Substitution.java

package org.ggp.base.util.prover.aima.substitution;

import java.util.HashMap;
import java.util.Map;

import org.ggp.base.util.gdl.grammar.GdlTerm;
import org.ggp.base.util.gdl.grammar.GdlVariable;


public final class Substitution
{

    private final Map<GdlVariable, GdlTerm> contents;

    public Substitution()
    {
        contents = new HashMap<GdlVariable, GdlTerm>();
    }

    public Substitution compose(Substitution thetaPrime)
    {
        Substitution result = new Substitution();

        result.contents.putAll(contents);
        result.contents.putAll(thetaPrime.contents);

        return result;
    }

    public boolean contains(GdlVariable variable)
    {
        return contents.containsKey(variable);
    }

    @Override
    public boolean equals(Object o)
    {
        if ((o != null) && (o instanceof Substitution))
        {
            Substitution substitution = (Substitution) o;
            return substitution.contents.equals(contents);
        }

        return false;
    }

    public GdlTerm get(GdlVariable variable)
    {
        return contents.get(variable);
    }

    @Override
    public int hashCode()
    {
        return contents.hashCode();
    }

    public void put(GdlVariable variable, GdlTerm term)
    {
        contents.put(variable, term);
    }

    /**
     * Creates an identical substitution.
     *
     * @return A new, identical substitution.
     */
    public Substitution copy()
    {
        Substitution copy = new Substitution();
        copy.contents.putAll(contents);
        return copy;
    }

    @Override
    public String toString()
    {
        StringBuilder sb = new StringBuilder();

        sb.append("{ ");
        for (GdlVariable variable : contents.keySet())
        {
            sb.append(variable + "/" + contents.get(variable) + " ");
        }
        sb.append("}");

        return sb.toString();
    }

}