export default function (childCollectionNode, filters, options, userId) {
    const linker = childCollectionNode.linker;
    const linkStorageField = linker.linkStorageField;
    const collection = childCollectionNode.collection;

    let pipeline = [];

    if (collection.firewall) {
        collection.firewall(filters, options, userId);
    }

    pipeline.push({$match: filters});

    if (options.sort) {
        pipeline.push({$sort: options.sort})
    }

    let _id = linkStorageField;
    if (linker.isMeta()) {
        _id += '._id';
    }

    let dataPush = {};
    _.each(options.fields, (value, field) => {
        dataPush[field] = '$' + field
    });

    if (!dataPush._id) {
        dataPush['_id'] = '$_id';
    }

    if (linker.isMeta()) {
        dataPush[linkStorageField] = '$' + linkStorageField;
    }

    pipeline.push({
        $group: {
            _id: "$" + _id,
            data: {
                $push: dataPush
            }
        }
    });

    if (options.limit || options.skip) {
        let $slice = ["$data"];
        if (options.skip) $slice.push(options.skip);
        if (options.limit) $slice.push(options.limit);

        pipeline.push({
            $project: {
                _id: 1,
                data: {$slice}
            }
        })
    }

    return pipeline;
}