[build] Add package declaration check to checkstyle (#2446)

Co-authored-by: Austin Shalit <austinshalit@gmail.com>

cameraserver/multiCameraServer/src/main/java/edu/wpi/Main.java

@@ -0,0 +1,213 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2018-2020 FIRST. All Rights Reserved.                        */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+package edu.wpi;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Paths;
+import java.util.ArrayList;
+import java.util.List;
+
+import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
+import com.google.gson.JsonArray;
+import com.google.gson.JsonElement;
+import com.google.gson.JsonObject;
+import com.google.gson.JsonParser;
+
+import edu.wpi.cscore.VideoSource;
+import edu.wpi.first.cameraserver.CameraServer;
+import edu.wpi.first.networktables.NetworkTableInstance;
+
+/*
+   JSON format:
+   {
+       "team": <team number>,
+       "ntmode": <"client" or "server", "client" if unspecified>
+       "cameras": [
+           {
+               "name": <camera name>
+               "path": <path, e.g. "/dev/video0">
+               "pixel format": <"MJPEG", "YUYV", etc>   // optional
+               "width": <video mode width>              // optional
+               "height": <video mode height>            // optional
+               "fps": <video mode fps>                  // optional
+               "brightness": <percentage brightness>    // optional
+               "white balance": <"auto", "hold", value> // optional
+               "exposure": <"auto", "hold", value>      // optional
+               "properties": [                          // optional
+                   {
+                       "name": <property name>
+                       "value": <property value>
+                   }
+               ]
+           }
+       ]
+   }
+ */
+
+public final class Main {
+  private static String configFile = "/boot/frc.json";
+
+  @SuppressWarnings("MemberName")
+  public static class CameraConfig {
+    public String name;
+    public String path;
+    public JsonObject config;
+  }
+
+  public static int team;
+  public static boolean server;
+  public static List<CameraConfig> cameras = new ArrayList<>();
+
+  private Main() {
+  }
+
+  /**
+   * Report parse error.
+   */
+  public static void parseError(String str) {
+    System.err.println("config error in '" + configFile + "': " + str);
+  }
+
+  /**
+   * Read single camera configuration.
+   */
+  public static boolean readCameraConfig(JsonObject config) {
+    CameraConfig cam = new CameraConfig();
+
+    // name
+    JsonElement nameElement = config.get("name");
+    if (nameElement == null) {
+      parseError("could not read camera name");
+      return false;
+    }
+    cam.name = nameElement.getAsString();
+
+    // path
+    JsonElement pathElement = config.get("path");
+    if (pathElement == null) {
+      parseError("camera '" + cam.name + "': could not read path");
+      return false;
+    }
+    cam.path = pathElement.getAsString();
+
+    cam.config = config;
+
+    cameras.add(cam);
+    return true;
+  }
+
+  /**
+   * Read configuration file.
+   */
+  @SuppressWarnings("PMD.CyclomaticComplexity")
+  public static boolean readConfig() {
+    // parse file
+    JsonElement top;
+    try {
+      top = new JsonParser().parse(Files.newBufferedReader(Paths.get(configFile)));
+    } catch (IOException ex) {
+      System.err.println("could not open '" + configFile + "': " + ex);
+      return false;
+    }
+
+    // top level must be an object
+    if (!top.isJsonObject()) {
+      parseError("must be JSON object");
+      return false;
+    }
+    JsonObject obj = top.getAsJsonObject();
+
+    // team number
+    JsonElement teamElement = obj.get("team");
+    if (teamElement == null) {
+      parseError("could not read team number");
+      return false;
+    }
+    team = teamElement.getAsInt();
+
+    // ntmode (optional)
+    if (obj.has("ntmode")) {
+      String str = obj.get("ntmode").getAsString();
+      if ("client".equalsIgnoreCase(str)) {
+        server = false;
+      } else if ("server".equalsIgnoreCase(str)) {
+        server = true;
+      } else {
+        parseError("could not understand ntmode value '" + str + "'");
+      }
+    }
+
+    // cameras
+    JsonElement camerasElement = obj.get("cameras");
+    if (camerasElement == null) {
+      parseError("could not read cameras");
+      return false;
+    }
+    JsonArray cameras = camerasElement.getAsJsonArray();
+    for (JsonElement camera : cameras) {
+      if (!readCameraConfig(camera.getAsJsonObject())) {
+        return false;
+      }
+    }
+
+    return true;
+  }
+
+  /**
+   * Start running the camera.
+   */
+  public static void startCamera(CameraConfig config) {
+    System.out.println("Starting camera '" + config.name + "' on " + config.path);
+    VideoSource camera = CameraServer.getInstance().startAutomaticCapture(
+        config.name, config.path);
+
+    Gson gson = new GsonBuilder().create();
+
+    camera.setConfigJson(gson.toJson(config.config));
+  }
+
+  /**
+   * Main.
+   */
+  public static void main(String... args) {
+    if (args.length > 0) {
+      configFile = args[0];
+    }
+
+    // read configuration
+    if (!readConfig()) {
+      return;
+    }
+
+    // start NetworkTables
+    NetworkTableInstance ntinst = NetworkTableInstance.getDefault();
+    if (server) {
+      System.out.println("Setting up NetworkTables server");
+      ntinst.startServer();
+    } else {
+      System.out.println("Setting up NetworkTables client for team " + team);
+      ntinst.startClientTeam(team);
+    }
+
+    // start cameras
+    for (CameraConfig camera : cameras) {
+      startCamera(camera);
+    }
+
+    // loop forever
+    for (;;) {
+      try {
+        Thread.sleep(10000);
+      } catch (InterruptedException ex) {
+        return;
+      }
+    }
+  }
+}