token refresh added

.gitignore

@@ -1,3 +1,4 @@
 credentials.json
 create-expense
 token.json
+tokenRefresh

tokenRefresh.go

@@ -0,0 +1,121 @@
+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])
+		}
+	}
+
+}