const pump = require('pump');
const papaparse = require('papaparse');
const fs = require('fs-extra');

/**
 * 
 * @param {string} path - The path to the CSV to prepare
 * @param {Object.<string, string>} headerMapping - An object whose keys are headers in the input CSV and values are the header to replace it with
 * @param {Array<string>} [defaultLabels] - A list of labels to apply to every parsed member row
 * @returns 
 */
module.exports = (path, headerMapping, defaultLabels = []) => {
    return new Promise(function (resolve, reject) {
        const csvFileStream = fs.createReadStream(path);
        const csvParserStream = papaparse.parse(papaparse.NODE_STREAM_INPUT, {
            header: true,
            transformHeader(_header) {
                const cleanHeader = _header.replace(papaparse.BYTE_ORDER_MARK, ''); //Removing BOM characters for Unicode-based encodings
                if (!headerMapping || !Reflect.has(headerMapping, cleanHeader)) {
                    return undefined;
                }
                return headerMapping[cleanHeader];
            },
            transform(value, header) {
                if (header === 'labels') {
                    if (value && typeof value === 'string') {
                        return value.split(',').map(name => ({name}));
                    }
                }

                if (header === 'subscribed') {
                    return value.toLowerCase() !== 'false';
                }

                if (header === 'complimentary_plan') {
                    return value.toLowerCase() === 'true';
                }

                if (value === '') {
                    return null;
                }

                if (value === 'undefined') {
                    return null;
                }

                if (value.toLowerCase() === 'false') {
                    return false;
                }

                if (value.toLowerCase() === 'true') {
                    return true;
                }

                return value;
            }
        });

        const rows = [];
        const parsedCSVStream = pump(csvFileStream, csvParserStream, (err) => {
            if (err) {
                return reject(err);
            }
            resolve(rows);
        });

        parsedCSVStream.on('data', (row) => {
            // unmapped columns end up being assigned to 'undefined' property
            // in the transformHeader stage, those should be removed completely
            if (Reflect.has(row, 'undefined')) {
                delete row.undefined;
            }

            // skip a rows with no data
            if (!Object.keys(row).length){
                return;
            }

            if (row.labels) {
                row.labels = row.labels.concat(defaultLabels);
            } else {
                row.labels = defaultLabels;
            }

            rows.push(row);
        });
    });
};