import _ from 'lodash/fp';
import { isRelation } from '../../../utils/types.mjs';

const getRootLevelPopulate = (meta)=>{
    const populate = {};
    for (const attributeName of Object.keys(meta.attributes)){
        const attribute = meta.attributes[attributeName];
        if (attribute.type === 'relation') {
            populate[attributeName] = true;
        }
    }
    return populate;
};
/**
 * Converts and prepares the query for populate
 *
 * @param {boolean|string[]|object} populate populate param
 * @param {object} ctx query context
 * @param {object} ctx.db database instance
 * @param {object} ctx.qb query builder instance
 * @param {string} ctx.uid model uid
 */ const processPopulate = (populate, ctx)=>{
    const { qb, db, uid } = ctx;
    const meta = db.metadata.get(uid);
    let populateMap = {};
    if (populate === false || _.isNil(populate)) {
        return null;
    }
    if (populate === true) {
        populateMap = getRootLevelPopulate(meta);
    } else if (Array.isArray(populate)) {
        for (const key of populate){
            const [root, ...rest] = key.split('.');
            if (rest.length > 0) {
                const subPopulate = rest.join('.');
                if (populateMap[root]) {
                    const populateValue = populateMap[root];
                    if (populateValue === true) {
                        populateMap[root] = {
                            populate: [
                                subPopulate
                            ]
                        };
                    } else {
                        populateValue.populate = [
                            subPopulate
                        ].concat(populateValue.populate ?? []);
                    }
                } else {
                    populateMap[root] = {
                        populate: [
                            subPopulate
                        ]
                    };
                }
            } else {
                populateMap[root] = populateMap[root] ? populateMap[root] : true;
            }
        }
    } else {
        populateMap = populate;
    }
    if (!_.isPlainObject(populateMap)) {
        throw new Error('Populate must be an object');
    }
    const finalPopulate = {};
    for (const key of Object.keys(populateMap)){
        const attribute = meta.attributes[key];
        if (!attribute) {
            continue;
        }
        if (!isRelation(attribute.type)) {
            continue;
        }
        // Make sure to query the join column value if needed,
        // so that we can apply the populate later on
        if ('joinColumn' in attribute && attribute.joinColumn) {
            qb.addSelect(attribute.joinColumn.name);
        }
        // Make sure id is present for future populate queries
        if (_.has('id', meta.attributes)) {
            qb.addSelect('id');
        }
        finalPopulate[key] = populateMap[key];
    }
    return finalPopulate;
};

export { processPopulate as default };
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