<?php
declare(strict_types=1);

header('Content-Type: application/json; charset=utf-8');
header('Cache-Control: no-store');

require __DIR__ . '/im_web_bootstrap.php';

function clampLimit(mixed $value, int $default, int $max): int
{
    $limit = (int)$value;
    if ($limit <= 0) {
        return $default;
    }

    return min($limit, $max);
}

function placeholders(array $values): string
{
    return implode(',', array_fill(0, count($values), '?'));
}

function payloadBool(mixed $value): bool
{
    return filter_var($value, FILTER_VALIDATE_BOOLEAN);
}

function timestampMs(?string $datetime, string $messageId = '0'): int
{
    $id = (int)$messageId;
    if ($id > 0) {
        return ($id >> 21) + 1514736000000;
    }

    if ($datetime !== null && $datetime !== '') {
        $date = DateTimeImmutable::createFromFormat(
            'Y-m-d H:i:s',
            $datetime,
            new DateTimeZone(IM_DB_TIMEZONE)
        );
        if ($date instanceof DateTimeImmutable) {
            return $date->getTimestamp() * 1000;
        }
    }

    return (int)floor(microtime(true) * 1000);
}

function nowMs(): int
{
    return (int)floor(microtime(true) * 1000);
}

function markUserDelivered(PDO $db, string $userId, int $timestamp): void
{
    if ($userId === '' || $timestamp <= 0) {
        return;
    }

    $statement = $db->prepare(
        'insert into `t_delivery_report` (`_uid`, `_dt`) values (?, ?)'
        . ' on duplicate key update `_dt` = if(`_dt` < values(`_dt`), values(`_dt`), `_dt`)'
    );
    $statement->execute([$userId, $timestamp]);
}

function markConversationRead(PDO $db, string $userId, string $targetId, int $timestamp): void
{
    if ($userId === '' || $targetId === '' || $timestamp <= 0) {
        return;
    }

    $statement = $db->prepare(
        'select `id`, `_dt` from `t_read_report`'
        . ' where `_uid` = ? and `_type` = 0 and `_line` = 0 and `_target` = ?'
        . ' order by `_dt` desc limit 1'
    );
    $statement->execute([$userId, $targetId]);
    $row = $statement->fetch();

    if ($row) {
        if ($timestamp > (int)$row['_dt']) {
            $update = $db->prepare('update `t_read_report` set `_dt` = ? where `id` = ?');
            $update->execute([$timestamp, (int)$row['id']]);
        }
        return;
    }

    $insert = $db->prepare(
        'insert into `t_read_report` (`_uid`, `_type`, `_line`, `_target`, `_dt`) values (?, 0, 0, ?, ?)'
    );
    $insert->execute([$userId, $targetId, $timestamp]);
}

function resolveUserId(PDO $db, string $value): string
{
    if ($value === '') {
        return '';
    }

    $statement = $db->prepare(
        'select `_uid` from `t_user` where `_uid` = ? or `_mobile` = ? or `_name` = ? limit 1'
    );
    $statement->execute([$value, $value, $value]);
    $uid = $statement->fetchColumn();

    return is_string($uid) && $uid !== '' ? $uid : $value;
}

function peerFromConversationTarget(string $userId, string $target): string
{
    $parts = array_values(array_filter(explode('|', $target), static fn($part) => $part !== ''));
    if (count($parts) < 2) {
        return $target !== $userId ? $target : '';
    }

    return $parts[0] === $userId ? $parts[1] : $parts[0];
}

function fetchMessageRows(PDO $db, array $messageIds): array
{
    $messageIds = array_values(array_unique(array_filter(array_map('strval', $messageIds))));
    if (!$messageIds) {
        return [];
    }

    $idsByTable = [];
    foreach ($messageIds as $messageId) {
        $idsByTable[imMessageTable($messageId)][] = $messageId;
    }

    $messages = [];
    foreach ($idsByTable as $table => $ids) {
        $sql = 'select `_mid`, `_from`, `_type`, `_target`, `_line`, `_searchable_key`, `_dt`, `_content_type`, `_to`'
            . ' from `' . $table . '` where `_mid` in (' . placeholders($ids) . ')';
        $statement = $db->prepare($sql);
        $statement->execute($ids);
        foreach ($statement->fetchAll() as $row) {
            $messages[(string)$row['_mid']] = $row;
        }
    }

    return $messages;
}

function fetchMessageEditMap(PDO $db, array $messageIds): array
{
    $messageIds = array_values(array_unique(array_filter(array_map('strval', $messageIds))));
    if (!$messageIds) {
        return [];
    }

    try {
        $statement = $db->prepare(
            'select `message_uid`, `edited_at_ms` from `t_web_message_edits`'
            . ' where `message_uid` in (' . placeholders($messageIds) . ')'
        );
        $statement->execute($messageIds);
    } catch (Throwable) {
        return [];
    }

    $edits = [];
    foreach ($statement->fetchAll() as $row) {
        $edits[(string)$row['message_uid']] = [
            'editedAt' => (int)$row['edited_at_ms'],
        ];
    }

    return $edits;
}

function normalizeAttachmentRow(array $row): array
{
    return [
        'type' => (string)$row['attachment_type'],
        'url' => (string)$row['url'],
        'name' => (string)($row['name'] ?? ''),
        'mime' => (string)($row['mime'] ?? ''),
        'size' => (int)($row['size_bytes'] ?? 0),
    ];
}

function fetchAttachmentMap(PDO $appDb, array $messageIds): array
{
    $messageIds = array_values(array_unique(array_filter(array_map('strval', $messageIds))));
    if (!$messageIds) {
        return [];
    }

    ensureWebImAppTables();
    $statement = $appDb->prepare(
        'select `message_uid`, `attachment_type`, `url`, `name`, `mime`, `size_bytes`'
        . ' from `t_web_message_attachments`'
        . ' where `message_uid` in (' . placeholders($messageIds) . ')'
    );
    $statement->execute($messageIds);

    $attachments = [];
    foreach ($statement->fetchAll() as $row) {
        $attachments[(string)$row['message_uid']] = normalizeAttachmentRow($row);
    }

    return $attachments;
}

function attachmentFallbackText(?array $attachment): string
{
    if (!$attachment) {
        return '';
    }
    if ((string)$attachment['type'] === 'image') {
        return '[图片]';
    }

    return '[文件] ' . ((string)($attachment['name'] ?? '') ?: '文件');
}

function attachmentDisplayText(string $text, ?array $attachment): string
{
    if (!$attachment) {
        return $text;
    }

    return $text === attachmentFallbackText($attachment) ? '' : $text;
}

function messagePreviewText(?array $message): string
{
    if (!$message) {
        return '';
    }
    $attachment = is_array($message['attachment'] ?? null) ? $message['attachment'] : null;
    if ($attachment) {
        $text = trim((string)($message['text'] ?? ''));
        return $text !== '' ? $text : attachmentFallbackText($attachment);
    }

    return (string)($message['text'] ?? '');
}

function fetchUserInfoMap(PDO $db, array $userIds, string $ownerId = ''): array
{
    $userIds = array_values(array_unique(array_filter(array_map('strval', $userIds))));
    if (!$userIds) {
        return [];
    }

    $statement = $db->prepare(
        'select `_uid`, `_name`, `_display_name`, `_mobile`, `_portrait`, `_address` from `t_user`'
        . ' where `_uid` in (' . placeholders($userIds) . ')'
    );
    $statement->execute($userIds);

    $users = [];
    foreach ($statement->fetchAll() as $row) {
        $row['_is_friend'] = false;
        $row['_alias'] = '';
        $row['_friend_alias'] = '';
        $row['_remark_alias'] = '';
        $users[(string)$row['_uid']] = $row;
    }

    if ($ownerId !== '') {
        $aliasStatement = $db->prepare(
            'select `_friend_uid`, `_alias` from `t_friend` where `_uid` = ?'
            . ' and `_friend_uid` in (' . placeholders($userIds) . ')'
        );
        $aliasStatement->execute(array_merge([$ownerId], $userIds));
        foreach ($aliasStatement->fetchAll() as $row) {
            $friendUid = (string)$row['_friend_uid'];
            if (!isset($users[$friendUid])) {
                continue;
            }
            $users[$friendUid]['_is_friend'] = true;
            $users[$friendUid]['_friend_alias'] = trim((string)($row['_alias'] ?? ''));
        }

        try {
            ensureWebImAppTables();
            $remarkMap = fetchWebUserRemarkMap(imAppDb(), $ownerId, $userIds);
        } catch (Throwable) {
            $remarkMap = [];
        }
        foreach ($remarkMap as $targetUid => $alias) {
            if (!isset($users[$targetUid])) {
                continue;
            }
            $users[$targetUid]['_remark_alias'] = $alias;
        }

        foreach ($users as $uid => $user) {
            $friendAlias = trim((string)($user['_friend_alias'] ?? ''));
            $remarkAlias = trim((string)($user['_remark_alias'] ?? ''));
            $users[$uid]['_alias'] = $friendAlias !== '' ? $friendAlias : $remarkAlias;
        }
    }

    return $users;
}

function userTitle(array $users, string $userId): string
{
    $user = $users[$userId] ?? null;
    if (!$user) {
        return $userId;
    }

    return (string)($user['_alias'] ?? '')
        ?: (string)($user['_display_name'] ?? '')
        ?: (string)($user['_name'] ?? '')
        ?: (string)($user['_mobile'] ?? '')
        ?: $userId;
}

function loadPeerReceiptState(PDO $db, string $currentUserId, string $peerId): array
{
    $deliveryStatement = $db->prepare('select `_dt` from `t_delivery_report` where `_uid` = ? limit 1');
    $deliveryStatement->execute([$peerId]);
    $deliveredAt = $deliveryStatement->fetchColumn();

    $readTargets = array_values(array_unique([
        $currentUserId,
        $currentUserId . '|' . $peerId,
        $peerId . '|' . $currentUserId,
    ]));
    $readStatement = $db->prepare(
        'select max(`_dt`) from `t_read_report`'
        . ' where `_uid` = ? and `_type` = 0 and `_line` = 0'
        . ' and `_target` in (' . placeholders($readTargets) . ')'
    );
    $readStatement->execute(array_merge([$peerId], $readTargets));
    $readAt = $readStatement->fetchColumn();

    return [
        'deliveredAt' => is_numeric($deliveredAt) ? (int)$deliveredAt : 0,
        'readAt' => is_numeric($readAt) ? (int)$readAt : 0,
    ];
}

function loadOwnReadStateMap(PDO $db, string $userId, array $peerIds): array
{
    $peerIds = array_values(array_unique(array_filter(array_map('strval', $peerIds))));
    if (!$peerIds) {
        return [];
    }

    $statement = $db->prepare(
        'select `_target`, max(`_dt`) as `_read_at` from `t_read_report`'
        . ' where `_uid` = ? and `_type` = 0 and `_line` = 0'
        . ' and `_target` in (' . placeholders($peerIds) . ')'
        . ' group by `_target`'
    );
    $statement->execute(array_merge([$userId], $peerIds));

    $readAtByPeer = [];
    foreach ($statement->fetchAll() as $row) {
        $readAtByPeer[(string)$row['_target']] = (int)$row['_read_at'];
    }

    return $readAtByPeer;
}

function outgoingDeliveryStatus(int $timestamp, array $receiptState): string
{
    $readAt = (int)($receiptState['readAt'] ?? 0);
    if ($readAt > 0 && $timestamp <= $readAt) {
        return 'read';
    }

    $deliveredAt = (int)($receiptState['deliveredAt'] ?? 0);
    if ($deliveredAt > 0 && $timestamp <= $deliveredAt) {
        return 'delivered';
    }

    return 'sent';
}

function messageActivityTimestamp(int $timestamp, array $editState = []): int
{
    return max($timestamp, (int)($editState['editedAt'] ?? 0));
}

function normalizeConversationType(mixed $value): string
{
    $type = strtolower(trim((string)$value));
    if (in_array($type, ['1', 'group', 'channel'], true)) {
        return 'group';
    }

    return 'single';
}

function isWebGroupTarget(PDO $appDb, string $targetId): bool
{
    if ($targetId === '') {
        return false;
    }

    ensureWebImAppTables();
    $statement = $appDb->prepare('select 1 from `t_web_groups` where `group_id` = ? and `deleted` = 0 limit 1');
    $statement->execute([$targetId]);

    return (bool)$statement->fetchColumn();
}

function markWebGroupRead(PDO $appDb, string $userId, string $groupId, int $timestamp): void
{
    if ($userId === '' || $groupId === '' || $timestamp <= 0) {
        return;
    }

    $now = nowMs();
    $statement = $appDb->prepare(
        'insert into `t_web_group_reads` (`group_id`, `user_id`, `read_at_ms`, `updated_at_ms`)'
        . ' values (?, ?, ?, ?)'
        . ' on duplicate key update'
        . ' `read_at_ms` = if(`read_at_ms` < values(`read_at_ms`), values(`read_at_ms`), `read_at_ms`),'
        . ' `updated_at_ms` = values(`updated_at_ms`)'
    );
    $statement->execute([$groupId, $userId, $timestamp, $now]);
}

function webGroupRole(PDO $appDb, string $userId, string $groupId): string
{
    $statement = $appDb->prepare(
        'select `role` from `t_web_group_members`'
        . ' where `group_id` = ? and `user_id` = ? and `status` = 0 limit 1'
    );
    $statement->execute([$groupId, $userId]);
    $role = $statement->fetchColumn();

    return is_string($role) && $role !== '' ? $role : '';
}

function formatWebGroupMessage(
    array $row,
    string $currentUserId,
    array $group,
    ?array $attachment = null,
    array $users = []
): array
{
    $groupId = (string)$row['group_id'];
    $from = (string)$row['sender_uid'];
    $senderUser = $users[$from] ?? [];
    $senderAlias = trim((string)($row['sender_alias'] ?? ''));
    $senderContactAlias = trim((string)($senderUser['_alias'] ?? ''));
    $senderFriendAlias = trim((string)($senderUser['_friend_alias'] ?? ''));
    $senderRemarkAlias = trim((string)($senderUser['_remark_alias'] ?? ''));
    $senderRawName = trim((string)($senderUser['_display_name'] ?? ''))
        ?: trim((string)($senderUser['_name'] ?? ''))
        ?: trim((string)($senderUser['_mobile'] ?? ''))
        ?: $from;
    $senderName = $senderContactAlias
        ?: $senderAlias
        ?: $senderRawName;
    $senderRole = (string)($row['sender_role'] ?? 'member');
    if (!in_array($senderRole, ['owner', 'admin'], true)) {
        $senderRole = 'member';
    }
    $timestamp = (int)$row['created_at_ms'];
    $editedAt = (int)($row['edited_at_ms'] ?? 0);
    $activityTimestamp = max($timestamp, $editedAt);
    $direction = $from === $currentUserId ? 'out' : 'in';

    $messageType = $attachment ? (string)$attachment['type'] : 'text';
    $contentType = $messageType === 'image' ? 3 : ($messageType === 'file' ? 5 : 1);
    return [
        'id' => (string)$row['message_uid'],
        'messageUid' => (string)$row['message_uid'],
        'conversationId' => 'group-' . $groupId,
        'from' => $from,
        'senderRole' => $senderRole,
        'senderName' => $senderName,
        'senderPortrait' => (string)($senderUser['_portrait'] ?? ''),
        'senderProfile' => [
            'uid' => $from,
            'displayName' => $senderName,
            'rawName' => $senderRawName,
            'contactAlias' => $senderContactAlias,
            'friendAlias' => $senderFriendAlias,
            'remarkAlias' => $senderRemarkAlias,
            'groupAlias' => $senderAlias,
            'isContact' => (bool)($senderUser['_is_friend'] ?? false),
            'mobile' => (string)($senderUser['_mobile'] ?? ''),
            'address' => (string)($senderUser['_address'] ?? ''),
            'portrait' => (string)($senderUser['_portrait'] ?? ''),
            'role' => $senderRole,
        ],
        'to' => $groupId,
        'target' => $groupId,
        'direction' => $direction,
        'type' => $messageType,
        'contentType' => $contentType,
        'text' => attachmentDisplayText((string)$row['text'], $attachment),
        'attachment' => $attachment,
        'status' => $direction === 'out' ? 'sent' : 'sent',
        'deliveryStatus' => $direction === 'out' ? 'sent' : '',
        'recalled' => false,
        'recallStatus' => '',
        'editedAt' => $editedAt,
        'timestamp' => $timestamp,
        'activityTimestamp' => $activityTimestamp,
        'displayTimestamp' => $timestamp,
        'conversationType' => (string)($group['category'] ?? 'group'),
    ];
}

function loadWebGroupMessages(PDO $appDb, string $userId, string $groupId, int $limit, bool $markRead): array
{
    ensureWebImAppTables();
    $role = webGroupRole($appDb, $userId, $groupId);
    if ($role === '') {
        return [];
    }

    $groupStatement = $appDb->prepare('select * from `t_web_groups` where `group_id` = ? and `deleted` = 0 limit 1');
    $groupStatement->execute([$groupId]);
    $group = $groupStatement->fetch();
    if (!$group) {
        return [];
    }

    $statement = $appDb->prepare(
        'select msg.*,'
        . ' coalesce(sender_member.`role`, if(g.`owner_uid` = msg.`sender_uid`, "owner", "member")) as `sender_role`,'
        . ' coalesce(sender_member.`alias`, "") as `sender_alias`'
        . ' from `t_web_group_messages` msg'
        . ' join `t_web_groups` g on g.`group_id` = msg.`group_id` and g.`deleted` = 0'
        . ' left join `t_web_group_members` sender_member'
        . ' on sender_member.`group_id` = msg.`group_id`'
        . ' and sender_member.`user_id` = msg.`sender_uid`'
        . ' and sender_member.`status` = 0'
        . ' where msg.`group_id` = ? and msg.`recalled` = 0'
        . ' order by msg.`created_at_ms` desc, msg.`id` desc limit ' . $limit
    );
    $statement->execute([$groupId]);
    $rows = array_reverse($statement->fetchAll());
    $attachmentMap = fetchAttachmentMap($appDb, array_column($rows, 'message_uid'));
    $users = fetchUserInfoMap(imDb(), array_column($rows, 'sender_uid'), $userId);

    $readTimestamp = 0;
    $messages = [];
    foreach ($rows as $row) {
        $messageId = (string)$row['message_uid'];
        $message = formatWebGroupMessage($row, $userId, $group, $attachmentMap[$messageId] ?? null, $users);
        $readTimestamp = max($readTimestamp, (int)$message['activityTimestamp']);
        $messages[] = $message;
    }

    if ($markRead) {
        markWebGroupRead($appDb, $userId, $groupId, $readTimestamp);
    }

    return $messages;
}

function loadWebGroupConversations(PDO $appDb, string $userId, int $limit): array
{
    ensureWebImAppTables();
    $statement = $appDb->prepare(
        'select g.*, m.`role`'
        . ' from `t_web_groups` g'
        . ' join `t_web_group_members` m on m.`group_id` = g.`group_id` and m.`status` = 0'
        . ' where g.`deleted` = 0 and m.`user_id` = ?'
        . ' order by g.`updated_at_ms` desc limit ' . min(max($limit, 50), 100)
    );
    $statement->execute([$userId]);
    $groups = $statement->fetchAll();
    if (!$groups) {
        return [];
    }

    $lastMessageStatement = $appDb->prepare(
        'select * from `t_web_group_messages`'
        . ' where `group_id` = ? and `recalled` = 0'
        . ' order by greatest(`created_at_ms`, `edited_at_ms`) desc, `id` desc limit 1'
    );
    $readStatement = $appDb->prepare(
        'select `read_at_ms` from `t_web_group_reads` where `group_id` = ? and `user_id` = ? limit 1'
    );
    $lastAttachmentStatement = $appDb->prepare(
        'select `attachment_type`, `url`, `name`, `mime`, `size_bytes`'
        . ' from `t_web_message_attachments` where `message_uid` = ? limit 1'
    );
    $unreadStatement = $appDb->prepare(
        'select count(*) from `t_web_group_messages`'
        . ' where `group_id` = ? and `sender_uid` <> ? and `recalled` = 0'
        . ' and greatest(`created_at_ms`, `edited_at_ms`) > ?'
    );
    $memberCountStatement = $appDb->prepare(
        'select count(*) from `t_web_group_members` where `group_id` = ? and `status` = 0'
    );

    $conversations = [];
    foreach ($groups as $group) {
        $groupId = (string)$group['group_id'];
        $lastMessageStatement->execute([$groupId]);
        $lastMessage = $lastMessageStatement->fetch();
        $readStatement->execute([$groupId, $userId]);
        $readAt = (int)($readStatement->fetchColumn() ?: 0);
        $unreadStatement->execute([$groupId, $userId, $readAt]);
        $unread = (int)$unreadStatement->fetchColumn();
        $memberCountStatement->execute([$groupId]);
        $memberCount = (int)$memberCountStatement->fetchColumn();

        $title = (string)$group['name'];
        $category = (string)$group['category'];
        $isChannel = $category === 'channel';
        $lastAttachment = null;
        if ($lastMessage) {
            $lastAttachmentStatement->execute([(string)$lastMessage['message_uid']]);
            $lastAttachmentRow = $lastAttachmentStatement->fetch();
            $lastAttachment = $lastAttachmentRow ? normalizeAttachmentRow($lastAttachmentRow) : null;
        }
        $subtitle = $lastMessage
            ? (messagePreviewText([
                'text' => attachmentDisplayText((string)$lastMessage['text'], $lastAttachment),
                'attachment' => $lastAttachment,
            ]) ?: (string)$lastMessage['text'])
            : ($isChannel ? '公告群' : ($memberCount > 0 ? $memberCount . ' 位成员' : '群组'));
        $updatedAt = $lastMessage
            ? max((int)$lastMessage['created_at_ms'], (int)($lastMessage['edited_at_ms'] ?? 0))
            : (int)$group['updated_at_ms'];

        $conversations[] = [
            'id' => 'group-' . $groupId,
            'type' => $isChannel ? 'channel' : 'group',
            'target' => $groupId,
            'title' => $title,
            'subtitle' => $subtitle,
            'unread' => $unread,
            'avatarText' => mb_strtoupper(mb_substr($title, 0, 1, 'UTF-8'), 'UTF-8'),
            'updatedAt' => $updatedAt,
            'role' => (string)$group['role'],
            'memberCount' => $memberCount,
            'raw' => [
                'type' => 'group',
                'target' => $groupId,
                'line' => 0,
                'category' => $category,
                'role' => (string)$group['role'],
            ],
        ];
    }

    return $conversations;
}

function isRecallMessage(array $row): bool
{
    return (int)($row['_content_type'] ?? 0) === 80;
}

function shouldDisplayMessageForUser(array $row, string $currentUserId): bool
{
    if (!isRecallMessage($row)) {
        return true;
    }

    return (string)$row['_from'] === $currentUserId;
}

function formatMessage(
    array $row,
    string $currentUserId,
    string $peerId,
    array $receiptState = [],
    array $editState = [],
    ?array $attachment = null
): array
{
    $messageId = (string)$row['_mid'];
    $from = (string)$row['_from'];
    $contentType = (int)($row['_content_type'] ?? 0);
    $isRecalled = $contentType === 80;
    $text = (string)($row['_searchable_key'] ?? '');
    $timestamp = timestampMs((string)($row['_dt'] ?? ''), $messageId);
    $direction = $from === $currentUserId ? 'out' : 'in';
    $messageType = $attachment ? (string)$attachment['type'] : (($contentType === 1 || $isRecalled) ? 'text' : 'unknown');
    $messageText = $text !== '' ? $text : ($isRecalled || $attachment ? '' : '[暂不支持的消息类型]');
    $messageText = attachmentDisplayText($messageText, $attachment);
    $editedAt = (int)($editState['editedAt'] ?? 0);
    $activityTimestamp = messageActivityTimestamp($timestamp, $editState);
    $deliveryStatus = $direction === 'out' && !$isRecalled
        ? outgoingDeliveryStatus($activityTimestamp, $receiptState)
        : '';

    return [
        'id' => $messageId,
        'messageUid' => $messageId,
        'conversationId' => 'single-' . $peerId,
        'from' => $from,
        'to' => $from === $currentUserId ? $peerId : $currentUserId,
        'target' => $peerId,
        'direction' => $direction,
        'type' => $messageType,
        'contentType' => $attachment ? ((string)$attachment['type'] === 'image' ? 3 : 5) : $contentType,
        'text' => $messageText,
        'attachment' => $attachment,
        'status' => $isRecalled && $direction === 'out' ? 'recalled' : ($direction === 'out' ? $deliveryStatus : 'sent'),
        'deliveryStatus' => $deliveryStatus,
        'recalled' => $isRecalled,
        'recallStatus' => $isRecalled ? '已撤回' : '',
        'editedAt' => $editedAt,
        'timestamp' => $timestamp,
        'activityTimestamp' => $activityTimestamp,
        'displayTimestamp' => $timestamp,
    ];
}

function loadConversationMessages(PDO $db, string $userId, string $targetId, int $limit, bool $markRead): array
{
    $table = imUserMessagesTable($userId);
    $conversationKeys = [$userId . '|' . $targetId, $targetId . '|' . $userId];
    $scanLimit = min(max($limit * 4, $limit), 400);
    $statement = $db->prepare(
        'select `_mid`, `_dt` from `' . $table . '`'
        . ' where `_uid` = ? and `_type` = 0 and `_line` = 0'
        . ' and `_target` in (?, ?)'
        . ' order by `_mid` desc limit ' . $scanLimit
    );
    $statement->execute([$userId, $conversationKeys[0], $conversationKeys[1]]);
    $userRows = $statement->fetchAll();
    $messageRows = fetchMessageRows($db, array_column($userRows, '_mid'));
    $editMap = fetchMessageEditMap($db, array_column($userRows, '_mid'));
    $attachmentMap = fetchAttachmentMap(imAppDb(), array_column($userRows, '_mid'));
    $receiptState = loadPeerReceiptState($db, $userId, $targetId);

    $messages = [];
    $seenMessageIds = [];
    $readTimestamp = 0;
    foreach ($userRows as $userRow) {
        $messageId = (string)$userRow['_mid'];
        if (isset($seenMessageIds[$messageId]) || !isset($messageRows[$messageId])) {
            continue;
        }
        $seenMessageIds[$messageId] = true;
        if (!shouldDisplayMessageForUser($messageRows[$messageId], $userId)) {
            continue;
        }
        $message = formatMessage(
            $messageRows[$messageId],
            $userId,
            $targetId,
            $receiptState,
            $editMap[$messageId] ?? [],
            $attachmentMap[$messageId] ?? null
        );
        $messages[] = $message;
        $readTimestamp = max($readTimestamp, (int)$message['activityTimestamp']);
        if (count($messages) >= $limit) {
            break;
        }
    }
    $messages = array_reverse($messages);

    if ($markRead) {
        markConversationRead($db, $userId, $targetId, $readTimestamp);
    }

    return $messages;
}

function loadRecentConversations(PDO $db, string $userId, int $limit): array
{
    $table = imUserMessagesTable($userId);
    $scanLimit = min(max($limit * 20, 200), 1000);
    $statement = $db->prepare(
        'select `_mid`, `_target`, `_dt` from `' . $table . '`'
        . ' where `_uid` = ? and `_type` = 0 and `_line` = 0'
        . ' order by `_mid` desc limit ' . $scanLimit
    );
    $statement->execute([$userId]);

    $scanRows = $statement->fetchAll();
    $messageRows = fetchMessageRows($db, array_column($scanRows, '_mid'));
    $editMap = fetchMessageEditMap($db, array_column($scanRows, '_mid'));
    $attachmentMap = fetchAttachmentMap(imAppDb(), array_column($scanRows, '_mid'));
    $latestByPeer = [];
    foreach ($scanRows as $row) {
        $messageId = (string)$row['_mid'];
        $message = $messageRows[$messageId] ?? null;
        $peerId = peerFromConversationTarget($userId, (string)$row['_target']);
        if ($peerId === '' || !$message) {
            continue;
        }
        if (!shouldDisplayMessageForUser($message, $userId)) {
            continue;
        }
        $activityTimestamp = messageActivityTimestamp(
            timestampMs((string)($message['_dt'] ?? ''), $messageId),
            $editMap[$messageId] ?? []
        );
        if (!isset($latestByPeer[$peerId]) || $activityTimestamp > (int)($latestByPeer[$peerId]['_activity_at'] ?? 0)) {
            $row['_activity_at'] = $activityTimestamp;
            $latestByPeer[$peerId] = $row;
        }
    }
    uasort($latestByPeer, static fn($a, $b) => (int)($b['_activity_at'] ?? 0) <=> (int)($a['_activity_at'] ?? 0));
    $latestByPeer = array_slice($latestByPeer, 0, $limit, true);

    $users = fetchUserInfoMap($db, array_keys($latestByPeer), $userId);
    $readAtByPeer = loadOwnReadStateMap($db, $userId, array_keys($latestByPeer));
    $unreadByPeer = [];
    $seenUnreadMessageIds = [];

    foreach ($scanRows as $row) {
        $messageId = (string)$row['_mid'];
        if (isset($seenUnreadMessageIds[$messageId])) {
            continue;
        }
        $seenUnreadMessageIds[$messageId] = true;
        $peerId = peerFromConversationTarget($userId, (string)$row['_target']);
        $message = $messageRows[$messageId] ?? null;
        if ($peerId === '' || !$message || !isset($latestByPeer[$peerId])) {
            continue;
        }
        if ((string)$message['_from'] === $userId) {
            continue;
        }
        if (isRecallMessage($message)) {
            continue;
        }
        $timestamp = timestampMs((string)($message['_dt'] ?? ''), $messageId);
        $activityTimestamp = messageActivityTimestamp($timestamp, $editMap[$messageId] ?? []);
        if ($activityTimestamp > (int)($readAtByPeer[$peerId] ?? 0)) {
            $unreadByPeer[$peerId] = (int)($unreadByPeer[$peerId] ?? 0) + 1;
        }
    }

    $conversations = [];

    foreach ($latestByPeer as $peerId => $userRow) {
        $messageId = (string)$userRow['_mid'];
        $message = isset($messageRows[$messageId])
            ? formatMessage($messageRows[$messageId], $userId, $peerId, [], $editMap[$messageId] ?? [], $attachmentMap[$messageId] ?? null)
            : null;
        $title = userTitle($users, $peerId);
        $conversations[] = [
            'id' => 'single-' . $peerId,
            'type' => 'single',
            'target' => $peerId,
            'title' => $title,
            'subtitle' => $message ? (messagePreviewText($message) !== '' ? messagePreviewText($message) : (empty($message['recalled']) ? '' : '已撤回')) : '',
            'unread' => (int)($unreadByPeer[$peerId] ?? 0),
            'portrait' => (string)($users[$peerId]['_portrait'] ?? ''),
            'avatarText' => mb_strtoupper(mb_substr($title, 0, 1, 'UTF-8'), 'UTF-8'),
            'updatedAt' => $message ? $message['activityTimestamp'] : timestampMs((string)($userRow['_dt'] ?? ''), $messageId),
            'raw' => ['type' => 'single', 'target' => $peerId, 'line' => 0],
        ];
    }

    try {
        $conversations = array_merge($conversations, loadWebGroupConversations(imAppDb(), $userId, $limit));
    } catch (Throwable) {
        // Keep single-chat sync available if appdata group metadata is temporarily unavailable.
    }

    usort($conversations, static fn($a, $b) => $b['updatedAt'] <=> $a['updatedAt']);

    return array_slice($conversations, 0, $limit);
}

$payload = readJsonPayload();
$userId = trim((string)($payload['userId'] ?? ''));
$target = trim((string)($payload['target'] ?? ''));
$limit = clampLimit($payload['limit'] ?? 50, 50, 100);
$markRead = payloadBool($payload['markRead'] ?? false);
$conversationType = normalizeConversationType($payload['conversationType'] ?? $payload['type'] ?? 0);

if ($userId === '') {
    respond(400, '缺少用户ID');
}

try {
    $db = imDb();
    $userId = resolveUserId($db, $userId);
    markUserDelivered($db, $userId, nowMs());

    if ($target !== '') {
        $targetId = resolveUserId($db, $target);
        if ($conversationType === 'group' || isWebGroupTarget(imAppDb(), $target)) {
            respond(0, 'success', [
                'messages' => loadWebGroupMessages(imAppDb(), $userId, $target, $limit, $markRead),
            ]);
        }
        respond(0, 'success', [
            'messages' => loadConversationMessages($db, $userId, $targetId, $limit, $markRead),
        ]);
    }

    respond(0, 'success', [
        'conversations' => loadRecentConversations($db, $userId, $limit),
    ]);
} catch (Throwable $error) {
    respond(500, $error->getMessage() ?: '消息同步失败');
}