/*=============================================================================#
 # Copyright (c) 2017, 2021 Stephan Wahlbrink and others.
 # 
 # This program and the accompanying materials are made available under the
 # terms of the Eclipse Public License 2.0 which is available at
 # https://www.eclipse.org/legal/epl-2.0, or the Apache License, Version 2.0
 # which is available at https://www.apache.org/licenses/LICENSE-2.0.
 # 
 # SPDX-License-Identifier: EPL-2.0 OR Apache-2.0
 # 
 # Contributors:
 #     Stephan Wahlbrink <sw@wahlbrink.eu> - initial API and implementation
 #=============================================================================*/

package org.eclipse.statet.ecommons.ui.util;

import org.eclipse.core.databinding.observable.Diffs;
import org.eclipse.core.databinding.observable.list.ListDiffEntry;
import org.eclipse.core.databinding.observable.list.WritableList;

import org.eclipse.statet.jcommons.lang.NonNull;
import org.eclipse.statet.jcommons.lang.NonNullByDefault;


@NonNullByDefault
public class InputHistory<E> extends WritableList<E>{
	
	
	private final int maxLength;
	
	
	public InputHistory(final int maxLength) {
		this.maxLength= maxLength;
	}
	
	
	public void append(final E element) {
		checkRealm();
		
		final int idx= this.wrappedList.indexOf(element);
		switch (idx) {
		case 0:
			return;
		case -1:
			addToTop(element);
			return;
		default:
			moveToTop(idx);
			return;
		}
	}
	
	private void moveToTop(final int idx) {
		if (idx == 0) {
			return;
		}
		
		final ListDiffEntry<E>[] diffs= new @NonNull ListDiffEntry[2];
		
		final E element= this.wrappedList.remove(idx);
		diffs[0]= Diffs.createListDiffEntry(idx, false, element);
		this.wrappedList.add(0, element);
		diffs[1]= Diffs.createListDiffEntry(0, true, element);
		
		fireListChange(Diffs.createListDiff(diffs));
	}
	
	private void addToTop(final E element) {
		int size= this.wrappedList.size();
		final ListDiffEntry<E>[] diffs= new @NonNull ListDiffEntry[Math.max(size - this.maxLength + 2, 1)];
		
		int iDiff= 0;
		while (size >= this.maxLength) {
			size--;
			final E removed= this.wrappedList.remove(size);
			diffs[iDiff++]= Diffs.createListDiffEntry(size, false, removed);
		}
		this.wrappedList.add(0, element);
		diffs[iDiff++]= Diffs.createListDiffEntry(0, true, element);
		
		fireListChange(Diffs.createListDiff(diffs));
	}
	
}