added saving and refreshing token

backend/services/spotify.go

@@ -1,9 +1,15 @@
 package services
 
 import (
+	"context"
+	"encoding/json"
 	"fmt"
+	"os"
+	"time"
 
+	"github.com/zmb3/spotify/v2"
 	spotifyauth "github.com/zmb3/spotify/v2/auth"
+	"golang.org/x/oauth2"
 )
 
 type SpotifyConfig struct {
@@ -13,7 +19,58 @@ type SpotifyConfig struct {
 	ClientSecret string
 }
 
-func InitSpotifyAuth(config SpotifyConfig) *spotifyauth.Authenticator {
+const SPOTIFY_TOKEN_JSON_PATH = "spotify_token.json"
+
+func SaveSpotifyToken(path string, tok *oauth2.Token) error {
+	data := struct {
+		AccessToken  string    `json:"access_token"`
+		RefreshToken string    `json:"refresh_token"`
+		TokenType    string    `json:"token_type"`
+		Expiry       time.Time `json:"expiry"`
+	}{
+		AccessToken:  tok.AccessToken,
+		RefreshToken: tok.RefreshToken,
+		TokenType:    tok.TokenType,
+		Expiry:       tok.Expiry,
+	}
+
+	jsonBytes, err := json.MarshalIndent(data, "", "  ")
+	if err != nil {
+		return err
+	}
+
+	// 0600 ensures only your user can read/write the file
+	return os.WriteFile(path, jsonBytes, 0600)
+}
+
+func LoadSpotifyToken(path string) (*oauth2.Token, error) {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return nil, err
+	}
+
+	var saved struct {
+		AccessToken  string    `json:"access_token"`
+		RefreshToken string    `json:"refresh_token"`
+		TokenType    string    `json:"token_type"`
+		Expiry       time.Time `json:"expiry"`
+	}
+
+	if err := json.Unmarshal(data, &saved); err != nil {
+		return nil, err
+	}
+
+	tok := &oauth2.Token{
+		AccessToken:  saved.AccessToken,
+		RefreshToken: saved.RefreshToken,
+		TokenType:    saved.TokenType,
+		Expiry:       saved.Expiry,
+	}
+
+	return tok, nil
+}
+
+func InitSpotifyAuth(config SpotifyConfig) (*spotifyauth.Authenticator, *spotify.Client) {
 	auth := spotifyauth.New(
 		spotifyauth.WithRedirectURL(config.RedirectURL),
 		spotifyauth.WithClientID(config.ClientID),
@@ -24,8 +81,34 @@ func InitSpotifyAuth(config SpotifyConfig) *spotifyauth.Authenticator {
 		),
 	)
 
-	fmt.Println("Authenticate spotify with:")
-	fmt.Println(auth.AuthURL(config.AuthState))
+	// check if token exists locally
+	token, err := LoadSpotifyToken(SPOTIFY_TOKEN_JSON_PATH)
+	if err != nil || token == nil {
+		fmt.Println("No token saved. Authenticate Spotify with:")
+		fmt.Println(auth.AuthURL(config.AuthState))
+		return auth, nil
+	}
 
-	return auth
+	// refresh token and client
+	client, err := RefreshClient(auth, token)
+	if err != nil {
+		fmt.Println("Failed to refresh token. Authenticate Spotify with:")
+		fmt.Println(auth.AuthURL(config.AuthState))
+		return auth, nil
+	}
+
+	return auth, client
+}
+
+func RefreshClient(auth *spotifyauth.Authenticator, token *oauth2.Token) (*spotify.Client, error) {
+	ctx := context.Background()
+
+	token, err := auth.RefreshToken(ctx, token)
+	if err != nil {
+		return nil, err
+	}
+
+	client := spotify.New(auth.Client(ctx, token))
+
+	return client, nil
 }