A simple CSV parser

CSVParser.swift

/// Parses a csv string and returns a 2d array.
///
/// Size of the array will be equal to the number of rows.
/// And Size of the subarray will be equal to the
/// number of fields.
///
/// Note: Delimiter can be changed to a different character
/// like semicolon.
func parse(string: String, delimiter: Character = ",") -> [[String]]{

    let rows = string.split(separator: "\n")
    let commaSeparatedValues =
        rows.map {
            $0
                .split(separator: String(delimiter))
                .map { String($0) }
    }
    return commaSeparatedValues
}

extension String {

    /// Splits a string into an array of subsequences
    /// using a separator.
    ///
    /// Note: Separator is ignored inside enclosure characters.
    func split(separator: String, enclosure: Character = "\"") -> [String] {
        var values: [String] = []
        // Index of the last processed separator
        var lastSeparatorIndex = startIndex
        var isInsideDoubleQuotes = false

        for index in 0..<count {
            let substringStartIndex = self.index(startIndex, offsetBy: index)
            let substringEndIndex = self.index(substringStartIndex, offsetBy: separator.count)

            guard index < count - separator.count else {
                // No more separators
                // Add remaining characters
                values.append(String(self[lastSeparatorIndex..<endIndex]))
                break
            }
            let substring = self[substringStartIndex..<substringEndIndex]

            if substring == separator && !isInsideDoubleQuotes {
                let newstr = String(self[lastSeparatorIndex..<substringStartIndex])
                values.append(newstr)
                lastSeparatorIndex = substringEndIndex
            } else if self[substringStartIndex] == enclosure {
                isInsideDoubleQuotes = !isInsideDoubleQuotes
            }
        }
        return values
    }
}

CSVParserTests.swift

class CSVParserTests: XCTestCase {

    func testSingleLineString() {
        let sampleText = "john,UK,2000"
        XCTAssertEqual(
            parse(string: sampleText),
            [["john", "UK", "2000"]])
    }

    func testMultiLineString() {
        let sampleText = """
                            john,UK,2000
                            jack,UK,2005
                            """
        XCTAssertEqual(
            parse(string: sampleText),
            [["john", "UK", "2000"],["jack", "UK", "2005"]])
    }

    func testSingleLineStringWithDoubleQuotes() {
        let sampleText = "\"john, last\",UK,2000"
        XCTAssertEqual(
            parse(string: sampleText),
            [["\"john, last\"", "UK", "2000"]])
    }

    func testMultiLineStringWithDoubleQuotes() {
        let sampleText = """
                            john,UK,2000
                            jack,UK,2005
                            "natasha
                             obama",UK,2009
                            """
        XCTAssertEqual(parse(string: sampleText), [
            ["john", "UK", "2000"],
            ["jack", "UK", "2005"],
            ["\"natasha\n obama\"","UK","2009"]])
    }

    func testStringWithDoubleQuoteInsideDoubleQuotes() {
        let sampleText = "\"aaa\",\"b\"\"bb\",\"ccc\""
        XCTAssertEqual(
            parse(string: sampleText),
            [["\"aaa\"", "\"b\"\"bb\"", "\"ccc\""]])
    }

    func testStringWithWhiteSpace() {
        let sampleText = " aaa, bbb, ccc"
        XCTAssertEqual(
            parse(string: sampleText),
            [[" aaa", " bbb", " ccc"]])
    }

    func testStringWithSingleValue() {
        XCTAssertEqual(parse(string: "UK"), [["UK"]])
    }

    func testStringWithEmptyValue() {
        XCTAssertEqual(parse(string: ""), [])
    }
}