import { getAgentDir, type ExtensionAPI } from "@earendil-works/pi-coding-agent";
import { writeFile } from "node:fs/promises";
import { join } from "node:path";

const NOTICE_MARKER_FILENAME = ".pi-radius-mcp-migration-notice-v1";

/** Atomically claim the one-time notice across packages and running Pi processes. */
async function claimMigrationNotice(): Promise<boolean> {
	try {
		await writeFile(join(getAgentDir(), NOTICE_MARKER_FILENAME), "shown\n", {
			encoding: "utf8",
			flag: "wx",
			mode: 0o600,
		});
		return true;
	} catch (error) {
		if ((error as NodeJS.ErrnoException).code === "EEXIST") return false;
		// A read-only config directory should not suppress the migration guidance.
		return true;
	}
}

export default function (pi: ExtensionAPI): void {
	pi.on("session_start", async (_event, ctx) => {
		if (ctx.mode !== "tui" || !(await claimMigrationNotice())) return;
		ctx.ui.notify(
			[
				"The Radius Pi extensions are deprecated in favor of the Radius MCP.",
				"pi mcp add radius --url https://radius.pi.dev/mcp",
			].join("\n"),
			"warning",
		);
	});
}