var Promise = require('bluebird'),
    csvParser = require('csv-parser'),
    _ = require('lodash'),
    fs = require('fs');

function readCSV(options) {
    var columnsToExtract = options.columnsToExtract || [],
        results = [], rows = [];

    return new Promise(function (resolve, reject) {
        var readFile = fs.createReadStream(options.path);

        readFile.on('err', function (err) {
            reject(err);
        })
        .pipe(csvParser())
        .on('data', function (row) {
            rows.push(row);
        })
        .on('end', function () {
            // If CSV is single column - return all values including header
            var headers = _.keys(rows[0]), result = {}, columnMap = {};
            if (columnsToExtract.length === 1 && headers.length === 1) {
                results = _.map(rows, function (value) {
                    result = {};
                    result[columnsToExtract[0].name] = value[headers[0]];
                    return result;
                });

                // Add first row
                result = {};
                result[columnsToExtract[0].name] = headers[0];
                results = [result].concat(results);
            } else {
                // If there are multiple columns in csv file
                // try to match headers using lookup value

                _.map(columnsToExtract, function findMatches(column) {
                    _.each(headers, function checkheader(header) {
                        if (column.lookup.test(header)) {
                            columnMap[column.name] = header;
                        }
                    });
                });

                results = _.map(rows, function evaluateRow(row) {
                    var result = {};
                    _.each(columnMap, function returnMatches(value, key) {
                        result[key] = row[value];
                    });
                    return result;
                });
            }
            resolve(results);
        });
    });
}

module.exports = readCSV;