import {
	existsSync,
	mkdirSync,
	readFileSync,
	statSync,
	writeFileSync,
} from "node:fs";
import { homedir } from "node:os";
import { dirname, resolve } from "node:path";
import { webPreferencesPath } from "../../../../src/app-paths.ts";
import { discoverProjects } from "../../../../src/web/project-discovery-service.ts";

export const runtime = "nodejs";
export const dynamic = "force-dynamic";

/** Shape of persisted web preferences. */
interface WebPreferences {
	devRoot?: string;
	lastActiveProject?: string;
}

/** Expand leading `~/` to the user's home directory. */
function expandTilde(p: string): string {
	if (p === "~") return homedir();
	if (p.startsWith("~/")) return homedir() + p.slice(1);
	return p;
}

/**
 * POST /api/switch-root
 *
 * Validates the new root path, persists it as the `devRoot` preference,
 * and returns the discovered projects under the new root.
 *
 * Request body: { "devRoot": "/absolute/path" }
 * Response:     { "devRoot": "/resolved/path", "projects": [...] }
 */
export async function POST(request: Request): Promise<Response> {
	try {
		const body = (await request.json()) as Record<string, unknown>;
		const rawDevRoot =
			typeof body.devRoot === "string" ? body.devRoot.trim() : "";

		if (!rawDevRoot) {
			return Response.json(
				{ error: "Missing devRoot in request body" },
				{ status: 400 },
			);
		}

		const expanded = expandTilde(rawDevRoot);
		const resolved = resolve(expanded);

		// Validate: path must exist
		if (!existsSync(resolved)) {
			return Response.json(
				{ error: `Path does not exist: ${resolved}` },
				{ status: 400 },
			);
		}

		// Validate: path must be a directory
		try {
			const stat = statSync(resolved);
			if (!stat.isDirectory()) {
				return Response.json(
					{ error: `Not a directory: ${resolved}` },
					{ status: 400 },
				);
			}
		} catch {
			return Response.json(
				{ error: `Cannot access path: ${resolved}` },
				{ status: 400 },
			);
		}

		// Read existing preferences and merge
		let existing: WebPreferences = {};
		try {
			if (existsSync(webPreferencesPath)) {
				existing = JSON.parse(readFileSync(webPreferencesPath, "utf-8"));
			}
		} catch {
			// Corrupt file — start fresh
		}

		const prefs: WebPreferences = {
			...existing,
			devRoot: resolved,
			// Clear last active project since we're changing the root
			lastActiveProject: undefined,
		};

		// Ensure parent directory exists
		const dir = dirname(webPreferencesPath);
		if (!existsSync(dir)) {
			mkdirSync(dir, { recursive: true });
		}

		writeFileSync(webPreferencesPath, JSON.stringify(prefs, null, 2), "utf-8");

		// Discover projects under the new root
		const projects = discoverProjects(resolved, true);

		return Response.json({
			devRoot: resolved,
			projects,
		});
	} catch (err) {
		return Response.json(
			{
				error: `Failed to switch root: ${err instanceof Error ? err.message : String(err)}`,
			},
			{ status: 500 },
		);
	}
}