Resolve port: CLI > config > default (#29)

* Resolve port: CLI > config > default

* Wire port resolution to AppConfig/ConfigLoader and update docs/tests

* Update PortConfigurationGuide.md

* Update PortConfigurationGuide.md

* Remove ServerPortResolver; use ConfigLoader for port

* Update PortConfigurationGuide.md

* Update PortConfigurationGuide.md

* may be done

Author: viktorlindell12

PortConfigurationGuide.md

@@ -0,0 +1,49 @@
+# Konfiguration: port (CLI → config-fil → default)
+
+Det här projektet väljer vilken port servern ska starta på enligt följande prioritet:
+
+1. **CLI-argument** (`--port <port>`) – högst prioritet
+2. **Config-fil** (`application.yml`: `server.port`)
+3. **Default** (`8080`) – används om port saknas i config eller om config-filen saknas
+
+---
+
+## 1) Default-värde
+
+Om varken CLI eller config anger port används:
+
+- **8080** (default för `server.port` i `AppConfig`)
+
+---
+
+## 2) Config-fil: `application.yml`
+
+### Var ska filen ligga?
+Standard:
+- `src/main/resources/application.yml`
+
+### Exempel
+```yaml
+server:
+port: 9090
+```
+
+---
+
+## 3) CLI-argument
+
+CLI kan användas för att override:a config:
+
+```bash
+java -cp target/classes org.example.App --port 8000
+```
+
+---
+
+## 4) Sammanfattning
+
+Prioritet:
+
+1. CLI (`--port`)
+2. `application.yml` (`server.port`)
+3. Default (`8080`)

src/main/java/org/example/App.java

@@ -6,11 +6,50 @@
 import java.nio.file.Path;
 
 public class App {
+
+    private static final String PORT_FLAG = "--port";
+
     public static void main(String[] args) {
         Path configPath = Path.of("src/main/resources/application.yml");
 
         AppConfig appConfig = ConfigLoader.loadOnce(configPath);
-        int port = appConfig.server().port();
+
+        int port = resolvePort(args, appConfig.server().port());
+
         new TcpServer(port).start();
     }
+
+    static int resolvePort(String[] args, int configPort) {
+        Integer cliPort = parsePortFromCli(args);
+        if (cliPort != null) {
+            return validatePort(cliPort, "CLI argument " + PORT_FLAG);
+        }
+        return validatePort(configPort, "configuration server.port");
+    }
+
+    static Integer parsePortFromCli(String[] args) {
+        if (args == null) return null;
+
+        for (int i = 0; i < args.length; i++) {
+            if (PORT_FLAG.equals(args[i])) {
+                int valueIndex = i + 1;
+                if (valueIndex >= args.length) {
+                    throw new IllegalArgumentException("Missing value after " + PORT_FLAG);
+                }
+                try {
+                    return Integer.parseInt(args[valueIndex]);
+                } catch (NumberFormatException e) {
+                    throw new IllegalArgumentException("Invalid port value after " + PORT_FLAG + ": " + args[valueIndex], e);
+                }
+            }
+        }
+        return null;
+    }
+
+    static int validatePort(int port, String source) {
+        if (port < 1 || port > 65535) {
+            throw new IllegalArgumentException("Port out of range (1-65535) from " + source + ": " + port);
+        }
+        return port;
+    }
 }

src/test/java/org/example/AppPortResolutionTest.java

@@ -0,0 +1,21 @@
+package org.example;
+
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class AppPortResolutionTest {
+
+    @Test
+    void cli_port_wins_over_config() {
+        int port = App.resolvePort(new String[]{"--port", "8000"}, 9090);
+        assertThat(port).isEqualTo(8000);
+    }
+
+    @Test
+    void config_port_used_when_no_cli_arg() {
+        int port = App.resolvePort(new String[]{}, 9090);
+        assertThat(port).isEqualTo(9090);
+    }
+}