/**
 * Loads specialist agent system prompts from `agents/<name>.md`.
 * The YAML frontmatter is metadata; the body is passed to spawned `pi` via
 * `--system-prompt` (subprocess backend) or as the system message (session
 * backend).
 *
 * Agent files live NEXT TO this module's compiled output: `<package>/agents/`.
 * The path is resolved from `import.meta.url` so it works both when run from
 * source (`.ts`) via pi's loader and when installed via `pi package add`.
 */

import { readFileSync, readdirSync } from "node:fs";
import { join, dirname } from "node:path";
import { fileURLToPath } from "node:url";

const MODULE_DIR = dirname(fileURLToPath(import.meta.url));
const AGENTS_DIR = join(MODULE_DIR, "..", "agents");
const cache = new Map<string, string>();

function stripFrontmatter(md: string): string {
	if (!md.startsWith("---")) return md;
	const end = md.indexOf("\n---", 3);
	if (end === -1) return md;
	return md.slice(end + 4).replace(/^\s*\n/, "");
}

export function loadAgentPrompt(name: string): string {
	const cached = cache.get(name);
	if (cached !== undefined) return cached;
	const path = join(AGENTS_DIR, `${name}.md`);
	let body: string;
	try {
		body = stripFrontmatter(readFileSync(path, "utf8"));
	} catch {
		throw new Error(`stock-analysis: unknown agent "${name}" (no file at ${path})`);
	}
	cache.set(name, body);
	return body;
}

export function agentsDirectory(): string {
	return AGENTS_DIR;
}

/** Enumerate the available specialist agent names (for the structure test +
 *  diagnostics). Returns basenames without the `.md` extension. */
export function listAgents(): string[] {
	try {
		return readdirSync(AGENTS_DIR)
			.filter((f) => f.endsWith(".md"))
			.map((f) => f.slice(0, -3));
	} catch {
		return [];
	}
}