package xrand

import (
	"math/rand"
	"time"
)

var rd *rand.Rand

func init() {
	rd = rand.New(rand.NewSource(time.Now().UnixNano()))
}

// 随机值
func Rand[T int | int32 | int64 | uint32 | uint64 | float32 | float64]() T {
	switch any(T(0)).(type) {
	case int:
		return T(rd.Int())
	case int32:
		return T(rd.Int31())
	case int64:
		return T(rd.Int63())
	case uint32:
		return T(rd.Uint32())
	case uint64:
		return T(rd.Uint64())
	case float32:
		return T(rd.Float32())
	case float64:
		return T(rd.Float64())
	default:
		panic("不支持的类型")
	}
}

// 从[0,n)范围里随机值
func RandN[T int | int32 | int64 | uint32 | uint64](n T) T {
	if int64(n) < 1 {
		return 0
	}
	switch any(n).(type) {
	case int:
		return T(rd.Intn(int(n))) // [0,n) 的随机整数
	case int32:
		return T(rd.Int31n(int32(n)))
	case int64:
		return T(rd.Int63n(int64(n)))
	case uint32:
		return T(rd.Uint32() % uint32(n)) // 注意：这里有小偏差
	case uint64:
		return T(rand.Uint64() % uint64(n))
	default:
		panic("不支持的类型")
	}
}

// 从[0,n)范围里随机值
func RandRange[T int | int32 | int64 | uint32 | uint64](min, max T) T {
	if int64(max) < 1 || int64(min) < 1 || max < min {
		return 0
	}
	return RandN[T](max-min) + min
}

func Perm(n int) []int {
	return rd.Perm(n)
}

func Read(p []byte) (n int, err error) {
	return rd.Read(p)
}

func Shuffle[T any](slice []T) {
	rand.Shuffle(len(slice), func(i, j int) {
		slice[i], slice[j] = slice[j], slice[i]
	})
}

const letterBytes = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"

func RandomString(n int) string {
	b := make([]byte, n)
	for i := range b {
		b[i] = letterBytes[rd.Intn(len(letterBytes))]
	}
	return string(b)
}