import { readdirSync, readFileSync } from "node:fs";
import { homedir } from "node:os";
import { basename, dirname, join, resolve } from "node:path";

// Codex registers a role from a standalone `agents/*.toml` (keyed by its `name`, else the
// file stem) or from an `[agents.<name>]` table in config.toml. It reads both under
// CODEX_HOME and under a project's `.codex/`. Codex still validates the role itself (trust,
// required fields); this only answers "does a role file declare this name".

const NAME_LINE = /^\s*name\s*=\s*"([^"\n]+)"\s*(?:#.*)?$/m;
const AGENT_TABLE = /^\s*\[agents\.(?:"([^"\n]+)"|([A-Za-z0-9_-]+))\]\s*(?:#.*)?$/gm;

function readText(path: string): string | null {
	try {
		return readFileSync(path, "utf8");
	} catch {
		return null;
	}
}

function standaloneRoleNames(agentsDir: string): string[] {
	let entries: string[];
	try {
		entries = readdirSync(agentsDir);
	} catch {
		return [];
	}
	const names: string[] = [];
	for (const entry of entries) {
		if (!entry.endsWith(".toml")) continue;
		const text = readText(join(agentsDir, entry));
		if (text === null) continue;
		names.push(text.match(NAME_LINE)?.[1] ?? basename(entry, ".toml"));
	}
	return names;
}

function configTableRoleNames(configPath: string): string[] {
	const text = readText(configPath);
	if (text === null) return [];
	return [...text.matchAll(AGENT_TABLE)].map((match) => match[1] ?? match[2] ?? "").filter(Boolean);
}

function codexDirs(cwd: string, env: NodeJS.ProcessEnv): string[] {
	const dirs = [resolve(env["CODEX_HOME"]?.trim() || join(homedir(), ".codex"))];
	for (let dir = resolve(cwd); ; dir = dirname(dir)) {
		dirs.push(join(dir, ".codex"));
		if (dirname(dir) === dir) break;
	}
	return [...new Set(dirs)];
}

export function registeredAgentRoles(cwd: string, env: NodeJS.ProcessEnv = process.env): ReadonlySet<string> {
	const names = new Set<string>();
	for (const dir of codexDirs(cwd, env)) {
		for (const name of standaloneRoleNames(join(dir, "agents"))) names.add(name);
		for (const name of configTableRoleNames(join(dir, "config.toml"))) names.add(name);
	}
	return names;
}