[examples] Add one that adds consequtive signatures

packages/examples/src/multiple-signatures.js

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+var fs = require('fs');
+var path = require('path');
+var plainAddPlaceholder = require('@signpdf/placeholder-plain').plainAddPlaceholder;
+var signpdf = require('@signpdf/signpdf').default;
+var P12Signer = require('@signpdf/signer-p12').P12Signer;
+
+function buyerSign(pdfBuffer, targetPath) {
+    // Add a placeholder for John Doe - the customer
+    var pdfWithPlaceholder = plainAddPlaceholder({
+        pdfBuffer: pdfBuffer,
+        reason: 'Agrees to buy the truck trailer.',
+        contactInfo: 'john@example.com',
+        name: 'John Doe',
+        location: 'Free Text Str., Free World',
+    });
+
+    // John signs the PDF
+    // certificate.p12 is the certificate that is going to be used to sign
+    var certificateBuffer = fs.readFileSync(path.join(__dirname, '/../../../resources/certificate.p12'));
+    var signer = new P12Signer(certificateBuffer);
+    return signpdf
+        .sign(pdfWithPlaceholder, signer)
+        .then(function (signedPdf) {
+            // signedPdf is a Buffer of an electronically signed PDF. Store it.
+            fs.writeFileSync(targetPath, signedPdf);
+
+            return signedPdf;
+        })
+}
+
+function sellerSign(pdfBuffer, targetPath) {
+    // Add a placeholder for John Doe - the customer
+    var pdfWithPlaceholder = plainAddPlaceholder({
+        pdfBuffer: pdfBuffer,
+        reason: 'Agrees to sell a truck trailer to John Doe.',
+        contactInfo: 'dealer@example.com',
+        name: 'Thug Dealer',
+        location: 'Automotive Str., Free World',
+    });
+
+    // The seller signs the PDF
+    // bundle.p12 is the certificate bundle that is going to be used to sign
+    var certificateBuffer = fs.readFileSync(path.join(__dirname, '/../../../resources/bundle.p12'));
+    var signer = new P12Signer(certificateBuffer);
+    return signpdf
+        .sign(pdfWithPlaceholder, signer)
+        .then(function (signedPdf) {
+            // signedPdf is a Buffer of an electronically signed PDF. Store it.
+            fs.writeFileSync(targetPath, signedPdf);
+
+            return signedPdf;
+        })
+}
+
+/**
+ * John Doe is buying a truck trailer from Thug Dealer.
+ * The PDF is signed by both parties in two copies.
+ * The first copy is signed by John Doe and then by Thug Dealer.
+ * The second copy is signed by Thug Dealer and then by John Doe.
+ * 4 PDFs are created in the output folder.
+ */
+function work() {
+    // contributing.pdf is the "contract" they are going to sign.
+    var pdfBuffer = fs.readFileSync(path.join(__dirname, '/../../../resources/contributing.pdf'));
+
+    // A copy of the PDF is signed by the buyer and then by the seller.
+    buyerSign(
+        pdfBuffer,
+        path.join(__dirname, '/../output/multiple-signatures-buyer-seller-1.pdf'
+    ))
+        .then(function (signedByCustomer) {
+            return sellerSign(
+                signedByCustomer,
+                path.join(__dirname, '/../output/multiple-signatures-buyer-seller-2.pdf')
+            );
+        });
+
+    // A copy of the PDF is signed by the seller and then by the buyer.
+    sellerSign(
+        pdfBuffer,
+        path.join(__dirname, '/../output/multiple-signatures-seller-buyer-1.pdf'
+    ))
+        .then(function (signedBySeller) {
+            return buyerSign(
+                signedBySeller,
+                path.join(__dirname, '/../output/multiple-signatures-seller-buyer-2.pdf')
+            );
+        });
+}
+
+work();