use core::arch::wasm32::v128;

use crate::memmem::{genericsimd, NeedleInfo};

/// A `v128` accelerated vectorized substring search routine that only works on
/// small needles.
#[derive(Clone, Copy, Debug)]
pub(crate) struct Forward(genericsimd::Forward);

impl Forward {
    /// Create a new "generic simd" forward searcher. If one could not be
    /// created from the given inputs, then None is returned.
    pub(crate) fn new(ninfo: &NeedleInfo, needle: &[u8]) -> Option<Forward> {
        if !cfg!(memchr_runtime_simd) {
            return None;
        }
        genericsimd::Forward::new(ninfo, needle).map(Forward)
    }

    /// Returns the minimum length of haystack that is needed for this searcher
    /// to work. Passing a haystack with a length smaller than this will cause
    /// `find` to panic.
    #[inline(always)]
    pub(crate) fn min_haystack_len(&self) -> usize {
        self.0.min_haystack_len::<v128>()
    }

    #[inline(always)]
    pub(crate) fn find(
        &self,
        haystack: &[u8],
        needle: &[u8],
    ) -> Option<usize> {
        self.find_impl(haystack, needle)
    }

    /// The implementation of find marked with the appropriate target feature.
    #[target_feature(enable = "simd128")]
    fn find_impl(&self, haystack: &[u8], needle: &[u8]) -> Option<usize> {
        unsafe { genericsimd::fwd_find::<v128>(&self.0, haystack, needle) }
    }
}

#[cfg(all(test, feature = "std", not(miri)))]
mod tests {
    use crate::memmem::{prefilter::PrefilterState, NeedleInfo};

    fn find(
        _: &mut PrefilterState,
        ninfo: &NeedleInfo,
        haystack: &[u8],
        needle: &[u8],
    ) -> Option<usize> {
        super::Forward::new(ninfo, needle).unwrap().find(haystack, needle)
    }

    #[test]
    fn prefilter_permutations() {
        use crate::memmem::prefilter::tests::PrefilterTest;

        unsafe {
            PrefilterTest::run_all_tests_filter(find, |t| {
                // This substring searcher only works on certain configs, so
                // filter our tests such that Forward::new will be guaranteed
                // to succeed. (And also remove tests with a haystack that is
                // too small.)
                let fwd = match super::Forward::new(&t.ninfo, &t.needle) {
                    None => return false,
                    Some(fwd) => fwd,
                };
                t.haystack.len() >= fwd.min_haystack_len()
            })
        }
    }
}