poc calendar service

internal/calendar/service.go

@@ -0,0 +1,113 @@
+package calendar
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"log"
+	"net/http"
+	"os"
+	"time"
+
+	"golang.org/x/oauth2"
+	"golang.org/x/oauth2/google"
+	"google.golang.org/api/calendar/v3"
+	"google.golang.org/api/option"
+)
+
+const tokFile = "token.json"
+
+type Service struct {
+	*calendar.Service
+}
+
+func NewService(ctx context.Context, credJson string) *Service {
+	b := []byte(credJson)
+
+	config, err := google.ConfigFromJSON(b, calendar.CalendarReadonlyScope)
+	if err != nil {
+		log.Fatalf("Unable to parse client secret file to config: %v", err)
+	}
+	client := getClient(ctx, config)
+
+	srv, err := calendar.NewService(ctx, option.WithHTTPClient(client))
+	if err != nil {
+		log.Fatalf("Unable to retrieve Calendar client: %v", err)
+	}
+
+	return &Service{srv}
+}
+
+// TODO: implement create event, list events in a period, delete event
+
+// TODO: Delete this. It is just for Proof of Concept
+func (s Service) ListNextEvents() (*calendar.Events, error) {
+	t := time.Now().Format(time.RFC3339)
+	events, err := s.Events.List("primary").ShowDeleted(false).
+		SingleEvents(true).TimeMin(t).MaxResults(10).OrderBy("startTime").Do()
+	if err != nil {
+		return nil, fmt.Errorf("unable to retrieve next ten of the user's events: %w", err)
+	}
+	if len(events.Items) == 0 {
+		return nil, errors.New("no upcoming events found")
+	} else {
+		// TODO: return a custom type
+		return events, nil
+	}
+}
+
+// Retrieve a token, saves the token, then returns the generated client.
+func getClient(ctx context.Context, 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.
+	tok, err := tokenFromFile(tokFile)
+	if err != nil {
+		tok = getTokenFromWeb(config)
+		saveToken(tokFile, tok)
+	}
+	return config.Client(ctx, 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("Click on the following link to open in your browser \n%v\n", authURL)
+
+	// TODO: write a callback endpoint that will parse the auth code from the URL
+	var authCode string
+	fmt.Print("Type the authorization code: \n> ")
+	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)
+}