document.addEventListener("DOMContentLoaded", function () {
  const yearDropdown = document.getElementById("year");
  const errorDiv = document.getElementById("yearError");
  const form = document.querySelector("form");

  const tableName = form.id.toLowerCase(); // ao, cit, etc.

  const currentYear = new Date().getFullYear();
  const startYear = 1990;

  /* ---------- Fill Year Dropdown ---------- */
  for (let y = currentYear; y >= startYear; y--) {
    let nextYear = y + 1;

    let option = document.createElement("option");
    option.value = y;                       // IMPORTANT
    option.textContent = `AY ${y}-${nextYear}`;

    yearDropdown.appendChild(option);
  }

  /* ---------- Validate on Change ---------- */
  yearDropdown.addEventListener("change", function () {
    const selectedYear = this.value;

    // If empty → block submit
    if (!selectedYear) {
      errorDiv.style.display = "block";
      errorDiv.innerText = "Please select an Assessment Year.";
      form.onsubmit = () => false;
      return;
    }

    fetch("/check_year", {
      method: "POST",
      headers: { "Content-Type": "application/json" },
      body: JSON.stringify({
        table: tableName,
        year: selectedYear
      })
    })
      .then(res => res.json())
      .then(data => {
        if (data.exists) {
          errorDiv.style.display = "block";
          errorDiv.innerText = `AY ${selectedYear}-${parseInt(selectedYear) + 1} already exists!`;
          form.onsubmit = () => false;
        } else {
          errorDiv.style.display = "none";
          errorDiv.innerText = "";
          form.onsubmit = null; // allow submit
        }
      })
      .catch(() => {
        errorDiv.style.display = "block";
        errorDiv.innerText = "Error validating year. Please try again.";
        form.onsubmit = () => false;
      });
  });

  /* ---------- Final Safety Check on Submit ---------- */
  form.addEventListener("submit", function (e) {
    if (!yearDropdown.value) {
      e.preventDefault();
      errorDiv.style.display = "block";
      errorDiv.innerText = "Assessment Year is required.";
    }
  });
});