ComplexCsvParser.js

/**
 * We need valid CSV parser!
 *
 * A CSV (Comma-Separated Values) file is a file that represents tabular data in a simple,
 * text-only manner. At it's simplest, a CSV file contains rows of data separated by newlines,
 * and each field is separated by commas.
 *
 * This parser needs to not only handle CSVs using commas to delimit fields, but it also needs
 * to handle complex field values (which may be wrapped in quotes, and may span multiple lines),
 * and also different delimiters and quote characters.
 *
 * ###Examples
 *
 * A simple CSV would look like this:
 *
 * a,b,c
 * d,e,f
 * which should parse to:
 *
 * [['a', 'b', 'c'], ['d', 'e', 'f']
 * While a more complex one might be:
 *
 * one,"two wraps
 * onto ""two"" lines",three
 * 4,,6
 * that becomes
 *
 * [['one', 'two wraps\nonto "two" lines', 'three'], ['4', '', '6']]
 * ##Specification:
 *
 * Basics
 *
 * The parser should return an array of arrays, one array for each row of the CSV file
 * (not necessarily each line of text!).
 * Rows are delimited by the newline character ("\n").
 * Each row is divided by a separator character, by default the comma (,).
 * All characters between separators are part of the value — do not trim the field value.
 * Fields are assumed to be strings — don't convert them to numbers or other types in this kata.
 * Empty fields are valid — don't discard empty values at the beginning, middle or end of a row.
 * These should be included as an empty string.
 * Likewise, an empty row is still valid, and effectively contains a single empty field.
 * For this kata, expect uneven rows. Just include the actual fields in each row, even if the rows
 * have a different number of fields.
 * Quoted Fields
 *
 * The parser should handle quoted fields.
 * A quoted field starts and ends with the same character, and every character in between makes up
 * the field value, including separator characters. The default quote character is a double quote (").
 * Quoted fields may span multiple lines — don't assume a newline means a new row!
 * Quoted fields only start immediately following a separator character, newline,
 * or start of the file. If a quote character occurs anywhere else,
 * it should be treated as a normal field value.
 * They should be immediately followed by a separator, newline, or the end of the file.
 * If a quote character occurs within a quoted field, it is simply doubled.
 * For example, the value foo "bar" baz will be encoded as "foo ""bar"" baz".
 * The parser should identify and unescape these values.
 * You should check for unclosed quoted fields, and throw an error, but this is not tested here.
 * Alternate Characters
 *
 * The parser should handle alternate characters for the separator and quote.
 * You may safely assume that the values provided are a single character,
 * but bonus points for error checking.
 */
function parseCSV(input, separator = ',', quote = '"') {
    const newString = []
        , newLine = '\n'
        , specialCharacters = '$\\'
        , quoteRegStr = specialCharacters.indexOf(quote) > -1
        ? '\\' + quote + '\\' + quote
        : quote + quote

    let tempWord = ''
        , char = ''
        , tmp = []
        , pos
        , replaceRegEx = new RegExp(quoteRegStr, 'g')
        , replaceQuotes = function (str) {
        const self = str + ''
        let replaced = self.replace(replaceRegEx, quote)
        if (replaced[0] === quote) {
            replaced = replaced.slice(1)
        }
        if (replaced[replaced.length - 1] === quote) {
            replaced = replaced.slice(0, self.length - 1)
        }
        return replaced
    }
        , pushResult = () => {
        newString.push(tmp)
        tmp = []
    }

    const addCurrentChar = function (i = 1, push = true) {
        const part = input.slice(0, pos)
        tmp.push(replaceQuotes(part))
        if (push) {
            pushResult()
        }
        input = input.slice(pos + i)
    }

    while (input.length) {
        char = input[0]
        if (char === quote) {
            pos = input.indexOf(quote + separator, 1)
            if (pos === -1) {
                pos = input.indexOf(quote + newLine, 1)
                if (pos === -1) {
                    pos = input.indexOf(quote, 1)
                    addCurrentChar()
                } else {
                    addCurrentChar(2)
                }
            } else {
                addCurrentChar(2, false)
            }
        } else if (char === separator || char === newLine) {
            tmp.push(tempWord)
            tempWord = ''
            input = input.slice(1)
            if (char === newLine) {
                pushResult()
            }
        } else {
            tempWord += char
            input = input.slice(1)
        }
    }

    if (tmp.length > 0) {
        tmp.push(tempWord)
        newString.push(tmp)
    }
    return newString.length === 0
        ? [[""]]
        : newString
}