use crate::constants::{FINAL_MIX, SECRET, STRIPE_SECRET};
use crate::math::{avalanche, folded_multiply};
use crate::memory::{r_u32, r_u64};

mod scalar;

#[cfg(target_arch = "aarch64")]
mod aarch64;

#[cfg(target_arch = "x86_64")]
mod x86_64;

#[allow(dead_code)]
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub(crate) enum Backend {
    Scalar,
    #[cfg(target_arch = "aarch64")]
    Aarch64AesNeon,
    #[cfg(target_arch = "x86_64")]
    X86_64AesAvx2,
}

#[inline(always)]
pub(crate) unsafe fn hash_bytes_short(ptr: *const u8, len: usize, acc: u64) -> u64 {
    let h = if len >= 8 {
        let a = unsafe { r_u64(ptr) } ^ SECRET[1] ^ (len as u64);
        let b = unsafe { r_u64(ptr.add(len - 8)) } ^ STRIPE_SECRET[1] ^ acc;
        folded_multiply(a, b)
    } else if len >= 4 {
        let a = (unsafe { r_u32(ptr) } as u64) ^ SECRET[2] ^ (len as u64);
        let b = (unsafe { r_u32(ptr.add(len - 4)) } as u64) ^ STRIPE_SECRET[2] ^ acc;
        folded_multiply(a, b)
    } else if len > 0 {
        let a = unsafe { *ptr } as u64;
        let b = unsafe { *ptr.add(len >> 1) } as u64;
        let c = unsafe { *ptr.add(len - 1) } as u64;
        let val = (a << 16) | (b << 8) | c;
        folded_multiply(val ^ SECRET[0] ^ (len as u64), STRIPE_SECRET[3] ^ acc)
    } else {
        folded_multiply(acc ^ SECRET[0], STRIPE_SECRET[0])
    };
    avalanche(h)
}

#[inline(always)]
unsafe fn hash_bytes_17_32(ptr: *const u8, len: usize, acc: u64) -> u64 {
    let a = unsafe { r_u64(ptr) };
    let b = unsafe { r_u64(ptr.add(8)) };
    let c = unsafe { r_u64(ptr.add(len - 16)) };
    let d = unsafe { r_u64(ptr.add(len - 8)) };

    let x = folded_multiply(a ^ SECRET[0], b ^ STRIPE_SECRET[0] ^ acc);
    let y = folded_multiply(c ^ SECRET[1], d ^ STRIPE_SECRET[1] ^ (len as u64));
    folded_multiply(x ^ y.rotate_left(17), acc ^ (len as u64))
}

#[inline(always)]
unsafe fn hash_bytes_33_64(ptr: *const u8, len: usize, acc: u64) -> u64 {
    let w0 = unsafe { r_u64(ptr) };
    let w1 = unsafe { r_u64(ptr.add(8)) };
    let w2 = unsafe { r_u64(ptr.add(16)) };
    let w3 = unsafe { r_u64(ptr.add(24)) };

    let w4 = unsafe { r_u64(ptr.add(len - 32)) };
    let w5 = unsafe { r_u64(ptr.add(len - 24)) };
    let w6 = unsafe { r_u64(ptr.add(len - 16)) };
    let w7 = unsafe { r_u64(ptr.add(len - 8)) };

    let m0 = folded_multiply(w0 ^ SECRET[0], w1 ^ STRIPE_SECRET[0] ^ acc);
    let m1 = folded_multiply(w2 ^ SECRET[1], w3 ^ STRIPE_SECRET[1]);
    let m2 = folded_multiply(w4 ^ SECRET[2], w5 ^ STRIPE_SECRET[2] ^ (len as u64));
    let m3 = folded_multiply(w6 ^ SECRET[3], w7 ^ STRIPE_SECRET[3]);

    let x = folded_multiply(m0 ^ m1.rotate_left(17), STRIPE_SECRET[0] ^ acc);
    let y = folded_multiply(m2 ^ m3.rotate_left(17), STRIPE_SECRET[1] ^ (len as u64));

    folded_multiply(x ^ y.rotate_left(19), acc ^ (len as u64))
}

#[inline(always)]
unsafe fn hash_bytes_65_128(ptr: *const u8, len: usize, acc: u64) -> u64 {
    let w0 = unsafe { r_u64(ptr) };
    let w1 = unsafe { r_u64(ptr.add(8)) };
    let w2 = unsafe { r_u64(ptr.add(16)) };
    let w3 = unsafe { r_u64(ptr.add(24)) };
    let w4 = unsafe { r_u64(ptr.add(32)) };
    let w5 = unsafe { r_u64(ptr.add(40)) };
    let w6 = unsafe { r_u64(ptr.add(48)) };
    let w7 = unsafe { r_u64(ptr.add(56)) };

    let w8 = unsafe { r_u64(ptr.add(len - 64)) };
    let w9 = unsafe { r_u64(ptr.add(len - 56)) };
    let wa = unsafe { r_u64(ptr.add(len - 48)) };
    let wb = unsafe { r_u64(ptr.add(len - 40)) };
    let wc = unsafe { r_u64(ptr.add(len - 32)) };
    let wd = unsafe { r_u64(ptr.add(len - 24)) };
    let we = unsafe { r_u64(ptr.add(len - 16)) };
    let wf = unsafe { r_u64(ptr.add(len - 8)) };

    let m0 = folded_multiply(w0 ^ SECRET[0], w1 ^ STRIPE_SECRET[0] ^ acc);
    let m1 = folded_multiply(w2 ^ SECRET[1], w3 ^ STRIPE_SECRET[1]);
    let m2 = folded_multiply(w4 ^ SECRET[2], w5 ^ STRIPE_SECRET[2]);
    let m3 = folded_multiply(w6 ^ SECRET[3], w7 ^ STRIPE_SECRET[3]);

    let m4 = folded_multiply(w8 ^ SECRET[0], w9 ^ STRIPE_SECRET[0] ^ (len as u64));
    let m5 = folded_multiply(wa ^ SECRET[1], wb ^ STRIPE_SECRET[1]);
    let m6 = folded_multiply(wc ^ SECRET[2], wd ^ STRIPE_SECRET[2]);
    let m7 = folded_multiply(we ^ SECRET[3], wf ^ STRIPE_SECRET[3]);

    let s0 = m0 ^ m4.rotate_left(17);
    let s1 = m1 ^ m5.rotate_left(19);
    let s2 = m2 ^ m6.rotate_left(23);
    let s3 = m3 ^ m7.rotate_left(29);

    let x = folded_multiply(s0 ^ STRIPE_SECRET[0], s1 ^ STRIPE_SECRET[1]);
    let y = folded_multiply(s2 ^ STRIPE_SECRET[2], s3 ^ STRIPE_SECRET[3]);

    folded_multiply(x ^ y.rotate_left(17), acc ^ (len as u64))
}

#[inline(always)]
fn hash_bytes_long(ptr: *const u8, len: usize, acc: u64) -> u64 {
    match selected_backend() {
        #[cfg(target_arch = "aarch64")]
        Backend::Aarch64AesNeon => {
            // SAFETY: selected_backend only returns this variant when CPU support is present.
            unsafe { aarch64::hash_bytes_long(ptr, len, acc) }
        }
        #[cfg(target_arch = "x86_64")]
        Backend::X86_64AesAvx2 => {
            // SAFETY: selected_backend only returns this variant when CPU support is present.
            unsafe { x86_64::hash_bytes_long(ptr, len, acc) }
        }
        Backend::Scalar => {
            // SAFETY: scalar path only reads within the provided byte slice bounds.
            unsafe { scalar::hash_bytes_long(ptr, len, acc) }
        }
    }
}

#[inline(always)]
pub(crate) fn hash_bytes_core(bytes: &[u8], acc: u64) -> u64 {
    let len = bytes.len();
    let rotated = acc.rotate_right(len as u32);
    unsafe {
        if len <= 16 {
            hash_bytes_short(bytes.as_ptr(), len, rotated)
        } else if len <= 32 {
            hash_bytes_17_32(bytes.as_ptr(), len, rotated)
        } else if len <= 64 {
            hash_bytes_33_64(bytes.as_ptr(), len, rotated)
        } else if len <= 128 {
            hash_bytes_65_128(bytes.as_ptr(), len, rotated)
        } else {
            hash_bytes_long(bytes.as_ptr(), len, rotated)
        }
    }
}

#[cfg(all(target_arch = "aarch64", feature = "std"))]
#[inline(always)]
pub(crate) fn selected_backend() -> Backend {
    if std::arch::is_aarch64_feature_detected!("aes")
        && std::arch::is_aarch64_feature_detected!("neon")
    {
        Backend::Aarch64AesNeon
    } else {
        Backend::Scalar
    }
}

#[cfg(all(
    target_arch = "aarch64",
    not(feature = "std"),
    target_feature = "aes",
    target_feature = "neon"
))]
#[inline(always)]
pub(crate) fn selected_backend() -> Backend {
    Backend::Aarch64AesNeon
}

#[cfg(all(
    target_arch = "aarch64",
    not(feature = "std"),
    not(all(target_feature = "aes", target_feature = "neon"))
))]
#[inline(always)]
pub(crate) fn selected_backend() -> Backend {
    Backend::Scalar
}

#[cfg(all(target_arch = "x86_64", feature = "std"))]
#[inline(always)]
pub(crate) fn selected_backend() -> Backend {
    if std::arch::is_x86_feature_detected!("aes") && std::arch::is_x86_feature_detected!("avx2")
    {
        Backend::X86_64AesAvx2
    } else {
        Backend::Scalar
    }
}

#[cfg(all(
    target_arch = "x86_64",
    not(feature = "std"),
    target_feature = "aes",
    target_feature = "avx2"
))]
#[inline(always)]
pub(crate) fn selected_backend() -> Backend {
    Backend::X86_64AesAvx2
}

#[cfg(all(
    target_arch = "x86_64",
    not(feature = "std"),
    not(all(target_feature = "aes", target_feature = "avx2"))
))]
#[inline(always)]
pub(crate) fn selected_backend() -> Backend {
    Backend::Scalar
}

#[cfg(not(any(target_arch = "aarch64", target_arch = "x86_64")))]
#[inline(always)]
pub(crate) fn selected_backend() -> Backend {
    Backend::Scalar
}

#[inline(always)]
pub(super) fn finalize_vector(lo: u64, hi: u64, len: usize) -> u64 {
    folded_multiply(lo ^ FINAL_MIX, hi ^ (len as u64))
}
