//! A simple variant of the API, that expects an array of `[usize; N]` indices.
//!
//! The array has to be sorted, and each element unique. This ensures that
//! only `N` comparisons are needed at runtime to verify the indices are in bounds.

#[inline]
fn check_indices_valid(indices: &[usize], len: usize) -> bool {
    let mut valid = true;

    for &[a, b] in indices.array_windows() {
        valid &= a < b;
    }

    if let Some(&idx) = indices.last() {
        valid &= idx < len;
    }

    valid
}

pub unsafe fn index_many_unchecked<'a, T, const N: usize>(
    slice: &'a [T],
    indices: [usize; N],
) -> [&'a T; N] {
    crate::get_many_internal(slice, indices)
}

pub unsafe fn index_many_mut_unchecked<'a, T, const N: usize>(
    slice: &'a mut [T],
    indices: [usize; N],
) -> [&'a mut T; N] {
    crate::get_many_internal_mut(slice, indices)
}

pub fn get_many<'a, T, const N: usize>(slice: &[T], indices: [usize; N]) -> Option<[&T; N]> {
    if !check_indices_valid(&indices, slice.len()) {
        return None;
    }
    unsafe { Some(index_many_unchecked(slice, indices)) }
}

pub fn get_many_mut<'a, T, const N: usize>(
    slice: &mut [T],
    indices: [usize; N],
) -> Option<[&mut T; N]> {
    if !check_indices_valid(&indices, slice.len()) {
        return None;
    }
    unsafe { Some(index_many_mut_unchecked(slice, indices)) }
}

pub fn index_many<'a, T, const N: usize>(slice: &[T], indices: [usize; N]) -> [&T; N] {
    let len = slice.len();
    match get_many(slice, indices) {
        Some(s) => s,
        None => {
            let tmp = indices;
            crate::sorted_bound_check_failed(&tmp, len)
        }
    }
}

pub fn index_many_mut<'a, T, const N: usize>(slice: &mut [T], indices: [usize; N]) -> [&mut T; N] {
    let len = slice.len();
    match get_many_mut(slice, indices) {
        Some(s) => s,
        None => {
            let tmp = indices;
            crate::sorted_bound_check_failed(&tmp, len)
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_mut_normal() {
        let mut v = vec![1, 2, 3, 4, 5];
        let [a, b, c] = index_many_mut(&mut v, [0, 2, 4]);
        *a += 10;
        *b += 100;
        *c += 1000;
        assert_eq!(v, vec![11, 2, 103, 4, 1005]);
    }

    #[test]
    fn test_ref_normal() {
        let v = vec![1, 2, 3, 4, 5];
        let [a, b, c] = index_many(&v, [0, 2, 4]);
        assert_eq!(a, &1);
        assert_eq!(b, &3);
        assert_eq!(c, &5);
        assert_eq!(v, vec![1, 2, 3, 4, 5]);
    }

    #[test]
    fn test_mut_empty() {
        let mut v = vec![1, 2, 3, 4, 5];
        let [] = index_many_mut(&mut v, []);
        assert_eq!(v, vec![1, 2, 3, 4, 5]);
    }

    #[test]
    fn test_ref_empty() {
        let v = vec![1, 2, 3, 4, 5];
        let [] = index_many(&v, []);
        assert_eq!(v, vec![1, 2, 3, 4, 5]);
    }

    #[test]
    fn test_mut_single_first() {
        let mut v = vec![1, 2, 3, 4, 5];
        let [a] = index_many_mut(&mut v, [0]);
        *a += 10;
        assert_eq!(v, vec![11, 2, 3, 4, 5]);
    }

    #[test]
    fn test_ref_single_first() {
        let v = vec![1, 2, 3, 4, 5];
        let [a] = index_many(&v, [0]);
        assert_eq!(a, &1);
        assert_eq!(v, vec![1, 2, 3, 4, 5]);
    }

    #[test]
    fn test_mut_single_last() {
        let mut v = vec![1, 2, 3, 4, 5];
        let [a] = index_many_mut(&mut v, [4]);
        *a += 10;
        assert_eq!(v, vec![1, 2, 3, 4, 15]);
    }

    #[test]
    fn test_ref_single_last() {
        let v = vec![1, 2, 3, 4, 5];
        let [a] = index_many(&v, [4]);
        assert_eq!(a, &5);
        assert_eq!(v, vec![1, 2, 3, 4, 5]);
    }

    #[test]
    #[should_panic(
        expected = "Index 5 is out of bounds of slice with len 5 (indices [5], position 0)"
    )]
    fn test_mut_oob_nonempty() {
        let mut v = vec![1, 2, 3, 4, 5];
        index_many_mut(&mut v, [5]);
    }

    #[test]
    #[should_panic(
        expected = "Index 5 is out of bounds of slice with len 5 (indices [5], position 0)"
    )]
    fn test_ref_oob_nonempty() {
        let v = vec![1, 2, 3, 4, 5];
        index_many(&v, [5]);
    }

    #[test]
    #[should_panic(
        expected = "Index 0 is out of bounds of slice with len 0 (indices [0], position 0)"
    )]
    fn test_mut_oob_empty() {
        let mut v: Vec<i32> = vec![];
        index_many_mut(&mut v, [0]);
    }

    #[test]
    #[should_panic(
        expected = "Index 0 is out of bounds of slice with len 0 (indices [0], position 0)"
    )]
    fn test_ref_oob_empty() {
        let v: Vec<i32> = vec![];
        index_many(&v, [0]);
    }

    #[test]
    #[should_panic(expected = "Indices [3, 1, 4] are not sorted")]
    fn test_mut_unsorted() {
        let mut v = vec![1, 2, 3, 4, 5];
        index_many_mut(&mut v, [3, 1, 4]);
    }

    #[test]
    #[should_panic(expected = "Indices [3, 1, 4] are not sorted")]
    fn test_ref_unsorted() {
        let v = vec![1, 2, 3, 4, 5];
        index_many(&v, [3, 1, 4]);
    }

    #[test]
    #[should_panic(
        expected = "Index 3 appears more than once (indices [1, 3, 3, 4], position 1 and 2)"
    )]
    fn test_mut_duplicate() {
        let mut v = vec![1, 2, 3, 4, 5];
        index_many_mut(&mut v, [1, 3, 3, 4]);
    }

    #[test]
    #[should_panic(
        expected = "Index 3 appears more than once (indices [1, 3, 3, 4], position 1 and 2)"
    )]
    fn test_ref_duplicate() {
        let v = vec![1, 2, 3, 4, 5];
        index_many(&v, [1, 3, 3, 4]);
    }
}