import * as path from "node:path";
import type { ExtensionAPI } from "@earendil-works/pi-coding-agent";
import { packageRoot } from "../lib/base-paths.ts";
import { resolveRuleFiles } from "../lib/rules.ts";

const LOCAL_RULES_SUBDIR = path.join(".agent", "rules");

export default function agentRulesExtension(pi: ExtensionAPI) {
	let rules: { label: string }[] = [];

	pi.on("session_start", async (_event, ctx) => {
		const baseDir = path.join(packageRoot(), "rules");
		const localDir = path.join(ctx.cwd, LOCAL_RULES_SUBDIR);
		rules = resolveRuleFiles(baseDir, localDir).map((r) => ({
			label: path.relative(ctx.cwd, r.absPath),
		}));
		if (rules.length > 0) ctx.ui.notify(`Found ${rules.length} rule(s) (base + local)`, "info");
	});

	pi.on("before_agent_start", async (event) => {
		if (rules.length === 0) return;
		const list = rules.map((r) => `- ${r.label}`).join("\n");
		return {
			systemPrompt:
				event.systemPrompt +
				`\n\n## Project Rules\n\nThe following rules are available (base package + local overrides):\n\n${list}\n\nWhen working on tasks that touch one of these areas, read the relevant rule file(s) before acting.\n`,
		};
	});
}