import { existsSync, mkdirSync, readFileSync, writeFileSync } from "node:fs";
import { homedir } from "node:os";
import { dirname, join } from "node:path";
import { parse as parseYaml, stringify as stringifyYaml } from "yaml";

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

const NO_STORE = { "Cache-Control": "no-store" } as const;

// ─── Helpers (same pattern as remote-questions/route.ts) ─────────────────────

function getPreferencesPath(): string {
	return join(homedir(), ".sf", "PREFERENCES.md");
}

function parseFrontmatter(content: string): {
	data: Record<string, unknown>;
	body: string;
} {
	const startMarker = content.startsWith("---\r\n") ? "---\r\n" : "---\n";
	if (!content.startsWith(startMarker)) return { data: {}, body: content };
	const searchStart = startMarker.length;
	const endIdx = content.indexOf("\n---", searchStart);
	if (endIdx === -1) return { data: {}, body: content };
	const block = content.slice(searchStart, endIdx);
	const afterFrontmatter = content.slice(endIdx + 4);
	try {
		const parsed = parseYaml(block.replace(/\r/g, ""));
		const data =
			typeof parsed === "object" && parsed !== null
				? (parsed as Record<string, unknown>)
				: {};
		return { data, body: afterFrontmatter };
	} catch {
		return { data: {}, body: content };
	}
}

function writeFrontmatter(data: Record<string, unknown>, body: string): string {
	const yamlStr = stringifyYaml(data, { lineWidth: 0 }).trimEnd();
	return `---\n${yamlStr}\n---${body}`;
}

function readPrefs(): { data: Record<string, unknown>; body: string } {
	const path = getPreferencesPath();
	if (!existsSync(path)) return { data: {}, body: "\n" };
	const content = readFileSync(path, "utf-8");
	return parseFrontmatter(content);
}

function writePrefs(data: Record<string, unknown>, body: string): void {
	const path = getPreferencesPath();
	const dir = dirname(path);
	if (!existsSync(dir)) mkdirSync(dir, { recursive: true });
	writeFileSync(path, writeFrontmatter(data, body), "utf-8");
}

// ─── GET — read current experimental flags ───────────────────────────────────

export async function GET(): Promise<Response> {
	try {
		const { data } = readPrefs();
		const exp =
			typeof data.experimental === "object" && data.experimental !== null
				? (data.experimental as Record<string, unknown>)
				: {};
		return Response.json({ rtk: exp.rtk === true }, { headers: NO_STORE });
	} catch (err) {
		const message = err instanceof Error ? err.message : String(err);
		return Response.json(
			{ error: message },
			{ status: 500, headers: NO_STORE },
		);
	}
}

// ─── PATCH — toggle an experimental flag ────────────────────────────────────
//
// Body: { flag: "rtk", enabled: boolean }

export async function PATCH(request: Request): Promise<Response> {
	try {
		const body = (await request.json()) as Record<string, unknown>;
		const { flag, enabled } = body;

		const KNOWN_FLAGS = new Set(["rtk"]);
		if (typeof flag !== "string" || !KNOWN_FLAGS.has(flag)) {
			return Response.json(
				{
					error: `Unknown experimental flag "${flag}". Known flags: ${[...KNOWN_FLAGS].join(", ")}`,
				},
				{ status: 400, headers: NO_STORE },
			);
		}
		if (typeof enabled !== "boolean") {
			return Response.json(
				{ error: "enabled must be a boolean" },
				{ status: 400, headers: NO_STORE },
			);
		}

		const { data, body: mdBody } = readPrefs();

		// Merge into experimental block
		const existing =
			typeof data.experimental === "object" && data.experimental !== null
				? { ...(data.experimental as Record<string, unknown>) }
				: {};
		existing[flag] = enabled;
		data.experimental = existing;

		writePrefs(data, mdBody);

		return Response.json({ [flag]: enabled }, { headers: NO_STORE });
	} catch (err) {
		const message = err instanceof Error ? err.message : String(err);
		return Response.json(
			{ error: `Failed to update experimental flag: ${message}` },
			{ status: 500, headers: NO_STORE },
		);
	}
}