package helpers

import (
	"slices"
	"strconv"
	"strings"
	"sync"
	"unsafe"

	"github.com/minio/sha256-simd"
	"golang.org/x/exp/constraints"
)

const MAX_LOCKS = 50

var (
	namedMutexPool = make([]sync.Mutex, MAX_LOCKS)
)

//go:noescape
//go:linkname memhash runtime.memhash
func memhash(p unsafe.Pointer, h, s uintptr) uintptr

func NamedLock(name string) (unlock func()) {
	sptr := unsafe.StringData(name)
	idx := uint64(memhash(unsafe.Pointer(sptr), 0, uintptr(len(name)))) % MAX_LOCKS
	namedMutexPool[idx].Lock()
	return namedMutexPool[idx].Unlock
}

func Similar[E constraints.Ordered](as, bs []E) bool {
	if len(as) != len(bs) {
		return false
	}

	for _, a := range as {
		for _, b := range bs {
			if b == a {
				goto next
			}
		}
		// didn't find a B that corresponded to the current A
		return false

	next:
		continue
	}

	return true
}

// EscapeString for JSON encoding according to RFC8259.
// Also encloses result in quotation marks "".
func EscapeString(dst []byte, s string) []byte {
	dst = append(dst, '"')
	for i := 0; i < len(s); i++ {
		c := s[i]
		switch {
		case c == '"':
			// quotation mark
			dst = append(dst, []byte{'\\', '"'}...)
		case c == '\\':
			// reverse solidus
			dst = append(dst, []byte{'\\', '\\'}...)
		case c >= 0x20:
			// default, rest below are control chars
			dst = append(dst, c)
		case c == 0x08:
			dst = append(dst, []byte{'\\', 'b'}...)
		case c < 0x09:
			dst = append(dst, []byte{'\\', 'u', '0', '0', '0', '0' + c}...)
		case c == 0x09:
			dst = append(dst, []byte{'\\', 't'}...)
		case c == 0x0a:
			dst = append(dst, []byte{'\\', 'n'}...)
		case c == 0x0c:
			dst = append(dst, []byte{'\\', 'f'}...)
		case c == 0x0d:
			dst = append(dst, []byte{'\\', 'r'}...)
		case c < 0x10:
			dst = append(dst, []byte{'\\', 'u', '0', '0', '0', 0x57 + c}...)
		case c < 0x1a:
			dst = append(dst, []byte{'\\', 'u', '0', '0', '1', 0x20 + c}...)
		case c < 0x20: // maybe default?
			dst = append(dst, []byte{'\\', 'u', '0', '0', '1', 0x47 + c}...)
		}
	}
	dst = append(dst, '"')
	return dst
}

func ArePointerValuesEqual[V comparable](a *V, b *V) bool {
	if a == nil && b == nil {
		return true
	}
	if a != nil && b != nil {
		return *a == *b
	}
	return false
}

func SubIdToSerial(subId string) int64 {
	n := strings.Index(subId, ":")
	if n < 0 || n > len(subId) {
		return -1
	}
	serialId, _ := strconv.ParseInt(subId[0:n], 10, 64)
	return serialId
}

func IsLowerHex(thing string) bool {
	for _, charNumber := range thing {
		if (charNumber >= 48 && charNumber <= 57) || (charNumber >= 97 && charNumber <= 102) {
			continue
		}
		return false
	}
	return true
}

// Hash is a little helper generate a hash and return a slice instead of an
// array.
func Hash(in []byte) (out []byte) {
	h := sha256.Sum256(in)
	return h[:]
}

// RemoveDuplicates removes repeated items in any slice of comparable items. This would not be
// appropriate for pointers unless they were assembled from the same source where a pointer is
// equal to a unique reference to the content.
func RemoveDuplicates[T comparable](s []T) []T {
	alreadySeen := make(map[T]struct{}, len(s))
	return slices.DeleteFunc(s, func(val T) bool {
		_, duplicate := alreadySeen[val]
		alreadySeen[val] = struct{}{}
		return duplicate
	})
}