const downloadRangeButtons = Array.from(document.querySelectorAll("[data-download-range]"));
const customDateFields = document.querySelector("[data-custom-date-fields]");
const customDateCollapse = customDateFields ? new bootstrap.Collapse(customDateFields, { toggle: false }) : null;
const downloadFrom = document.querySelector("#download-from");
const downloadTo = document.querySelector("#download-to");
const errorBanner = document.querySelector("[data-downloads-error]");
const form = document.querySelector("form.downloads-form");
let submittedButton = null;

downloadRangeButtons.forEach(option => {
  option.addEventListener("change", () => {
    const custom = option.value === "custom";

    if (customDateCollapse) {
      custom ? customDateCollapse.show() : customDateCollapse.hide();
    }

    if (custom) {
      downloadFrom?.focus();
      return;
    }

    if (downloadFrom) {
      downloadFrom.value = option.dataset.from;
    }

    if (downloadTo) {
      downloadTo.value = option.dataset.to;
    }
  });
});

function showError(message) {
  if (!errorBanner) return;
  errorBanner.textContent = message;
  errorBanner.classList.remove("d-none");
}

function clearError() {
  if (!errorBanner) return;
  errorBanner.textContent = "";
  errorBanner.classList.add("d-none");
}

function triggerDownload(blob, filename) {
  const url = URL.createObjectURL(blob);
  const link = document.createElement("a");
  link.href = url;
  link.download = filename;
  document.body.appendChild(link);
  link.click();
  link.remove();
  URL.revokeObjectURL(url);
}

function filenameFromResponse(response) {
  const header = response.headers.get("Content-Disposition") || "";
  const match = header.match(/filename="([^"]+)"/);
  return match ? match[1] : "readings.csv";
}

function setDownloadPending(button, pending) {
  if (!button) return;

  button.disabled = pending;
  button.setAttribute("aria-busy", pending ? "true" : "false");
  button.querySelector("[data-download-spinner]")?.classList.toggle("d-none", !pending);
}

if (form) {
  form.querySelectorAll("[data-download-button]").forEach(button => {
    button.addEventListener("click", () => {
      submittedButton = button;
    });
  });

  form.addEventListener("submit", async event => {
    event.preventDefault();
    clearError();

    const button = event.submitter || submittedButton || form.querySelector("[data-download-button]");
    const params = new URLSearchParams(new FormData(form));
    const action = button?.getAttribute("formaction") || form.action;
    const url = new URL(action, window.location.origin);
    url.search = params;
    setDownloadPending(button, true);

    try {
      const response = await fetch(url);

      if (!response.ok) {
        const text = await response.text();
        showError(text || `Download failed (HTTP ${response.status}).`);
        return;
      }

      const blob = await response.blob();
      triggerDownload(blob, filenameFromResponse(response));
    } catch (err) {
      showError("Could not reach the server. Check your connection and try again.");
    } finally {
      setDownloadPending(button, false);
      submittedButton = null;
    }
  });
}