export const engine = async (
	input: TEngineInput,
	toolIterationInfo?: TToolIterationInfo,
): Promise<TEngineOutput> => {
	const { messages, response, inLoop, contextLimit } = input;

	// Build current message (assistant response + tool results)
	const currentMessage = AssistantMessage({
		content: [
			{
				type: "TEXT",
				toolCalls: response.toolCalls,
				text: response.content,
				tokens: response.tokens.output + response.tokens.reasoning,
			},
			{ type: "TOOL_RESULT", toolResults: response.toolResults },
		],
		reasoning: response.reasoning,
	});

	// Calculate token counts for each section
	const chatHistorySoFarTokens = getTokens(messages);
	const inLoopTokens = calculateMessagesTokens(inLoop);
	const inLoopSummaryIfPossibleTokens = calculateMessagesTokens(inLoop, true);
	const currentMessageTokens = calculateMessagesTokens([currentMessage]);
	const currentMessageSummaryIfPossibleTokens = calculateMessagesTokens(
		[currentMessage],
		true,
	);

	// Default summary size
	const DEFAULT_SUMMARY_SIZE = 1024;

	// Build token cost table for layout selection
	const tokenTable: TTokenTable = {
		HISTORY: {
			FULL: chatHistorySoFarTokens,
			TOOL_PROVIDED_SUMMARY_IF_POSSIBLE: Infinity, // Never use for history
			SUMMARY: DEFAULT_SUMMARY_SIZE,
		},
		IN_LOOP: {
			FULL: inLoopTokens,
			TOOL_PROVIDED_SUMMARY_IF_POSSIBLE: inLoopSummaryIfPossibleTokens,
			SUMMARY: DEFAULT_SUMMARY_SIZE,
		},
		CURRENT_MESSAGE: {
			FULL: currentMessageTokens,
			TOOL_PROVIDED_SUMMARY_IF_POSSIBLE: currentMessageSummaryIfPossibleTokens,
			SUMMARY: DEFAULT_SUMMARY_SIZE,
		},
	};

	// Choose optimal layout (cheapest that fits within contextLimit)
	const bestLayout = chooseOptimalLayout(contextLimit, tokenTable);
	if (!bestLayout) throw new Error("LAYOUT_NOT_FOUND");

	if (toolIterationInfo) {
		toolIterationInfo.layout = bestLayout;
	}

	// Execute handlers for each section
	const history_ = await HANDLER_MAP[bestLayout.HISTORY]({
		messages,
		config: input,
		section: "HISTORY",
	});

	const inLoop_ = await HANDLER_MAP[bestLayout.IN_LOOP]({
		messages: inLoop,
		config: input,
		section: "IN_LOOP",
	});

	const currentMessage_ = await HANDLER_MAP[bestLayout.CURRENT_MESSAGE]({
		messages: [currentMessage],
		config: input,
		section: "CURRENT_MESSAGE",
	});

	return {
		inLoop: [...inLoop_.trimmedMessages, ...currentMessage_.trimmedMessages],
		summary: history_?.summary,
		shouldDumpSummaryInDB:
			chatHistorySoFarTokens +
				inLoopSummaryIfPossibleTokens +
				currentMessageSummaryIfPossibleTokens >
			contextLimit,
	};
};