cheogram/src/main/java/eu/siacs/conversations/ui/widget/ListSelectionManager.java

package eu.siacs.conversations.ui.widget;

import java.lang.reflect.Field;
import java.lang.reflect.Method;

import android.os.Handler;
import android.os.Looper;
import android.os.Message;
import android.text.Selection;
import android.text.Spannable;
import android.view.ActionMode;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.TextView;

public class ListSelectionManager {

	private static final int MESSAGE_SEND_RESET = 1;
	private static final int MESSAGE_RESET = 2;
	private static final int MESSAGE_START_SELECTION = 3;

	private static final Handler HANDLER = new Handler(Looper.getMainLooper(), new Handler.Callback() {

		@Override
		public boolean handleMessage(Message msg) {
			switch (msg.what) {
				case MESSAGE_SEND_RESET: {
					// Skip one more message queue loop
					HANDLER.obtainMessage(MESSAGE_RESET, msg.obj).sendToTarget();
					return true;
				}
				case MESSAGE_RESET: {
					final ListSelectionManager listSelectionManager = (ListSelectionManager) msg.obj;
					listSelectionManager.futureSelectionIdentifier = null;
					return true;
				}
				case MESSAGE_START_SELECTION: {
					final StartSelectionHolder holder = (StartSelectionHolder) msg.obj;
					holder.listSelectionManager.futureSelectionIdentifier = null;
					startSelection(holder.textView, holder.start, holder.end);
					return true;
				}
			}
			return false;
		}
	});

	private static class StartSelectionHolder {

		public final ListSelectionManager listSelectionManager;
		public final TextView textView;
		public final int start;
		public final int end;

		public StartSelectionHolder(ListSelectionManager listSelectionManager, TextView textView,
				int start, int end) {
			this.listSelectionManager = listSelectionManager;
			this.textView = textView;
			this.start = start;
			this.end = end;
		}
	}

	private ActionMode selectionActionMode;
	private Object selectionIdentifier;
	private TextView selectionTextView;

	private Object futureSelectionIdentifier;
	private int futureSelectionStart;
	private int futureSelectionEnd;

	public void onCreate(TextView textView, ActionMode.Callback additionalCallback) {
		final CustomCallback callback = new CustomCallback(textView, additionalCallback);
		textView.setCustomSelectionActionModeCallback(callback);
	}

	public void onUpdate(TextView textView, Object identifier) {
		if (SUPPORTED) {
			CustomCallback callback = (CustomCallback) textView.getCustomSelectionActionModeCallback();
			callback.identifier = identifier;
			if (futureSelectionIdentifier == identifier) {
				HANDLER.obtainMessage(MESSAGE_START_SELECTION, new StartSelectionHolder(this,
						textView, futureSelectionStart, futureSelectionEnd)).sendToTarget();
			}
		}
	}

	public void onBeforeNotifyDataSetChanged() {
		if (SUPPORTED) {
			HANDLER.removeMessages(MESSAGE_SEND_RESET);
			HANDLER.removeMessages(MESSAGE_RESET);
			HANDLER.removeMessages(MESSAGE_START_SELECTION);
			if (selectionActionMode != null) {
				final CharSequence text = selectionTextView.getText();
				futureSelectionIdentifier = selectionIdentifier;
				futureSelectionStart = Selection.getSelectionStart(text);
				futureSelectionEnd = Selection.getSelectionEnd(text);
				selectionActionMode.finish();
				selectionActionMode = null;
				selectionIdentifier = null;
				selectionTextView = null;
			}
		}
	}

	public void onAfterNotifyDataSetChanged() {
		if (SUPPORTED && futureSelectionIdentifier != null) {
			HANDLER.obtainMessage(MESSAGE_SEND_RESET, this).sendToTarget();
		}
	}

	private class CustomCallback implements ActionMode.Callback {

		private final TextView textView;
		private final ActionMode.Callback additionalCallback;
		public Object identifier;

		public CustomCallback(TextView textView, ActionMode.Callback additionalCallback) {
			this.textView = textView;
			this.additionalCallback = additionalCallback;
		}

		@Override
		public boolean onCreateActionMode(ActionMode mode, Menu menu) {
			selectionActionMode = mode;
			selectionIdentifier = identifier;
			selectionTextView = textView;
			if (additionalCallback != null) {
				additionalCallback.onCreateActionMode(mode, menu);
			}
			return true;
		}

		@Override
		public boolean onPrepareActionMode(ActionMode mode, Menu menu) {
			if (additionalCallback != null) {
				additionalCallback.onPrepareActionMode(mode, menu);
			}
			return true;
		}

		@Override
		public boolean onActionItemClicked(ActionMode mode, MenuItem item) {
			if (additionalCallback != null && additionalCallback.onActionItemClicked(mode, item)) {
				return true;
			}
			return false;
		}

		@Override
		public void onDestroyActionMode(ActionMode mode) {
			if (additionalCallback != null) {
				additionalCallback.onDestroyActionMode(mode);
			}
			if (selectionActionMode == mode) {
				selectionActionMode = null;
				selectionIdentifier = null;
				selectionTextView = null;
			}
		}
	}

	private static final Field FIELD_EDITOR;
	private static final Method METHOD_START_SELECTION;
	private static final boolean SUPPORTED;

	static {
		Field editor;
		try {
			editor = TextView.class.getDeclaredField("mEditor");
			editor.setAccessible(true);
		} catch (Exception e) {
			editor = null;
		}
		FIELD_EDITOR = editor;
		Method startSelection = null;
		if (editor != null) {
			String[] startSelectionNames = {"startSelectionActionMode", "startSelectionActionModeWithSelection"};
			for (String startSelectionName : startSelectionNames) {
				try {
					startSelection = editor.getType().getDeclaredMethod(startSelectionName);
					startSelection.setAccessible(true);
					break;
				} catch (Exception e) {
					startSelection = null;
				}
			}
		}
		METHOD_START_SELECTION = startSelection;
		SUPPORTED = FIELD_EDITOR != null && METHOD_START_SELECTION != null;
	}

	public static boolean isSupported() {
		return SUPPORTED;
	}

	public static void startSelection(TextView textView) {
		startSelection(textView, 0, textView.getText().length());
	}

	public static void startSelection(TextView textView, int start, int end) {
		final CharSequence text = textView.getText();
		if (SUPPORTED && start >= 0 && end > start && textView.isTextSelectable() && text instanceof Spannable) {
			final Spannable spannable = (Spannable) text;
			start = Math.min(start, spannable.length());
			end = Math.min(end, spannable.length());
			Selection.setSelection(spannable, start, end);
			try {
				final Object editor = FIELD_EDITOR != null ? FIELD_EDITOR.get(textView) : textView;
				METHOD_START_SELECTION.invoke(editor);
			} catch (Exception e) {
			}
		}
	}
}