#![cfg(not(target_arch = "wasm32"))]

use std::mem::MaybeUninit;
use std::str;

use core::num::flt2dec::strategy::grisu::format_exact_opt;
use core::num::flt2dec::strategy::grisu::format_shortest_opt;
use core::num::flt2dec::MAX_SIG_DIGITS;
use core::num::flt2dec::{decode, DecodableFloat, Decoded, FullDecoded};

use rand::distributions::{Distribution, Uniform};
use rand::rngs::StdRng;
use rand::SeedableRng;

pub fn decode_finite<T: DecodableFloat>(v: T) -> Decoded {
    match decode(v).1 {
        FullDecoded::Finite(decoded) => decoded,
        full_decoded => panic!("expected finite, got {full_decoded:?} instead"),
    }
}

fn iterate<F, G, V>(func: &str, k: usize, n: usize, mut f: F, mut g: G, mut v: V) -> (usize, usize)
where
    F: for<'a> FnMut(&Decoded, &'a mut [MaybeUninit<u8>]) -> Option<(&'a [u8], i16)>,
    G: for<'a> FnMut(&Decoded, &'a mut [MaybeUninit<u8>]) -> (&'a [u8], i16),
    V: FnMut(usize) -> Decoded,
{
    assert!(k <= 1024);

    let mut npassed = 0; // f(x) = Some(g(x))
    let mut nignored = 0; // f(x) = None

    for i in 0..n {
        if (i & 0xfffff) == 0 {
            println!(
                "in progress, {:x}/{:x} (ignored={} passed={} failed={})",
                i,
                n,
                nignored,
                npassed,
                i - nignored - npassed
            );
        }

        let decoded = v(i);
        let mut buf1 = [MaybeUninit::new(0); 1024];
        if let Some((buf1, e1)) = f(&decoded, &mut buf1[..k]) {
            let mut buf2 = [MaybeUninit::new(0); 1024];
            let (buf2, e2) = g(&decoded, &mut buf2[..k]);
            if e1 == e2 && buf1 == buf2 {
                npassed += 1;
            } else {
                println!(
                    "equivalence test failed, {:x}/{:x}: {:?} f(i)={}e{} g(i)={}e{}",
                    i,
                    n,
                    decoded,
                    str::from_utf8(buf1).unwrap(),
                    e1,
                    str::from_utf8(buf2).unwrap(),
                    e2
                );
            }
        } else {
            nignored += 1;
        }
    }
    println!(
        "{}({}): done, ignored={} passed={} failed={}",
        func,
        k,
        nignored,
        npassed,
        n - nignored - npassed
    );
    assert!(
        nignored + npassed == n,
        "{}({}): {} out of {} values returns an incorrect value!",
        func,
        k,
        n - nignored - npassed,
        n
    );
    (npassed, nignored)
}

pub fn f32_random_equivalence_test<F, G>(f: F, g: G, k: usize, n: usize)
where
    F: for<'a> FnMut(&Decoded, &'a mut [MaybeUninit<u8>]) -> Option<(&'a [u8], i16)>,
    G: for<'a> FnMut(&Decoded, &'a mut [MaybeUninit<u8>]) -> (&'a [u8], i16),
{
    if cfg!(target_os = "emscripten") {
        return; // using rng pulls in i128 support, which doesn't work
    }
    let mut rng = StdRng::from_entropy();
    let f32_range = Uniform::new(0x0000_0001u32, 0x7f80_0000);
    iterate("f32_random_equivalence_test", k, n, f, g, |_| {
        let x = f32::from_bits(f32_range.sample(&mut rng));
        decode_finite(x)
    });
}

pub fn f64_random_equivalence_test<F, G>(f: F, g: G, k: usize, n: usize)
where
    F: for<'a> FnMut(&Decoded, &'a mut [MaybeUninit<u8>]) -> Option<(&'a [u8], i16)>,
    G: for<'a> FnMut(&Decoded, &'a mut [MaybeUninit<u8>]) -> (&'a [u8], i16),
{
    if cfg!(target_os = "emscripten") {
        return; // using rng pulls in i128 support, which doesn't work
    }
    let mut rng = StdRng::from_entropy();
    let f64_range = Uniform::new(0x0000_0000_0000_0001u64, 0x7ff0_0000_0000_0000);
    iterate("f64_random_equivalence_test", k, n, f, g, |_| {
        let x = f64::from_bits(f64_range.sample(&mut rng));
        decode_finite(x)
    });
}

pub fn f32_exhaustive_equivalence_test<F, G>(f: F, g: G, k: usize)
where
    F: for<'a> FnMut(&Decoded, &'a mut [MaybeUninit<u8>]) -> Option<(&'a [u8], i16)>,
    G: for<'a> FnMut(&Decoded, &'a mut [MaybeUninit<u8>]) -> (&'a [u8], i16),
{
    // we have only 2^23 * (2^8 - 1) - 1 = 2,139,095,039 positive finite f32 values,
    // so why not simply testing all of them?
    //
    // this is of course very stressful (and thus should be behind an `#[ignore]` attribute),
    // but with `-C opt-level=3 -C lto` this only takes about an hour or so.

    // iterate from 0x0000_0001 to 0x7f7f_ffff, i.e., all finite ranges
    let (npassed, nignored) =
        iterate("f32_exhaustive_equivalence_test", k, 0x7f7f_ffff, f, g, |i: usize| {
            let x = f32::from_bits(i as u32 + 1);
            decode_finite(x)
        });
    assert_eq!((npassed, nignored), (2121451881, 17643158));
}

#[test]
fn shortest_random_equivalence_test() {
    use core::num::flt2dec::strategy::dragon::format_shortest as fallback;
    // Miri is too slow
    let n = if cfg!(miri) { 10 } else { 10_000 };

    f64_random_equivalence_test(format_shortest_opt, fallback, MAX_SIG_DIGITS, n);
    f32_random_equivalence_test(format_shortest_opt, fallback, MAX_SIG_DIGITS, n);
}

#[test]
#[ignore] // it is too expensive
fn shortest_f32_exhaustive_equivalence_test() {
    // it is hard to directly test the optimality of the output, but we can at least test if
    // two different algorithms agree to each other.
    //
    // this reports the progress and the number of f32 values returned `None`.
    // with `--nocapture` (and plenty of time and appropriate rustc flags), this should print:
    // `done, ignored=17643158 passed=2121451881 failed=0`.

    use core::num::flt2dec::strategy::dragon::format_shortest as fallback;
    f32_exhaustive_equivalence_test(format_shortest_opt, fallback, MAX_SIG_DIGITS);
}

#[test]
#[ignore] // it is too expensive
fn shortest_f64_hard_random_equivalence_test() {
    // this again probably has to use appropriate rustc flags.

    use core::num::flt2dec::strategy::dragon::format_shortest as fallback;
    f64_random_equivalence_test(format_shortest_opt, fallback, MAX_SIG_DIGITS, 100_000_000);
}

#[test]
fn exact_f32_random_equivalence_test() {
    use core::num::flt2dec::strategy::dragon::format_exact as fallback;
    // Miri is too slow
    let n = if cfg!(miri) { 3 } else { 1_000 };

    for k in 1..21 {
        f32_random_equivalence_test(
            |d, buf| format_exact_opt(d, buf, i16::MIN),
            |d, buf| fallback(d, buf, i16::MIN),
            k,
            n,
        );
    }
}

#[test]
fn exact_f64_random_equivalence_test() {
    use core::num::flt2dec::strategy::dragon::format_exact as fallback;
    // Miri is too slow
    let n = if cfg!(miri) { 2 } else { 1_000 };

    for k in 1..21 {
        f64_random_equivalence_test(
            |d, buf| format_exact_opt(d, buf, i16::MIN),
            |d, buf| fallback(d, buf, i16::MIN),
            k,
            n,
        );
    }
}