script.js

let states = {
  "Andaman and Nicobar Islands": 1,
  "Andhra Pradesh": 2,
  "Arunachal Pradesh": 3,
  Assam: 4,
  Bihar: 5,
  Chandigarh: 6,
  Chhattisgarh: 7,
  "Dadra and Nagar Haveli": 8,
  "Daman and Diu": 37,
  Delhi: 9,
  Goa: 10,
  Gujarat: 11,
  Haryana: 12,
  "Himachal Pradesh": 13,
  "Jammu and Kashmir": 14,
  Jharkhand: 15,
  Karnataka: 16,
  Kerala: 17,
  Ladakh: 18,
  Lakshadweep: 19,
  "Madhya Pradesh": 20,
  Maharashtra: 21,
  Manipur: 22,
  Meghalaya: 23,
  Mizoram: 24,
  Nagaland: 25,
  Odisha: 26,
  Puducherry: 27,
  Punjab: 28,
  Rajasthan: 29,
  Sikkim: 30,
  "Tamil Nadu": 31,
  Telangana: 32,
  Tripura: 33,
  "Uttar Pradesh": 34,
  Uttarakhand: 35,
  "West Bengal": 36,
};
let districts = {};

let dateField = document.getElementById("date");
let age18 = document.getElementById("18+");
let date = document.getElementById("date");
let results = document.getElementById("results");
let state = document.getElementById("state");
let district = document.getElementById("district");

function getDate() {
  const d = dateField.value;
  return d.split("-").reverse().join("-");
}

function getAge() {
  return age18.checked ? 18 : 45;
}

function setStates() {
  for (const s in states) {
    const opt = document.createElement("option");
    opt.value = states[s];
    opt.text = s;
    state.appendChild(opt);
  }
}

function setDistricts(d = null) {
  let req = new XMLHttpRequest();
  const url = `https://cdn-api.co-vin.in/api/v2/admin/location/districts/${state.value}`;
  req.open("GET", url, true);
  req.responseType = "json";
  req.onload = function () {
    let status = req.status;
    if (status === 200) {
      districts = req.response.districts;
      const def = district.children[0];
      district.innerHTML = "";
      district.appendChild(def);
      for (const d of districts) {
        let opt = document.createElement("option");
        opt.value = d.district_id;
        opt.text = d.district_name;
        district.appendChild(opt);
      }
      if (d) district.value = d;
    }
  };
  req.send();
}

function getDistrictId() {
  return district.value;
}

function get(callback) {
  let req = new XMLHttpRequest();
  const district_id = district.value;
  const date = getDate();
  const url = `https://cdn-api.co-vin.in/api/v2/appointment/sessions/public/calendarByDistrict?district_id=${district_id}&date=${date}`;
  req.open("GET", url, true);
  req.responseType = "json";
  req.onload = function () {
    let status = req.status;
    if (status === 200) callback(null, req.response);
    else callback(status, req.response);
  };
  req.send();
}

function check() {
  get((err, res) => {
    if (err) return alert(`Error: ${err}`);
    const date = getDate();
    const age = getAge();
    let count = 0;
    const available = res.centers.filter((center) => {
      count += center.sessions[0].min_age_limit === age;
      return center.sessions.some(
        (s) => s.available_capacity > 0 && s.min_age_limit === age
      );
    });
    console.log(available);
    const template = (center) => `
            <div class="p-1" style="border: 1px solid black">
                <b>${center.name}, Pincode: ${center.pincode}</b><br>
                ${center.sessions
                  .filter((s) => s.available_capacity > 0)
                  .map((s) => s.date + ": " + s.available_capacity)
                  .join("<br>")}<br>
            </div>
        `;
    if (available.length === 0) {
      results.innerHTML = `
                <div class="alert alert-danger">
                    Found ${count} centers listed for ${age}+ age group in your district, and all of them are fully booked right now.<br>
                    Please keep checking for updates.
                </div>
            `;
    } else {
      results.innerHTML = `<div class="alert alert-success">Found <b>${count} centers</b> listed for ${age}+ age group in your district, out of which <b>${available.length} centers</b> have available slots, head over to the <b><a href="https://selfregistration.cowin.gov.in/" target="_blank">official CoWIN website</a></b> to book the slot</div>`;
      results.innerHTML += available.map((c) => template(c)).join(" ");
    }
  });
}

state.onchange = () => {
  localStorage.setItem("state", state.value);
  setDistricts();
};

district.onchange = () => localStorage.setItem("district", district.value);

window.onload = () => {
  const s = localStorage.getItem("state");
  const d = localStorage.getItem("district");
  setStates();
  if (s) {
    state.value = s;
    setDistricts(d);
  }
  date.valueAsDate = new Date();
};