<?php

declare(strict_types=1);

namespace KTXM\ServiceDav;

use DI\Attribute\Inject;

/**
 * Bidirectional mapping between DAV object URIs (chosen by clients) and entity
 * identifiers assigned by the provider stores.
 *
 * Stored as a pair of JSON files per logical "map" (keyed by a mapId that
 * encodes tenant / user / calendar-or-addressbook context).  File locking is
 * used to guard against concurrent modifications.
 *
 * This class is intentionally simple: it is a best-effort persistence layer for
 * single-server deployments.  A database-backed implementation should be
 * substituted for high-concurrency or multi-node environments.
 */
class DavUriMap
{
    private string $dir;

    public function __construct(#[Inject('rootDir')] string $rootDir)
    {
        $this->dir = $rootDir . '/var/dav';
    }

    // -------------------------------------------------------------------------
    // Public API
    // -------------------------------------------------------------------------

    /**
     * Look up the provider entity identifier for a given DAV object URI.
     *
     * @param string $mapId   Logical map bucket (e.g. "{tenant}:{user}:cal:{calId}")
     * @param string $objectUri DAV leaf URI (e.g. "abc-123.ics")
     */
    public function getEntityId(string $mapId, string $objectUri): ?string
    {
        return $this->read($mapId)['obj_to_ent'][$objectUri] ?? null;
    }

    /**
     * Look up the DAV object URI for a given provider entity identifier.
     */
    public function getObjectUri(string $mapId, string $entityId): ?string
    {
        return $this->read($mapId)['ent_to_obj'][(string) $entityId] ?? null;
    }

    /**
     * Record a mapping from a DAV object URI to a provider entity identifier.
     */
    public function set(string $mapId, string $objectUri, string|int $entityId): void
    {
        $entityId = (string) $entityId;
        $this->update($mapId, static function (array $data) use ($objectUri, $entityId): array {
            $data['obj_to_ent'][$objectUri] = $entityId;
            $data['ent_to_obj'][$entityId]  = $objectUri;
            return $data;
        });
    }

    /**
     * Remove the mapping for a DAV object URI.
     */
    public function delete(string $mapId, string $objectUri): void
    {
        $this->update($mapId, static function (array $data) use ($objectUri): array {
            $entityId = $data['obj_to_ent'][$objectUri] ?? null;
            if ($entityId !== null) {
                unset($data['ent_to_obj'][$entityId]);
            }
            unset($data['obj_to_ent'][$objectUri]);
            return $data;
        });
    }

    // -------------------------------------------------------------------------
    // Internal helpers
    // -------------------------------------------------------------------------

    private function mapFile(string $mapId): string
    {
        return $this->dir . '/map_' . md5($mapId) . '.json';
    }

    private function read(string $mapId): array
    {
        $file = $this->mapFile($mapId);
        if (!file_exists($file)) {
            return ['obj_to_ent' => [], 'ent_to_obj' => []];
        }
        $contents = file_get_contents($file);
        if ($contents === false) {
            return ['obj_to_ent' => [], 'ent_to_obj' => []];
        }
        return json_decode($contents, true) ?? ['obj_to_ent' => [], 'ent_to_obj' => []];
    }

    private function update(string $mapId, callable $updater): void
    {
        if (!is_dir($this->dir)) {
            mkdir($this->dir, 0750, true);
        }

        $file = $this->mapFile($mapId);
        $fh   = fopen($file, 'c+');
        if ($fh === false) {
            return;
        }

        try {
            flock($fh, LOCK_EX);
            $contents = stream_get_contents($fh);
            $data     = json_decode($contents ?: '{}', true)
                        ?? ['obj_to_ent' => [], 'ent_to_obj' => []];
            if (!isset($data['obj_to_ent'])) {
                $data['obj_to_ent'] = [];
            }
            if (!isset($data['ent_to_obj'])) {
                $data['ent_to_obj'] = [];
            }
            $data = $updater($data);
            ftruncate($fh, 0);
            rewind($fh);
            fwrite($fh, json_encode($data, JSON_PRETTY_PRINT | JSON_UNESCAPED_UNICODE));
        } finally {
            flock($fh, LOCK_UN);
            fclose($fh);
        }
    }
}