From dd77e4628f1a65f332f0cb81c82a19c0fcfa40c2 Mon Sep 17 00:00:00 2001
From: Vyacheslav <6242627+vkryl@users.noreply.github.com>
Date: Wed, 25 Oct 2023 00:52:34 +0600
Subject: [PATCH] Strong typed API for synchronous TDLib method execution in
 Java interface

`Client.execute` in Java interface is now strongly typed: returned TDLib object type depends on the return type defined in the corresponding Function class.

When TDLib error is occurred, method now throws `Client.ExecutionError`.

This change adds compile-time protection against return type change and allows using this pattern:

```
try {
  TdApi.SpecificReturnType result = Client.execute(function);
  // work with strongly typed resultl without casting and type checks
} catch (Client.ExecutionError error) {
  // Handle error
}
```
---
 example/java/org/drinkless/tdlib/Client.java | 31 ++++++++++++++++++--
 1 file changed, 29 insertions(+), 2 deletions(-)

diff --git a/example/java/org/drinkless/tdlib/Client.java b/example/java/org/drinkless/tdlib/Client.java
index 2dd324f132e9..55d53566c3fd 100644
--- a/example/java/org/drinkless/tdlib/Client.java
+++ b/example/java/org/drinkless/tdlib/Client.java
@@ -62,6 +62,24 @@ public interface LogMessageHandler {
         void onLogMessage(int verbosityLevel, String message);
     }
 
+    /**
+     * Exception class thrown when TDLib error occurred while performing {@link #execute(TdApi.Function)}.
+     */
+    public static class ExecutionError extends Throwable {
+        /**
+         * Original TDLib error occurred when performing one of the synchronous functions.
+         */
+        public final TdApi.Error error;
+
+        /**
+         * @param error TDLib error occurred while performing {@link #execute(TdApi.Function)}.
+         */
+        ExecutionError (TdApi.Error error) {
+            super(error.code + ": " + error.message);
+            this.error = error;
+        }
+    }
+
     /**
      * Sends a request to the TDLib.
      *
@@ -102,8 +120,17 @@ public void send(TdApi.Function query, ResultHandler resultHandler) {
      * @return request result.
      * @throws NullPointerException if query is null.
      */
-    public static TdApi.Object execute(TdApi.Function query) {
-        return nativeClientExecute(query);
+    public static <T extends TdApi.Object> T execute(TdApi.Function<T> query) throws ExecutionError {
+        TdApi.Object object = nativeClientExecute(query);
+        if (object instanceof TdApi.Error) {
+            throw new ExecutionError((TdApi.Error) object);
+        }
+        if (object == null) {
+            // unreachable
+            throw new NullPointerException();
+        }
+        //noinspection unchecked
+        return (T) object;
     }
 
     /**