/**
 * Copyright (c) 2014, University of Warsaw
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification, are permitted
 * provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice, this list of
 * conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice, this list of
 * conditions and the following disclaimer in the documentation and/or other materials provided
 * with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
 * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY
 * WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package pl.edu.mimuw.cloudatlas.model;

/**
 * Represents an attribute (without value, name only).
 * <p>
 * A valid attribute name is an identifier starting with a letter and containing only letters and digits. It can
 * additionally start with an ampersand - such names are reserved for queries.
 * <p>
 * This class is immutable.
 */
public class Attribute {
    private final String name;

    /**
     * Creates a new <code>Attribute</code> object with the specified <code>name</code>.
     *
     * @param name the name of the attribute
     * @throws IllegalArgumentException if the <code>name</code> does not meet the rules
     */
    public Attribute(String name) {
        if(!name.matches("^&?[a-zA-Z]{1}[a-zA-z0-9_]*$"))
            throw new IllegalArgumentException("Invalid name: may contain only letters, digits, underscores, "
                    + "must start with a letter and may optionally have an ampersand at the beginning.");
        this.name = name;
    }

    /* Kryo needs a no-args constructor */
    private Attribute() {
        this.name = "";
    }

    /**
     * Indicates whether an <code>attribute</code> represents a query. This is true if and only if the attribute's name starts with an ampersand.
     *
     * @param attribute the attribute to check
     * @return whether the <code>attribute</code> represents a query
     */
    public static boolean isQuery(Attribute attribute) {
        return attribute.getName().startsWith("&");
    }

    /**
     * Gets the name of this attribute.
     *
     * @return string representing name
     */
    public String getName() {
        return name;
    }

    /**
     * Returns a hash code value for this attribute. For proper behavior when using <code>Attribute</code> objects in
     * <code>HashMap</code>, <code>HashSet</code> etc. this is the hash code of a string representing the attribute's name.
     *
     * @return hash code for this attribute
     */
    @Override
    public int hashCode() {
        return name.hashCode();
    }

    /**
     * Indicates whether another object is equal to this attribute.
     *
     * @param object the object to check
     * @return true if and only if the <code>object</code> is an instance of <code>Attribute</code> class and has
     * an identical name
     */
    @Override
    public boolean equals(Object object) {
        if(object == null)
            return false;
        if(getClass() != object.getClass())
            return false;
        return name.equals(((Attribute)object).name);
    }

    /**
     * Returns a textual representation of this attribute.
     *
     * @return the name of this attribute
     */
    @Override
    public String toString() {
        return name;
    }
}