Introduced operation infos helper

index.js

@@ -1,10 +1,10 @@
 const array = require('./src/array');
 const object = require('./src/object');
-const operations = require('./src/operations');
+const infos = require('./src/infos');
 
 module.exports = {
   array,
   object,
-  operations,
+  infos,
 };
 

src/errors.js

@@ -1,8 +1,9 @@
 
-const errors = {
-  notAllowed(methodName) {
-    return new Error(`${methodName} not allowed`);
-  }
-};
 
-module.exports = errors;
+function notAllowed(methodName) {
+  return new Error(`${methodName} not allowed`);
+}
+
+module.exports = {
+  notAllowed,
+};

src/infos.js

@@ -0,0 +1,32 @@
+
+/**
+ * QUESTION(lbays): ot.go indicates that SpliceInfo will take empty collections
+ * to indicate deletions, but the splice implementation is richer than this. A
+ * caller may use splice to simultaneously insert and delete. Should we
+ * separate these mutations into different methods or add information to this
+ * info object?
+ *
+ * Also, if this info object must store two collection references before and
+ * after a mutation, this seems like a memory and performance problem for
+ * even moderately sized collections.
+ */
+function spliceInfo(offset, beforeSet, afterSet) {
+  return {
+    offset: offset,
+    before: beforeSet,
+    after: afterSet,
+  };
+}
+
+function setInfo(key, beforeSet, afterSet) {
+  return {
+    key: key,
+    before: beforeSet,
+    after: afterSet,
+  };
+}
+
+module.exports = {
+  setInfo,
+  spliceInfo,
+};

test/infos_test.js

@@ -0,0 +1,31 @@
+const assert = require('chai').assert;
+const object = require('../').object;
+const infos = require('../').infos;
+
+describe('infos', () => {
+  let arr;
+  let obj;
+
+  beforeEach(() => {
+    arr = ['a', 'b', 'c'];
+    obj = {a: 10, b: 20, c: 30};
+  });
+
+  it('creates a spliceInfo object', () => {
+    const after = [];
+    const info = infos.spliceInfo(1, arr, after);
+    assert(info);
+    assert.equal(info.offset, 1);
+    assert(info.before === arr);
+    assert(info.after === after);
+  });
+
+  it('creates setInfo object', () => {
+    const after = {};
+    const info = infos.setInfo('b', obj, object.set(obj, 'b', 40));
+    assert(info);
+    assert.equal(info.key, 'b');
+    assert.equal(info.before.b, 20);
+    assert.equal(info.after.b, 40);
+  });
+});