use core::array;
use core::convert::TryFrom;
use core::sync::atomic::{AtomicUsize, Ordering};

#[test]
fn array_from_ref() {
    let value: String = "Hello World!".into();
    let arr: &[String; 1] = array::from_ref(&value);
    assert_eq!(&[value.clone()], arr);
}

#[test]
fn array_from_mut() {
    let mut value: String = "Hello World".into();
    let arr: &mut [String; 1] = array::from_mut(&mut value);
    arr[0].push_str("!");
    assert_eq!(&value, "Hello World!");
}

#[test]
fn array_try_from() {
    macro_rules! test {
        ($($N:expr)+) => {
            $({
                type Array = [u8; $N];
                let array: Array = [0; $N];
                let slice: &[u8] = &array[..];

                let result = <&Array>::try_from(slice);
                assert_eq!(&array, result.unwrap());
            })+
        }
    }
    test! {
         0  1  2  3  4  5  6  7  8  9
        10 11 12 13 14 15 16 17 18 19
        20 21 22 23 24 25 26 27 28 29
        30 31 32
    }
}

#[test]
fn iterator_collect() {
    let arr = [0, 1, 2, 5, 9];
    let v: Vec<_> = IntoIterator::into_iter(arr.clone()).collect();
    assert_eq!(&arr[..], &v[..]);
}

#[test]
fn iterator_rev_collect() {
    let arr = [0, 1, 2, 5, 9];
    let v: Vec<_> = IntoIterator::into_iter(arr.clone()).rev().collect();
    assert_eq!(&v[..], &[9, 5, 2, 1, 0]);
}

#[test]
fn iterator_nth() {
    let v = [0, 1, 2, 3, 4];
    for i in 0..v.len() {
        assert_eq!(IntoIterator::into_iter(v.clone()).nth(i).unwrap(), v[i]);
    }
    assert_eq!(IntoIterator::into_iter(v.clone()).nth(v.len()), None);

    let mut iter = IntoIterator::into_iter(v);
    assert_eq!(iter.nth(2).unwrap(), v[2]);
    assert_eq!(iter.nth(1).unwrap(), v[4]);
}

#[test]
fn iterator_last() {
    let v = [0, 1, 2, 3, 4];
    assert_eq!(IntoIterator::into_iter(v).last().unwrap(), 4);
    assert_eq!(IntoIterator::into_iter([0]).last().unwrap(), 0);

    let mut it = IntoIterator::into_iter([0, 9, 2, 4]);
    assert_eq!(it.next_back(), Some(4));
    assert_eq!(it.last(), Some(2));
}

#[test]
fn iterator_clone() {
    let mut it = IntoIterator::into_iter([0, 2, 4, 6, 8]);
    assert_eq!(it.next(), Some(0));
    assert_eq!(it.next_back(), Some(8));
    let mut clone = it.clone();
    assert_eq!(it.next_back(), Some(6));
    assert_eq!(clone.next_back(), Some(6));
    assert_eq!(it.next_back(), Some(4));
    assert_eq!(clone.next_back(), Some(4));
    assert_eq!(it.next(), Some(2));
    assert_eq!(clone.next(), Some(2));
}

#[test]
fn iterator_fused() {
    let mut it = IntoIterator::into_iter([0, 9, 2]);
    assert_eq!(it.next(), Some(0));
    assert_eq!(it.next(), Some(9));
    assert_eq!(it.next(), Some(2));
    assert_eq!(it.next(), None);
    assert_eq!(it.next(), None);
    assert_eq!(it.next(), None);
    assert_eq!(it.next(), None);
    assert_eq!(it.next(), None);
}

#[test]
fn iterator_len() {
    let mut it = IntoIterator::into_iter([0, 1, 2, 5, 9]);
    assert_eq!(it.size_hint(), (5, Some(5)));
    assert_eq!(it.len(), 5);
    assert_eq!(it.is_empty(), false);

    assert_eq!(it.next(), Some(0));
    assert_eq!(it.size_hint(), (4, Some(4)));
    assert_eq!(it.len(), 4);
    assert_eq!(it.is_empty(), false);

    assert_eq!(it.next_back(), Some(9));
    assert_eq!(it.size_hint(), (3, Some(3)));
    assert_eq!(it.len(), 3);
    assert_eq!(it.is_empty(), false);

    // Empty
    let it = IntoIterator::into_iter([] as [String; 0]);
    assert_eq!(it.size_hint(), (0, Some(0)));
    assert_eq!(it.len(), 0);
    assert_eq!(it.is_empty(), true);
}

#[test]
fn iterator_count() {
    let v = [0, 1, 2, 3, 4];
    assert_eq!(IntoIterator::into_iter(v.clone()).count(), 5);

    let mut iter2 = IntoIterator::into_iter(v);
    iter2.next();
    iter2.next();
    assert_eq!(iter2.count(), 3);
}

#[test]
fn iterator_flat_map() {
    assert!((0..5).flat_map(|i| IntoIterator::into_iter([2 * i, 2 * i + 1])).eq(0..10));
}

#[test]
fn iterator_debug() {
    let arr = [0, 1, 2, 5, 9];
    assert_eq!(format!("{:?}", IntoIterator::into_iter(arr)), "IntoIter([0, 1, 2, 5, 9])",);
}

#[test]
fn iterator_drops() {
    use core::cell::Cell;

    // This test makes sure the correct number of elements are dropped. The `R`
    // type is just a reference to a `Cell` that is incremented when an `R` is
    // dropped.

    #[derive(Clone)]
    struct Foo<'a>(&'a Cell<usize>);

    impl Drop for Foo<'_> {
        fn drop(&mut self) {
            self.0.set(self.0.get() + 1);
        }
    }

    fn five(i: &Cell<usize>) -> [Foo<'_>; 5] {
        // This is somewhat verbose because `Foo` does not implement `Copy`
        // since it implements `Drop`. Consequently, we cannot write
        // `[Foo(i); 5]`.
        [Foo(i), Foo(i), Foo(i), Foo(i), Foo(i)]
    }

    // Simple: drop new iterator.
    let i = Cell::new(0);
    {
        IntoIterator::into_iter(five(&i));
    }
    assert_eq!(i.get(), 5);

    // Call `next()` once.
    let i = Cell::new(0);
    {
        let mut iter = IntoIterator::into_iter(five(&i));
        let _x = iter.next();
        assert_eq!(i.get(), 0);
        assert_eq!(iter.count(), 4);
        assert_eq!(i.get(), 4);
    }
    assert_eq!(i.get(), 5);

    // Check `clone` and calling `next`/`next_back`.
    let i = Cell::new(0);
    {
        let mut iter = IntoIterator::into_iter(five(&i));
        iter.next();
        assert_eq!(i.get(), 1);
        iter.next_back();
        assert_eq!(i.get(), 2);

        let mut clone = iter.clone();
        assert_eq!(i.get(), 2);

        iter.next();
        assert_eq!(i.get(), 3);

        clone.next();
        assert_eq!(i.get(), 4);

        assert_eq!(clone.count(), 2);
        assert_eq!(i.get(), 6);
    }
    assert_eq!(i.get(), 8);

    // Check via `nth`.
    let i = Cell::new(0);
    {
        let mut iter = IntoIterator::into_iter(five(&i));
        let _x = iter.nth(2);
        assert_eq!(i.get(), 2);
        let _y = iter.last();
        assert_eq!(i.get(), 3);
    }
    assert_eq!(i.get(), 5);

    // Check every element.
    let i = Cell::new(0);
    for (index, _x) in IntoIterator::into_iter(five(&i)).enumerate() {
        assert_eq!(i.get(), index);
    }
    assert_eq!(i.get(), 5);

    let i = Cell::new(0);
    for (index, _x) in IntoIterator::into_iter(five(&i)).rev().enumerate() {
        assert_eq!(i.get(), index);
    }
    assert_eq!(i.get(), 5);
}

// This test does not work on targets without panic=unwind support.
// To work around this problem, test is marked is should_panic, so it will
// be automagically skipped on unsuitable targets, such as
// wasm32-unknown-unkown.
//
// It means that we use panic for indicating success.
#[test]
#[should_panic(expected = "test succeeded")]
fn array_default_impl_avoids_leaks_on_panic() {
    use core::sync::atomic::{AtomicUsize, Ordering::Relaxed};
    static COUNTER: AtomicUsize = AtomicUsize::new(0);
    #[derive(Debug)]
    struct Bomb(usize);

    impl Default for Bomb {
        fn default() -> Bomb {
            if COUNTER.load(Relaxed) == 3 {
                panic!("bomb limit exceeded");
            }

            COUNTER.fetch_add(1, Relaxed);
            Bomb(COUNTER.load(Relaxed))
        }
    }

    impl Drop for Bomb {
        fn drop(&mut self) {
            COUNTER.fetch_sub(1, Relaxed);
        }
    }

    let res = std::panic::catch_unwind(|| <[Bomb; 5]>::default());
    let panic_msg = match res {
        Ok(_) => unreachable!(),
        Err(p) => p.downcast::<&'static str>().unwrap(),
    };
    assert_eq!(*panic_msg, "bomb limit exceeded");
    // check that all bombs are successfully dropped
    assert_eq!(COUNTER.load(Relaxed), 0);
    panic!("test succeeded")
}

#[test]
fn empty_array_is_always_default() {
    struct DoesNotImplDefault;

    let _arr = <[DoesNotImplDefault; 0]>::default();
}

#[test]
fn array_map() {
    let a = [1, 2, 3];
    let b = a.map(|v| v + 1);
    assert_eq!(b, [2, 3, 4]);

    let a = [1u8, 2, 3];
    let b = a.map(|v| v as u64);
    assert_eq!(b, [1, 2, 3]);
}

// See note on above test for why `should_panic` is used.
#[test]
#[should_panic(expected = "test succeeded")]
fn array_map_drop_safety() {
    static DROPPED: AtomicUsize = AtomicUsize::new(0);
    struct DropCounter;
    impl Drop for DropCounter {
        fn drop(&mut self) {
            DROPPED.fetch_add(1, Ordering::SeqCst);
        }
    }

    let num_to_create = 5;
    let success = std::panic::catch_unwind(|| {
        let items = [0; 10];
        let mut nth = 0;
        items.map(|_| {
            assert!(nth < num_to_create);
            nth += 1;
            DropCounter
        });
    });
    assert!(success.is_err());
    assert_eq!(DROPPED.load(Ordering::SeqCst), num_to_create);
    panic!("test succeeded")
}

#[test]
fn cell_allows_array_cycle() {
    use core::cell::Cell;

    #[derive(Debug)]
    struct B<'a> {
        a: [Cell<Option<&'a B<'a>>>; 2],
    }

    impl<'a> B<'a> {
        fn new() -> B<'a> {
            B { a: [Cell::new(None), Cell::new(None)] }
        }
    }

    let b1 = B::new();
    let b2 = B::new();
    let b3 = B::new();

    b1.a[0].set(Some(&b2));
    b1.a[1].set(Some(&b3));

    b2.a[0].set(Some(&b2));
    b2.a[1].set(Some(&b3));

    b3.a[0].set(Some(&b1));
    b3.a[1].set(Some(&b2));
}

#[test]
fn array_from_fn() {
    let array = core::array::from_fn(|idx| idx);
    assert_eq!(array, [0, 1, 2, 3, 4]);
}

#[test]
fn array_try_from_fn() {
    #[derive(Debug, PartialEq)]
    enum SomeError {
        Foo,
    }

    let array = core::array::try_from_fn(|i| Ok::<_, SomeError>(i));
    assert_eq!(array, Ok([0, 1, 2, 3, 4]));

    let another_array = core::array::try_from_fn::<SomeError, _, (), 2>(|_| Err(SomeError::Foo));
    assert_eq!(another_array, Err(SomeError::Foo));
}

#[cfg(not(panic = "abort"))]
#[test]
fn array_try_from_fn_drops_inserted_elements_on_err() {
    static DROP_COUNTER: AtomicUsize = AtomicUsize::new(0);

    struct CountDrop;
    impl Drop for CountDrop {
        fn drop(&mut self) {
            DROP_COUNTER.fetch_add(1, Ordering::SeqCst);
        }
    }

    let _ = catch_unwind_silent(move || {
        let _: Result<[CountDrop; 4], ()> = core::array::try_from_fn(|idx| {
            if idx == 2 {
                return Err(());
            }
            Ok(CountDrop)
        });
    });

    assert_eq!(DROP_COUNTER.load(Ordering::SeqCst), 2);
}

#[cfg(not(panic = "abort"))]
#[test]
fn array_try_from_fn_drops_inserted_elements_on_panic() {
    static DROP_COUNTER: AtomicUsize = AtomicUsize::new(0);

    struct CountDrop;
    impl Drop for CountDrop {
        fn drop(&mut self) {
            DROP_COUNTER.fetch_add(1, Ordering::SeqCst);
        }
    }

    let _ = catch_unwind_silent(move || {
        let _: Result<[CountDrop; 4], ()> = core::array::try_from_fn(|idx| {
            if idx == 2 {
                panic!("peek a boo");
            }
            Ok(CountDrop)
        });
    });

    assert_eq!(DROP_COUNTER.load(Ordering::SeqCst), 2);
}

// https://stackoverflow.com/a/59211505
fn catch_unwind_silent<F, R>(f: F) -> std::thread::Result<R>
where
    F: FnOnce() -> R + core::panic::UnwindSafe,
{
    let prev_hook = std::panic::take_hook();
    std::panic::set_hook(Box::new(|_| {}));
    let result = std::panic::catch_unwind(f);
    std::panic::set_hook(prev_hook);
    result
}