license-lib/src/main/java/de/winniepat/licenselib/LicenseClient.java

package de.winniepat.licenselib;

import com.google.gson.Gson;
import com.google.gson.JsonObject;

import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import java.time.Duration;

/**
 * A client for checking plugin licenses against a license server.
 */
public class LicenseClient {

    private static final Gson GSON = new Gson();
    private static final HttpClient HTTP_CLIENT = HttpClient.newBuilder()
            .connectTimeout(Duration.ofSeconds(10))
            .build();

    /**
     * Private constructor to prevent instantiation of this utility class.
     */
    private LicenseClient() {
        throw new UnsupportedOperationException("Utility class");
    }

    /**
     * Checks the validity of a license key for a given plugin and server ID against the license server API.
     * @param apiUrl Server API url
     * @param plugin Plugin id matching the one on the backend api
     * @param licenseKey License key issued by the api
     * @param serverId Server id matching the one on the backend api
     * @return LicenseResult with the data from the backend
     */
    public static LicenseResult check(
            String apiUrl,
            String plugin,
            String licenseKey,
            String serverId // can be null
    ) {
        try {
            JsonObject payload = new JsonObject();
            payload.addProperty("plugin", plugin);
            payload.addProperty("licenseKey", licenseKey);

            if (serverId != null) {
                payload.addProperty("serverId", serverId);
            }

            HttpRequest request = HttpRequest.newBuilder()
                    .uri(URI.create(apiUrl))
                    .timeout(Duration.ofSeconds(10))
                    .header("Content-Type", "application/json")
                    .POST(HttpRequest.BodyPublishers.ofString(GSON.toJson(payload)))
                    .build();

            HttpResponse<String> response = HTTP_CLIENT.send(
                    request,
                    HttpResponse.BodyHandlers.ofString()
            );

            JsonObject json = GSON.fromJson(response.body(), JsonObject.class);

            return new LicenseResult(
                    json.get("valid").getAsBoolean(),
                    json.get("status").getAsString(),
                    json.get("message").getAsString()
            );
        } catch (Exception e) {
            return new LicenseResult(
                    false,
                    "error",
                    e.getMessage()
            );
        }
    }

    /**
     * Represents the result of a license check.
     * @param isValid boolean if the license is valid or not
     * @param status license status
     * @param message additional message from the backend
     */
    public record LicenseResult(
            boolean isValid,
            String status,
            String message
    ) { }
}