// Minimal webhook receiver for Finzep - Java 11+, no dependencies. Save as WebhookReceiver.java next to FzpClient.java.
// Specification: payout-api-guide.html (section "Webhooks")
//
//   javac FzpClient.java WebhookReceiver.java   &&   java WebhookReceiver     (set PORT, CLIENT_PRIVATE_KEY, SERVER_PUBLIC_KEY in the environment)
//
// Verifies OUR signature, decrypts the event with YOUR private key, ignores an event it has already handled (events can arrive more
// than once) and answers HTTP 200 quickly. Do the real work in handle(). This file uses a bare ServerSocket only to stay dependency
// free - in your application put the same few lines into your own web framework's handler (Spring, Jakarta servlet ...) behind https.
import java.io.ByteArrayOutputStream;
import java.io.InputStream;
import java.net.ServerSocket;
import java.net.Socket;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;

public class WebhookReceiver {
    static final Set<String> handled = ConcurrentHashMap.newKeySet();   // use your database in production: eventId is unique

    static void handle(String eventJson) {
        // event: payout.success | payout.failed | refund.accepted | refund.rejected | webhook.test
        System.out.println("webhook " + eventJson);
    }

    public static void main(String[] args) throws Exception {
        PrivateKey clientPrivate = FzpClient.privateKey(Files.readString(Path.of(System.getenv().getOrDefault("CLIENT_PRIVATE_KEY", "client-private.pem"))));
        PublicKey serverPublic = FzpClient.publicKey(Files.readString(Path.of(System.getenv().getOrDefault("SERVER_PUBLIC_KEY", "server-public.pem"))));
        int port = Integer.parseInt(System.getenv().getOrDefault("PORT", "8080"));

        try (ServerSocket server = new ServerSocket(port)) {
            System.out.println("listening on " + port);
            while (true) {
                Socket socket = server.accept();
                new Thread(() -> serve(socket, clientPrivate, serverPublic)).start();
            }
        }
    }

    static void serve(Socket socket, PrivateKey clientPrivate, PublicKey serverPublic) {
        try (socket) {
            InputStream in = socket.getInputStream();
            readLine(in);                                                   // request line: POST /path HTTP/1.1
            Map<String, String> headers = new HashMap<>();
            for (String line = readLine(in); line != null && !line.isEmpty(); line = readLine(in)) {
                int colon = line.indexOf(':');
                if (colon > 0) headers.put(line.substring(0, colon).trim().toLowerCase(), line.substring(colon + 1).trim());
            }
            byte[] body = in.readNBytes(Integer.parseInt(headers.getOrDefault("content-length", "0")));

            int status = 200;
            String answer = "ok";
            try {
                String json = FzpClient.openWebhook(new String(body, StandardCharsets.UTF_8), headers.get("x-webhook-id"), clientPrivate, serverPublic);
                String eventId = FzpClient.field(json, "eventId");
                if (handled.add(eventId)) handle(json);
            } catch (Exception e) {
                System.err.println("rejected webhook: " + e.getMessage());
                status = 400;       // we will retry later
                answer = "invalid";
            }
            byte[] out = answer.getBytes(StandardCharsets.UTF_8);
            String head = "HTTP/1.1 " + status + (status == 200 ? " OK" : " Bad Request") + "\r\nContent-Length: " + out.length + "\r\nConnection: close\r\n\r\n";
            socket.getOutputStream().write(head.getBytes(StandardCharsets.UTF_8));   // any 2xx tells us it arrived
            socket.getOutputStream().write(out);
            socket.getOutputStream().flush();
        } catch (Exception e) {
            System.err.println("connection error: " + e.getMessage());
        }
    }

    static String readLine(InputStream in) throws java.io.IOException {
        ByteArrayOutputStream buf = new ByteArrayOutputStream();
        for (int b = in.read(); b != -1 && b != '\n'; b = in.read()) if (b != '\r') buf.write(b);
        return buf.toString(StandardCharsets.UTF_8);
    }
}