// Configuration resolution: defaults <- global json <- project json (if trusted)
// <- env overrides. Much smaller than the container model — no image, runtime,
// packages, GC, or env mirroring (the sandbox inherits the host env directly).

import { existsSync, readFileSync } from "node:fs";
import { join } from "node:path";
import { CONFIG_DIR_NAME, getAgentDir } from "@earendil-works/pi-coding-agent";
import type { Backend } from "./sandbox.ts";

export type Mode = "off" | "readonly" | "restricted";

export interface GuardConfig {
	backend: "auto" | Backend; // auto => bwrap on Linux, sandbox-exec on macOS
	mode: Mode;
	allow: string[]; // extra rw dirs (restricted mode)
}

const DEFAULTS: GuardConfig = {
	backend: "auto",
	mode: "readonly",
	allow: [],
};

function readJson(path: string): Partial<GuardConfig> {
	if (!existsSync(path)) return {};
	try {
		return JSON.parse(readFileSync(path, "utf8"));
	} catch (e) {
		console.error(`pi-guard: could not parse ${path}: ${e}`);
		return {};
	}
}

function merge(base: GuardConfig, o: Partial<GuardConfig>): GuardConfig {
	return {
		backend: o.backend ?? base.backend,
		mode: o.mode ?? base.mode,
		allow: o.allow ?? base.allow,
	};
}

/** Load config: defaults <- global json <- project json (if trusted) <- env overrides. */
export function loadConfig(cwd: string, trusted = false): GuardConfig {
	const globalPath = join(getAgentDir(), "extensions", "pi-guard.json");
	let cfg = merge(DEFAULTS, readJson(globalPath));
	if (trusted) {
		const projectPath = join(cwd, CONFIG_DIR_NAME, "pi-guard.json");
		cfg = merge(cfg, readJson(projectPath));
	}

	const envBackend = process.env.PI_GUARD_BACKEND;
	if (envBackend === "auto" || envBackend === "bwrap" || envBackend === "sandbox-exec") {
		cfg = { ...cfg, backend: envBackend };
	}
	const envMode = process.env.PI_GUARD_MODE;
	if (envMode === "off" || envMode === "readonly" || envMode === "restricted") {
		cfg = { ...cfg, mode: envMode };
	}
	return cfg;
}