/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.vfs2;

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

import org.apache.commons.vfs2.provider.AbstractFileObject;
import org.apache.commons.vfs2.util.FileObjectUtils;
import org.junit.Assert;

/**
 * A file selector that asserts that all files are visited, in the correct order.
 */
public class VerifyingFileSelector extends Assert implements FileSelector {
    private final FileInfo rootFile;
    private final List<FileObject> files = new ArrayList<>();

    private FileInfo currentFolderInfo;
    private FileObject currentFolder;
    private Set<String> children;
    private final List<Set<String>> stack = new ArrayList<>();

    public VerifyingFileSelector(final FileInfo fileInfo) {
        this.rootFile = fileInfo;
        children = new HashSet<>();
        children.add(rootFile.baseName);
    }

    /**
     * Determines if a file or folder should be selected.
     */
    @Override
    public boolean includeFile(final FileSelectInfo fileInfo) throws FileSystemException {
        final FileObject file = fileInfo.getFile();
        if (file == currentFolder) {
            // Pop current folder
            assertEquals(0, children.size());
            currentFolder = currentFolder.getParent();
            currentFolderInfo = currentFolderInfo.getParent();
            children = stack.remove(0);
        }

        final String baseName = file.getName().getBaseName();

        final FileInfo childInfo = getChild(baseName);
        assertSame(childInfo.type, file.getType());

        final boolean isChild = children.remove(baseName);
        assertTrue(isChild);

        files.add(file);
        return true;
    }

    /**
     * Determines whether a folder should be traversed.
     */
    @Override
    public boolean traverseDescendents(final FileSelectInfo fileInfo) throws FileSystemException {
        // Check that the given file is a folder
        final FileObject folder = FileObjectUtils.getAbstractFileObject(fileInfo.getFile());
        assertSame(FileType.FOLDER, folder.getType());
        assertTrue(folder.isFolder());

        // Locate the info for the folder
        final String baseName = folder.getName().getBaseName();
        if (currentFolder == null) {
            assertEquals(rootFile.baseName, baseName);
            currentFolderInfo = rootFile;
        } else {
            final AbstractFileObject parent = FileObjectUtils.getAbstractFileObject(folder.getParent());
            assertSame(currentFolder, parent);

            // Locate the info for the child, and make sure it is folder
            currentFolderInfo = getChild(baseName);
            assertSame(FileType.FOLDER, currentFolderInfo.type);
        }

        // Push the folder
        stack.add(0, children);
        children = new HashSet<>(currentFolderInfo.children.keySet());
        currentFolder = folder;

        return true;
    }

    /**
     * Finds a child of the current folder.
     */
    private FileInfo getChild(final String baseName) {
        if (currentFolderInfo == null) {
            assertEquals(rootFile.baseName, baseName);
            return rootFile;
        }
        final FileInfo child = currentFolderInfo.children.get(baseName);
        assertNotNull("Could not locate child " + baseName, child);
        return child;
    }

    /**
     * Asserts that the selector has seen all the files.
     *
     * @return The files in the order they where visited.
     */
    public List<FileObject> finish() {
        assertEquals(0, children.size());
        return files;
    }
}