import { execFileSync } from "node:child_process";
import fs from "node:fs";
import path from "node:path";
import {
	MAX_SOCKET_PATH_BYTES,
	RUNTIME_DIR_NAME,
	SOCKET_NAME,
} from "./constants.ts";

export type RuntimePaths = {
	/** Canonical Darwin per-user temp + `pi-caps-blink-v1`. */
	runtimeDir: string;
	/** Socket path: `{runtimeDir}/s`. */
	socketPath: string;
};

export class RuntimePathError extends Error {
	constructor(message: string) {
		super(message);
		this.name = "RuntimePathError";
	}
}

export type ResolveRuntimePathsOptions = {
	/** Override `getconf DARWIN_USER_TEMP_DIR` result (tests). */
	tempRoot?: string;
	/** Override realpath (tests). */
	realpath?: (input: string) => string;
};

/**
 * Canonical runtime directory: realpath(`/usr/bin/getconf DARWIN_USER_TEMP_DIR`)
 * + fixed `pi-caps-blink-v1`, with socket path UTF-8 length < 104.
 */
export function resolveRuntimePaths(
	options: ResolveRuntimePathsOptions = {},
): RuntimePaths {
	const rawTemp =
		options.tempRoot ??
		execFileSync("/usr/bin/getconf", ["DARWIN_USER_TEMP_DIR"], {
			encoding: "utf8",
		}).trim();

	if (!rawTemp) {
		throw new RuntimePathError("getconf DARWIN_USER_TEMP_DIR returned empty");
	}

	const realpath = options.realpath ?? ((p: string) => fs.realpathSync(p));
	const tempRoot = realpath(rawTemp);
	const runtimeDir = path.join(tempRoot, RUNTIME_DIR_NAME);
	const socketPath = path.join(runtimeDir, SOCKET_NAME);
	const bytes = Buffer.byteLength(socketPath, "utf8");

	if (bytes >= MAX_SOCKET_PATH_BYTES) {
		throw new RuntimePathError(
			`socket path is ${bytes} UTF-8 bytes; must be < ${MAX_SOCKET_PATH_BYTES}: ${socketPath}`,
		);
	}

	return { runtimeDir, socketPath };
}