Feat/changeset ts (#6594)

* Migrated changeset

* Added more tests.

* Fixed test scopes

src/static/js/MergingOpAssembler.ts

@@ -0,0 +1,73 @@
+import {OpAssembler} from "./OpAssembler";
+import Op from "./Op";
+import {clearOp, copyOp} from "./Changeset";
+
+export class MergingOpAssembler {
+  private assem: OpAssembler;
+  private readonly bufOp: Op;
+  private bufOpAdditionalCharsAfterNewline: number;
+
+  constructor() {
+    this.assem = new OpAssembler()
+    this.bufOp = new Op()
+    // If we get, for example, insertions [xxx\n,yyy], those don't merge,
+    // but if we get [xxx\n,yyy,zzz\n], that merges to [xxx\nyyyzzz\n].
+    // This variable stores the length of yyy and any other newline-less
+    // ops immediately after it.
+    this.bufOpAdditionalCharsAfterNewline = 0;
+  }
+
+  /**
+   * @param {boolean} [isEndDocument]
+   */
+  flush = (isEndDocument?: boolean) => {
+    if (!this.bufOp.opcode) return;
+    if (isEndDocument && this.bufOp.opcode === '=' && !this.bufOp.attribs) {
+      // final merged keep, leave it implicit
+    } else {
+      this.assem.append(this.bufOp);
+      if (this.bufOpAdditionalCharsAfterNewline) {
+        this.bufOp.chars = this.bufOpAdditionalCharsAfterNewline;
+        this.bufOp.lines = 0;
+        this.assem.append(this.bufOp);
+        this.bufOpAdditionalCharsAfterNewline = 0;
+      }
+    }
+    this.bufOp.opcode = '';
+  }
+
+  append = (op: Op) => {
+    if (op.chars <= 0) return;
+    if (this.bufOp.opcode === op.opcode && this.bufOp.attribs === op.attribs) {
+      if (op.lines > 0) {
+        // bufOp and additional chars are all mergeable into a multi-line op
+        this.bufOp.chars += this.bufOpAdditionalCharsAfterNewline + op.chars;
+        this.bufOp.lines += op.lines;
+        this.bufOpAdditionalCharsAfterNewline = 0;
+      } else if (this.bufOp.lines === 0) {
+        // both bufOp and op are in-line
+        this.bufOp.chars += op.chars;
+      } else {
+        // append in-line text to multi-line bufOp
+        this.bufOpAdditionalCharsAfterNewline += op.chars;
+      }
+    } else {
+      this.flush();
+      copyOp(op, this.bufOp);
+    }
+  }
+
+  endDocument = () => {
+    this.flush(true);
+  };
+
+  toString = () => {
+    this.flush();
+    return this.assem.toString();
+  };
+
+  clear = () => {
+    this.assem.clear();
+    clearOp(this.bufOp);
+  };
+}