// captcha source origin: https://codepen.io/hirensojitra/pen/OJBpVvB

    $(document).ready(function () {

        // Generate captcha on page load

        generateCaptcha();

        // Handle captcha refresh button click

        $("#refresh-captcha").click(function () {

          generateCaptcha();

          $("#captcha-input").val("");

        });

        // Handle form submit

        $("#captcha-form").submit(function (event) {

          

          // Validate captcha

          var captchaInput = $("#captcha-input").val();

          var captchaCode = sessionStorage.getItem("captchaCode");

          if (captchaInput != captchaCode) {

            alert("Nesprávně opsaný CAPTCHA kód. Dodržujte velká-malá písmena!");

            event.preventDefault();

            generateCaptcha();

            $("#captcha-input").val("");

            return;

          }

          // Form validation successful, submit form

          alert("E-mail úspěšně odeslán. Kopie dorazí na Vaší adresu.");

          //$("#captcha-form").submit();

          generateCaptcha();

        });

  

        // Define the function generateCaptcha()

        function generateCaptcha() {

          // Get the canvas element with ID captcha and create an instance of its canvas rendering context

          var a = $("#captcha")[0],

              b = a.getContext("2d");

            // Clear the canvas

            b.clearRect(0, 0, a.width, a.height);

            // Define the string of characters that can be included in the captcha

            var f = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789",

                e = "",

                g = -45,

                h = 45,

                i = h - g,

                j = 20,

                k = 30,

                l = k - j;

            // Generate each character of the captcha

            for (var m = 0; m < 6; m++) {

              // Select random letter from the pool to be part of the captcha

              var n = f.charAt(Math.floor(Math.random() * f.length));

              e += n;

              

              // Set up the text formatting

              b.font = j + Math.random() * l + "px Arial";

              b.textAlign = "center";

              b.textBaseline = "middle";

              

              // Set the color of the text

              b.fillStyle = "rgb(" + Math.floor(Math.random() * 256) + "," + Math.floor(Math.random() * 256) + "," + Math.floor(Math.random() * 256) + ")";

          

              // Add the character to the canvas

              var o = g + Math.random() * i;

              b.translate(20 + m * 30, a.height / 2);

              b.rotate(o * Math.PI / 180);

              b.fillText(n, 0, 0);

              b.rotate(-1 * o * Math.PI / 180);

              b.translate(-(20 + m * 30), -1 * a.height / 2);

            }

            // Set the captcha code in session storage

            sessionStorage.setItem("captchaCode", e);

        }

      })