pub const XxHash3 = struct {
    const Block = @Vector(8, u64);
    const default_secret: [192]u8 = .{
        0xb8, 0xfe, 0x6c, 0x39, 0x23, 0xa4, 0x4b, 0xbe, 0x7c, 0x01, 0x81, 0x2c, 0xf7, 0x21, 0xad, 0x1c,
        0xde, 0xd4, 0x6d, 0xe9, 0x83, 0x90, 0x97, 0xdb, 0x72, 0x40, 0xa4, 0xa4, 0xb7, 0xb3, 0x67, 0x1f,
        0xcb, 0x79, 0xe6, 0x4e, 0xcc, 0xc0, 0xe5, 0x78, 0x82, 0x5a, 0xd0, 0x7d, 0xcc, 0xff, 0x72, 0x21,
        0xb8, 0x08, 0x46, 0x74, 0xf7, 0x43, 0x24, 0x8e, 0xe0, 0x35, 0x90, 0xe6, 0x81, 0x3a, 0x26, 0x4c,
        0x3c, 0x28, 0x52, 0xbb, 0x91, 0xc3, 0x00, 0xcb, 0x88, 0xd0, 0x65, 0x8b, 0x1b, 0x53, 0x2e, 0xa3,
        0x71, 0x64, 0x48, 0x97, 0xa2, 0x0d, 0xf9, 0x4e, 0x38, 0x19, 0xef, 0x46, 0xa9, 0xde, 0xac, 0xd8,
        0xa8, 0xfa, 0x76, 0x3f, 0xe3, 0x9c, 0x34, 0x3f, 0xf9, 0xdc, 0xbb, 0xc7, 0xc7, 0x0b, 0x4f, 0x1d,
        0x8a, 0x51, 0xe0, 0x4b, 0xcd, 0xb4, 0x59, 0x31, 0xc8, 0x9f, 0x7e, 0xc9, 0xd9, 0x78, 0x73, 0x64,
        0xea, 0xc5, 0xac, 0x83, 0x34, 0xd3, 0xeb, 0xc3, 0xc5, 0x81, 0xa0, 0xff, 0xfa, 0x13, 0x63, 0xeb,
        0x17, 0x0d, 0xdd, 0x51, 0xb7, 0xf0, 0xda, 0x49, 0xd3, 0x16, 0x55, 0x26, 0x29, 0xd4, 0x68, 0x9e,
        0x2b, 0x16, 0xbe, 0x58, 0x7d, 0x47, 0xa1, 0xfc, 0x8f, 0xf8, 0xb8, 0xd1, 0x7a, 0xd0, 0x31, 0xce,
        0x45, 0xcb, 0x3a, 0x8f, 0x95, 0x16, 0x04, 0x28, 0xaf, 0xd7, 0xfb, 0xca, 0xbb, 0x4b, 0x40, 0x7e,
    };

    const prime_mx1 = 0x165667919E3779F9;
    const prime_mx2 = 0x9FB21C651E98DF25;

    inline fn avalanche(mode: union(enum) { h3, h64, rrmxmx: u64 }, x0: u64) u64 {
        switch (mode) {
            .h3 => {
                const x1 = (x0 ^ (x0 >> 37)) *% prime_mx1;
                return x1 ^ (x1 >> 32);
            },
            .h64 => {
                const x1 = (x0 ^ (x0 >> 33)) *% XxHash64.prime_2;
                const x2 = (x1 ^ (x1 >> 29)) *% XxHash64.prime_3;
                return x2 ^ (x2 >> 32);
            },
            .rrmxmx => |len| {
                const x1 = (x0 ^ rotl(u64, x0, 49) ^ rotl(u64, x0, 24)) *% prime_mx2;
                const x2 = (x1 ^ ((x1 >> 35) +% len)) *% prime_mx2;
                return x2 ^ (x2 >> 28);
            },
        }
    }

    inline fn fold(a: u64, b: u64) u64 {
        const wide: [2]u64 = @bitCast(@as(u128, a) *% b);
        return wide[0] ^ wide[1];
    }

    inline fn swap(x: anytype) @TypeOf(x) {
        return if (native_endian == .big) @byteSwap(x) else x;
    }

    inline fn disableAutoVectorization(x: anytype) void {
        if (!@inComptime()) asm volatile (""
            :
            : [x] "r" (x),
        );
    }

    inline fn mix16(seed: u64, input: []const u8, secret: []const u8) u64 {
        const blk: [4]u64 = @bitCast([_][16]u8{ input[0..16].*, secret[0..16].* });
        disableAutoVectorization(seed);

        return fold(
            swap(blk[0]) ^ (swap(blk[2]) +% seed),
            swap(blk[1]) ^ (swap(blk[3]) -% seed),
        );
    }

    const Accumulator = extern struct {
        consumed: usize = 0,
        seed: u64,
        secret: [192]u8 = undefined,
        state: Block = Block{
            XxHash32.prime_3,
            XxHash64.prime_1,
            XxHash64.prime_2,
            XxHash64.prime_3,
            XxHash64.prime_4,
            XxHash32.prime_2,
            XxHash64.prime_5,
            XxHash32.prime_1,
        },

        inline fn init(seed: u64) Accumulator {
            var self = Accumulator{ .seed = seed };
            for (
                std.mem.bytesAsSlice(Block, &self.secret),
                std.mem.bytesAsSlice(Block, &default_secret),
            ) |*dst, src| {
                dst.* = swap(swap(src) +% Block{
                    seed, @as(u64, 0) -% seed,
                    seed, @as(u64, 0) -% seed,
                    seed, @as(u64, 0) -% seed,
                    seed, @as(u64, 0) -% seed,
                });
            }
            return self;
        }

        inline fn round(
            noalias state: *Block,
            noalias input_block: *align(1) const Block,
            noalias secret_block: *align(1) const Block,
        ) void {
            const data = swap(input_block.*);
            const mixed = data ^ swap(secret_block.*);
            state.* +%= (mixed & @as(Block, @splat(0xffffffff))) *% (mixed >> @splat(32));
            state.* +%= @shuffle(u64, data, undefined, [_]i32{ 1, 0, 3, 2, 5, 4, 7, 6 });
        }

        fn accumulate(noalias self: *Accumulator, blocks: []align(1) const Block) void {
            const secret = std.mem.bytesAsSlice(u64, self.secret[self.consumed * 8 ..]);
            for (blocks, secret[0..blocks.len]) |*input_block, *secret_block| {
                @prefetch(@as([*]const u8, @ptrCast(input_block)) + 320, .{});
                round(&self.state, input_block, @ptrCast(secret_block));
            }
        }

        fn scramble(self: *Accumulator) void {
            const secret_block: Block = @bitCast(self.secret[192 - @sizeOf(Block) .. 192].*);
            self.state ^= self.state >> @splat(47);
            self.state ^= swap(secret_block);
            self.state *%= @as(Block, @splat(XxHash32.prime_1));
        }

        fn consume(noalias self: *Accumulator, input_blocks: []align(1) const Block) void {
            const blocks_per_scramble = 1024 / @sizeOf(Block);
            std.debug.assert(self.consumed <= blocks_per_scramble);

            var blocks = input_blocks;
            var blocks_until_scramble = blocks_per_scramble - self.consumed;
            while (blocks.len >= blocks_until_scramble) {
                self.accumulate(blocks[0..blocks_until_scramble]);
                self.scramble();

                self.consumed = 0;
                blocks = blocks[blocks_until_scramble..];
                blocks_until_scramble = blocks_per_scramble;
            }

            self.accumulate(blocks);
            self.consumed += blocks.len;
        }

        fn digest(noalias self: *Accumulator, total_len: u64, noalias last_block: *align(1) const Block) u64 {
            const secret_block = self.secret[192 - @sizeOf(Block) - 7 ..][0..@sizeOf(Block)];
            round(&self.state, last_block, @ptrCast(secret_block));

            const merge_block: Block = @bitCast(self.secret[11 .. 11 + @sizeOf(Block)].*);
            self.state ^= swap(merge_block);

            var result = XxHash64.prime_1 *% total_len;
            inline for (0..4) |i| {
                result +%= fold(self.state[i * 2], self.state[i * 2 + 1]);
            }
            return avalanche(.h3, result);
        }
    };

    // Public API - Oneshot

    pub fn hash(seed: u64, input: anytype) u64 {
        const secret = &default_secret;
        if (input.len > 240) return hashLong(seed, input);
        if (input.len > 128) return hash240(seed, input, secret);
        if (input.len > 16) return hash128(seed, input, secret);
        if (input.len > 8) return hash16(seed, input, secret);
        if (input.len > 3) return hash8(seed, input, secret);
        if (input.len > 0) return hash3(seed, input, secret);

        const flip: [2]u64 = @bitCast(secret[56..72].*);
        const key = swap(flip[0]) ^ swap(flip[1]);
        return avalanche(.h64, seed ^ key);
    }

    fn hash3(seed: u64, input: anytype, noalias secret: *const [192]u8) u64 {
        @branchHint(.unlikely);
        std.debug.assert(input.len > 0 and input.len < 4);

        const flip: [2]u32 = @bitCast(secret[0..8].*);
        const blk: u32 = @bitCast([_]u8{
            input[input.len - 1],
            @truncate(input.len),
            input[0],
            input[input.len / 2],
        });

        const key = @as(u64, swap(flip[0]) ^ swap(flip[1])) +% seed;
        return avalanche(.h64, key ^ swap(blk));
    }

    fn hash8(seed: u64, input: anytype, noalias secret: *const [192]u8) u64 {
        @branchHint(.cold);
        std.debug.assert(input.len >= 4 and input.len <= 8);

        const flip: [2]u64 = @bitCast(secret[8..24].*);
        const blk: [2]u32 = @bitCast([_][4]u8{
            input[0..4].*,
            input[input.len - 4 ..][0..4].*,
        });

        const mixed = seed ^ (@as(u64, @byteSwap(@as(u32, @truncate(seed)))) << 32);
        const key = (swap(flip[0]) ^ swap(flip[1])) -% mixed;
        const combined = (@as(u64, swap(blk[0])) << 32) +% swap(blk[1]);
        return avalanche(.{ .rrmxmx = input.len }, key ^ combined);
    }

    fn hash16(seed: u64, input: anytype, noalias secret: *const [192]u8) u64 {
        @branchHint(.unlikely);
        std.debug.assert(input.len > 8 and input.len <= 16);

        const flip: [4]u64 = @bitCast(secret[24..56].*);
        const blk: [2]u64 = @bitCast([_][8]u8{
            input[0..8].*,
            input[input.len - 8 ..][0..8].*,
        });

        const lo = swap(blk[0]) ^ ((swap(flip[0]) ^ swap(flip[1])) +% seed);
        const hi = swap(blk[1]) ^ ((swap(flip[2]) ^ swap(flip[3])) -% seed);
        const combined = @as(u64, input.len) +% @byteSwap(lo) +% hi +% fold(lo, hi);
        return avalanche(.h3, combined);
    }

    fn hash128(seed: u64, input: anytype, noalias secret: *const [192]u8) u64 {
        @branchHint(.unlikely);
        std.debug.assert(input.len > 16 and input.len <= 128);

        var acc = XxHash64.prime_1 *% @as(u64, input.len);
        inline for (0..4) |i| {
            const in_offset = 48 - (i * 16);
            const scrt_offset = 96 - (i * 32);
            if (input.len > scrt_offset) {
                acc +%= mix16(seed, input[in_offset..], secret[scrt_offset..]);
                acc +%= mix16(seed, input[input.len - (in_offset + 16) ..], secret[scrt_offset + 16 ..]);
            }
        }
        return avalanche(.h3, acc);
    }

    fn hash240(seed: u64, input: anytype, noalias secret: *const [192]u8) u64 {
        @branchHint(.unlikely);
        std.debug.assert(input.len > 128 and input.len <= 240);

        var acc = XxHash64.prime_1 *% @as(u64, input.len);
        inline for (0..8) |i| {
            acc +%= mix16(seed, input[i * 16 ..], secret[i * 16 ..]);
        }

        var acc_end = mix16(seed, input[input.len - 16 ..], secret[136 - 17 ..]);
        for (8..(input.len / 16)) |i| {
            acc_end +%= mix16(seed, input[i * 16 ..], secret[((i - 8) * 16) + 3 ..]);
            disableAutoVectorization(i);
        }

        acc = avalanche(.h3, acc) +% acc_end;
        return avalanche(.h3, acc);
    }

    noinline fn hashLong(seed: u64, input: []const u8) u64 {
        @branchHint(.unlikely);
        std.debug.assert(input.len >= 240);

        const block_count = ((input.len - 1) / @sizeOf(Block)) * @sizeOf(Block);
        const last_block = input[input.len - @sizeOf(Block) ..][0..@sizeOf(Block)];

        var acc = Accumulator.init(seed);
        acc.consume(std.mem.bytesAsSlice(Block, input[0..block_count]));
        return acc.digest(input.len, @ptrCast(last_block));
    }

    // Public API - Streaming

    buffered: usize = 0,
    buffer: [256]u8 = undefined,
    total_len: usize = 0,
    accumulator: Accumulator,

    pub fn init(seed: u64) XxHash3 {
        return .{ .accumulator = Accumulator.init(seed) };
    }

    pub fn update(self: *XxHash3, input: anytype) void {
        self.total_len += input.len;
        std.debug.assert(self.buffered <= self.buffer.len);

        // Copy the input into the buffer if we haven't filled it up yet.
        const remaining = self.buffer.len - self.buffered;
        if (input.len <= remaining) {
            @memcpy(self.buffer[self.buffered..][0..input.len], input);
            self.buffered += input.len;
            return;
        }

        // Input will overflow the buffer. Fill up the buffer with some input and consume it.
        var consumable: []const u8 = input;
        if (self.buffered > 0) {
            @memcpy(self.buffer[self.buffered..], consumable[0..remaining]);
            consumable = consumable[remaining..];

            self.accumulator.consume(std.mem.bytesAsSlice(Block, &self.buffer));
            self.buffered = 0;
        }

        // The input isn't small enough to fit in the buffer. Consume it directly.
        if (consumable.len > self.buffer.len) {
            const block_count = ((consumable.len - 1) / @sizeOf(Block)) * @sizeOf(Block);
            self.accumulator.consume(std.mem.bytesAsSlice(Block, consumable[0..block_count]));
            consumable = consumable[block_count..];

            // In case we consume all remaining input, write the last block to end of the buffer
            // to populate the last_block_copy in final() similar to hashLong()'s last_block.
            @memcpy(
                self.buffer[self.buffer.len - @sizeOf(Block) .. self.buffer.len],
                (consumable.ptr - @sizeOf(Block))[0..@sizeOf(Block)],
            );
        }

        // Copy in any remaining input into the buffer.
        std.debug.assert(consumable.len <= self.buffer.len);
        @memcpy(self.buffer[0..consumable.len], consumable);
        self.buffered = consumable.len;
    }

    pub fn final(self: *XxHash3) u64 {
        std.debug.assert(self.buffered <= self.total_len);
        std.debug.assert(self.buffered <= self.buffer.len);

        // Use Oneshot hashing for smaller sizes as it doesn't use Accumulator like hashLong.
        if (self.total_len <= 240) {
            return hash(self.accumulator.seed, self.buffer[0..self.total_len]);
        }

        // Make a copy of the Accumulator state in case `self` needs to update() / be used later.
        var accumulator_copy = self.accumulator;
        var last_block_copy: [@sizeOf(Block)]u8 = undefined;

        // Digest the last block onthe Accumulator copy.
        return accumulator_copy.digest(self.total_len, last_block: {
            if (self.buffered >= @sizeOf(Block)) {
                const block_count = ((self.buffered - 1) / @sizeOf(Block)) * @sizeOf(Block);
                accumulator_copy.consume(std.mem.bytesAsSlice(Block, self.buffer[0..block_count]));
                break :last_block @ptrCast(self.buffer[self.buffered - @sizeOf(Block) ..][0..@sizeOf(Block)]);
            } else {
                const remaining = @sizeOf(Block) - self.buffered;
                @memcpy(last_block_copy[0..remaining], self.buffer[self.buffer.len - remaining ..][0..remaining]);
                @memcpy(last_block_copy[remaining..][0..self.buffered], self.buffer[0..self.buffered]);
                break :last_block @ptrCast(&last_block_copy);
            }
        });
    }
}