Merge origin/main into odweta-stunning-engine

Datum vystaveni defaults to today and Datum splatnosti defaults to
14 days after the issue date. Both fields are now optional date
inputs and only override the default when a user enters a custom
value. Applies to the invoice editor and generated PDF.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

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) => {
@@ -227,6 +227,33 @@ app.put('/api/supplier', requireAuth, async (req, res, next) => {
     }
 });
 
+app.get('/api/settings', requireAuth, async (req, res, next) => {
+    try {
+        const result = await pool.query('SELECT invoice_starting_number FROM user_settings WHERE user_id = $1', [req.userId]);
+        res.json({ settings: { invoiceStartingNumber: result.rowCount ? result.rows[0].invoice_starting_number : 1 } });
+    } catch (error) {
+        next(error);
+    }
+});
+
+app.put('/api/settings', requireAuth, async (req, res, next) => {
+    try {
+        const invoiceStartingNumber = Number.parseInt(req.body.invoiceStartingNumber, 10);
+        if (!Number.isInteger(invoiceStartingNumber) || invoiceStartingNumber < 1) {
+            res.status(400).json({ error: 'Počáteční číslo faktury musí být kladné celé číslo.' });
+            return;
+        }
+        const result = await pool.query(`
+            INSERT INTO user_settings (user_id, invoice_starting_number) VALUES ($1, $2)
+            ON CONFLICT (user_id) DO UPDATE SET invoice_starting_number = EXCLUDED.invoice_starting_number
+            RETURNING invoice_starting_number
+            `, [req.userId, invoiceStartingNumber]);
+        res.json({ settings: { invoiceStartingNumber: result.rows[0].invoice_starting_number } });
+    } catch (error) {
+        next(error);
+    }
+});
+
 app.get('/api/clients', requireAuth, async (req, res, next) => {
     try {
         const result = await pool.query('SELECT * FROM clients WHERE user_id = $1 ORDER BY created_at, id', [req.userId]);
@@ -376,13 +403,21 @@ app.post('/api/invoices', requireAuth, async (req, res, next) => {
 
         const invoiceYear = new Date().getFullYear();
         await client.query('BEGIN');
+        const settingsResult = await client.query(
+            'SELECT invoice_starting_number FROM user_settings WHERE user_id = $1',
+            [req.userId]
+        );
+        const invoiceStartingNumber = settingsResult.rowCount ? settingsResult.rows[0].invoice_starting_number : 1;
         await client.query(`
             INSERT INTO invoice_counters (user_id, invoice_year, last_number)
-            SELECT $1, $2, COALESCE(MAX((substring(invoice_number FROM '^F-[0-9]{4}-([0-9]+)$'))::integer), 0)
+            SELECT $1, $2, GREATEST(
+                COALESCE(MAX((substring(invoice_number FROM '^F-[0-9]{4}-([0-9]+)$'))::integer), 0),
+                $4 - 1
+            )
             FROM invoices
             WHERE user_id = $1 AND invoice_number LIKE $3
             ON CONFLICT (user_id, invoice_year) DO NOTHING
-        `, [req.userId, invoiceYear, `F-${invoiceYear}-%`]);
+        `, [req.userId, invoiceYear, `F-${invoiceYear}-%`, invoiceStartingNumber]);
         const counterResult = await client.query(`
             UPDATE invoice_counters
             SET last_number = last_number + 1
@@ -445,6 +480,20 @@ app.delete('/api/invoices', requireAuth, async (req, res, next) => {
 });
 
 const pdfText = (value) => String(value || 'Neuvedeno');
+const formatCzechDate = (value) => {
+    const date = new Date(`${value}T00:00:00`);
+    return Number.isNaN(date.getTime()) ? '' : date.toLocaleDateString('cs-CZ');
+};
+const toDateInputValue = (date) => date.toISOString().slice(0, 10);
+const resolveIssueDate = (issueDate) => issueDate || toDateInputValue(new Date());
+const resolveDueDate = (dueDate, issueDate) => {
+    if (dueDate) {
+        return dueDate;
+    }
+    const due = new Date(`${resolveIssueDate(issueDate)}T00:00:00`);
+    due.setDate(due.getDate() + 14);
+    return toDateInputValue(due);
+};
 const formatCzechNumber = (value) => Number(value || 0).toLocaleString('cs-CZ', {
     minimumFractionDigits: 2,
     maximumFractionDigits: 2
@@ -500,6 +549,7 @@ 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';
@@ -518,13 +568,25 @@ const renderInvoicePdf = async (document, invoice) => {
     const partyWidth = (pageWidth - 24) / 2;
     const customerX = document.page.margins.left + partyWidth + 24;
 
+    const issueDate = resolveIssueDate(data.issueDate);
+    const dueDate = resolveDueDate(data.dueDate, data.issueDate);
+
     const headerY = document.y;
     document.fillColor(navy).font(boldFont).fontSize(25).text('Faktura', document.page.margins.left, headerY);
     document.fillColor(navy).font(boldFont).fontSize(16).text(invoice.invoice_number, customerX, headerY, {
         width: partyWidth,
         align: 'right'
     });
-    document.y = headerY + 40;
+    document.fillColor(bodyText).font(regularFont).fontSize(9)
+        .text(`Datum vystavení: ${formatCzechDate(issueDate)}`, customerX, headerY + 22, {
+            width: partyWidth,
+            align: 'right'
+        })
+        .text(`Datum splatnosti: ${formatCzechDate(dueDate)}`, customerX, headerY + 35, {
+            width: partyWidth,
+            align: 'right'
+        });
+    document.y = headerY + 52;
 
     const partyTop = document.y;
     const drawParty = (x, title, profile, name) => {
@@ -539,28 +601,29 @@ const renderInvoicePdf = async (document, invoice) => {
 
     const tableTop = document.y + 12;
     const columns = [0, pageWidth * 0.52, pageWidth * 0.68, pageWidth * 0.82, pageWidth];
-    const rowHeight = 25;
+    const headerRowHeight = 25;
-    document.rect(document.page.margins.left, tableTop, pageWidth, rowHeight).fill('#eef1f3');
+    const itemRowHeight = 22.5;
+    document.rect(document.page.margins.left, tableTop, pageWidth, headerRowHeight).fill('#eef1f3');
     document.fillColor(navy).font(boldFont).fontSize(9);
     ['Položka', 'Množství', 'MJ', 'Cena za MJ'].forEach((heading, index) => {
         document.text(heading, document.page.margins.left + columns[index] + 6, tableTop + 8, {
             width: columns[index + 1] - columns[index] - 12
         });
     });
-    document.y = tableTop + rowHeight;
+    document.y = tableTop + headerRowHeight;
     (data.items || []).forEach((item, index) => {
         const rowTop = document.y;
-        document.rect(document.page.margins.left, rowTop, pageWidth, rowHeight)
+        document.rect(document.page.margins.left, rowTop, pageWidth, itemRowHeight)
             .fill(index % 2 ? lightBlue : warm);
-        document.moveTo(document.page.margins.left, rowTop + rowHeight)
+        document.moveTo(document.page.margins.left, rowTop + itemRowHeight)
-            .lineTo(document.page.margins.left + pageWidth, rowTop + rowHeight)
+            .lineTo(document.page.margins.left + pageWidth, rowTop + itemRowHeight)
             .strokeColor(line).lineWidth(0.7).stroke();
         document.fillColor(bodyText).font(regularFont).fontSize(9);
         [pdfText(item.popis), formatCzechNumber(item.mnozstvi), pdfText(item.mernaJednotka), `${formatCzechNumber(item.cenaZaMj)} Kč`]
-            .forEach((value, columnIndex) => document.text(value, document.page.margins.left + columns[columnIndex] + 6, rowTop + 8, {
+            .forEach((value, columnIndex) => document.text(value, document.page.margins.left + columns[columnIndex] + 6, rowTop + 6, {
                 width: columns[columnIndex + 1] - columns[columnIndex] - 12
             }));
-        document.y = rowTop + rowHeight;
+        document.y = rowTop + itemRowHeight;
     });
 
     document.y += 18;
@@ -576,6 +639,15 @@ const renderInvoicePdf = async (document, invoice) => {
     const paymentTop = document.page.height - document.page.margins.bottom - paymentCardHeight;
     const paymentLineHeight = 18;
     const qrSize = paymentLineHeight * 3;
+    if (signatureBuffer) {
+        const signatureWidth = 145;
+        const signatureHeight = signatureWidth / 2;
+        const signatureGap = 8;
+        const signatureX = document.page.margins.left + pageWidth - signatureWidth;
+        document.image(signatureBuffer, signatureX, paymentTop - signatureGap - signatureHeight, {
+            fit: [signatureWidth, signatureHeight]
+        });
+    }
     document.roundedRect(document.page.margins.left, paymentTop, pageWidth, paymentCardHeight, 4)
         .fillAndStroke('#f4f7fb', line);
     document.fillColor(navy).font(boldFont).fontSize(11).text('Platební údaje', document.page.margins.left + 10, paymentTop + 10);

app/src/db.js

@@ -65,6 +65,11 @@ const initializeDatabase = () => {
                 PRIMARY KEY (user_id, invoice_year)
             );
 
+            CREATE TABLE IF NOT EXISTS user_settings (
+                user_id INTEGER PRIMARY KEY REFERENCES users(id) ON DELETE CASCADE,
+                invoice_starting_number INTEGER NOT NULL DEFAULT 1 CHECK (invoice_starting_number > 0)
+            );
+
             CREATE TABLE IF NOT EXISTS payment_presets (
                 id SERIAL PRIMARY KEY,
                 user_id INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,

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

@@ -65,11 +65,28 @@
                 <summary><span class="account-mark" aria-hidden="true"></span><span id="navEmail" class="signed-in-email"></span></summary>
                 <div class="nav-menu-content account-menu-content">
                     <button type="button" id="passwordButton" class="text-button">Změnit heslo</button>
+                    <button type="button" id="numberingSettingsButton" class="text-button">Číslování faktur</button>
                     <button type="button" id="logoutButton" class="text-button">Odhlásit se</button>
                 </div>
             </details>
         </nav>
 
+        <section id="numberingSettingsPanel" class="password-panel" hidden>
+            <div id="numberingSettingsForm">
+                <h3>Číslování faktur</h3>
+                <div class="form-group">
+                    <label for="invoiceStartingNumber">Počáteční číslo faktury (pro aktuální rok)</label>
+                    <input id="invoiceStartingNumber" type="number" min="1" step="1" placeholder="1" />
+                    <p class="field-hint">Určuje, od jakého čísla se budou generovat nové faktury v roce, kdy zatím žádnou nemáte. Výchozí hodnota je 1.</p>
+                </div>
+                <div class="saved-data-actions">
+                    <button type="button" id="saveNumberingSettingsButton">Uložit</button>
+                    <button type="button" id="cancelNumberingSettingsButton" class="secondary-button">Zrušit</button>
+                    <span id="numberingSettingsStatus" role="status" aria-live="polite"></span>
+                </div>
+            </div>
+        </section>
+
         <section id="passwordPanel" class="password-panel" hidden>
             <div id="passwordForm">
                 <h3>Změnit heslo</h3>
@@ -308,13 +325,28 @@
 
                     <div class="due-date-group">
                         <div class="form-group">
-                            <label for="dueDateOption">Datum splatnosti</label>
+                            <label for="issueDate">Datum vystavení</label>
-                            <select id="dueDateOption">
+                            <input type="date" id="issueDate" name="issueDate" placeholder="Dnešní datum" />
-                                <option value="14">14 dní</option>
-                                <option value="30">30 dní</option>
-                            </select>
                         </div>
-                        <output id="dueDateDisplay" class="due-date-display"></output>
+                        <div class="form-group">
+                            <label for="dueDate">Datum splatnosti</label>
+                            <input type="date" id="dueDate" name="dueDate" placeholder="14 dní od vystavení" />
+                        </div>
+                    </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>
 

app/src/static/script.js

@@ -40,11 +40,23 @@ const passwordForm = document.getElementById("passwordForm");
 const savePasswordButton = document.getElementById("savePasswordButton");
 const cancelPasswordButton = document.getElementById("cancelPasswordButton");
 const passwordStatus = document.getElementById("passwordStatus");
-const dueDateOption = document.getElementById("dueDateOption");
+const numberingSettingsButton = document.getElementById("numberingSettingsButton");
-const dueDateDisplay = document.getElementById("dueDateDisplay");
+const numberingSettingsPanel = document.getElementById("numberingSettingsPanel");
+const invoiceStartingNumberInput = document.getElementById("invoiceStartingNumber");
+const saveNumberingSettingsButton = document.getElementById("saveNumberingSettingsButton");
+const cancelNumberingSettingsButton = document.getElementById("cancelNumberingSettingsButton");
+const numberingSettingsStatus = document.getElementById("numberingSettingsStatus");
+const issueDateInput = document.getElementById("issueDate");
+const dueDateInput = document.getElementById("dueDate");
 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 +80,93 @@ 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",
@@ -108,17 +207,17 @@ const getClientLabel = (client) => [
 
 const formatCzechDate = (dateValue) => new Date(`${dateValue}T00:00:00`).toLocaleDateString("cs-CZ");
 
-const getDueDays = () => Number.parseInt(dueDateOption.value, 10) || 14;
+const toDateInputValue = (date) => date.toISOString().slice(0, 10);
+
+const getIssueDate = () => issueDateInput.value || toDateInputValue(new Date());
 
 const getDueDate = () => {
-    const dueDate = new Date();
+    if (dueDateInput.value) {
-    dueDate.setHours(0, 0, 0, 0);
+        return dueDateInput.value;
-    dueDate.setDate(dueDate.getDate() + getDueDays());
+    }
-    return dueDate.toISOString().slice(0, 10);
+    const dueDate = new Date(`${getIssueDate()}T00:00:00`);
-};
+    dueDate.setDate(dueDate.getDate() + 14);
-
+    return toDateInputValue(dueDate);
-const updateDueDate = () => {
-    dueDateDisplay.textContent = `Splatnost: ${formatCzechDate(getDueDate())}`;
 };
 
 const updateClientTypeFields = () => {
@@ -234,6 +333,8 @@ deletePaymentPresetButton.addEventListener("click", async () => {
 });
 
 const readInvoiceData = () => ({
+    issueDate: getIssueDate(),
+    dueDate: getDueDate(),
     supplier: {
         ...readProfileFields("dodavatel"),
         typSubjektu: supplierTypeSelect.value
@@ -247,6 +348,7 @@ 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");
@@ -263,6 +365,8 @@ const clearInvoiceEditor = () => {
     currentInvoiceId = null;
     invoiceNumberDisplay.textContent = "Nová faktura";
     invoiceSaveStatus.textContent = "";
+    issueDateInput.value = "";
+    dueDateInput.value = "";
     writeProfileFields("odberatel", {});
     clientSelect.value = "";
     clientTypeSelect.value = "osoba";
@@ -273,6 +377,8 @@ const clearInvoiceEditor = () => {
     ["cisloUctu", "iban", "swift"].forEach((id) => {
         document.getElementById(id).value = "";
     });
+    applySignaturePreview(null);
+    setSignatureStatus("");
     itemsContainer.replaceChildren();
     itemIndex = 0;
     updateTotal();
@@ -282,6 +388,8 @@ const loadInvoiceIntoEditor = (invoice) => {
     currentInvoiceId = invoice.id;
     invoiceNumberDisplay.textContent = invoice.invoiceNumber;
     invoiceSaveStatus.textContent = "";
+    issueDateInput.value = invoice.data.issueDate || "";
+    dueDateInput.value = invoice.data.dueDate || "";
     writeProfileFields("dodavatel", invoice.data.supplier || {});
     supplierTypeSelect.value = invoice.data.supplier?.typSubjektu || "osoba";
     updateSupplierTypeFields();
@@ -294,6 +402,8 @@ 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));
@@ -519,10 +629,27 @@ deleteClientButton.addEventListener("click", async () => {
 const showInvoiceApp = async () => {
     authScreen.hidden = true;
     document.getElementById("main-container").hidden = false;
-    await Promise.all([loadSupplier(), loadClients(), loadInvoices(), loadPaymentPresets()]);
+    await Promise.all([loadSupplier(), loadClients(), loadInvoices(), loadPaymentPresets(), loadNumberingSettings()]);
     showInvoiceScreen("list");
 };
 
+const loadNumberingSettings = async () => {
+    try {
+        const { settings } = await apiRequest("/api/settings");
+        invoiceStartingNumberInput.value = settings.invoiceStartingNumber;
+        invoiceStartingNumberInput.placeholder = String(settings.invoiceStartingNumber);
+    } catch {
+        // Keep the placeholder default if settings cannot be loaded.
+    }
+};
+
+const showNumberingSettingsPanel = (visible) => {
+    numberingSettingsPanel.hidden = !visible;
+    if (!visible) {
+        numberingSettingsStatus.textContent = "";
+    }
+};
+
 const showPasswordPanel = (visible) => {
     passwordPanel.hidden = !visible;
     if (!visible) {
@@ -575,6 +702,24 @@ logoutButton.addEventListener("click", async () => {
 passwordButton.addEventListener("click", () => showPasswordPanel(passwordPanel.hidden));
 cancelPasswordButton.addEventListener("click", () => showPasswordPanel(false));
 
+numberingSettingsButton.addEventListener("click", () => showNumberingSettingsPanel(numberingSettingsPanel.hidden));
+cancelNumberingSettingsButton.addEventListener("click", () => showNumberingSettingsPanel(false));
+
+saveNumberingSettingsButton.addEventListener("click", async () => {
+    numberingSettingsStatus.textContent = "";
+    const invoiceStartingNumber = Number.parseInt(invoiceStartingNumberInput.value, 10) || 1;
+    try {
+        const { settings } = await apiRequest("/api/settings", {
+            method: "PUT",
+            body: JSON.stringify({ invoiceStartingNumber })
+        });
+        invoiceStartingNumberInput.value = settings.invoiceStartingNumber;
+        numberingSettingsStatus.textContent = "Uloženo";
+    } catch (error) {
+        numberingSettingsStatus.textContent = error.message;
+    }
+});
+
 savePasswordButton.addEventListener("click", async () => {
     passwordStatus.textContent = "";
     try {

app/src/static/style.css

@@ -595,6 +595,12 @@ body {
     outline-offset: 1px;
 }
 
+.field-hint {
+    margin: 0.35rem 0 0;
+    color: var(--muted-ink);
+    font-size: 0.8rem;
+}
+
 .form-group output {
     min-height: 1.5rem;
     padding: 0.25rem 0;
@@ -621,6 +627,72 @@ 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();
+    });
 });