Path.java

/*
 * Copyright 2012 Jakob Külzer
 * 
 * Licensed 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.om.core.api.path;

/**
 * Describes a path. A path has always the following form:
 * <ul>
 * <li>Starts with a slash
 * <li>has zero or more segments, delimited by a slash each
 * </ul>
 * 
 * This class is immutable, i.e. instances, once created, cannot be modified.
 * All methods that modify the path, return a new instance.
 * 
 * @author Jakob Külzer
 * 
 */
public class Path {

	public static final String SLASH = "/";

	private final int length;

	private final String path;

	public Path(String path) {
		if (path == null)
			throw new RuntimeException("Cannot construct path from null");

		this.path = cleanPath(path);
		this.length = calculateLength();
	}

	public Path append(String append) {
		return new Path(path + SLASH + append);
	}

	private int calculateLength() {
		if (isRoot())
			return 0;

		int counter = 0;
		for (char c : path.toCharArray()) {
			if (c == SLASH.charAt(0))
				counter++;
		}
		return counter;
	}

	private String cleanPath(String path) {
		// Remove whitespace:
		path = path.trim();

		// Remove multiple path delimiters:
		path = path.replaceAll("//+", "/");

		// Remove trailing slash:
		path = !path.equals(SLASH) && path.length() > 2 && path.endsWith(SLASH) ? path.substring(0, path.length() - 1) : path;
		return path;
	}

	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (getClass() != obj.getClass())
			return false;
		Path other = (Path) obj;
		if (path == null) {
			if (other.path != null)
				return false;
		} else if (!path.equals(other.path))
			return false;
		return true;
	}

	/**
	 * Returns the lenght of this path in segments. If this path only describes
	 * root, this method will return 0.
	 * 
	 * @return
	 */
	public int getLength() {
		return length;
	}

	public Path getParent() {
		if (isRoot())
			return this;

		return new Path(path.substring(0, path.lastIndexOf(SLASH) + 1));
	}

	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + ((path == null) ? 0 : path.hashCode());
		return result;
	}

	/**
	 * Retuns true if this path describes only the root.
	 * 
	 * @return
	 */
	public boolean isRoot() {
		return path.equals(SLASH);
	}

	@Override
	public String toString() {
		return path;
	}
}