package main

import (
	"crypto/sha1"
	"fmt"
	"math/rand"
	"sort"
	"strings"
	"time"
)

//BuildTextMsg Given a text message send it to wechat client
func BuildTextMsg(txt string, ToUserName string) (string, error) {

	template := `<xml>
 <ToUserName><![CDATA[%s]]></ToUserName>
 <FromUserName><![CDATA[%s]]></FromUserName>
 <CreateTime>%d</CreateTime>
 <MsgType><![CDATA[text]]></MsgType>
 <Content><![CDATA[%s]]></Content>
 </xml>`
	msg := fmt.Sprintf(template, ToUserName, APIConfig.PublicAccountID, int32(time.Now().Unix()), txt)
	e := Encode(msg)
	str, _, _, _ := signMsg(e)
	return str, nil
}

func signMsg(content string) (xml string, timestamp int32, nonce int32, signature string) {
	timestamp = int32(time.Now().Unix())
	nonce = rand.Int31()

	strTimestamp := fmt.Sprintf("%d", timestamp)
	strNonce := fmt.Sprintf("%d", nonce)
	signature = getSignature(APIConfig.Token, strTimestamp, strNonce, content)
	xml = "<xml>" +
		"<Encrypt>" + content + "</Encrypt>" +
		"<MsgSignature>" + signature + "</MsgSignature>" +
		"<TimeStamp>" + strTimestamp + "</TimeStamp>" +
		"<Nonce>" + strNonce + "</Nonce>" +
		"</xml>"
	return
}

func getSignature(token string, timestamp string, nonce string, content string) (signature string) {
	strs := []string{token, timestamp, nonce, content}
	sort.Strings(strs)
	s := strings.Join(strs, "")
	h := sha1.New()
	h.Write([]byte(s))
	signature = fmt.Sprintf("%x", h.Sum(nil))
	return
}