Feat/changeset ts (#6594)

* Migrated changeset

* Added more tests.

* Fixed test scopes

src/static/js/StringIterator.ts

@@ -0,0 +1,54 @@
+import {assert} from "./Changeset";
+
+/**
+ * A custom made String Iterator
+ *
+ * @typedef {object} StringIterator
+ * @property {Function} newlines -
+ * @property {Function} peek -
+ * @property {Function} remaining -
+ * @property {Function} skip -
+ * @property {Function} take -
+ */
+
+/**
+ * @param {string} str - String to iterate over
+ * @returns {StringIterator}
+ */
+export class StringIterator {
+  private curIndex: number;
+  private newLines: number;
+  private str: String
+
+  constructor(str: string) {
+    this.curIndex = 0;
+    this.str = str
+    this.newLines = str.split('\n').length - 1;
+  }
+  remaining = () => this.str.length - this.curIndex;
+
+  getnewLines = () => this.newLines;
+
+  assertRemaining = (n: number) => {
+    assert(n <= this.remaining(), `!(${n} <= ${this.remaining()})`);
+  }
+
+  take = (n: number) => {
+    this.assertRemaining(n);
+    const s = this.str.substring(this.curIndex, this.curIndex+n);
+    this.newLines -= s.split('\n').length - 1;
+    this.curIndex += n;
+    return s;
+  }
+
+  peek = (n: number) => {
+    this.assertRemaining(n);
+    return this.str.substring(this.curIndex, this.curIndex+n);
+  }
+
+  skip = (n: number) => {
+    this.assertRemaining(n);
+    this.curIndex += n;
+  }
+
+}