use std::simd::{
    cmp::{SimdPartialEq, SimdPartialOrd},
    simd_swizzle, u8x16,
};

#[must_use]
pub fn dateparse(s: &str) -> Option<(usize, usize, usize)> {
    // inf and sup for indiv. values
    const LO: u8x16 = u8x16::from_array([
        b'0', b'0', b'/', b'0', b'0', b'/', b'0', b'0', //
        0, 0, 0, 0, 0, 0, 0, 0, // load_or_default isnt const
    ]);
    const HI: u8x16 = u8x16::from_array([
        b'1', b'9', b'/', b'3', b'9', b'/', b'9', b'9', //
        0xFF, 0xFF, 0xFF, 0xFF, //
        0xFF, 0xFF, 0xFF, 0xFF, //
    ]);
    const INTMSK: u8x16 = u8x16::from_array([b'0'; 16]);
    const SLHMSK: u8x16 = u8x16::from_array([b'/'; 16]);
    const NUMMSK: u8x16 = u8x16::from_array([
        10, 1, 0, // [m_10, m_1] -> m_10 * 10 + m_1 (0 is slash)
        10, 1, 0, // dd ..
        10, 1, 0, // yy ..
        0, 0, 0, 0, 0, 0, 0,
    ]);
    let b = s.as_bytes();
    let v = u8x16::load_or_default(b);
    let mut valid = true;
    // index 16 for swizzles with INTMSK is b'0'
    // index 15 is 0
    // this will compile to a shuffle, but a relaxed_laneselect would be cool
    let mut v = match (b.len(), v.simd_eq(SLHMSK).to_bitmask()) {
        // m/d/yy
        (6, 0b1010) => simd_swizzle!(
            v,
            INTMSK,
            [16, 0, 1, 16, 2, 3, 4, 5, 15, 15, 15, 15, 15, 15, 15, 15]
        ),
        // m/dd/yy
        (7, 0b10010) => simd_swizzle!(
            v,
            INTMSK,
            [16, 0, 1, 2, 3, 4, 5, 6, 15, 15, 15, 15, 15, 15, 15, 15]
        ),
        // mm/d/yy
        (7, 0b10100) => simd_swizzle!(
            v,
            INTMSK,
            [0, 1, 2, 16, 3, 4, 5, 6, 15, 15, 15, 15, 15, 15, 15, 15]
        ),
        // mm/dd/yy
        (8, 0b100100) => v,
        _ => {
            valid = false;
            v
        }
    };

    // est-ce numerique?
    valid &= (v.simd_ge(LO) & v.simd_le(HI)).all();

    // parse
    //   '0' '3' '/' '3' '1' '/' '2' '6'
    // - '0' '0' '0' '0' '0' '0' '0' '0'
    // ---------------------------------
    //    0   3   .   3   1   .   2   6
    // * 10   1   0  10   1   0  10   1
    // ---------------------------------
    //    0   3   0  30   1   0  20   6
    // +  3   0  30   1   0  20   6<<<<
    // ---------------------------------
    //    3   .   .  31   .   .  26
    v -= INTMSK;
    v *= NUMMSK;
    v += v.rotate_elements_left::<1>();
    let n = v.to_array();
    let (m, d, y) = (n[0], n[3], n[6]);

    (valid & (1..=12).contains(&m) & (1..=31).contains(&d))
        .then(|| (m.into(), d.into(), y.into()))
}