Add section diff utility for VE

index.js

@@ -1,5 +1,6 @@
 'use strict';
 
 module.exports = {
-    sections: require('./lib/sections')
+    sections: require('./lib/sections'),
+    sectionDiff: require('./lib/section_diff'),
 };

lib/section_diff.js

@@ -0,0 +1,53 @@
+'use strict';
+var assert = require('assert');
+
+/**
+ * Simple utility for full-document editing with the section API introduced in
+ * https://phabricator.wikimedia.org/T94890.
+ */
+
+/**
+ * Compute section changes from an array of original IDs & an array of
+ * modified nodes.
+ *
+ * @param {Array<string>} oldIds, the array of original section ids.
+ * @param {Array<object>} newNodes, objects with
+ *   - {string} id: The id of the node. Absent for new and copy/pasted
+ *   (including moved) content.
+ *   - {boolean} modified, indicating whether this node's content was
+ *   modified.
+ *   - {string} value, the outerHTML of this section. Should exclude ID
+ *   attributes for copy/pasted (duplicated) content, but can include the ids
+ *   for moved content.
+ * @return {object} Object with changes to the document, ready to be sent to
+ * the REST section to wikitext transform API.
+ */
+function sectionDiff(oldIds, newNodes) {
+    var changes = {};
+    var oldIdx = 0;
+    var prevNode = {id: 'mw0', value: ''};
+    for (var n = 0; n < newNodes.length; n++) {
+        // New content
+        while (n < newNodes.length && !newNodes[n].id) {
+            prevNode.value += newNodes[n].value;
+            changes[prevNode.id] = prevNode.value;
+            n++;
+        }
+
+        // Modified sections
+        var newNode = newNodes[n];
+        if (newNode.modified) { changes[newNode.id] = newNode.value; }
+
+        // Deletions
+        while (oldIds[oldIdx] !== newNode.id && oldIdx < oldIds.length) {
+            changes[oldIds[oldIdx]] = '';
+            oldIdx++;
+        }
+        oldIdx++;
+        prevNode = newNode;
+    }
+    for (;oldIdx < oldIds.length; oldIdx++) { changes[oldIds[oldIdx]] = ''; }
+    return changes;
+}
+
+module.exports = sectionDiff;

test/section_diff.js

@@ -0,0 +1,43 @@
+'use strict';
+
+const assert = require('assert');
+const sectionDiff = require('../').sectionDiff;
+
+const origIds = ['a','b','c','d','e','f'];
+
+// Basic tests
+module.exports = {
+    'Section diff': {
+        'No change': () => {
+            assert.deepEqual(sectionDiff(origIds, [{id:'a',value:'a'},{id:'b',value:'b'},{id:'c',value:'c'},{id:'d',value:'d'},{id:'e',value:'e'},{id:'f',value:'f'}]), {});
+        },
+        'Single deleted section': () => {
+            assert.deepEqual(sectionDiff(origIds, [{id:'b',value:'b'},{id:'c',value:'c'},{id:'d',value:'d'},{id:'e',value:'e'},{id:'f',value:'f'}]), {a:''});
+        },
+        'Single deleted section, middle': () => {
+            assert.deepEqual(sectionDiff(origIds, [{id:'a',value:'a'},{id:'c',value:'c'},{id:'d',value:'d'},{id:'e',value:'e'},{id:'f',value:'f'}]), {'b':''});
+        },
+        'Delete everything': () => {
+            assert.deepEqual(sectionDiff(origIds, []), {a:'',b:'',c:'',d:'',e:'',f:''});
+        },
+        'Replace first section': () => {
+            assert.deepEqual(sectionDiff(origIds, [{value:'foo'},{id:'b',value:'b'},{id:'c',value:'c'},{id:'d',value:'d'},{id:'e',value:'e'},{id:'f',value:'f'}]), {mw0:'foo',a:''});
+        },
+        'Edit + section replacement': () => {
+            assert.deepEqual(sectionDiff(origIds, [{id:'a',value:'a'},{id:'b', modified: true, value: 'bar'},{id:'d', modified: true, value: 'deee'},{id:'e',value:'e'},{id:'f',value:'f'}]), {b:'bar',c:'',d:'deee'});
+        },
+        'Delete last section': () => {
+            assert.deepEqual(sectionDiff(origIds, [{id:'a',value:'a'},{id:'b',value:'b'},{id:'c',value:'c'},{id:'d',value:'d'},{id:'e',value:'e'}]), {f:''});
+        },
+        'Prepend & delete last section': () => {
+            assert.deepEqual(sectionDiff(origIds,
+                        [{value: 'foo'},{id:'a',value:'a'},{id:'b',value:'b'},{id:'c',value:'c'},{id:'d',value:'d'},{id:'e'}]),
+                        {'mw0':'foo',f: ''});
+        },
+        'Reorder sections 1': () => {
+            assert.deepEqual(sectionDiff(origIds, [{id:'a', value:'aa'}, {id: 'b',
+                value:'b'}, {value: 'foo'}, {id:'e', value: 'e'}]), {'b':'bfoo',c:
+                '', d:'', f:''});
+        }
+    }
+};