/**
 * This file is part of Graylog.
 *
 * Graylog is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Graylog 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Graylog.  If not, see <http://www.gnu.org/licenses/>.
 */
package org.graylog2.dashboards.widgets;

import com.codahale.metrics.Counter;
import com.codahale.metrics.Meter;
import com.codahale.metrics.MetricRegistry;
import com.codahale.metrics.Timer;
import com.google.common.base.Supplier;
import com.google.common.base.Suppliers;
import com.google.common.collect.Maps;
import org.graylog2.plugin.dashboards.widgets.ComputationResult;
import org.graylog2.plugin.dashboards.widgets.WidgetStrategy;

import javax.inject.Inject;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.TimeUnit;

import static com.codahale.metrics.MetricRegistry.name;

public class WidgetResultCache {
    private final ConcurrentMap<String, Supplier<ComputationResult>> cache;
    private final MetricRegistry metricRegistry;
    private final WidgetStrategyFactory widgetStrategyFactory;
    private final Counter counter;

    @Inject
    public WidgetResultCache(MetricRegistry metricRegistry, WidgetStrategyFactory widgetStrategyFactory) {
        this.metricRegistry = metricRegistry;
        this.widgetStrategyFactory = widgetStrategyFactory;
        this.cache = Maps.newConcurrentMap();
        this.counter = metricRegistry.counter(name(getClass(), "cacheEntries"));
    }

    public ComputationResult getComputationResultForDashboardWidget(final DashboardWidget dashboardWidget) throws InvalidWidgetConfigurationException {
        final String widgetId = dashboardWidget.getId();
        if (!this.cache.containsKey(widgetId)) {
            final WidgetStrategy widgetStrategy = this.widgetStrategyFactory.getWidgetForType(dashboardWidget.getType(),
                    dashboardWidget.getConfig(), dashboardWidget.getTimeRange(), widgetId);
            final Supplier<ComputationResult> supplier = this.cache.putIfAbsent(widgetId, Suppliers.memoizeWithExpiration(
                    new ComputationResultSupplier(metricRegistry, dashboardWidget, widgetStrategy),
                    dashboardWidget.getCacheTime(),
                    TimeUnit.SECONDS
            ));

            if (supplier == null) {
                // Only increment the counter if there has been no value for the widget ID before.
                counter.inc();
            }
        }
        return this.cache.get(widgetId).get();
    }

    public void invalidate(final String widgetId) {
        this.cache.remove(widgetId);
        this.counter.dec();
    }

    private static class ComputationResultSupplier implements Supplier<ComputationResult> {
        private final MetricRegistry metricRegistry;
        private final DashboardWidget dashboardWidget;
        private final WidgetStrategy widgetStrategy;

        public ComputationResultSupplier(MetricRegistry metricRegistry,
                                         DashboardWidget dashboardWidget,
                                         WidgetStrategy widgetStrategy) {
            this.metricRegistry = metricRegistry;
            this.dashboardWidget = dashboardWidget;
            this.widgetStrategy = widgetStrategy;
        }

        @Override
        public ComputationResult get() {
            try (Timer.Context timer = getCalculationTimer().time()) {
                return this.widgetStrategy.compute();
            } finally {
                getCalculationMeter().mark();
            }
        }

        private Timer getCalculationTimer() {
            return metricRegistry.timer(name(this.getClass(), this.dashboardWidget.getId(), "calculationTime"));
        }

        private Meter getCalculationMeter() {
            return metricRegistry.meter(name(this.getClass(), this.dashboardWidget.getId(), "calculations"));
        }
    }
}