Combine xpath-util and xpath into a single module

There was no good reason for the separation between the two any more.

src/annotator/anchoring/test/xpath-test.js

@@ -1,6 +1,99 @@
-import { nodeFromXPath } from '../xpath';
+import { nodeFromXPath, xpathFromNode } from '../xpath';
 
 describe('annotator/anchoring/xpath', () => {
+  describe('xpathFromNode', () => {
+    let container;
+    const html = `
+        <h1 id="h1-1">text</h1>
+        <p id="p-1">text<br/><br/><a id="a-1">text</a></p>
+        <p id="p-2">text<br/><em id="em-1"><br/>text</em>text</p>
+        <span>
+          <ul>
+            <li id="li-1">text1</li>
+            <li id="li-2">text</li>
+            <li id="li-3">text</li>
+          </ul>
+        </span>`;
+
+    beforeEach(() => {
+      container = document.createElement('div');
+      container.innerHTML = html;
+      document.body.appendChild(container);
+    });
+
+    afterEach(() => {
+      container.remove();
+    });
+
+    it('throws an error if the provided node is not a descendant of the root node', () => {
+      const node = document.createElement('p'); // not attached to DOM
+      assert.throws(() => {
+        xpathFromNode(node, document.body);
+      }, 'Node is not a descendant of root');
+    });
+
+    [
+      {
+        id: 'a-1',
+        xpaths: ['/div[1]/p[1]/a[1]', '/div[1]/p[1]/a[1]/text()[1]'],
+      },
+      {
+        id: 'h1-1',
+        xpaths: ['/div[1]/h1[1]', '/div[1]/h1[1]/text()[1]'],
+      },
+      {
+        id: 'p-1',
+        xpaths: ['/div[1]/p[1]', '/div[1]/p[1]/text()[1]'],
+      },
+      {
+        id: 'a-1',
+        xpaths: ['/div[1]/p[1]/a[1]', '/div[1]/p[1]/a[1]/text()[1]'],
+      },
+      {
+        id: 'p-2',
+        xpaths: [
+          '/div[1]/p[2]',
+          '/div[1]/p[2]/text()[1]',
+          '/div[1]/p[2]/text()[2]',
+        ],
+      },
+      {
+        id: 'em-1',
+        xpaths: ['/div[1]/p[2]/em[1]', '/div[1]/p[2]/em[1]/text()[1]'],
+      },
+      {
+        id: 'li-3',
+        xpaths: [
+          '/div[1]/span[1]/ul[1]/li[3]',
+          '/div[1]/span[1]/ul[1]/li[3]/text()[1]',
+        ],
+      },
+    ].forEach(test => {
+      it('produces the correct xpath for the provided node', () => {
+        let node = document.getElementById(test.id);
+        assert.equal(xpathFromNode(node, document.body), test.xpaths[0]);
+      });
+
+      it('produces the correct xpath for the provided text node(s)', () => {
+        let node = document.getElementById(test.id).firstChild;
+        // collect all text nodes after the target queried node.
+        const textNodes = [];
+        while (node) {
+          if (node.nodeType === Node.TEXT_NODE) {
+            textNodes.push(node);
+          }
+          node = node.nextSibling;
+        }
+        textNodes.forEach((node, index) => {
+          assert.equal(
+            xpathFromNode(node, document.body),
+            test.xpaths[index + 1]
+          );
+        });
+      });
+    });
+  });
+
   describe('nodeFromXPath', () => {
     let container;
     const html = `

src/annotator/anchoring/xpath.js

@@ -1,4 +1,65 @@
-export { xpathFromNode } from './xpath-util';
+/**
+ * Get the node name for use in generating an xpath expression.
+ *
+ * @param {Node} node
+ */
+function getNodeName(node) {
+  const nodeName = node.nodeName.toLowerCase();
+  let result = nodeName;
+  if (nodeName === '#text') {
+    result = 'text()';
+  }
+  return result;
+}
+
+/**
+ * Get the index of the node as it appears in its parent's child list
+ *
+ * @param {Node} node
+ */
+function getNodePosition(node) {
+  let pos = 0;
+  /** @type {Node|null} */
+  let tmp = node;
+  while (tmp) {
+    if (tmp.nodeName === node.nodeName) {
+      pos += 1;
+    }
+    tmp = tmp.previousSibling;
+  }
+  return pos;
+}
+
+function getPathSegment(node) {
+  const name = getNodeName(node);
+  const pos = getNodePosition(node);
+  return `${name}[${pos}]`;
+}
+
+/**
+ * A simple XPath generator which can generate XPaths of the form
+ * /tag[index]/tag[index].
+ *
+ * @param {Node} node - The node to generate a path to
+ * @param {Node} root - Root node to which the returned path is relative
+ */
+export function xpathFromNode(node, root) {
+  let xpath = '';
+
+  /** @type {Node|null} */
+  let elem = node;
+  while (elem !== root) {
+    if (!elem) {
+      throw new Error('Node is not a descendant of root');
+    }
+    xpath = getPathSegment(elem) + '/' + xpath;
+    elem = elem.parentNode;
+  }
+  xpath = '/' + xpath;
+  xpath = xpath.replace(/\/$/, ''); // Remove trailing slash
+
+  return xpath;
+}
 
 /**
  * Return the `index`'th immediate child of `element` whose tag name is