import XCTest
@testable import FunctionalKata

class FunctionalKataTests: XCTestCase {

    // Create a function to count the elements contained in a list
    func count(list: [Any?]) -> Int {
        if let _ = list.first {
            let tail = Array(list.dropFirst())
            return 1 + count(list: tail)
        }
        return 0
    }

    func sum(_ list: [Int]) -> Int {
        return list.reduce(0, +)
    }

    // Sample implementation of +
    func plus(_ left: Int, _ right: Int) -> Int { return left + right }

    func testListOfNilValues_Count_ReturnsNumberOfNilValues() {
        let list: [String?] = [nil, nil]
        XCTAssertEqual(count(list: list), 2)
    }

    func testEmptyList_Count_ReturnsZero() {
        XCTAssertEqual(count(list: [String]()), 0)
    }

    func testListOneElement_Count_ReturnsOne() {
        XCTAssertEqual(count(list: ["element"]), 1)
    }

    func testListTwoElements_Count_ReturnsTwo() {
        XCTAssertEqual(count(list: ["element", "anotherElement"]), 2)
    }

    func testSumZeroToZero_ReturnsZero() {
        XCTAssertEqual(sum([]), 0)
    }

    func testSum123Returns6() {
        XCTAssertEqual(sum([1,2,3]), 6)
    }

    func testSumMinusOneToOne_Returns0() {
        XCTAssertEqual(sum([-1,1]), 0)
    }

    func test1Plus2_Returns3() {
        XCTAssertEqual(plus(1,2), 3)
    }
}