package main

import (
	"io/ioutil"
	"net/http"
	"os"
	"time"

	"net/url"

	"encoding/json"

	"github.com/gin-gonic/gin"
	log "github.com/sirupsen/logrus"
)

type Token struct {
	AccessToken  string `json:"access_token"`
	ExpiresIn    int    `json:"expires_in"`
	RefreshToken string `json:"refresh_token"`
	BaseTime     time.Time
	ExpiresTime  time.Time
}

type ViewToken struct {
	Token       string
	ExpiresTime int64
}

var (
	clientId     string
	clientSecret string
	token        *Token
)

func init() {
	loadToken()
	clientId = os.Getenv("CLIENT_ID")
	clientSecret = os.Getenv("CLIENT_SECRET")
	if clientId == "" || clientSecret == "" {
		log.Fatal("Please set environment variable CLIENT_ID and CLIENT_SECRET")
	}
	if shouldFetchToken() {
		fetchToken()
	}
	log.Info("Say-it is ready to go!")
}

func main() {
	router := gin.Default()
	router.GET("/", landing)
	router.GET("/api/token", fetchTokenHandler)
	router.Run()
}

func landing(c *gin.Context) {
	c.JSON(200, gin.H{"msg": "Hello, I am say-it. Please go to https://github.com/wahyd4/say-it-backend to get more details."})
}

func fetchTokenHandler(c *gin.Context) {
	if time.Now().After(token.ExpiresTime) {
		log.Info("Token expires, try to refresh one.")
		fetchToken()
	}
	if token != nil {
		c.JSON(200, ViewToken{Token: token.AccessToken, ExpiresTime: token.ExpiresTime.Unix()})
		return
	}
	c.JSON(404, gin.H{"message": "No Available Token, please concat the Admin: wahyd4@gmail.com. Thanks!"})
}

func fetchToken() {
	log.Info("Start fetching token")
	params := url.Values{}
	params.Add("grant_type", "client_credentials")
	params.Add("client_id", clientId)
	params.Add("client_secret", clientSecret)

	resp, err := http.PostForm("https://openapi.baidu.com/oauth/2.0/token", params)
	if err != nil {
		log.Errorln("Fetch Baidu access token failed" + err.Error())
	}

	defer resp.Body.Close()
	body, _ := ioutil.ReadAll(resp.Body)

	if resp.Status != "200 OK" {
		log.Errorln("The response of fetch Baidu access token not success: " + string(body))
		return
	}

	var t Token
	err = json.Unmarshal(body, &t)
	if err != nil {
		log.Warn("Unmarshal json failed: " + err.Error())
	}
	t.BaseTime = time.Now()
	t.ExpiresTime = t.BaseTime.Add(time.Second * time.Duration(t.ExpiresIn))

	writeToFile(&t)
	token = &t
}

func writeToFile(token *Token) {
	log.Info("Write updated token to file")
	tokenJSON, _ := json.Marshal(token)
	ioutil.WriteFile("./token.json", tokenJSON, 0644)
}

func loadToken() {
	log.Info("Loading token from local file")
	tokenString, err := ioutil.ReadFile("./token.json")
	if err != nil {
		log.Warn("Load json file failed, maybe there " + err.Error())
		return
	}

	var t Token
	json.Unmarshal(tokenString, &t)
	token = &t
}

func shouldFetchToken() bool {
	return token == nil || token.AccessToken == "" || time.Now().After(token.ExpiresTime)
}