/**
 * Copyright (C) 2009-2013 FoundationDB, LLC
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

package com.foundationdb.server.types.mcompat.mfuncs;

import com.foundationdb.server.types.LazyList;
import com.foundationdb.server.types.TExecutionContext;
import com.foundationdb.server.types.TScalar;
import com.foundationdb.server.types.TOverloadResult;
import com.foundationdb.server.types.mcompat.mtypes.MNumeric;
import com.foundationdb.server.types.value.ValueSource;
import com.foundationdb.server.types.value.ValueTarget;
import com.foundationdb.server.types.texpressions.TInputSetBuilder;
import com.foundationdb.server.types.texpressions.TScalarBase;

public abstract class MPeriodArith extends TScalarBase {

    private final String name;
    
    public static final TScalar[] INSTANCES = {
        new MPeriodArith("PERIOD_ADD") {

            @Override
            protected void doEvaluate(TExecutionContext context, LazyList<? extends ValueSource> inputs, ValueTarget output) {
                long period = inputs.get(0).getInt64();
                long offsetMonths = inputs.get(1).getInt64();

                // COMPATIBILITY: MySQL currently has undefined behavior for negative numbers
                // Our behavior follows our B.C. year numbering (-199402 + 1 = -199401)
                // Java's mod returns negative numbers: -1994 % 100 = -94
                long periodInMonths = fromPeriod(period);
                long totalMonths = periodInMonths + offsetMonths;

                // Handle the case where the period changes sign (e.g. -YYMM to YYMM)
                // as a result of adding. Since 0000 months is not really a date,
                // this leads to an off by one error
                if (Long.signum(periodInMonths) * Long.signum(totalMonths) == -1) {
                    totalMonths -= Long.signum(totalMonths) * 2;
                }

                long result = toPeriod(totalMonths);
                output.putInt64(result);
            }
        },
        new MPeriodArith("PERIOD_DIFF") {

            @Override
            protected void doEvaluate(TExecutionContext context, LazyList<? extends ValueSource> inputs, ValueTarget output) {
                // COMPATIBILITY: MySQL currently has undefined behavior for negative numbers
                // Our behavior follows our B.C. year numbering (-199402 + 1 = -199401)
                long periodLeft = inputs.get(0).getInt64();
                long periodRight = inputs.get(1).getInt64();

                long result = fromPeriod(periodLeft) - fromPeriod(periodRight);
                output.putInt64(result);
            }
        }
    };
            
    private MPeriodArith(String name) {
        this.name = name;
    }
    
    @Override
    protected void buildInputSets(TInputSetBuilder builder) {
        builder.covers(MNumeric.BIGINT, 0, 1);
    }

    @Override
    public String displayName() {
        return name;
    }

    @Override
    public TOverloadResult resultType() {
        return TOverloadResult.fixed(MNumeric.BIGINT);
    }

    // Helper functions
    // Takes a period and returns the number of months from year 0
    protected static long fromPeriod(long period)
    {
        int periodSign = Long.signum(period);
        
        long rawMonth = period % 100;
        long rawYear = period / 100;

        long absValYear = Math.abs(rawYear);
        if (absValYear < 70)
            rawYear += periodSign * 2000;
        else if (absValYear < 100)
            rawYear += periodSign * 1900; 
        
        return (rawYear * 12 + rawMonth - (1 * periodSign));
    }
    
    // Create a YYYYMM format from a number of months
    protected static long toPeriod(long monthCount)
    {
        long year = monthCount / 12;
        long month = (monthCount % 12) + 1 * Long.signum(monthCount);
        return (year * 100) + month;
    }
    
    // End helper functions ***************************************************
}