package main

import (
	"context"
	"encoding/json"
	"fmt"
	"io/ioutil"
	"log"
	"net/http"
	"os"

	"golang.org/x/oauth2"
	"golang.org/x/oauth2/google"
	"google.golang.org/api/option"
	"google.golang.org/api/sheets/v4"
)

type Config struct {
	SpreadsheetID string `json:"spreadsheetID,omitempty"`
	Range         string `json:"range,omitempty"`
}

// Retrieve a token, saves the token, then returns the generated client.
func getClient(config *oauth2.Config) *http.Client {
	// The file token.json stores the user's access and refresh tokens, and is
	// created automatically when the authorization flow completes for the first
	// time.
	tokFile := "token.json"
	tok, err := tokenFromFile(tokFile)
	if err != nil {
		tok = getTokenFromWeb(config)
		saveToken(tokFile, tok)
	}
	return config.Client(context.Background(), tok)
}

// Request a token from the web, then returns the retrieved token.
func getTokenFromWeb(config *oauth2.Config) *oauth2.Token {
	authURL := config.AuthCodeURL("state-token", oauth2.AccessTypeOffline)
	fmt.Printf("Go to the following link in your browser then type the "+
		"authorization code: \n%v\n", authURL)

	var authCode string
	if _, err := fmt.Scan(&authCode); err != nil {
		log.Fatalf("Unable to read authorization code: %v", err)
	}

	tok, err := config.Exchange(context.TODO(), authCode)
	if err != nil {
		log.Fatalf("Unable to retrieve token from web: %v", err)
	}
	return tok
}

// Retrieves a token from a local file.
func tokenFromFile(file string) (*oauth2.Token, error) {
	f, err := os.Open(file)
	if err != nil {
		return nil, err
	}
	defer f.Close()
	tok := &oauth2.Token{}
	err = json.NewDecoder(f).Decode(tok)
	return tok, err
}

// Saves a token to a file path.
func saveToken(path string, token *oauth2.Token) {
	fmt.Printf("Saving credential file to: %s\n", path)
	f, err := os.OpenFile(path, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0600)
	if err != nil {
		log.Fatalf("Unable to cache oauth token: %v", err)
	}
	defer f.Close()
	json.NewEncoder(f).Encode(token)
}

func main() {
	// Get config
	var config Config
	jsonFile, err := os.Open("config.json")
	if err != nil {
		panic("config file read: " + err.Error())
	}
	byteValue, _ := ioutil.ReadAll(jsonFile)
	jsonFile.Close()
	err = json.Unmarshal(byteValue, &config)
	if err != nil {
		panic("config json unmarshal" + err.Error())
	}
	// Create sheets client
	ctx := context.Background()
	b, err := ioutil.ReadFile("credentials.json")
	if err != nil {
		log.Fatalf("Unable to read client secret file: %v", err)
	}
	conf, err := google.ConfigFromJSON(b, "https://www.googleapis.com/auth/spreadsheets")
	if err != nil {
		log.Fatalf("Unable to parse client secret file to config: %v", err)
	}
	client := getClient(conf)
	srv, err := sheets.NewService(ctx, option.WithHTTPClient(client))
	if err != nil {
		log.Fatalf("Unable to retrieve Sheets client: %v", err)
	}

	resp, err := srv.Spreadsheets.Values.Get(config.SpreadsheetID, config.Range).Do()
	if err != nil {
		log.Fatalf("Unable to retrieve data from sheet: %v", err)
	}

	if len(resp.Values) == 0 {
		fmt.Println("No data found.")
	} else {
		for _, row := range resp.Values {
			// Print columns A and E, which correspond to indices 0 and 4.
			fmt.Printf("%s, %s, %s, %s, %s\n", row[0], row[1], row[2], row[3], row[4])
		}
	}

}