<?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 KTXF\Resource\Delta\Delta;
use KTXF\Resource\Delta\DeltaCollection;
use KTXM\ProviderImap\Stores\MailboxStore;
use KTXM\ProviderImap\Stores\MessageStore;

/**
 * Answers "what changed since this signature?" for a cached mailbox.
 *
 * A signature is `<uidValidity>:<changeSeq>`. Read-only: harmonizing before
 * answering is the caller's decision.
 */
class MessageDeltaService
{
    public function __construct(
        private readonly MailboxStore $mailboxStore,
        private readonly MessageStore $messageStore,
    ) {}

    /**
     * Changes of a mailbox since a signature.
     *
     * - empty signature: the current signature and no changes, so the client gets a
     *   starting point; while the initial harmonization is incomplete the signature is
     *   `<uidValidity>:0`, so additions of the run in progress are not skipped
     * - signature of another UIDVALIDITY, older than the purged tombstones, or not
     *   understood: a reset, answered as changes since 0 (every message is an addition)
     * - otherwise: additions, modifications and deletions after the signature
     *
     * A mailbox that is not cached (or never harmonized) yields an empty delta.
     */
    public function delta(string $serviceId, string $mailbox, string $signature): Delta
    {
        $state = $this->mailboxStore->state($serviceId, $mailbox);
        if ($state['uidValidity'] === null) {
            return new Delta();
        }

        $uidValidity = (int) $state['uidValidity'];
        $current = self::signature($uidValidity, (int) $state['changeSeq']);

        if ($signature === '') {
            return new Delta(signature: $state['harmonizationComplete'] ? $current : self::signature($uidValidity, 0));
        }

        $since = self::since($signature, $uidValidity, (int) $state['purgedSeq'], (int) $state['changeSeq']) ?? 0;
        $changes = $this->messageStore->changes($serviceId, $mailbox, $uidValidity, $since);

        return new Delta(
            new DeltaCollection(array_map('strval', $changes['additions'])),
            new DeltaCollection(array_map('strval', $changes['modifications'])),
            new DeltaCollection(array_map('strval', $changes['deletions'])),
            $current,
        );
    }

    public static function signature(int $uidValidity, int $changeSeq): string
    {
        return $uidValidity . ':' . $changeSeq;
    }

    /**
     * The change sequence a signature refers to, or null when it needs a reset.
     */
    private static function since(string $signature, int $uidValidity, int $purgedSeq, int $changeSeq): ?int
    {
        if (preg_match('/^(\d+):(\d+)$/', $signature, $matches) !== 1) {
            return null;
        }

        $since = (int) $matches[2];
        if ((int) $matches[1] !== $uidValidity || $since < $purgedSeq || $since > $changeSeq) {
            return null;
        }

        return $since;
    }
}