package utility

import (
	"strconv"
	"strings"

	"github.com/rs/xid"
	"go.uber.org/zap"

	cryptoRand "crypto/rand"
	"fmt"
	"math"
	"math/big"
	"math/rand"
	"time"

	log "github.com/go-admin-team/go-admin-core/logger"
	"github.com/sony/sonyflake"
)

const base62Chars = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"

// GetXid Package xid is a globally unique id generator library
// 包xid是一个全局唯一的id生成器库
func GetXid() string {
	return xid.New().String()
}

// GetRandIntStr 生成len位的随机数字
func GetRandIntStr(len int, prefix string) string {
	rand.Seed(time.Now().UnixNano())

	num := rand.Int31n(int32(math.Pow(10, float64(len))))
	x := fmt.Sprintf("%s%0*d", prefix, len, num)
	return x
}

// GenerateRandString 生成指定位数的字符串
// 虽然繁琐 但理解之后就觉得很精妙
func GenerateRandString(length int) string {
	var chars = []byte(`ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789`) // 长度:(1,256)
	rand.Seed(time.Now().UnixNano())
	clen := len(chars)
	maxRb := 255 - (256 % clen) // [-1,255]  255 - (256%36) = 251  避免模偏倚 为了每个字符被取到的几率相等
	b := make([]byte, length)
	r := make([]byte, length+(length/4)) // storage for random bytes. 存储随机字节

	for i := 0; ; {
		//  将随机的byte值填充到byte数组中 以供使用
		if _, err := rand.Read(r); err != nil {
			log.Error(`GenerateRandString`, zap.Error(err))
			return ``
		}
		for _, rb := range r {
			c := int(rb)
			if c > maxRb {
				// Skip this number to avoid modulo bias.跳过这个数字以避免模偏倚
				continue
			}
			b[i] = chars[c%clen]
			i++
			if i == length { // 直到取到合适的长度
				return string(b)
			}
		}
	}
}

// GenerateBase62Key 生成指定长度的随机 Base62（数字 + 大小写字母）字符串
func GenerateBase62Key(length int) (string, error) {
	var b strings.Builder
	b.Grow(length)

	for i := 0; i < length; i++ {
		n, err := cryptoRand.Int(cryptoRand.Reader, big.NewInt(int64(len(base62Chars))))
		if err != nil {
			return "", err
		}
		b.WriteByte(base62Chars[n.Int64()])
	}

	return b.String(), nil
}

var sf *sonyflake.Sonyflake

func InitSnowflake() {
	sf = sonyflake.NewSonyflake(sonyflake.Settings{})
	if sf == nil {
		log.Fatalf("Failed to initialize sonyflake")
	}
}

func GenerateTraceID() string {
	id, err := sf.NextID()
	if err != nil {
		log.Fatalf("Failed to generate ID: %v", err)
	}
	return strconv.FormatUint(id, 10)
}