package net.minecraft.util.profiling.jfr.stats;

import java.time.Duration;
import java.time.Instant;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;
import jdk.jfr.consumer.RecordedEvent;

public record GcHeapStat(Instant timestamp, long heapUsed, GcHeapStat.Timing timing) {
	public static GcHeapStat from(final RecordedEvent event) {
		return new GcHeapStat(
			event.getStartTime(),
			event.getLong("heapUsed"),
			event.getString("when").equalsIgnoreCase("before gc") ? GcHeapStat.Timing.BEFORE_GC : GcHeapStat.Timing.AFTER_GC
		);
	}

	public static GcHeapStat.Summary summary(
		final Duration recordingDuration, final List<GcHeapStat> heapStats, final Duration gcTotalDuration, final int totalGCs
	) {
		return new GcHeapStat.Summary(recordingDuration, gcTotalDuration, totalGCs, calculateAllocationRatePerSecond(heapStats));
	}

	private static double calculateAllocationRatePerSecond(final List<GcHeapStat> heapStats) {
		long totalAllocations = 0L;
		Map<GcHeapStat.Timing, List<GcHeapStat>> byTiming = (Map<GcHeapStat.Timing, List<GcHeapStat>>)heapStats.stream()
			.collect(Collectors.groupingBy(it -> it.timing));
		List<GcHeapStat> beforeGcs = (List<GcHeapStat>)byTiming.get(GcHeapStat.Timing.BEFORE_GC);
		List<GcHeapStat> afterGcs = (List<GcHeapStat>)byTiming.get(GcHeapStat.Timing.AFTER_GC);

		for (int i = 1; i < beforeGcs.size(); i++) {
			GcHeapStat beforeGC = (GcHeapStat)beforeGcs.get(i);
			GcHeapStat previousGC = (GcHeapStat)afterGcs.get(i - 1);
			totalAllocations += beforeGC.heapUsed - previousGC.heapUsed;
		}

		Duration totalDuration = Duration.between(((GcHeapStat)heapStats.get(1)).timestamp, ((GcHeapStat)heapStats.get(heapStats.size() - 1)).timestamp);
		return (double)totalAllocations / totalDuration.getSeconds();
	}

	public record Summary(Duration duration, Duration gcTotalDuration, int totalGCs, double allocationRateBytesPerSecond) {
		public float gcOverHead() {
			return (float)this.gcTotalDuration.toMillis() / (float)this.duration.toMillis();
		}
	}

	public static enum Timing {
		BEFORE_GC,
		AFTER_GC;
	}
}