// License: GPL. For details, see LICENSE file.
package org.openstreetmap.josm;

import static org.openstreetmap.josm.tools.I18n.tr;

import java.awt.Component;
import java.awt.GraphicsEnvironment;
import java.io.IOException;
import java.lang.ref.WeakReference;
import java.net.URL;
import java.text.MessageFormat;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.EnumSet;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.Set;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

import javax.swing.Action;

import org.openstreetmap.josm.actions.JosmAction;
import org.openstreetmap.josm.data.Bounds;
import org.openstreetmap.josm.data.Preferences;
import org.openstreetmap.josm.data.UndoRedoHandler;
import org.openstreetmap.josm.data.coor.conversion.CoordinateFormatManager;
import org.openstreetmap.josm.data.coor.conversion.DecimalDegreesCoordinateFormat;
import org.openstreetmap.josm.data.coor.conversion.ICoordinateFormat;
import org.openstreetmap.josm.data.osm.DataSet;
import org.openstreetmap.josm.data.osm.OsmPrimitive;
import org.openstreetmap.josm.data.projection.Projection;
import org.openstreetmap.josm.data.projection.ProjectionChangeListener;
import org.openstreetmap.josm.gui.MainApplication;
import org.openstreetmap.josm.gui.MainMenu;
import org.openstreetmap.josm.gui.MainPanel;
import org.openstreetmap.josm.gui.MapFrame;
import org.openstreetmap.josm.gui.MapFrameListener;
import org.openstreetmap.josm.gui.layer.MainLayerManager;
import org.openstreetmap.josm.gui.preferences.ToolbarPreferences;
import org.openstreetmap.josm.io.FileWatcher;
import org.openstreetmap.josm.io.OnlineResource;
import org.openstreetmap.josm.io.OsmApi;
import org.openstreetmap.josm.spi.preferences.Config;
import org.openstreetmap.josm.tools.CheckParameterUtil;
import org.openstreetmap.josm.tools.ImageProvider;
import org.openstreetmap.josm.tools.JosmRuntimeException;
import org.openstreetmap.josm.tools.Logging;
import org.openstreetmap.josm.tools.Platform;
import org.openstreetmap.josm.tools.PlatformHook;
import org.openstreetmap.josm.tools.PlatformHookOsx;
import org.openstreetmap.josm.tools.PlatformHookWindows;
import org.openstreetmap.josm.tools.Shortcut;
import org.openstreetmap.josm.tools.Utils;
import org.openstreetmap.josm.tools.bugreport.BugReport;

/**
 * Abstract class holding various static global variables and methods used in large parts of JOSM application.
 * @since 98
 */
public abstract class Main {

    /**
     * The JOSM website URL.
     * @since 6897 (was public from 6143 to 6896)
     */
    private static final String JOSM_WEBSITE = "https://josm.openstreetmap.de";

    /**
     * The OSM website URL.
     * @since 6897 (was public from 6453 to 6896)
     */
    private static final String OSM_WEBSITE = "https://www.openstreetmap.org";

    /**
     * Replies true if JOSM currently displays a map view. False, if it doesn't, i.e. if
     * it only shows the MOTD panel.
     * <p>
     * You do not need this when accessing the layer manager. The layer manager will be empty if no map view is shown.
     *
     * @return <code>true</code> if JOSM currently displays a map view
     * @deprecated use {@link org.openstreetmap.josm.gui.MainApplication#isDisplayingMapView()}
     */
    @Deprecated
    public static boolean isDisplayingMapView() {
        return MainApplication.isDisplayingMapView();
    }

    /**
     * Global parent component for all dialogs and message boxes
     */
    public static Component parent;

    /**
     * Global application.
     */
    public static volatile Main main;

    /**
     * The worker thread slave. This is for executing all long and intensive
     * calculations. The executed runnables are guaranteed to be executed separately and sequential.
     * @deprecated use {@link MainApplication#worker} instead
     */
    @Deprecated
    public static ExecutorService worker;

    /**
     * Global application preferences
     */
    public static final Preferences pref = new Preferences();

    /**
     * The MapFrame.
     * <p>
     * There should be no need to access this to access any map data. Use {@link MainApplication#getLayerManager} instead.
     *
     * @deprecated Use {@link MainApplication#getMap()} instead
     * @see MainPanel
     */
    @Deprecated
    public static MapFrame map;

    /**
     * The toolbar preference control to register new actions.
     * @deprecated Use {@link MainApplication#getToolbar} instead
     */
    @Deprecated
    public static volatile ToolbarPreferences toolbar;

    /**
     * The commands undo/redo handler.
     */
    public final UndoRedoHandler undoRedo = new UndoRedoHandler();

    /**
     * The main menu bar at top of screen.
     * @deprecated Use {@link MainApplication#getMenu} instead
     */
    @Deprecated
    public MainMenu menu;

    /**
     * The main panel.
     * @deprecated Use {@link MainApplication#getMainPanel} instead
     * @since 12125
     */
    @Deprecated
    public MainPanel panel;

    /**
     * The file watcher service.
     */
    public static final FileWatcher fileWatcher = new FileWatcher();

    private static final Map<String, Throwable> NETWORK_ERRORS = new HashMap<>();

    private static final Set<OnlineResource> OFFLINE_RESOURCES = EnumSet.noneOf(OnlineResource.class);

    /**
     * Logging level (5 = trace, 4 = debug, 3 = info, 2 = warn, 1 = error, 0 = none).
     * @since 6248
     * @deprecated Use {@link Logging} class.
     */
    @Deprecated
    public static int logLevel = 3;

    /**
     * Replies the first lines of last 5 error and warning messages, used for bug reports
     * @return the first lines of last 5 error and warning messages
     * @since 7420
     * @deprecated Use {@link Logging#getLastErrorAndWarnings}.
     */
    @Deprecated
    public static final Collection<String> getLastErrorAndWarnings() {
        return Logging.getLastErrorAndWarnings();
    }

    /**
     * Clears the list of last error and warning messages.
     * @since 8959
     * @deprecated Use {@link Logging#clearLastErrorAndWarnings}.
     */
    @Deprecated
    public static void clearLastErrorAndWarnings() {
        Logging.clearLastErrorAndWarnings();
    }

    /**
     * Prints an error message if logging is on.
     * @param msg The message to print.
     * @since 6248
     * @deprecated Use {@link Logging#error(String)}.
     */
    @Deprecated
    public static void error(String msg) {
        Logging.error(msg);
    }

    /**
     * Prints a warning message if logging is on.
     * @param msg The message to print.
     * @deprecated Use {@link Logging#warn(String)}.
     */
    @Deprecated
    public static void warn(String msg) {
        Logging.warn(msg);
    }

    /**
     * Prints an informational message if logging is on.
     * @param msg The message to print.
     * @deprecated Use {@link Logging#info(String)}.
     */
    @Deprecated
    public static void info(String msg) {
        Logging.info(msg);
    }

    /**
     * Prints a debug message if logging is on.
     * @param msg The message to print.
     * @deprecated Use {@link Logging#debug(String)}.
     */
    @Deprecated
    public static void debug(String msg) {
        Logging.debug(msg);
    }

    /**
     * Prints a trace message if logging is on.
     * @param msg The message to print.
     * @deprecated Use {@link Logging#trace(String)}.
     */
    @Deprecated
    public static void trace(String msg) {
        Logging.trace(msg);
    }

    /**
     * Determines if debug log level is enabled.
     * Useful to avoid costly construction of debug messages when not enabled.
     * @return {@code true} if log level is at least debug, {@code false} otherwise
     * @since 6852
     * @deprecated Use {@link Logging#isDebugEnabled}.
     */
    @Deprecated
    public static boolean isDebugEnabled() {
        return Logging.isDebugEnabled();
    }

    /**
     * Determines if trace log level is enabled.
     * Useful to avoid costly construction of trace messages when not enabled.
     * @return {@code true} if log level is at least trace, {@code false} otherwise
     * @since 6852
     * @deprecated Use {@link Logging#isTraceEnabled}.
     */
    @Deprecated
    public static boolean isTraceEnabled() {
        return Logging.isTraceEnabled();
    }

    /**
     * Prints a formatted error message if logging is on. Calls {@link MessageFormat#format}
     * function to format text.
     * @param msg The formatted message to print.
     * @param objects The objects to insert into format string.
     * @since 6248
     * @deprecated Use {@link Logging#error(String, Object...)}.
     */
    @Deprecated
    public static void error(String msg, Object... objects) {
        Logging.error(msg, objects);
    }

    /**
     * Prints a formatted warning message if logging is on. Calls {@link MessageFormat#format}
     * function to format text.
     * @param msg The formatted message to print.
     * @param objects The objects to insert into format string.
     * @deprecated Use {@link Logging#warn(String, Object...)}.
     */
    @Deprecated
    public static void warn(String msg, Object... objects) {
        Logging.warn(msg, objects);
    }

    /**
     * Prints a formatted informational message if logging is on. Calls {@link MessageFormat#format}
     * function to format text.
     * @param msg The formatted message to print.
     * @param objects The objects to insert into format string.
     * @deprecated Use {@link Logging#info(String, Object...)}.
     */
    @Deprecated
    public static void info(String msg, Object... objects) {
        Logging.info(msg, objects);
    }

    /**
     * Prints a formatted debug message if logging is on. Calls {@link MessageFormat#format}
     * function to format text.
     * @param msg The formatted message to print.
     * @param objects The objects to insert into format string.
     * @deprecated Use {@link Logging#debug(String, Object...)}.
     */
    @Deprecated
    public static void debug(String msg, Object... objects) {
        Logging.debug(msg, objects);
    }

    /**
     * Prints a formatted trace message if logging is on. Calls {@link MessageFormat#format}
     * function to format text.
     * @param msg The formatted message to print.
     * @param objects The objects to insert into format string.
     * @deprecated Use {@link Logging#trace(String, Object...)}.
     */
    @Deprecated
    public static void trace(String msg, Object... objects) {
        Logging.trace(msg, objects);
    }

    /**
     * Prints an error message for the given Throwable.
     * @param t The throwable object causing the error
     * @since 6248
     * @deprecated Use {@link Logging#error(Throwable)}.
     */
    @Deprecated
    public static void error(Throwable t) {
        Logging.error(t);
    }

    /**
     * Prints a warning message for the given Throwable.
     * @param t The throwable object causing the error
     * @since 6248
     * @deprecated Use {@link Logging#warn(Throwable)}.
     */
    @Deprecated
    public static void warn(Throwable t) {
        Logging.warn(t);
    }

    /**
     * Prints a debug message for the given Throwable. Useful for exceptions usually ignored
     * @param t The throwable object causing the error
     * @since 10420
     * @deprecated Use {@link Logging#debug(Throwable)}.
     */
    @Deprecated
    public static void debug(Throwable t) {
        Logging.debug(t);
    }

    /**
     * Prints a trace message for the given Throwable. Useful for exceptions usually ignored
     * @param t The throwable object causing the error
     * @since 10420
     * @deprecated Use {@link Logging#trace(Throwable)}.
     */
    @Deprecated
    public static void trace(Throwable t) {
        Logging.trace(t);
    }

    /**
     * Prints an error message for the given Throwable.
     * @param t The throwable object causing the error
     * @param stackTrace {@code true}, if the stacktrace should be displayed
     * @since 6642
     * @deprecated Use {@link Logging#log(java.util.logging.Level, Throwable)}
     *              or {@link Logging#logWithStackTrace(java.util.logging.Level, Throwable)}.
     */
    @Deprecated
    public static void error(Throwable t, boolean stackTrace) {
        if (stackTrace) {
            Logging.log(Logging.LEVEL_ERROR, t);
        } else {
            Logging.logWithStackTrace(Logging.LEVEL_ERROR, t);
        }
    }

    /**
     * Prints an error message for the given Throwable.
     * @param t The throwable object causing the error
     * @param message additional error message
     * @since 10420
     * @deprecated Use {@link Logging#log(java.util.logging.Level, String, Throwable)}.
     */
    @Deprecated
    public static void error(Throwable t, String message) {
        Logging.log(Logging.LEVEL_ERROR, message, t);
    }

    /**
     * Prints a warning message for the given Throwable.
     * @param t The throwable object causing the error
     * @param stackTrace {@code true}, if the stacktrace should be displayed
     * @since 6642
     * @deprecated Use {@link Logging#log(java.util.logging.Level, Throwable)}
     *              or {@link Logging#logWithStackTrace(java.util.logging.Level, Throwable)}.
     */
    @Deprecated
    public static void warn(Throwable t, boolean stackTrace) {
        if (stackTrace) {
            Logging.log(Logging.LEVEL_WARN, t);
        } else {
            Logging.logWithStackTrace(Logging.LEVEL_WARN, t);
        }
    }

    /**
     * Prints a warning message for the given Throwable.
     * @param t The throwable object causing the error
     * @param message additional error message
     * @since 10420
     * @deprecated Use {@link Logging#log(java.util.logging.Level, String, Throwable)}.
     */
    @Deprecated
    public static void warn(Throwable t, String message) {
        Logging.log(Logging.LEVEL_WARN, message, t);
    }

    /**
     * Returns a human-readable message of error, also usable for developers.
     * @param t The error
     * @return The human-readable error message
     * @since 6642
     * @deprecated Use {@link Logging#getErrorMessage}.
     */
    @Deprecated
    public static String getErrorMessage(Throwable t) {
        if (t == null) {
            return null;
        } else {
            return Logging.getErrorMessage(t);
        }
    }

    /**
     * Platform specific code goes in here.
     * Plugins may replace it, however, some hooks will be called before any plugins have been loaded.
     * So if you need to hook into those early ones, split your class and send the one with the early hooks
     * to the JOSM team for inclusion.
     */
    public static volatile PlatformHook platform;

    private static volatile InitStatusListener initListener;

    /**
     * Initialization task listener.
     */
    public interface InitStatusListener {

        /**
         * Called when an initialization task updates its status.
         * @param event task name
         * @return new status
         */
        Object updateStatus(String event);

        /**
         * Called when an initialization task completes.
         * @param status final status
         */
        void finish(Object status);
    }

    /**
     * Sets initialization task listener.
     * @param listener initialization task listener
     */
    public static void setInitStatusListener(InitStatusListener listener) {
        CheckParameterUtil.ensureParameterNotNull(listener);
        initListener = listener;
    }

    /**
     * Constructs new {@code Main} object.
     * @see #initialize()
     */
    protected Main() {
        setInstance(this);
    }

    private static void setInstance(Main instance) {
        main = instance;
    }

    /**
     * Initializes the main object. A lot of global variables are initialized here.
     * @since 10340
     */
    public void initialize() {
        // Initializes tasks that must be run before parallel tasks
        runInitializationTasks(beforeInitializationTasks());

        // Initializes tasks to be executed (in parallel) by a ExecutorService
        try {
            ExecutorService service = Executors.newFixedThreadPool(
                    Runtime.getRuntime().availableProcessors(), Utils.newThreadFactory("main-init-%d", Thread.NORM_PRIORITY));
            for (Future<Void> i : service.invokeAll(parallelInitializationTasks())) {
                i.get();
            }
            // asynchronous initializations to be completed eventually
            asynchronousRunnableTasks().forEach(service::submit);
            asynchronousCallableTasks().forEach(service::submit);
            service.shutdown();
        } catch (InterruptedException | ExecutionException ex) {
            throw new JosmRuntimeException(ex);
        }

        // Initializes tasks that must be run after parallel tasks
        runInitializationTasks(afterInitializationTasks());
    }

    private static void runInitializationTasks(List<InitializationTask> tasks) {
        for (InitializationTask task : tasks) {
            try {
                task.call();
            } catch (JosmRuntimeException e) {
                // Can happen if the current projection needs NTV2 grid which is not available
                // In this case we want the user be able to change his projection
                BugReport.intercept(e).warn();
            }
        }
    }

    /**
     * Returns tasks that must be run before parallel tasks.
     * @return tasks that must be run before parallel tasks
     * @see #afterInitializationTasks
     * @see #parallelInitializationTasks
     */
    protected List<InitializationTask> beforeInitializationTasks() {
        return Collections.emptyList();
    }

    /**
     * Returns tasks to be executed (in parallel) by a ExecutorService.
     * @return tasks to be executed (in parallel) by a ExecutorService
     */
    protected Collection<InitializationTask> parallelInitializationTasks() {
        return Collections.emptyList();
    }

    /**
     * Returns asynchronous callable initializations to be completed eventually
     * @return asynchronous callable initializations to be completed eventually
     */
    protected List<Callable<?>> asynchronousCallableTasks() {
        return Collections.emptyList();
    }

    /**
     * Returns asynchronous runnable initializations to be completed eventually
     * @return asynchronous runnable initializations to be completed eventually
     */
    protected List<Runnable> asynchronousRunnableTasks() {
        return Collections.emptyList();
    }

    /**
     * Returns tasks that must be run after parallel tasks.
     * @return tasks that must be run after parallel tasks
     * @see #beforeInitializationTasks
     * @see #parallelInitializationTasks
     */
    protected List<InitializationTask> afterInitializationTasks() {
        return Collections.emptyList();
    }

    protected static final class InitializationTask implements Callable<Void> {

        private final String name;
        private final Runnable task;

        /**
         * Constructs a new {@code InitializationTask}.
         * @param name translated name to be displayed to user
         * @param task runnable initialization task
         */
        public InitializationTask(String name, Runnable task) {
            this.name = name;
            this.task = task;
        }

        @Override
        public Void call() {
            Object status = null;
            if (initListener != null) {
                status = initListener.updateStatus(name);
            }
            task.run();
            if (initListener != null) {
                initListener.finish(status);
            }
            return null;
        }
    }

    /**
     * Returns the main layer manager that is used by the map view.
     * @return The layer manager. The value returned will never change.
     * @since 10279
     * @deprecated use {@link MainApplication#getLayerManager} instead
     */
    @Deprecated
    public static MainLayerManager getLayerManager() {
        return MainApplication.getLayerManager();
    }

    /**
     * Replies the current selected primitives, from a end-user point of view.
     * It is not always technically the same collection of primitives than {@link DataSet#getSelected()}.
     * @return The current selected primitives, from a end-user point of view. Can be {@code null}.
     * @since 6546
     */
    public Collection<OsmPrimitive> getInProgressSelection() {
        return Collections.emptyList();
    }

    /**
     * Gets the active edit data set.
     * @return That data set, <code>null</code>.
     * @since 12691
     */
    public abstract DataSet getEditDataSet();

    /**
     * Sets the active data set.
     * @param ds New edit data set, or <code>null</code>
     * @since 12718
     */
    public abstract void setEditDataSet(DataSet ds);

    /**
     * Determines if the list of data sets managed by JOSM contains {@code ds}.
     * @param ds the data set to look for
     * @return {@code true} if the list of data sets managed by JOSM contains {@code ds}
     * @since 12718
     */
    public abstract boolean containsDataSet(DataSet ds);

    /**
     * Registers a {@code JosmAction} and its shortcut.
     * @param action action defining its own shortcut
     * @deprecated use {@link MainApplication#registerActionShortcut(JosmAction)} instead
     */
    @Deprecated
    public static void registerActionShortcut(JosmAction action) {
        MainApplication.registerActionShortcut(action);
    }

    /**
     * Registers an action and its shortcut.
     * @param action action to register
     * @param shortcut shortcut to associate to {@code action}
     * @deprecated use {@link MainApplication#registerActionShortcut(Action, Shortcut)} instead
     */
    @Deprecated
    public static void registerActionShortcut(Action action, Shortcut shortcut) {
        MainApplication.registerActionShortcut(action, shortcut);
    }

    /**
     * Unregisters a shortcut.
     * @param shortcut shortcut to unregister
     * @deprecated use {@link MainApplication#unregisterShortcut(Shortcut)} instead
     */
    @Deprecated
    public static void unregisterShortcut(Shortcut shortcut) {
        MainApplication.unregisterShortcut(shortcut);
    }

    /**
     * Unregisters a {@code JosmAction} and its shortcut.
     * @param action action to unregister
     * @deprecated use {@link MainApplication#unregisterActionShortcut(JosmAction)} instead
     */
    @Deprecated
    public static void unregisterActionShortcut(JosmAction action) {
        MainApplication.unregisterActionShortcut(action);
    }

    /**
     * Unregisters an action and its shortcut.
     * @param action action to unregister
     * @param shortcut shortcut to unregister
     * @deprecated use {@link MainApplication#unregisterActionShortcut(Action, Shortcut)} instead
     */
    @Deprecated
    public static void unregisterActionShortcut(Action action, Shortcut shortcut) {
        MainApplication.unregisterActionShortcut(action, shortcut);
    }

    /**
     * Replies the registered action for the given shortcut
     * @param shortcut The shortcut to look for
     * @return the registered action for the given shortcut
     * @deprecated use {@link MainApplication#getRegisteredActionShortcut(Shortcut)} instead
     * @since 5696
     */
    @Deprecated
    public static Action getRegisteredActionShortcut(Shortcut shortcut) {
        return MainApplication.getRegisteredActionShortcut(shortcut);
    }

    ///////////////////////////////////////////////////////////////////////////
    //  Implementation part
    ///////////////////////////////////////////////////////////////////////////

    /**
     * Should be called before the main constructor to setup some parameter stuff
     */
    public static void preConstructorInit() {
        // init default coordinate format
        ICoordinateFormat fmt = CoordinateFormatManager.getCoordinateFormat(Config.getPref().get("coordinates"));
        if (fmt == null) {
            fmt = DecimalDegreesCoordinateFormat.INSTANCE;
        }
        CoordinateFormatManager.setCoordinateFormat(fmt);
    }

    /**
     * Closes JOSM and optionally terminates the Java Virtual Machine (JVM).
     * @param exit If {@code true}, the JVM is terminated by running {@link System#exit} with a given return code.
     * @param exitCode The return code
     * @return {@code true}
     * @since 12636
     */
    public static boolean exitJosm(boolean exit, int exitCode) {
        if (Main.main != null) {
            Main.main.shutdown();
        }

        if (exit) {
            System.exit(exitCode);
        }
        return true;
    }

    /**
     * Shutdown JOSM.
     */
    protected void shutdown() {
        if (!GraphicsEnvironment.isHeadless()) {
            ImageProvider.shutdown(false);
        }
        try {
            pref.saveDefaults();
        } catch (IOException ex) {
            Logging.log(Logging.LEVEL_WARN, tr("Failed to save default preferences."), ex);
        }
        if (!GraphicsEnvironment.isHeadless()) {
            ImageProvider.shutdown(true);
        }
    }

    /**
     * Identifies the current operating system family and initializes the platform hook accordingly.
     * @since 1849
     */
    public static void determinePlatformHook() {
        platform = Platform.determinePlatform().accept(PlatformHook.CONSTRUCT_FROM_PLATFORM);
    }

    /* ----------------------------------------------------------------------------------------- */
    /* projection handling  - Main is a registry for a single, global projection instance        */
    /*                                                                                           */
    /* TODO: For historical reasons the registry is implemented by Main. An alternative approach */
    /* would be a singleton org.openstreetmap.josm.data.projection.ProjectionRegistry class.     */
    /* ----------------------------------------------------------------------------------------- */
    /**
     * The projection method used.
     * Use {@link #getProjection()} and {@link #setProjection(Projection)} for access.
     * Use {@link #setProjection(Projection)} in order to trigger a projection change event.
     */
    private static volatile Projection proj;

    /**
     * Replies the current projection.
     *
     * @return the currently active projection
     */
    public static Projection getProjection() {
        return proj;
    }

    /**
     * Sets the current projection
     *
     * @param p the projection
     */
    public static void setProjection(Projection p) {
        CheckParameterUtil.ensureParameterNotNull(p);
        Projection oldValue = proj;
        Bounds b = main != null ? main.getRealBounds() : null;
        proj = p;
        fireProjectionChanged(oldValue, proj, b);
    }

    /**
     * Returns the bounds for the current projection. Used for projection events.
     * @return the bounds for the current projection
     * @see #restoreOldBounds
     */
    protected Bounds getRealBounds() {
        // To be overriden
        return null;
    }

    /**
     * Restore clean state corresponding to old bounds after a projection change event.
     * @param oldBounds bounds previously returned by {@link #getRealBounds}, before the change of projection
     * @see #getRealBounds
     */
    protected void restoreOldBounds(Bounds oldBounds) {
        // To be overriden
    }

    /*
     * Keep WeakReferences to the listeners. This relieves clients from the burden of
     * explicitly removing the listeners and allows us to transparently register every
     * created dataset as projection change listener.
     */
    private static final List<WeakReference<ProjectionChangeListener>> listeners = new ArrayList<>();

    private static void fireProjectionChanged(Projection oldValue, Projection newValue, Bounds oldBounds) {
        if ((newValue == null ^ oldValue == null)
                || (newValue != null && oldValue != null && !Objects.equals(newValue.toCode(), oldValue.toCode()))) {
            synchronized (Main.class) {
                Iterator<WeakReference<ProjectionChangeListener>> it = listeners.iterator();
                while (it.hasNext()) {
                    WeakReference<ProjectionChangeListener> wr = it.next();
                    ProjectionChangeListener listener = wr.get();
                    if (listener == null) {
                        it.remove();
                        continue;
                    }
                    listener.projectionChanged(oldValue, newValue);
                }
            }
            if (newValue != null && oldBounds != null && main != null) {
                main.restoreOldBounds(oldBounds);
            }
            /* TODO - remove layers with fixed projection */
        }
    }

    /**
     * Register a projection change listener.
     * The listener is registered to be weak, so keep a reference of it if you want it to be preserved.
     *
     * @param listener the listener. Ignored if <code>null</code>.
     */
    public static void addProjectionChangeListener(ProjectionChangeListener listener) {
        if (listener == null) return;
        synchronized (Main.class) {
            for (WeakReference<ProjectionChangeListener> wr : listeners) {
                // already registered ? => abort
                if (wr.get() == listener) return;
            }
            listeners.add(new WeakReference<>(listener));
        }
    }

    /**
     * Removes a projection change listener.
     *
     * @param listener the listener. Ignored if <code>null</code>.
     */
    public static void removeProjectionChangeListener(ProjectionChangeListener listener) {
        if (listener == null) return;
        synchronized (Main.class) {
            // remove the listener - and any other listener which got garbage
            // collected in the meantime
            listeners.removeIf(wr -> wr.get() == null || wr.get() == listener);
        }
    }

    /**
     * Listener for window switch events.
     *
     * These are events, when the user activates a window of another application
     * or comes back to JOSM. Window switches from one JOSM window to another
     * are not reported.
     */
    public interface WindowSwitchListener {
        /**
         * Called when the user activates a window of another application.
         */
        void toOtherApplication();

        /**
         * Called when the user comes from a window of another application back to JOSM.
         */
        void fromOtherApplication();
    }

    /**
     * Registers a new {@code MapFrameListener} that will be notified of MapFrame changes.
     * <p>
     * It will fire an initial mapFrameInitialized event when the MapFrame is present.
     * Otherwise will only fire when the MapFrame is created or destroyed.
     * @param listener The MapFrameListener
     * @return {@code true} if the listeners collection changed as a result of the call
     * @see #addMapFrameListener
     * @deprecated use {@link MainApplication#addAndFireMapFrameListener} instead
     * @since 11904
     */
    @Deprecated
    public static boolean addAndFireMapFrameListener(MapFrameListener listener) {
        return MainApplication.addAndFireMapFrameListener(listener);
    }

    /**
     * Registers a new {@code MapFrameListener} that will be notified of MapFrame changes
     * @param listener The MapFrameListener
     * @return {@code true} if the listeners collection changed as a result of the call
     * @see #addAndFireMapFrameListener
     * @deprecated use {@link MainApplication#addMapFrameListener} instead
     * @since 5957
     */
    @Deprecated
    public static boolean addMapFrameListener(MapFrameListener listener) {
        return MainApplication.addMapFrameListener(listener);
    }

    /**
     * Unregisters the given {@code MapFrameListener} from MapFrame changes
     * @param listener The MapFrameListener
     * @return {@code true} if the listeners collection changed as a result of the call
     * @deprecated use {@link MainApplication#removeMapFrameListener} instead
     * @since 5957
     */
    @Deprecated
    public static boolean removeMapFrameListener(MapFrameListener listener) {
        return MainApplication.removeMapFrameListener(listener);
    }

    /**
     * Adds a new network error that occur to give a hint about broken Internet connection.
     * Do not use this method for errors known for sure thrown because of a bad proxy configuration.
     *
     * @param url The accessed URL that caused the error
     * @param t The network error
     * @return The previous error associated to the given resource, if any. Can be {@code null}
     * @since 6642
     */
    public static Throwable addNetworkError(URL url, Throwable t) {
        if (url != null && t != null) {
            Throwable old = addNetworkError(url.toExternalForm(), t);
            if (old != null) {
                Logging.warn("Already here "+old);
            }
            return old;
        }
        return null;
    }

    /**
     * Adds a new network error that occur to give a hint about broken Internet connection.
     * Do not use this method for errors known for sure thrown because of a bad proxy configuration.
     *
     * @param url The accessed URL that caused the error
     * @param t The network error
     * @return The previous error associated to the given resource, if any. Can be {@code null}
     * @since 6642
     */
    public static Throwable addNetworkError(String url, Throwable t) {
        if (url != null && t != null) {
            return NETWORK_ERRORS.put(url, t);
        }
        return null;
    }

    /**
     * Returns the network errors that occured until now.
     * @return the network errors that occured until now, indexed by URL
     * @since 6639
     */
    public static Map<String, Throwable> getNetworkErrors() {
        return new HashMap<>(NETWORK_ERRORS);
    }

    /**
     * Clears the network errors cache.
     * @since 12011
     */
    public static void clearNetworkErrors() {
        NETWORK_ERRORS.clear();
    }

    /**
     * Returns the JOSM website URL.
     * @return the josm website URL
     * @since 6897
     */
    public static String getJOSMWebsite() {
        if (Config.getPref() != null)
            return Config.getPref().get("josm.url", JOSM_WEBSITE);
        return JOSM_WEBSITE;
    }

    /**
     * Returns the JOSM XML URL.
     * @return the josm XML URL
     * @since 6897
     */
    public static String getXMLBase() {
        // Always return HTTP (issues reported with HTTPS)
        return "http://josm.openstreetmap.de";
    }

    /**
     * Returns the OSM website URL.
     * @return the OSM website URL
     * @since 6897
     */
    public static String getOSMWebsite() {
        if (Config.getPref() != null)
            return Config.getPref().get("osm.url", OSM_WEBSITE);
        return OSM_WEBSITE;
    }

    /**
     * Returns the OSM website URL depending on the selected {@link OsmApi}.
     * @return the OSM website URL depending on the selected {@link OsmApi}
     */
    private static String getOSMWebsiteDependingOnSelectedApi() {
        final String api = OsmApi.getOsmApi().getServerUrl();
        if (OsmApi.DEFAULT_API_URL.equals(api)) {
            return getOSMWebsite();
        } else {
            return api.replaceAll("/api$", "");
        }
    }

    /**
     * Replies the base URL for browsing information about a primitive.
     * @return the base URL, i.e. https://www.openstreetmap.org
     * @since 7678
     */
    public static String getBaseBrowseUrl() {
        if (Config.getPref() != null)
            return Config.getPref().get("osm-browse.url", getOSMWebsiteDependingOnSelectedApi());
        return getOSMWebsiteDependingOnSelectedApi();
    }

    /**
     * Replies the base URL for browsing information about a user.
     * @return the base URL, i.e. https://www.openstreetmap.org/user
     * @since 7678
     */
    public static String getBaseUserUrl() {
        if (Config.getPref() != null)
            return Config.getPref().get("osm-user.url", getOSMWebsiteDependingOnSelectedApi() + "/user");
        return getOSMWebsiteDependingOnSelectedApi() + "/user";
    }

    /**
     * Determines if we are currently running on OSX.
     * @return {@code true} if we are currently running on OSX
     * @since 6957
     */
    public static boolean isPlatformOsx() {
        return Main.platform instanceof PlatformHookOsx;
    }

    /**
     * Determines if we are currently running on Windows.
     * @return {@code true} if we are currently running on Windows
     * @since 7335
     */
    public static boolean isPlatformWindows() {
        return Main.platform instanceof PlatformHookWindows;
    }

    /**
     * Determines if the given online resource is currently offline.
     * @param r the online resource
     * @return {@code true} if {@code r} is offline and should not be accessed
     * @since 7434
     */
    public static boolean isOffline(OnlineResource r) {
        return OFFLINE_RESOURCES.contains(r) || OFFLINE_RESOURCES.contains(OnlineResource.ALL);
    }

    /**
     * Sets the given online resource to offline state.
     * @param r the online resource
     * @return {@code true} if {@code r} was not already offline
     * @since 7434
     */
    public static boolean setOffline(OnlineResource r) {
        return OFFLINE_RESOURCES.add(r);
    }

    /**
     * Sets the given online resource to online state.
     * @param r the online resource
     * @return {@code true} if {@code r} was offline
     * @since 8506
     */
    public static boolean setOnline(OnlineResource r) {
        return OFFLINE_RESOURCES.remove(r);
    }

    /**
     * Replies the set of online resources currently offline.
     * @return the set of online resources currently offline
     * @since 7434
     */
    public static Set<OnlineResource> getOfflineResources() {
        return EnumSet.copyOf(OFFLINE_RESOURCES);
    }
}