. */
final class StaleRevisionException extends RuntimeException
{
    public function __construct(public readonly int $currentRevision)
    {
        parent::__construct("Project was modified elsewhere (revision {$currentRevision})");
    }
}

/**
 * File-based project store: one JSON document per project in `data/projects/{id}.json`.
 * Each file wraps the project with metadata: { id, name, owner, revision, updatedAt, project }.
 * Writes are atomic (temp file + rename) and guarded by an integer revision so that a
 * stale client (second tab, old session) cannot silently overwrite newer work.
 *
 * A store belongs to one signed-in user: it lists, reads and writes only the projects whose
 * `owner` is that user. Someone else's project is answered as missing rather than as forbidden,
 * because "this id exists" is already more than a stranger should learn.
 *
 * An administrator's store (`$seesAll`, #179) reads, writes and deletes every project as if it
 * were their own, and a save keeps the owner it found. The list stays their own: the others are
 * reached through the user management, one account at a time.
 */
final class Store
{
    public function __construct(
        private readonly string $dir,
        private readonly string $owner,
        private readonly bool $seesAll = false,
    ) {
        if (!is_dir($this->dir) && !mkdir($this->dir, 0775, true) && !is_dir($this->dir)) {
            throw new RuntimeException("Cannot create data directory {$this->dir}");
        }
    }

    public static function isValidId(string $id): bool
    {
        return (bool) preg_match('/^[a-z0-9]{6,32}$/', $id);
    }

    public static function newId(): string
    {
        return substr(bin2hex(random_bytes(8)), 0, 12);
    }

    /** @return list<array{id:string,name:string,revision:int,updatedAt:string}> */
    public function list(): array
    {
        return $this->listOf($this->owner);
    }

    /** @return list<array{id:string,name:string,revision:int,updatedAt:string}> */
    public function listOf(string $owner): array
    {
        $items = [];
        foreach (glob($this->dir . '/*.json') ?: [] as $file) {
            $doc = $this->readFile($file);
            if ($doc === null || $doc['owner'] !== $owner) {
                continue;
            }
            $items[] = [
                'id' => $doc['id'],
                'name' => $doc['name'],
                'revision' => $doc['revision'],
                'updatedAt' => $doc['updatedAt'],
            ];
        }
        usort($items, static fn(array $a, array $b): int => strcmp($b['updatedAt'], $a['updatedAt']));
        return $items;
    }

    /** @return array{id:string,name:string,owner:string,revision:int,updatedAt:string,project:array}|null */
    public function load(string $id): ?array
    {
        return $this->own($this->readFile($this->path($id)));
    }

    /** @return array{id:string,name:string,owner:string,revision:int,updatedAt:string,project:array} */
    public function create(string $name): array
    {
        do {
            $id = self::newId();
        } while (file_exists($this->path($id)));

        $project = [
            'formatVersion' => 1,
            'id' => $id,
            'name' => $name,
            'assets' => [],
            'activeSceneId' => '',
        ];
        $doc = $this->document($id, $name, $this->owner, 1, $project);
        $this->writeFile($this->path($id), $doc);
        return $doc;
    }

    /**
     * Saves a project when `$expectedRevision` matches the stored one.
     * Returns the new document, null when the project does not exist, or throws
     * StaleRevisionException (carrying the current revision) on a conflict.
     */
    public function save(string $id, int $expectedRevision, array $project): ?array
    {
        $path = $this->path($id);
        return $this->locked($path, function () use ($path, $id, $expectedRevision, $project): ?array {
            $current = $this->own($this->readFile($path));
            if ($current === null) {
                return null;
            }
            if ($current['revision'] !== $expectedRevision) {
                throw new StaleRevisionException($current['revision']);
            }
            $name = is_string($project['name'] ?? null) && $project['name'] !== '' ? $project['name'] : $current['name'];
            $project['id'] = $id;
            $doc = $this->document($id, $name, $current['owner'], $expectedRevision + 1, $project);
            $this->writeFile($path, $doc);
            return $doc;
        });
    }

    public function delete(string $id): bool
    {
        $path = $this->path($id);
        // Under the save lock, or a save running at the same time writes the project back.
        $deleted = $this->locked($path, fn(): bool => $this->load($id) !== null && unlink($path));
        if ($deleted) {
            // Whoever still waits for the lock finds no project and writes nothing.
            @unlink($path . '.lock');
        }
        return $deleted;
    }

    /**
     * Hands every project of `$from` to `$to` – what renaming an account does, since the name is
     * the owner. Revision and date stay: nothing in the project changed, and a tab that has one of
     * them open must not be told it was modified elsewhere. Returns how many moved.
     */
    public function transfer(string $from, string $to): int
    {
        $moved = 0;
        foreach (glob($this->dir . '/*.json') ?: [] as $file) {
            // Under the save lock, or a save running at the same time writes the old owner back.
            $moved += $this->locked($file, function () use ($file, $from, $to): int {
                $doc = $this->readFile($file);
                if ($doc === null || $doc['owner'] !== $from) {
                    return 0;
                }
                $doc['owner'] = $to;
                $this->writeFile($file, $doc);
                return 1;
            });
        }
        return $moved;
    }

    /**
     * The lock file stays when the work is done. Removing it would let two saves in at once: one
     * still waiting holds the removed file, while the next one creates a new file and locks that.
     *
     * @template T
     * @param callable():T $work
     * @return T
     */
    private function locked(string $path, callable $work): mixed
    {
        $lock = fopen($path . '.lock', 'c');
        if ($lock === false || !flock($lock, LOCK_EX)) {
            throw new RuntimeException('Cannot acquire project lock');
        }
        try {
            return $work();
        } finally {
            flock($lock, LOCK_UN);
            fclose($lock);
        }
    }

    /** The document, or null when it belongs to someone else and this store does not see everything. */
    private function own(?array $doc): ?array
    {
        return $doc !== null && ($this->seesAll || $doc['owner'] === $this->owner) ? $doc : null;
    }

    private function path(string $id): string
    {
        return $this->dir . '/' . $id . '.json';
    }

    private function document(string $id, string $name, string $owner, int $revision, array $project): array
    {
        return [
            'id' => $id,
            'name' => $name,
            'owner' => $owner,
            'revision' => $revision,
            'updatedAt' => gmdate('c'),
            'project' => $project,
        ];
    }

    private function readFile(string $path): ?array
    {
        if (!is_file($path)) {
            return null;
        }
        $raw = file_get_contents($path);
        $doc = $raw === false ? null : json_decode($raw, true);
        if (!is_array($doc) || !isset($doc['id'], $doc['revision'], $doc['project'])) {
            return null;
        }
        $doc['name'] = is_string($doc['name'] ?? null) ? $doc['name'] : 'Untitled';
        // A file without an owner belongs to nobody and is therefore invisible to everybody –
        // the safe way round, and the one that shows up straight away if a migration is missed.
        $doc['owner'] = is_string($doc['owner'] ?? null) ? $doc['owner'] : '';
        $doc['updatedAt'] = is_string($doc['updatedAt'] ?? null) ? $doc['updatedAt'] : '';
        $doc['revision'] = (int) $doc['revision'];
        return $doc;
    }

    private function writeFile(string $path, array $doc): void
    {
        $json = json_encode($doc, JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE);
        if ($json === false) {
            throw new RuntimeException('Cannot encode project');
        }
        AtomicFile::write($path, $json, AtomicFile::HIDDEN, 'project file');
    }
}