interface ChromeDownloadsLike {
  download(
    options: {
      filename: string;
      saveAs?: boolean;
      url: string;
    },
    callback?: () => void
  ): Promise<unknown> | void;
}

interface ChromeRuntimeLike {
  onMessage?: {
    addListener(
      listener: (
        message: unknown,
        sender: unknown,
        sendResponse: (response: unknown) => void
      ) => boolean | void
    ): void;
  };
}

interface ChromeLike {
  downloads?: ChromeDownloadsLike;
  runtime?: ChromeRuntimeLike;
}

type DownloadMarketCsvMessage = {
  csv: string;
  filename: string;
  type: "download-market-csv";
};

export function registerBackgroundMessageHandler(
  chromeLike: ChromeLike = (
    globalThis as typeof globalThis & {
      chrome?: ChromeLike;
    }
  ).chrome ?? {}
): void {
  chromeLike.runtime?.onMessage?.addListener((message, _sender, sendResponse) => {
    if (!isDownloadMarketCsvMessage(message)) {
      return;
    }

    void triggerCsvDownload(chromeLike, message)
      .then(() => {
        sendResponse({ ok: true });
      })
      .catch((error) => {
        sendResponse({
          error: error instanceof Error ? error.message : String(error),
          ok: false
        });
      });

    return true;
  });
}

async function triggerCsvDownload(
  chromeLike: ChromeLike,
  message: DownloadMarketCsvMessage
): Promise<void> {
  if (!chromeLike.downloads?.download) {
    throw new Error("chrome.downloads.download is unavailable");
  }

  const csvUrl = `data:text/csv;charset=utf-8,${encodeURIComponent(`\uFEFF${message.csv}`)}`;
  await Promise.resolve(
    chromeLike.downloads.download({
      filename: message.filename,
      saveAs: false,
      url: csvUrl
    })
  );
}

function isDownloadMarketCsvMessage(
  message: unknown
): message is DownloadMarketCsvMessage {
  if (!message || typeof message !== "object") {
    return false;
  }

  const candidate = message as Partial<DownloadMarketCsvMessage>;
  return (
    candidate.type === "download-market-csv" &&
    typeof candidate.csv === "string" &&
    typeof candidate.filename === "string"
  );
}

registerBackgroundMessageHandler();