feat: create OAuthRequestFactory#getLoginUrl

Author: yvasyliev

src/main/java/io/github/yvasyliev/deezer/exception/DeezerException.java

@@ -8,4 +8,8 @@ public DeezerException(String message) {
     public DeezerException(Throwable cause) {
         super(cause);
     }
+
+    public DeezerException(String message, Throwable cause) {
+        super(message, cause);
+    }
 }

src/main/java/io/github/yvasyliev/deezer/factory/OAuthRequestFactory.java

@@ -1,15 +1,64 @@
 package io.github.yvasyliev.deezer.factory;
 
+import io.github.yvasyliev.deezer.exception.DeezerException;
 import io.github.yvasyliev.deezer.model.AccessToken;
+import io.github.yvasyliev.deezer.model.Permission;
 import io.github.yvasyliev.deezer.request.DeezerRequest;
 import io.github.yvasyliev.deezer.request.SimpleDeezerRequest;
 import io.github.yvasyliev.deezer.service.OAuthService;
 import lombok.RequiredArgsConstructor;
 
+import java.net.MalformedURLException;
+import java.net.URI;
+import java.net.URL;
+import java.net.URLEncoder;
+import java.nio.charset.StandardCharsets;
+import java.util.Collection;
+import java.util.stream.Collectors;
+
+/**
+ * Factory for creating OAuth-related requests.
+ */
 @RequiredArgsConstructor
 public class OAuthRequestFactory {
+    private static final String LOGIN_URL_TEMPLATE = "%s/oauth/auth.php?app_id=%d&redirect_uri=%s&perms=%s";
+    private final URL authHost;
     private final OAuthService oAuthService;
 
+    /**
+     * Generates the login URL for the OAuth flow.
+     *
+     * @param appId       the application ID
+     * @param redirectUri the URI to redirect to after login
+     * @param permissions the permissions to request
+     * @return the login URL
+     * @throws DeezerException if URL generation fails
+     */
+    public URL getLoginUrl(int appId, String redirectUri, Collection<Permission> permissions)
+            throws DeezerException {
+        try {
+            var perms = permissions.stream().map(Permission::getValue).collect(Collectors.joining(","));
+            var loginUrl = LOGIN_URL_TEMPLATE.formatted(
+                    authHost,
+                    appId,
+                    URLEncoder.encode(redirectUri, StandardCharsets.UTF_8),
+                    URLEncoder.encode(perms, StandardCharsets.UTF_8)
+            );
+
+            return URI.create(loginUrl).toURL();
+        } catch (MalformedURLException e) {
+            throw new DeezerException("Failed to generate login URL", e);
+        }
+    }
+
+    /**
+     * Exchanges the authorization code for an access token.
+     *
+     * @param appId  the application ID
+     * @param secret the application secret
+     * @param code   the authorization code received from the login flow
+     * @return an access token request
+     */
     public DeezerRequest<AccessToken> getAccessToken(int appId, String secret, String code) {
         return new SimpleDeezerRequest<>(() -> oAuthService.getAccessTokenAsync(appId, secret, code));
     }

src/main/java/io/github/yvasyliev/deezer/model/Permission.java

@@ -0,0 +1,48 @@
+package io.github.yvasyliev.deezer.model;
+
+import lombok.Getter;
+import lombok.RequiredArgsConstructor;
+
+/**
+ * Permissions that can be requested by the application.
+ */
+@RequiredArgsConstructor
+@Getter
+public enum Permission {
+    /**
+     * Access users basic information.
+     */
+    BASIC_ACCESS("basic_access"),
+
+    /**
+     * Get the user's email.
+     */
+    EMAIL("email"),
+
+    /**
+     * Access user data any time.
+     */
+    OFFLINE_ACCESS("offline_access"),
+
+    /**
+     * Manage users' library.
+     */
+    MANAGE_LIBRARY("manage_library"),
+
+    /**
+     * Manage users' friends.
+     */
+    MANAGE_COMMUNITY("manage_community"),
+
+    /**
+     * Delete library items.
+     */
+    DELETE_LIBRARY("delete_library"),
+
+    /**
+     * Allow the application to access the user's listening history.
+     */
+    LISTENING_HISTORY("listening_history");
+
+    private final String value;
+}