CipherApp/templates/CaesarDecrypt.html

<div class="form-group">
    <form method="POST" action="{{ url_for('encrypt_decrypt') }}">
        <label for="ciphertext_input">
            Enter Cipher text here:
        </label>
        <input type="text" id="ciphertext_input" name="ciphertext_input"
               placeholder="Enter your text here" class="form-control">
        <div class="form-group">
            <label for="key-input-decrypt">Shift Value:</label>
            <div class="input-group">
      <span class="input-group-prepend">
        <button class="btn btn-outline-secondary" type="button" onclick="decrementKeyDecrypt()">-</button>
      </span>
                <label for="key-input-decrypt"></label><input type="text" id="key-input-decrypt"
                                                              name="key-input-decrypt" class="form-control" min="1"
                                                              max="1000000000000000" value="3"
                                                              oninput="updateSliderValue()">
                <span class="input-group-append">
        <button class="btn btn-outline-secondary" type="button" onclick="incrementKeyDecrypt()">+</button>
          </span>
            </div>
        </div>
        <div>
            <label for="key-slider-decrypt">
                Enter Shift Value
            </label>
            <input type="range" id="key-slider-decrypt" name="key" min="1"
                   max="1000000000000000" value="3" class="form-control"
                   oninput="updateKeyInput()">
        </div>
        <div class="custom-file">
            <span class="string">Upload pad file:</span>
            <input type="file" id="file-input-decrypt" onchange="updateLabelDecrypt()">
            <label for="file-input-decrypt" id="file-label-decrypt">Choose file</label>
            <button id="remove-file-btn-decrypt" onclick="removeFileDecrypt()" style="display: none;">Remove
            </button>
        </div>
        <div class="container">
            <div class="row justify-content-center">
                <div class="col-lg-8">
                    <div class="form-group">
                        <label for="ciphertext-decrypt">Cipher Text:</label><input type="text" id="ciphertext-decrypt"
                                                                                   name="ciphertext-decrypt"
                                                                                   placeholder="Cipher Text"
                                                                                   class="form-control" readonly>
                    </div>
                </div>
            </div>
        </div>
        <div class="container">
            <div class="row justify-content-center">
                <div class="col-lg-8">
                    <div class="form-group alert alert-success">
                        <label for="cleartext-decrypt">Clear Text:</label>
                        <input type="text" id="cleartext-decrypt" name="cleartext-decrypt" placeholder="Clear Text"
                               class="form-control" readonly>
                    </div>
                </div>
            </div>
        </div>
    </form>
</div>

<script>
    function update_decrypt() {
        let ciphertext = document.getElementById('ciphertext_input').value;
        let key = document.getElementById('key-slider-decrypt').value;
        {#let xhrEncrypt = new XMLHttpRequest();#}
        let pad_file = document.getElementById('file-input').files[0];

        let formData = new FormData();
        formData.append('ciphertext_input', ciphertext);
        formData.append('key', key);
        formData.append('pad_file', pad_file);

        let xhrEncrypt = new XMLHttpRequest();
        xhrEncrypt.open('POST', '{{ url_for("encrypt_decrypt") }}');
        xhrEncrypt.onload = function () {
            let ciphertext = JSON.parse(xhrEncrypt.responseText)['ciphertext'];
            let cleartext = JSON.parse(xhrEncrypt.responseText)['cleartext'];
            document.getElementById('ciphertext-decrypt').value = ciphertext;
            document.getElementById('cleartext-decrypt').value = cleartext;
        };
        xhrEncrypt.send(formData);
    }

    function updateSliderValueDecrypt() {
        document.getElementById('key-slider-decrypt').value = document.getElementById('key-input-decrypt').value;
        update_decrypt();
    }

    function updateKeyInputDecrypt() {
        document.getElementById('key-input-decrypt').value = document.getElementById('key-slider-decrypt').value;
        update_decrypt();
    }

    function incrementKeyDecrypt() {
        let keyInput = document.getElementById('key-input-decrypt');
        let currentValue = parseInt(keyInput.value);
        if (currentValue < parseInt(keyInput.max)) {
            keyInput.value = currentValue + 1;
            updateSliderValueDecrypt();
        }
    }

    function decrementKeyDecrypt() {
        let keyInput = document.getElementById('key-input-decrypt');
        let currentValue = parseInt(keyInput.value);
        if (currentValue > parseInt(keyInput.min)) {
            keyInput.value = currentValue - 1;
            updateSliderValueDecrypt();
        }
    }

    function updateLabelDecrypt() {
        let fileInput = document.getElementById('file-input-decrypt');
        let fileLabel = document.getElementById('file-label-decrypt');
        let removeBtn = document.getElementById('remove-file-btn-decrypt');

        if (fileInput.value) {
            fileLabel.innerHTML = fileInput.value.match(/[\/\\]([\w\d\s\.\-\(\)]+)$/)[1];
            removeBtn.style.display = 'inline-block';
        } else {
            fileLabel.innerHTML = 'Choose file';
            removeBtn.style.display = 'none';
        }
    }

    function removeFileDecrypt() {
        let fileInput = document.getElementById('file-input-decrypt');
        let fileLabel = document.getElementById('file-label-decrypt');
        let removeBtn = document.getElementById('remove-file-btn-decrypt');

        fileInput.value = '';
        fileLabel.innerHTML = 'Choose file';
        removeBtn.style.display = 'none';
    }

    document.getElementById('ciphertext_input').addEventListener('input', update_decrypt);
    document.getElementById('key-slider-decrypt').addEventListener('input', updateKeyInputDecrypt);
    document.getElementById('key-input-decrypt').addEventListener('input', updateSliderValueDecrypt);
</script>