use prime_factors::*;

#[test]
fn zero() {
    let factors = factors(0);
    let expected = [];
    assert_eq!(factors, expected);
}

#[test]
fn no_factors() {
    let factors = factors(1);
    let expected = [];
    assert_eq!(factors, expected);
}

#[test]
fn prime_number() {
    let factors = factors(2);
    let expected = [2];
    assert_eq!(factors, expected);
}

#[test]
fn another_prime_number() {
    let factors = factors(3);
    let expected = [3];
    assert_eq!(factors, expected);
}

#[test]
fn square_of_a_prime() {
    let factors = factors(9);
    let expected = [3, 3];
    assert_eq!(factors, expected);
}

#[test]
fn product_of_first_prime() {
    let factors = factors(4);
    let expected = [2, 2];
    assert_eq!(factors, expected);
}

#[test]
fn cube_of_a_prime() {
    let factors = factors(8);
    let expected = [2, 2, 2];
    assert_eq!(factors, expected);
}

#[test]
fn product_of_second_prime() {
    let factors = factors(27);
    let expected = [3, 3, 3];
    assert_eq!(factors, expected);
}

#[test]
fn product_of_third_prime() {
    let factors = factors(625);
    let expected = [5, 5, 5, 5];
    assert_eq!(factors, expected);
}

#[test]
fn product_of_first_and_second_prime() {
    let factors = factors(6);
    let expected = [2, 3];
    assert_eq!(factors, expected);
}

#[test]
fn product_of_primes_and_non_primes() {
    let factors = factors(12);
    let expected = [2, 2, 3];
    assert_eq!(factors, expected);
}

#[test]
fn product_of_primes() {
    let factors = factors(901_255);
    let expected = [5, 17, 23, 461];
    assert_eq!(factors, expected);
}

#[test]
fn factors_include_a_large_prime() {
    let factors = factors(93_819_012_551);
    let expected = [11, 9_539, 894_119];
    assert_eq!(factors, expected);
}

#[test]
fn large_pow2() {
    let factors = factors(1 << 32);
    let expected = [2; 32];
    assert_eq!(factors, expected);
}

#[test]
fn fuzz() {
    for i in 1..(1 << 16) {
        let factors = factors(i);
        assert!(factors.iter().all(|x| is_prime(*x)), "{factors:?} of {i} are not all prime");
        let product: u64 = factors.iter().product();
        assert_eq!(product, i);
    }
}

fn is_prime(n: u64) -> bool {
    (2..=isqrt(n)).all(|x| n % x != 0)
}

fn isqrt(n: u64) -> u64 {
    (n as f64).sqrt() as _
}