package utils

import (
	"bytes"
	"crypto/rand"
	"math/big"
	"reflect"
	"unsafe"
)

func RandomString(len int) string {
	return RandomStringRange(len, "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890")
}

func RandomStringRange(len int, str string) string {
	var res string
	b := bytes.NewBufferString(str)
	length := b.Len()
	bigInt := big.NewInt(int64(length))
	for i := 0; i < len; i++ {
		randomInt, _ := rand.Int(rand.Reader, bigInt)
		res += string(str[randomInt.Int64()])
	}
	return res
}

func ChunkString(s string, chunkSize int) []string {
	var chunks []string
	runes := []rune(s)

	if len(runes) == 0 || len(runes) <= chunkSize {
		return []string{s}
	}

	for i := 0; i < len(runes); i += chunkSize {
		nn := i + chunkSize
		if nn > len(runes) {
			nn = len(runes)
		}
		chunks = append(chunks, string(runes[i:nn]))
	}
	return chunks
}

func ChineseLength(str string, limit int) int {
	sum := 0
	for _, r := range []rune(str) {
		switch {
		case r >= '\u0000' && r <= '\u007F':
			sum += 1
		case r >= '\u0080' && r <= '\u07FF':
			sum += 2
		case r >= '\u0800' && r <= '\uFFFF':
			sum += 3
		default:
			sum += 4
		}
		if sum >= limit {
			break
		}
	}
	return sum
}

// B2S converts byte slice to a string without memory allocation.
// See https://groups.google.com/forum/#!msg/Golang-Nuts/ENgbUzYvCuU/90yGx7GUAgAJ .
func B2S(b []byte) string {
	return *(*string)(unsafe.Pointer(&b))
}

// S2B converts string to a byte slice without memory allocation.
//
// Note it may break if string and/or slice header will change
// in the future go versions.
func S2B(s string) (b []byte) {
	sh := (*reflect.StringHeader)(unsafe.Pointer(&s))
	bh := (*reflect.SliceHeader)(unsafe.Pointer(&b))
	bh.Data = sh.Data
	bh.Cap = sh.Len
	bh.Len = sh.Len
	return
}