apiFeatures.js

class ApiFeatures {
    constructor(query, queryStr) {
        this.query = query;
        this.queryStr = queryStr;
    }

    // Search Feature
    search() {
        const keyword = this.queryStr.keyword ? {
            name: {
                $regex: this.queryStr.keyword,
                $options: "i", //Case insensitive M and m are same 
            }
        } : {};

        this.query = this.query.find({ ...keyword });
        return this;
    }

    // filter feature
    filter() {
        // const queryCopy = this.queryStr 
        // this will take the exact reference , changing one will change the other too, so we will use spread operator
        const queryCopy = { ...this.queryStr };
        // Removing some fields for category
        const removeFields = ["keyword", "page", "limit"];
        removeFields.forEach(key => delete queryCopy[key]);

        // Filter for price and rating
        let queryStr = JSON.stringify(queryCopy);
        queryStr = queryStr.replace(/\b(gt|gte|lt|lte)\b/g, key => `$${key}`);

        this.query = this.query.find(JSON.parse(queryStr));
        return this;
    }
    // categories can be case sensitive cauz user will not search for the category he/she will choose from the given ones

    // Pagination
    pagination(resultPerPage) {
        const currentPage = Number(this.queryStr.page) || 1;
        const skip = resultPerPage * (currentPage - 1);

        this.query = this.query.limit(resultPerPage).skip(skip);
        return this;
    }
}

module.exports = ApiFeatures;