✨ Support dynamic page margins

Pages with odd numbers ("recto") often need a larger margin on the left
than on the right. For duplex printing, the margins need to be reversed
on the even pages ("verso").

This commit adds support for dynamic page margins by accepting a
function in the `margin` attribute of a document definition.

CHANGELOG.md

@@ -1,6 +1,13 @@
 # Changelog
 
-## [0.5.0] - Unreleased
+## [0.5.1] - Unreleased
+
+### Added
+
+* The attribute `margin` in a document definition now supports a
+  function that returns the margin for a given page.
+
+## [0.5.0] - 2023-05-18
 
 ### Breaking changes
 

examples/sample.js

@@ -24,18 +24,27 @@ export default {
     liberty: { data: readFileSync('examples/liberty.jpg') },
   },
   pageSize: 'A4',
-  margin: { x: '2.5cm', y: '0.5cm' },
+  margin: ({ pageNumber }) =>
+    pageNumber % 2
+      ? { left: '25mm', right: '15mm', y: '0.5cm' }
+      : { left: '15mm', right: '25mm', y: '0.5cm' },
   defaultStyle: {
     fontSize: 14,
   },
-  header: {
+  header: ({ pageNumber }) => ({
     columns: [{ text: 'PDF Maker' }, { text: 'sample', textAlign: 'right' }],
-    margin: { x: '2.5cm', top: '1cm' },
-  },
+    margin:
+      pageNumber % 2
+        ? { left: '25mm', right: '15mm', top: '1cm' }
+        : { left: '15mm', right: '25mm', top: '1cm' },
+  }),
   footer: ({ pageNumber, pageCount }) => ({
     text: `${pageNumber}/${pageCount ?? 0}`,
     textAlign: 'right',
-    margin: { x: '2.5cm', bottom: '1cm' },
+    margin:
+      pageNumber % 2
+        ? { left: '25mm', right: '15mm', bottom: '1cm' }
+        : { left: '15mm', right: '25mm', bottom: '1cm' },
   }),
   content: [
     {