Initial marker API implementation

Part of #1325

src/Buffer.ts

@@ -5,6 +5,8 @@
 
 import { CircularList } from './utils/CircularList';
 import { LineData, CharData, ITerminal, IBuffer } from './Types';
+import { EventEmitter } from './EventEmitter';
+import { IDisposable, IMarker } from 'xterm';
 
 export const CHAR_DATA_ATTR_INDEX = 0;
 export const CHAR_DATA_CHAR_INDEX = 1;
@@ -31,6 +33,7 @@ export class Buffer implements IBuffer {
   public tabs: any;
   public savedY: number;
   public savedX: number;
+  public markers: Marker[] = [];
 
   /**
    * Create a new Buffer.
@@ -303,4 +306,50 @@ export class Buffer implements IBuffer {
     while (!this.tabs[++x] && x < this._terminal.cols);
     return x >= this._terminal.cols ? this._terminal.cols - 1 : x < 0 ? 0 : x;
   }
+
+  public addMarker(y: number): Marker {
+    const marker = new Marker(y);
+    this.markers.push(marker);
+    marker.disposables.push(this._lines.addDisposableListener('trim', amount => {
+      marker.line -= amount;
+      // The marker should be disposed when the line is trimmed from the buffer
+      if (marker.line < 0) {
+        marker.dispose();
+      }
+      // TODO: handle splice?
+    }));
+    marker.on('dispose', () => this._removeMarker(marker));
+    return marker;
+  }
+
+  private _removeMarker(marker: Marker): void {
+    // TODO: This could probably be optimized by relying on sort order and trimming the array using .length
+    this.markers = this.markers.splice(this.markers.indexOf(marker), 1);
+  }
+}
+
+export class Marker extends EventEmitter implements IMarker {
+  private static NEXT_ID = 1;
+
+  private _id: number = Marker.NEXT_ID++;
+  public isDisposed: boolean = false;
+  public disposables: IDisposable[] = [];
+
+  public get id(): number { return this._id; }
+
+  constructor(
+    public line: number
+  ) {
+    super();
+  }
+
+  public dispose(): void {
+    if (this.isDisposed) {
+      return;
+    }
+    this.isDisposed = true;
+    this.disposables.forEach(d => d.dispose());
+    this.disposables.length = 0;
+    this.emit('dispose');
+  }
 }