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Kiwi is a utility library. We really like Google's Guava, and also use Apache Commons. But if they don't have something we need, and we think it is useful, this is where we put it.

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package org.kiwiproject.dropwizard.metrics.health;

import static org.kiwiproject.io.TimeBasedDirectoryCleaner.DeleteError;

import com.codahale.metrics.health.HealthCheck;
import org.apache.commons.lang3.time.DurationFormatUtils;
import org.kiwiproject.io.TimeBasedDirectoryCleaner;

import java.time.Duration;
import java.time.ZonedDateTime;
import java.time.format.DateTimeFormatter;

/**
 * A health check for {@link TimeBasedDirectoryCleaner} that checks if there have been any delete errors within
 * a specific duration of time. Errors older than the warning threshold will not cause this to report as unhealthy;
 * it will report unhealthy only if there are errors within the warning threshold.
 */
public class TimeBasedDirectoryCleanerHealthCheck extends HealthCheck {

    public static final Duration DEFAULT_DELETE_ERROR_THRESHOLD = Duration.ofHours(1);

    private static final boolean SUPPRESS_LEADING_ZERO_ELEMENTS = true;
    private static final boolean SUPPRESS_TRAILING_ZERO_ELEMENTS = true;

    private final TimeBasedDirectoryCleaner cleaner;
    private final long warningThresholdInMillis;
    private final String warningThresholdDescription;
    private final String intializedAt;

    /**
     * Create with specified {@link TimeBasedDirectoryCleaner} and the default warning threshold.
     *
     * @param cleaner the TimeBasedDirectoryCleaner to use
     * @see #DEFAULT_DELETE_ERROR_THRESHOLD
     */
    public TimeBasedDirectoryCleanerHealthCheck(TimeBasedDirectoryCleaner cleaner) {
        this(cleaner, DEFAULT_DELETE_ERROR_THRESHOLD);
    }

    /**
     * Create with the specified {@link TimeBasedDirectoryCleaner} and warning threshold.
     *
     * @param cleaner          the TimeBasedDirectoryCleaner to use
     * @param warningThreshold the warning threshold
     */
    public TimeBasedDirectoryCleanerHealthCheck(TimeBasedDirectoryCleaner cleaner, Duration warningThreshold) {
        this.cleaner = cleaner;
        this.warningThresholdInMillis = warningThreshold.toMillis();
        this.warningThresholdDescription = DurationFormatUtils.formatDurationWords(warningThresholdInMillis,
                SUPPRESS_LEADING_ZERO_ELEMENTS,
                SUPPRESS_TRAILING_ZERO_ELEMENTS);

        var formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd hh:mm");
        this.intializedAt = ZonedDateTime.now().format(formatter);
    }

    @Override
    protected Result check() {
        var now = System.currentTimeMillis();
        var errorsWithinThreshold = cleaner.getRecentDeleteErrors().stream()
                .filter(error -> errorHasOccurredWithinWarningThreshold(now, error))
                .count();

        if (errorsWithinThreshold == 0) {
            return Result.healthy("No delete errors in last %s (%d total errors since %s)",
                    warningThresholdDescription,
                    cleaner.getDeleteErrorCount(),
                    intializedAt);
        }

        return Result.unhealthy("%d delete error(s) in last %s (%d total errors since %s)",
                errorsWithinThreshold,
                warningThresholdDescription,
                cleaner.getDeleteErrorCount(),
                intializedAt);
    }

    private boolean errorHasOccurredWithinWarningThreshold(long now, DeleteError error) {
        var ageInMillis = now - error.getTimestamp();
        return ageInMillis < warningThresholdInMillis;
    }
}