methods to get Buffer's length, first and last

Author: dhilt

src/modules/adapter.js

@@ -64,6 +64,14 @@ class Adapter {
       });
     }
 
+    // read-only immediately calculated public properties
+    const publicPropsImmediate = ['bufferFirst', 'bufferLast', 'bufferLength'];
+    for (let i = publicPropsImmediate.length - 1; i >= 0; i--) {
+      Object.defineProperty(this.publicContext, publicPropsImmediate[i], {
+        get: () => this[publicPropsImmediate[i]]
+      });
+    }
+
     // non-read-only public property
     Object.defineProperty(this.publicContext, 'disabled', {
       get: () => this.disabled,
@@ -87,6 +95,18 @@ class Adapter {
     return !this.buffer.length;
   }
 
+  get bufferLength() {
+    return this.buffer.getItems().length;
+  }
+
+  get bufferFirst() {
+    return this.buffer.getFirstItem();
+  }
+
+  get bufferLast() {
+    return this.buffer.getLastItem();
+  }
+
   append(newItems) {
     this.buffer.append(newItems);
     this.doAdjust();

src/modules/buffer.js

@@ -144,6 +144,26 @@ export default function ScrollBuffer(elementRoutines, bufferSize, startIndex) {
         }
       });
       return Math.max(0, bottom - top);
+    },
+
+    getItems() {
+      return buffer.filter(item => item.op === 'none');
+    },
+
+    getFirstItem() {
+      const list = buffer.getItems();
+      if (!list.length) {
+        return null;
+      }
+      return list[0].item;
+    },
+
+    getLastItem() {
+      const list = buffer.getItems();
+      if (!list.length) {
+        return null;
+      }
+      return list[list.length - 1].item;
     }
 
   });