package net.minecraft.client.gui.components.debug;

import java.lang.management.GarbageCollectorMXBean;
import java.lang.management.ManagementFactory;
import java.util.List;
import java.util.Locale;
import java.util.concurrent.TimeUnit;
import net.minecraft.resources.Identifier;
import net.minecraft.world.level.Level;
import net.minecraft.world.level.chunk.LevelChunk;
import org.jspecify.annotations.Nullable;

public class DebugEntryMemory implements DebugScreenEntry {
	private static final Identifier GROUP = Identifier.withDefaultNamespace("memory");
	private final DebugEntryMemory.AllocationRateCalculator allocationRateCalculator = new DebugEntryMemory.AllocationRateCalculator();

	@Override
	public void display(
		final DebugScreenDisplayer displayer,
		@Nullable final Level serverOrClientLevel,
		@Nullable final LevelChunk clientChunk,
		@Nullable final LevelChunk serverChunk
	) {
		long max = Runtime.getRuntime().maxMemory();
		long total = Runtime.getRuntime().totalMemory();
		long free = Runtime.getRuntime().freeMemory();
		long used = total - free;
		displayer.addToGroup(
			GROUP,
			List.of(
				String.format(Locale.ROOT, "Mem: %2d%% %03d/%03dMiB", used * 100L / max, bytesToMebibytes(used), bytesToMebibytes(max)),
				String.format(Locale.ROOT, "Allocation rate: %03dMiB/s", bytesToMebibytes(this.allocationRateCalculator.bytesAllocatedPerSecond(used))),
				String.format(Locale.ROOT, "Allocated: %2d%% %03dMiB", total * 100L / max, bytesToMebibytes(total))
			)
		);
	}

	private static long bytesToMebibytes(final long used) {
		return used / 1024L / 1024L;
	}

	@Override
	public boolean isAllowed(final boolean reducedDebugInfo) {
		return true;
	}

	private static class AllocationRateCalculator {
		private static final int UPDATE_INTERVAL_MS = 500;
		private static final List<GarbageCollectorMXBean> GC_MBEANS = ManagementFactory.getGarbageCollectorMXBeans();
		private long lastTime = 0L;
		private long lastHeapUsage = -1L;
		private long lastGcCounts = -1L;
		private long lastRate = 0L;

		private long bytesAllocatedPerSecond(final long currentHeapUsage) {
			long time = System.currentTimeMillis();
			if (time - this.lastTime < 500L) {
				return this.lastRate;
			} else {
				long gcCounts = gcCounts();
				if (this.lastTime != 0L && gcCounts == this.lastGcCounts) {
					double multiplier = (double)TimeUnit.SECONDS.toMillis(1L) / (time - this.lastTime);
					long delta = currentHeapUsage - this.lastHeapUsage;
					this.lastRate = Math.round(delta * multiplier);
				}

				this.lastTime = time;
				this.lastHeapUsage = currentHeapUsage;
				this.lastGcCounts = gcCounts;
				return this.lastRate;
			}
		}

		private static long gcCounts() {
			long total = 0L;

			for (GarbageCollectorMXBean gcBean : GC_MBEANS) {
				total += gcBean.getCollectionCount();
			}

			return total;
		}
	}
}