tasks/astrid/common-src/com/todoroo/andlib/sql/Operator.java

package com.todoroo.andlib.sql;

import static com.todoroo.andlib.sql.SqlConstants.SPACE;

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

@SuppressWarnings("nls")
public final class Operator {

    private final String operator;
    public static final Operator eq = new Operator("=");
    public static final Operator neq = new Operator("<>");
    public static final Operator isNull = new Operator("IS NULL");
    public static final Operator isNotNull = new Operator("IS NOT NULL");
    public static final Operator gt = new Operator(">");
    public static final Operator lt = new Operator("<");
    public static final Operator gte = new Operator(">=");
    public static final Operator lte = new Operator("<=");
    public static final Operator and = new Operator("AND");
    public static final Operator or = new Operator("OR");
    public static final Operator not = new Operator("NOT");
    public static final Operator exists = new Operator("EXISTS");
    public static final Operator like = new Operator("LIKE");
    public static final Operator in = new Operator("IN");

    private static final Map<Operator, Operator> contraryRegistry = new HashMap<Operator, Operator>();

    static {
        contraryRegistry.put(eq, neq);
        contraryRegistry.put(neq, eq);
        contraryRegistry.put(isNull, isNotNull);
        contraryRegistry.put(isNotNull, isNull);
        contraryRegistry.put(gt, lte);
        contraryRegistry.put(lte, gt);
        contraryRegistry.put(lt, gte);
        contraryRegistry.put(gte, lt);
    }

    private Operator(String operator) {
        this.operator = operator;
    }

    public Operator getContrary() {
        if(!contraryRegistry.containsKey(this)){
            Operator opposite = new Operator(not.toString() + SPACE + this.toString());
            contraryRegistry.put(this, opposite);
            contraryRegistry.put(opposite, this);
        }
        return contraryRegistry.get(this);
    }

    @Override
    public String toString() {
        return this.operator.toString();
    }
}