package net.minecraft.network.chat;

import it.unimi.dsi.fastutil.objects.ObjectArrayList;
import it.unimi.dsi.fastutil.objects.ObjectList;
import java.util.BitSet;
import java.util.Objects;
import org.jspecify.annotations.Nullable;

public class LastSeenMessagesTracker {
	private final LastSeenTrackedEntry[] trackedMessages;
	private int tail;
	private int offset;
	@Nullable
	private MessageSignature lastTrackedMessage;

	public LastSeenMessagesTracker(final int lastSeenCount) {
		this.trackedMessages = new LastSeenTrackedEntry[lastSeenCount];
	}

	public boolean addPending(final MessageSignature message, final boolean wasShown) {
		if (Objects.equals(message, this.lastTrackedMessage)) {
			return false;
		} else {
			this.lastTrackedMessage = message;
			this.addEntry(wasShown ? new LastSeenTrackedEntry(message, true) : null);
			return true;
		}
	}

	private void addEntry(@Nullable final LastSeenTrackedEntry entry) {
		int index = this.tail;
		this.tail = (index + 1) % this.trackedMessages.length;
		this.offset++;
		this.trackedMessages[index] = entry;
	}

	public void ignorePending(final MessageSignature pendingMessage) {
		for (int i = 0; i < this.trackedMessages.length; i++) {
			LastSeenTrackedEntry entry = this.trackedMessages[i];
			if (entry != null && entry.pending() && pendingMessage.equals(entry.signature())) {
				this.trackedMessages[i] = null;
				break;
			}
		}
	}

	public int getAndClearOffset() {
		int originalOffset = this.offset;
		this.offset = 0;
		return originalOffset;
	}

	public LastSeenMessagesTracker.Update generateAndApplyUpdate() {
		int offset = this.getAndClearOffset();
		BitSet acknowledged = new BitSet(this.trackedMessages.length);
		ObjectList<MessageSignature> lastSeenEntries = new ObjectArrayList<>(this.trackedMessages.length);

		for (int i = 0; i < this.trackedMessages.length; i++) {
			int index = (this.tail + i) % this.trackedMessages.length;
			LastSeenTrackedEntry message = this.trackedMessages[index];
			if (message != null) {
				acknowledged.set(i, true);
				lastSeenEntries.add(message.signature());
				this.trackedMessages[index] = message.acknowledge();
			}
		}

		LastSeenMessages lastSeen = new LastSeenMessages(lastSeenEntries);
		LastSeenMessages.Update update = new LastSeenMessages.Update(offset, acknowledged, lastSeen.computeChecksum());
		return new LastSeenMessagesTracker.Update(lastSeen, update);
	}

	public int offset() {
		return this.offset;
	}

	public record Update(LastSeenMessages lastSeen, LastSeenMessages.Update update) {
	}
}