app/src/app.js

@@ -10,7 +10,7 @@ const { normalizeInvoiceData } = require('./invoice-data');
 const app = express();
 const sessionDurationMs = 1000 * 60 * 60 * 24 * 30;
 
-app.use(express.json());
+app.use(express.json({ limit: '2mb' }));
 
 const hashPassword = (password, salt = crypto.randomBytes(16).toString('hex')) => new Promise((resolve, reject) => {
     crypto.scrypt(password, salt, 64, (error, derivedKey) => {
@@ -500,6 +500,7 @@ const renderInvoicePdf = async (document, invoice) => {
         width: 180,
         margin: 1
     }) : null;
+    const signatureBuffer = data.signature ? Buffer.from(data.signature.split(',')[1], 'base64') : null;
     const pageWidth = document.page.width - document.page.margins.left - document.page.margins.right;
     const navy = '#183b56';
     const line = '#d8d4cc';
@@ -573,6 +574,14 @@ const renderInvoicePdf = async (document, invoice) => {
     document.moveTo(document.page.margins.left, document.y).lineTo(document.page.margins.left + pageWidth, document.y)
         .strokeColor(navy).lineWidth(1.5).stroke();
     document.y += 12;
+    if (signatureBuffer) {
+        const signatureWidth = 145;
+        const signatureHeight = signatureWidth / 2;
+        const signatureGap = 8;
+        const signatureX = document.page.margins.left + pageWidth - signatureWidth;
+        document.image(signatureBuffer, signatureX, document.y, { fit: [signatureWidth, signatureHeight] });
+        document.y += signatureHeight + signatureGap;
+    }
     const paymentTop = document.y;
     document.roundedRect(document.page.margins.left, paymentTop, pageWidth, 165, 4).fillAndStroke('#f4f7fb', line);
     document.fillColor(navy).font(boldFont).fontSize(11).text('Platební údaje', document.page.margins.left + 10, paymentTop + 10);

app/src/invoice-data.js

@@ -1,3 +1,5 @@
+const SIGNATURE_DATA_URL_PATTERN = /^data:image\/(png|jpeg);base64,[A-Za-z0-9+/]+=*$/;
+
 const normalizeInvoiceData = (data) => {
     if (!data || !Array.isArray(data.items)) {
         return null;
@@ -16,11 +18,16 @@ const normalizeInvoiceData = (data) => {
         return null;
     }
 
+    const signature = typeof data.signature === 'string' && SIGNATURE_DATA_URL_PATTERN.test(data.signature)
+        ? data.signature
+        : null;
+
     return {
         supplier: data.supplier || {},
         customer: data.customer || {},
         payment: data.payment || {},
         items,
+        signature,
         total: items.reduce((sum, item) => sum + item.mnozstvi * item.cenaZaMj, 0)
     };
 };

app/src/static/index.html

@@ -318,6 +318,21 @@
                     </div>
                 </div>
 
+                <div class="form-chapter signature-row">
+                    <div class="form-group signature-group">
+                        <label for="signatureInput">Podpis (nepovinné)</label>
+                        <div id="signatureDropzone" class="signature-dropzone" tabindex="0" role="button" aria-label="Nahrát podpis kliknutím nebo přetažením souboru">
+                            <img id="signaturePreview" class="signature-preview" alt="Náhled podpisu" hidden />
+                            <p id="signatureDropzoneText" class="signature-dropzone-text">Přetáhněte sem obrázek podpisu (420×210 px, JPG nebo PNG) nebo klikněte pro výběr souboru</p>
+                            <input type="file" id="signatureInput" accept="image/png,image/jpeg" hidden />
+                        </div>
+                        <div class="signature-actions">
+                            <button type="button" id="removeSignatureButton" class="secondary-button" hidden>Odstranit podpis</button>
+                        </div>
+                        <p id="signatureStatus" class="signature-status" role="status" aria-live="polite"></p>
+                    </div>
+                </div>
+
                 <button type="button" id="printInvoiceButton">
                     Vygenerovat a vytisknout fakturu
                 </button>

app/src/static/script.js

@@ -45,6 +45,12 @@ const dueDateDisplay = document.getElementById("dueDateDisplay");
 const paymentPresetSelect = document.getElementById("paymentPresetSelect");
 const paymentPresetName = document.getElementById("paymentPresetName");
 const savePaymentPresetButton = document.getElementById("savePaymentPresetButton");
+const signatureDropzone = document.getElementById("signatureDropzone");
+const signatureInput = document.getElementById("signatureInput");
+const signaturePreview = document.getElementById("signaturePreview");
+const signatureDropzoneText = document.getElementById("signatureDropzoneText");
+const removeSignatureButton = document.getElementById("removeSignatureButton");
+const signatureStatus = document.getElementById("signatureStatus");
 const loadPaymentPresetButton = document.getElementById("loadPaymentPresetButton");
 const deletePaymentPresetButton = document.getElementById("deletePaymentPresetButton");
 
@@ -68,6 +74,93 @@ let invoices = [];
 let paymentPresets = [];
 let currentInvoiceId = null;
 let isRegistrationMode = false;
+let signatureDataUrl = null;
+
+const SIGNATURE_WIDTH = 420;
+const SIGNATURE_HEIGHT = 210;
+
+const setSignatureStatus = (message, isError = false) => {
+    signatureStatus.textContent = message || "";
+    signatureStatus.classList.toggle("is-error", Boolean(isError));
+};
+
+const applySignaturePreview = (dataUrl) => {
+    signatureDataUrl = dataUrl || null;
+    if (signatureDataUrl) {
+        signaturePreview.src = signatureDataUrl;
+        signaturePreview.hidden = false;
+        signatureDropzoneText.hidden = true;
+        removeSignatureButton.hidden = false;
+    } else {
+        signaturePreview.hidden = true;
+        signaturePreview.src = "";
+        signatureDropzoneText.hidden = false;
+        removeSignatureButton.hidden = true;
+    }
+};
+
+const readImageDimensions = (dataUrl) => new Promise((resolve, reject) => {
+    const image = new Image();
+    image.onload = () => resolve({ width: image.naturalWidth, height: image.naturalHeight });
+    image.onerror = () => reject(new Error("Obrázek se nepodařilo načíst."));
+    image.src = dataUrl;
+});
+
+const handleSignatureFile = async (file) => {
+    if (!file) {
+        return;
+    }
+    if (!["image/png", "image/jpeg"].includes(file.type)) {
+        setSignatureStatus("Podporovány jsou pouze soubory JPG nebo PNG.", true);
+        return;
+    }
+    try {
+        const dataUrl = await new Promise((resolve, reject) => {
+            const reader = new FileReader();
+            reader.onload = () => resolve(reader.result);
+            reader.onerror = () => reject(new Error("Soubor se nepodařilo načíst."));
+            reader.readAsDataURL(file);
+        });
+        const { width, height } = await readImageDimensions(dataUrl);
+        if (width !== SIGNATURE_WIDTH || height !== SIGNATURE_HEIGHT) {
+            setSignatureStatus(`Obrázek musí mít rozměry přesně ${SIGNATURE_WIDTH}×${SIGNATURE_HEIGHT} px (nahráno ${width}×${height} px).`, true);
+            return;
+        }
+        applySignaturePreview(dataUrl);
+        setSignatureStatus("Podpis byl nahrán.");
+    } catch (error) {
+        setSignatureStatus(error.message, true);
+    }
+};
+
+signatureDropzone.addEventListener("click", () => signatureInput.click());
+signatureDropzone.addEventListener("keydown", (event) => {
+    if (event.key === "Enter" || event.key === " ") {
+        event.preventDefault();
+        signatureInput.click();
+    }
+});
+signatureDropzone.addEventListener("dragover", (event) => {
+    event.preventDefault();
+    signatureDropzone.classList.add("is-dragover");
+});
+signatureDropzone.addEventListener("dragleave", () => {
+    signatureDropzone.classList.remove("is-dragover");
+});
+signatureDropzone.addEventListener("drop", (event) => {
+    event.preventDefault();
+    signatureDropzone.classList.remove("is-dragover");
+    handleSignatureFile(event.dataTransfer.files[0]);
+});
+signatureInput.addEventListener("change", () => {
+    handleSignatureFile(signatureInput.files[0]);
+    signatureInput.value = "";
+});
+removeSignatureButton.addEventListener("click", (event) => {
+    event.stopPropagation();
+    applySignaturePreview(null);
+    setSignatureStatus("");
+});
 
 const profileFieldMap = {
     nazevSpolecnosti: "NazevSpolecnosti",
@@ -247,6 +340,7 @@ const readInvoiceData = () => ({
         iban: getValue("iban"),
         swift: getValue("swift")
     },
+    signature: signatureDataUrl,
     total: Number.parseFloat(getValue("total").replace(",", ".")) || 0,
     items: Array.from(itemsContainer.querySelectorAll(".invoice-item")).map((item) => {
         const inputs = item.querySelectorAll("input");
@@ -273,6 +367,8 @@ const clearInvoiceEditor = () => {
     ["cisloUctu", "iban", "swift"].forEach((id) => {
         document.getElementById(id).value = "";
     });
+    applySignaturePreview(null);
+    setSignatureStatus("");
     itemsContainer.replaceChildren();
     itemIndex = 0;
     updateTotal();
@@ -294,6 +390,8 @@ const loadInvoiceIntoEditor = (invoice) => {
     ["cisloUctu", "iban", "swift"].forEach((id) => {
         document.getElementById(id).value = invoice.data.payment?.[id] || "";
     });
+    applySignaturePreview(invoice.data.signature || null);
+    setSignatureStatus("");
     itemsContainer.replaceChildren();
     itemIndex = 0;
     (invoice.data.items || []).forEach((item) => addInvoiceItem(item));

app/src/static/style.css

@@ -621,6 +621,72 @@ body {
     gap: 2rem;
 }
 
+.signature-row {
+    align-items: flex-start;
+}
+
+.signature-group {
+    width: 100%;
+    max-width: 420px;
+}
+
+.signature-dropzone {
+    display: flex;
+    flex-direction: column;
+    align-items: center;
+    justify-content: center;
+    gap: 0.5rem;
+    min-height: 120px;
+    padding: 1rem;
+    text-align: center;
+    color: var(--muted-ink);
+    background: #fff;
+    border: 2px dashed #c8d0d5;
+    border-radius: 0.5rem;
+    cursor: pointer;
+    transition: border-color 0.15s ease, background 0.15s ease;
+}
+
+.signature-dropzone:hover,
+.signature-dropzone:focus-visible {
+    border-color: var(--blue);
+    outline: none;
+}
+
+.signature-dropzone.is-dragover {
+    border-color: var(--blue);
+    background: rgba(43, 111, 143, 0.08);
+}
+
+.signature-dropzone-text {
+    margin: 0;
+    font-size: 0.85rem;
+    line-height: 1.4;
+}
+
+.signature-preview {
+    display: block;
+    max-width: 100%;
+    max-height: 130px;
+    object-fit: contain;
+    border-radius: 0.25rem;
+}
+
+.signature-actions {
+    margin-top: 0.5rem;
+}
+
+.signature-status {
+    margin: 0.4rem 0 0;
+    min-height: 1.1rem;
+    color: var(--muted-ink);
+    font-size: 0.8rem;
+}
+
+.signature-status.is-error {
+    color: #b3261e;
+}
+
 .total-amount-group {
     grid-column: 1 / -1;
     margin: 0;

app/test/app.test.js

@@ -30,4 +30,23 @@ describe('normalizeInvoiceData', () => {
             { mnozstvi: 'not-a-number', cenaZaMj: 10 }
         ] })).toBeNull();
     });
+
+    test('accepts a valid signature data URL and rejects invalid ones', () => {
+        const withValidSignature = normalizeInvoiceData({
+            items: [{ mnozstvi: 1, cenaZaMj: 10 }],
+            signature: 'data:image/png;base64,aGVsbG8='
+        });
+        expect(withValidSignature.signature).toBe('data:image/png;base64,aGVsbG8=');
+
+        const withInvalidSignature = normalizeInvoiceData({
+            items: [{ mnozstvi: 1, cenaZaMj: 10 }],
+            signature: 'not-a-data-url'
+        });
+        expect(withInvalidSignature.signature).toBeNull();
+
+        const withoutSignature = normalizeInvoiceData({
+            items: [{ mnozstvi: 1, cenaZaMj: 10 }]
+        });
+        expect(withoutSignature.signature).toBeNull();
+    });
 });