DeltaProcessor: Correct delta application

Deltas must be applied in reverse to reproduce the state of the bucket or
rate data at that point in time, which is then paired with the delta that
will transform it into the previous state.

1 files changed, 81 insertions, 21 deletions

diff --git a/src/system/DeltaProcessor.ts b/src/system/DeltaProcessor.ts
index d68615f..0e5201a 100644
--- a/src/system/DeltaProcessor.ts
+++ b/src/system/DeltaProcessor.ts
@@ -31,9 +31,18 @@ import {
     ReverseDelta,
 } from "../bucket/delta";
 
+/** Deltas and state of data prior to their application */
+type DeltaState = [
+    Delta<any>,
+    Record<string, any>,
+    Record<string, any>,
+];
+
 
 /**
  * Process deltas for a quote and publish to a queue
+ *
+ * TODO: Decouple from applyDelta
  */
 export class DeltaProcessor
 {
@@ -87,10 +96,12 @@ export class DeltaProcessor
         const deltas          = this._getTimestampSortedDeltas( doc );
         const doc_id          = doc.id;
         const bucket          = doc.data;
-        const ratedata        = doc.ratedata;
+        const ratedata        = doc.ratedata || {};
         const last_updated_ts = doc.lastUpdate;
 
-        return this._processNextDelta( doc_id, deltas, bucket, ratedata )
+        const history = this._applyDeltas( deltas, bucket, ratedata );
+
+        return this._processNextDelta( doc_id, history )
             .then( _ =>
                 this._dao.markDocumentAsProcessed( doc_id, last_updated_ts )
             )
@@ -106,41 +117,90 @@ export class DeltaProcessor
     }
 
 
+    /**
+     * Produce states of buckets at each point in history
+     *
+     * For bucket data, each tuple will contain the state of the bucket
+     * prior to the corresponding delta having been applied.  For rate data,
+     * the tuple will also contain the state of the bucket at the point of
+     * rating.
+     *
+     * @param deltas   - deltas to apply
+     * @param bucket   - current state of bucket prior to deltas
+     * @param ratedata - current state of ratedata prior to deltas
+     *
+     * @return deltas paired with state prior to its application
+     */
+    private _applyDeltas(
+        deltas:   Delta<any>[],
+        bucket:   Record<string, any>,
+        ratedata: Record<string, any>,
+    ): DeltaState[]
+    {
+        const pairs: DeltaState[] = [];
+
+        let bucket_state   = bucket;
+        let ratedata_state = ratedata;
+        let i              = deltas.length;
+
+        while ( i-- )
+        {
+            let delta = deltas[ i ];
+
+            pairs[ i ] = [
+                delta,
+                bucket_state,
+                ( delta.type === this.DELTA_RATEDATA ) ? ratedata_state : {},
+            ];
+
+            // Don't apply the final delta, since we won't use it
+            if ( i === 0 )
+            {
+                break;
+            }
+
+            if ( delta.type === this.DELTA_DATA )
+            {
+                bucket_state = applyDelta(
+                    Object.create( bucket_state ),
+                    deltas[ i ].data,
+                );
+            }
+            else
+            {
+                ratedata_state = applyDelta(
+                    Object.create( ratedata_state ),
+                    deltas[ i ].data,
+                );
+            }
+        }
+
+        return pairs;
+    }
+
+
     private _processNextDelta(
-        doc_id:    DocumentId,
-        deltas:    Delta<any>[],
-        bucket:    Record<string, any>,
-        ratedata?: Record<string, any>,
+        doc_id:  DocumentId,
+        history: DeltaState[],
     ): Promise<void>
     {
-        const delta = deltas.shift();
-
-        if ( !delta )
+        if ( history.length === 0 )
         {
             return Promise.resolve();
         }
 
+        const [ delta, bucket, ratedata ] = history[ 0 ];
+
         const delta_uid = doc_id + '_' + delta.timestamp + '_' + delta.type;
 
         this._emitter.emit( 'delta-process-start', delta_uid );
 
-        if ( delta.type == this.DELTA_DATA )
-        {
-            bucket = applyDelta( bucket, delta.data );
-        }
-        else
-        {
-            ratedata = applyDelta( ratedata, delta.data );
-        }
-
         return this._publisher.publish( doc_id, delta, bucket, ratedata )
             .then( _ => this._dao.advanceDeltaIndex( doc_id, delta.type ) )
             .then( _ => this._emitter.emit( 'delta-process-end', delta_uid ) )
             .then( _ => this._processNextDelta(
                 doc_id,
-                deltas,
-                bucket,
-                ratedata
+                history.slice( 1 ),
             ) );
     }