import { dirname, join } from 'node:path';

/**
 * n8n bundles `@langchain/openai` and `@n8n/ai-utilities` inside its own installation, and those
 * modules are only reachable by a plain `require` when the package was installed as a community
 * node (npm installs it below `~/.n8n/nodes`). When the package is mounted as a custom extension
 * the resolution starts from our own folder, so we additionally look next to n8n itself
 * (the directory of `require.main.filename` is n8n's CLI entry point).
 */
function candidateModuleDirs(): string[] {
	const dirs = new Set<string>();
	const addChain = (start: string | undefined): void => {
		if (!start) return;
		let current = start;
		for (;;) {
			dirs.add(join(current, 'node_modules'));
			const parent = dirname(current);
			if (parent === current) break;
			current = parent;
		}
	};

	addChain(__dirname);
	addChain(process.cwd());
	if (require.main?.filename) addChain(dirname(require.main.filename));
	return [...dirs];
}

export function loadN8nModule<T = unknown>(moduleName: string): T | undefined {
	try {
		return require(moduleName) as T;
	} catch {
		// Not reachable from our own folder - fall through to the n8n installation.
	}

	for (const dir of candidateModuleDirs()) {
		try {
			return require(join(dir, moduleName)) as T;
		} catch {
			// Keep looking.
		}
	}

	return undefined;
}

export type ChatOpenAiConstructor = new (config: Record<string, unknown>) => unknown;

export function loadChatOpenAi(): ChatOpenAiConstructor {
	const loaded = loadN8nModule<{ ChatOpenAI?: ChatOpenAiConstructor }>('@langchain/openai');
	if (typeof loaded?.ChatOpenAI !== 'function') {
		throw new Error(
			'Could not load "@langchain/openai" from the n8n installation. The Chat Model node needs the LangChain packages that ship with n8n (@n8n/n8n-nodes-langchain must be installed).',
		);
	}
	return loaded.ChatOpenAI;
}

/**
 * Token/cost accounting in the execution log is provided by n8n's own tracer. It is an internal
 * helper, so we use it when it is reachable and stay silent when it is not - the model itself
 * works either way.
 */
export function loadN8nLlmTracing(context: unknown): unknown | undefined {
	for (const moduleName of ['@n8n/ai-utilities', 'n8n-core']) {
		const loaded = loadN8nModule<{ N8nLlmTracing?: new (context: unknown) => unknown }>(moduleName);
		if (typeof loaded?.N8nLlmTracing === 'function') {
			try {
				return new loaded.N8nLlmTracing(context);
			} catch {
				return undefined;
			}
		}
	}
	return undefined;
}