package hashmap

import (
	"encoding/binary"
	"fmt"
	"math/bits"
	"reflect"
	"unsafe"
)

const (
	prime1 uint64 = 11400714785074694791
	prime2 uint64 = 14029467366897019727
	prime3 uint64 = 1609587929392839161
	prime4 uint64 = 9650029242287828579
	prime5 uint64 = 2870177450012600261
)

var prime1v = prime1

/*
Copyright (c) 2016 Caleb Spare

MIT License

Permission is hereby granted, free of charge, to any person obtaining
a copy of this software and associated documentation files (the
"Software"), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:

The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/

// setDefaultHasher sets the default hasher depending on the key type.
// Inlines hashing as anonymous functions for performance improvements, other options like
// returning an anonymous functions from another function turned out to not be as performant.
func (m *Map[Key, Value]) setDefaultHasher() {
	var key Key
	kind := reflect.ValueOf(&key).Elem().Type().Kind()

	switch kind {
	case reflect.Int, reflect.Uint, reflect.Uintptr:
		switch intSizeBytes {
		case 2:
			m.hasher = *(*func(Key) uintptr)(unsafe.Pointer(&xxHashWord))
		case 4:
			m.hasher = *(*func(Key) uintptr)(unsafe.Pointer(&xxHashDword))
		case 8:
			m.hasher = *(*func(Key) uintptr)(unsafe.Pointer(&xxHashQword))

		default:
			panic(fmt.Errorf("unsupported integer byte size %d", intSizeBytes))
		}

	case reflect.Int8, reflect.Uint8:
		m.hasher = *(*func(Key) uintptr)(unsafe.Pointer(&xxHashByte))
	case reflect.Int16, reflect.Uint16:
		m.hasher = *(*func(Key) uintptr)(unsafe.Pointer(&xxHashWord))
	case reflect.Int32, reflect.Uint32:
		m.hasher = *(*func(Key) uintptr)(unsafe.Pointer(&xxHashDword))
	case reflect.Int64, reflect.Uint64:
		m.hasher = *(*func(Key) uintptr)(unsafe.Pointer(&xxHashQword))
	case reflect.Float32:
		m.hasher = *(*func(Key) uintptr)(unsafe.Pointer(&xxHashFloat32))
	case reflect.Float64:
		m.hasher = *(*func(Key) uintptr)(unsafe.Pointer(&xxHashFloat64))
	case reflect.String:
		m.hasher = *(*func(Key) uintptr)(unsafe.Pointer(&xxHashString))

	default:
		panic(fmt.Errorf("unsupported key type %T of kind %v", key, kind))
	}
}

// Specialized xxhash hash functions, optimized for the bit size of the key where available,
// for all supported types beside string.

var xxHashByte = func(key uint8) uintptr {
	h := prime5 + 1
	h ^= uint64(key) * prime5
	h = bits.RotateLeft64(h, 11) * prime1

	h ^= h >> 33
	h *= prime2
	h ^= h >> 29
	h *= prime3
	h ^= h >> 32

	return uintptr(h)
}

var xxHashWord = func(key uint16) uintptr {
	h := prime5 + 2
	h ^= (uint64(key) & 0xff) * prime5
	h = bits.RotateLeft64(h, 11) * prime1
	h ^= ((uint64(key) >> 8) & 0xff) * prime5
	h = bits.RotateLeft64(h, 11) * prime1

	h ^= h >> 33
	h *= prime2
	h ^= h >> 29
	h *= prime3
	h ^= h >> 32

	return uintptr(h)
}

var xxHashDword = func(key uint32) uintptr {
	h := prime5 + 4
	h ^= uint64(key) * prime1
	h = bits.RotateLeft64(h, 23)*prime2 + prime3

	h ^= h >> 33
	h *= prime2
	h ^= h >> 29
	h *= prime3
	h ^= h >> 32

	return uintptr(h)
}

var xxHashFloat32 = func(key float32) uintptr {
	h := prime5 + 4
	h ^= uint64(key) * prime1
	h = bits.RotateLeft64(h, 23)*prime2 + prime3

	h ^= h >> 33
	h *= prime2
	h ^= h >> 29
	h *= prime3
	h ^= h >> 32

	return uintptr(h)
}

var xxHashFloat64 = func(key float64) uintptr {
	h := prime5 + 4
	h ^= uint64(key) * prime1
	h = bits.RotateLeft64(h, 23)*prime2 + prime3

	h ^= h >> 33
	h *= prime2
	h ^= h >> 29
	h *= prime3
	h ^= h >> 32

	return uintptr(h)
}

var xxHashQword = func(key uint64) uintptr {
	k1 := key * prime2
	k1 = bits.RotateLeft64(k1, 31)
	k1 *= prime1
	h := (prime5 + 8) ^ k1
	h = bits.RotateLeft64(h, 27)*prime1 + prime4

	h ^= h >> 33
	h *= prime2
	h ^= h >> 29
	h *= prime3
	h ^= h >> 32

	return uintptr(h)
}

var xxHashString = func(key string) uintptr {
	sh := (*reflect.StringHeader)(unsafe.Pointer(&key))
	bh := reflect.SliceHeader{
		Data: sh.Data,
		Len:  sh.Len,
		Cap:  sh.Len, // cap needs to be set, otherwise xxhash fails on ARM Macs
	}

	b := *(*[]byte)(unsafe.Pointer(&bh))
	var h uint64

	if sh.Len >= 32 {
		v1 := prime1v + prime2
		v2 := prime2
		v3 := uint64(0)
		v4 := -prime1v
		for len(b) >= 32 {
			v1 = round(v1, binary.LittleEndian.Uint64(b[0:8:len(b)]))
			v2 = round(v2, binary.LittleEndian.Uint64(b[8:16:len(b)]))
			v3 = round(v3, binary.LittleEndian.Uint64(b[16:24:len(b)]))
			v4 = round(v4, binary.LittleEndian.Uint64(b[24:32:len(b)]))
			b = b[32:len(b):len(b)]
		}
		h = rol1(v1) + rol7(v2) + rol12(v3) + rol18(v4)
		h = mergeRound(h, v1)
		h = mergeRound(h, v2)
		h = mergeRound(h, v3)
		h = mergeRound(h, v4)
	} else {
		h = prime5
	}

	h += uint64(sh.Len)

	i, end := 0, len(b)
	for ; i+8 <= end; i += 8 {
		k1 := round(0, binary.LittleEndian.Uint64(b[i:i+8:len(b)]))
		h ^= k1
		h = rol27(h)*prime1 + prime4
	}
	if i+4 <= end {
		h ^= uint64(binary.LittleEndian.Uint32(b[i:i+4:len(b)])) * prime1
		h = rol23(h)*prime2 + prime3
		i += 4
	}
	for ; i < end; i++ {
		h ^= uint64(b[i]) * prime5
		h = rol11(h) * prime1
	}

	h ^= h >> 33
	h *= prime2
	h ^= h >> 29
	h *= prime3
	h ^= h >> 32

	return uintptr(h)
}

func round(acc, input uint64) uint64 {
	acc += input * prime2
	acc = rol31(acc)
	acc *= prime1
	return acc
}

func mergeRound(acc, val uint64) uint64 {
	val = round(0, val)
	acc ^= val
	acc = acc*prime1 + prime4
	return acc
}

func rol1(x uint64) uint64  { return bits.RotateLeft64(x, 1) }
func rol7(x uint64) uint64  { return bits.RotateLeft64(x, 7) }
func rol11(x uint64) uint64 { return bits.RotateLeft64(x, 11) }
func rol12(x uint64) uint64 { return bits.RotateLeft64(x, 12) }
func rol18(x uint64) uint64 { return bits.RotateLeft64(x, 18) }
func rol23(x uint64) uint64 { return bits.RotateLeft64(x, 23) }
func rol27(x uint64) uint64 { return bits.RotateLeft64(x, 27) }
func rol31(x uint64) uint64 { return bits.RotateLeft64(x, 31) }