/*
* Copyright 2010-2019 Amazon.com, Inc. or its affiliates. All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License").
* You may not use this file except in compliance with the License.
* A copy of the License is located at
*
*  http://aws.amazon.com/apache2.0
*
* or in the "license" file accompanying this file. This file 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 software.amazon.cloudformation.scheduler;

import java.time.Clock;
import java.time.Instant;
import java.time.OffsetDateTime;
import java.time.ZoneOffset;
import java.time.format.DateTimeFormatter;

public class CronHelper {

    private final Clock clock;

    public CronHelper() {
        this.clock = Clock.systemUTC();
    }

    /**
     * This .ctor provided for testing
     *
     * @param clock current clock system usually {@link Clock#systemUTC()}
     */
    public CronHelper(final Clock clock) {
        this.clock = clock;
    }

    /**
     * Schedule a re-invocation of the executing handler no less than 1 minute from
     * now
     *
     *
     * /** Creates a cron(..) expression for a single instance at Now+minutesFromNow
     * NOTE: CloudWatchEvents only support a 1minute granularity for re-invoke
     * Anything less should be handled inside the original handler request
     *
     * Expression is of form cron(minutes, hours, day-of-month, month, day-of-year,
     * year) where day-of-year is not necessary when the day-of-month and
     * month-of-year fields are supplied
     *
     * @param minutesFromNow The number of minutes from now for building the cron
     *            expression
     * @return A cron expression for use with CloudWatchEvents putRule(..) API
     */
    public String generateOneTimeCronExpression(final int minutesFromNow) {
        // Add additional 1 minute, since rule can be created after scheduled time, like
        // "13:40:59" -> cron(41 13 30)
        Instant instant = Instant.now(this.clock).plusSeconds(60L * (minutesFromNow + 1));
        OffsetDateTime odt = instant.atOffset(ZoneOffset.UTC);

        return DateTimeFormatter.ofPattern("'cron('m H d M ? u')'").format(odt);
    }
}