package rand

import (
	"crypto/rand"
	"io"
	_ "unsafe"

	"github.com/charlienet/go-mixed/bytesconv"
)

const (
	uppercase = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
	lowercase = "abcdefghijklmnopqrstuvwxyz"
	digit     = "0123456789"
	nomix     = "BCDFGHJKMPQRTVWXY2346789"
	letter    = uppercase + lowercase
	allChars  = uppercase + lowercase + digit
	hex       = digit + "ABCDEF"
	_         = allChars + "/+"
)

var rng = NewFastRandGenerator() // NewRandGenerator()

type charScope struct {
	bytes  []byte
	length int
	max    int
	bits   int
	mask   int
}

var (
	Uppercase = StringScope(uppercase) // 大写字母
	Lowercase = StringScope(lowercase) // 小写字母
	Digit     = StringScope(digit)     // 数字
	Nomix     = StringScope(nomix)     // 不混淆字符
	Letter    = StringScope(letter)    // 字母
	Hex       = StringScope(hex)       // 十六进制字符
	AllChars  = StringScope(allChars)  // 所有字符
)

func StringScope(str string) *charScope {
	len := len(str)

	scope := &charScope{
		bytes:  bytesconv.StringToBytes(str),
		length: len,
		bits:   1,
	}

	for scope.mask < len {
		scope.bits++
		scope.mask = 1<<scope.bits - 1
	}

	scope.max = scope.mask / scope.bits

	return scope
}

// 生成指定长度的随机字符串
func (scope *charScope) Generate(length int) string {
	n := length
	ret := make([]byte, n)

	for i, cache, remain := n-1, rng.Int63(), scope.max; i >= 0; {
		if remain == 0 {
			cache, remain = rng.Int63(), scope.max
		}

		if idx := int(cache & int64(scope.mask)); idx < scope.length {
			ret[i] = scope.bytes[idx]
			i--
		}

		cache >>= int64(scope.bits)
		remain--
	}

	return bytesconv.BytesToString(ret)
}

type scopeConstraint interface {
	~int | ~int32 | ~int64 | ~uint32
}

func Int[T scopeConstraint]() T {
	return T(rng.Int31())
}

// 生成区间 n >= 0, n < max
func Intn[T scopeConstraint](max T) T {
	n := rng.Int63n(int64(max))
	return T(n) % max
}

// 生成区间 n >= min, n < max
func IntRange[T scopeConstraint](min, max T) T {
	n := Intn(max - min)
	return T(n + min)
}

func RandBytes(len int) ([]byte, error) {
	r := make([]byte, len)
	_, err := io.ReadFull(rand.Reader, r)
	return r, err
}