<?php

declare(strict_types=1);

/**
 * SPDX-FileCopyrightText: Sebastian Krupinski <krupinski01@gmail.com>
 * SPDX-License-Identifier: AGPL-3.0-or-later
 */

namespace KTXM\ProviderImap\Service\Cache;

use KTXM\ProviderImap\Providers\CollectionResource;
use KTXM\ProviderImap\Providers\EntityResource;
use KTXM\ProviderImap\Service\Remote\RemoteMailService;
use KTXM\ProviderImap\Stores\MessageStore;

/**
 * Cache Service — IMAP Sync Orchestrator
 *
 * Keeps the local MongoDB cache in sync with a remote IMAP server.
 *
 * Strategy (UID-based):
 *  1. Fetch the complete remote UID set.
 *  2. Compare against cached UIDs.
 *  3. Fetch and store new UIDs; remove stale UIDs from the cache.
 *
 * This is always a full-range UID comparison.  A CONDSTORE/HIGHESTMODSEQ
 * strategy can be layered on later for servers that support RFC 7162.
 */
class CacheService
{
    public function __construct(
        private readonly RemoteMailService $remoteMailService,
        private readonly MessageStore      $messageStore,
        private readonly string            $provider,
        private readonly string|int        $service,
    ) {}

    // ── Mailbox sync ──────────────────────────────────────────────────────────

    /**
     * Synchronise the mailbox list for this service.
     *
     * Inserts/updates every selectable mailbox returned by the remote server
     * and removes cached mailboxes that no longer exist remotely.
     *
     * @return array{added: string[], removed: string[]}
     */
    public function syncMailboxes(): array
    {
        $remoteCollections = $this->remoteMailService->collectionList();

        $added   = [];
        $removed = [];

        // Upsert every remote mailbox
        foreach ($remoteCollections as $name => $resource) {
            $doc = array_merge(
                $resource->toStore(),
                ['sid' => (string) $this->service],
            );
            $this->messageStore->upsertMailbox($doc);
            $added[] = $name;
        }

        // Remove cached mailboxes that no longer exist on the server
        $cached = $this->messageStore->listMailboxes((string) $this->service);
        foreach ($cached as $cachedDoc) {
            $name = $cachedDoc['name'] ?? ($cachedDoc['identifier'] ?? null);
            if ($name === null) {
                continue;
            }
            if (!isset($remoteCollections[$name])) {
                $this->messageStore->deleteMailbox((string) $this->service, $name);
                $removed[] = $name;
            }
        }

        return ['added' => $added, 'removed' => $removed];
    }

    // ── Message sync ──────────────────────────────────────────────────────────

    /**
     * Synchronise all messages in one mailbox.
     *
     * Fetches new UIDs from the remote server, stores them in MongoDB, and
     * removes UIDs from the cache that no longer exist on the server.
     *
     * @return array{added: int[], removed: int[]}
     */
    public function syncMessages(string $mailbox): array
    {
        $remoteUids = $this->remoteMailService->entityList($mailbox);
        $cachedUids = $this->messageStore->listUids((string) $this->service, $mailbox);

        $remoteSet  = array_fill_keys($remoteUids, true);
        $cachedSet  = array_fill_keys($cachedUids, true);

        $newUids     = array_keys(array_diff_key($remoteSet, $cachedSet));
        $removedUids = array_keys(array_diff_key($cachedSet, $remoteSet));

        // Stream-fetch new messages one at a time and store each
        foreach ($this->remoteMailService->entitySyncStream($mailbox, $newUids) as $uid => $resource) {
            /** @var EntityResource $resource */
            $doc = array_merge(
                $resource->toStore(),
                [
                    'sid'     => (string) $this->service,
                    'mailbox' => $mailbox,
                    'uid'     => $uid,
                ],
            );
            $this->messageStore->upsertMessage($doc);
        }

        // Purge stale UIDs from cache
        if (!empty($removedUids)) {
            $this->messageStore->deleteMessages((string) $this->service, $mailbox, $removedUids);
        }

        return [
            'added'   => $newUids,
            'removed' => $removedUids,
        ];
    }

    /**
     * Perform a full sync: mailboxes first, then all messages in each selectable mailbox.
     *
     * @return array{mailboxes: array, messages: array<string, array>}
     */
    public function syncAll(): array
    {
        $mailboxResult   = $this->syncMailboxes();
        $messagesResults = [];

        foreach ($this->remoteMailService->collectionList() as $name => $collection) {
            try {
                $messagesResults[$name] = $this->syncMessages($name);
            } catch (\Throwable $e) {
                $messagesResults[$name] = ['error' => $e->getMessage()];
            }
        }

        return [
            'mailboxes' => $mailboxResult,
            'messages'  => $messagesResults,
        ];
    }

    // ── Partial helpers ───────────────────────────────────────────────────────

    /**
     * Sync only the flags of already-cached messages in a mailbox.
     *
     * This is cheaper than a full message sync: it fetches FLAGS only from
     * the remote server and updates cached documents in place.
     */
    public function syncFlags(string $mailbox): void
    {
        $cachedUids = $this->messageStore->listUids((string) $this->service, $mailbox);

        if (empty($cachedUids)) {
            return;
        }

        // Fetch only FLAGS + UID from remote
        $items = ['FLAGS', 'UID'];

        foreach ($this->remoteMailService->entitySyncStream($mailbox, $cachedUids, $items) as $uid => $resource) {
            /** @var EntityResource $resource */
            $existing = $this->messageStore->fetchMessage((string) $this->service, $mailbox, $uid);
            if ($existing === null) {
                continue;
            }

            // Merge updated flags into the cached document
            $existingProperties = $existing['properties'] ?? [];
            $updatedProperties  = $resource->toStore()['properties'] ?? [];

            // Only overwrite flag-related fields
            foreach (['read', 'flagged', 'answered', 'draft', 'deleted', 'junk'] as $field) {
                if (isset($updatedProperties[$field])) {
                    $existingProperties[$field] = $updatedProperties[$field];
                }
            }

            $existing['properties'] = $existingProperties;
            $this->messageStore->upsertMessage($existing);
        }
    }
}