package net.minecraft.network.chat;

import it.unimi.dsi.fastutil.objects.ObjectArrayList;
import it.unimi.dsi.fastutil.objects.ObjectList;
import org.jspecify.annotations.Nullable;

public class LastSeenMessagesValidator {
	private final int lastSeenCount;
	private final ObjectList<LastSeenTrackedEntry> trackedMessages = new ObjectArrayList<>();
	@Nullable
	private MessageSignature lastPendingMessage;

	public LastSeenMessagesValidator(final int lastSeenCount) {
		this.lastSeenCount = lastSeenCount;

		for (int i = 0; i < lastSeenCount; i++) {
			this.trackedMessages.add(null);
		}
	}

	public void addPending(final MessageSignature message) {
		if (!message.equals(this.lastPendingMessage)) {
			this.trackedMessages.add(new LastSeenTrackedEntry(message, true));
			this.lastPendingMessage = message;
		}
	}

	public int trackedMessagesCount() {
		return this.trackedMessages.size();
	}

	public void applyOffset(final int offset) throws LastSeenMessagesValidator.ValidationException {
		int maxOffset = this.trackedMessages.size() - this.lastSeenCount;
		if (offset >= 0 && offset <= maxOffset) {
			this.trackedMessages.removeElements(0, offset);
		} else {
			throw new LastSeenMessagesValidator.ValidationException("Advanced last seen window by " + offset + " messages, but expected at most " + maxOffset);
		}
	}

	public LastSeenMessages applyUpdate(final LastSeenMessages.Update update) throws LastSeenMessagesValidator.ValidationException {
		this.applyOffset(update.offset());
		ObjectList<MessageSignature> lastSeenEntries = new ObjectArrayList<>(update.acknowledged().cardinality());
		if (update.acknowledged().length() > this.lastSeenCount) {
			throw new LastSeenMessagesValidator.ValidationException(
				"Last seen update contained " + update.acknowledged().length() + " messages, but maximum window size is " + this.lastSeenCount
			);
		} else {
			for (int i = 0; i < this.lastSeenCount; i++) {
				boolean acknowledged = update.acknowledged().get(i);
				LastSeenTrackedEntry message = (LastSeenTrackedEntry)this.trackedMessages.get(i);
				if (acknowledged) {
					if (message == null) {
						throw new LastSeenMessagesValidator.ValidationException("Last seen update acknowledged unknown or previously ignored message at index " + i);
					}

					this.trackedMessages.set(i, message.acknowledge());
					lastSeenEntries.add(message.signature());
				} else {
					if (message != null && !message.pending()) {
						throw new LastSeenMessagesValidator.ValidationException(
							"Last seen update ignored previously acknowledged message at index " + i + " and signature " + message.signature()
						);
					}

					this.trackedMessages.set(i, null);
				}
			}

			LastSeenMessages lastSeen = new LastSeenMessages(lastSeenEntries);
			if (!update.verifyChecksum(lastSeen)) {
				throw new LastSeenMessagesValidator.ValidationException("Checksum mismatch on last seen update: the client and server must have desynced");
			} else {
				return lastSeen;
			}
		}
	}

	public static class ValidationException extends Exception {
		public ValidationException(final String message) {
			super(message);
		}
	}
}