Fix negative citation propagation

forum-network/src/classes/forum.js

@@ -112,43 +112,32 @@ export class Forum extends ReputationHolder {
   }
 
   async propagateValue(rewardsAccumulator, fromActor, post, increment, depth = 0) {
-    if (params.referenceChainLimit >= 0 && depth > params.referenceChainLimit) {
-      return increment;
-    }
-
-    if (increment < 0 && depth > 1) {
-      return increment;
-    }
-
     this.actions.propagateValue.log(fromActor, post, `(${increment})`);
 
     // Recursively distribute reputation to citations, according to weights
     let totalOutboundAmount = 0;
-    let refundFromOutbound = 0;
-    for (const { postId: citedPostId, weight } of post.citations) {
-      const citedPost = this.getPost(citedPostId);
-      const outboundAmount = weight * increment;
-      totalOutboundAmount += outboundAmount;
-      refundFromOutbound += await this.propagateValue(rewardsAccumulator, post, citedPost, outboundAmount, depth + 1);
+    if (params.referenceChainLimit >= 0 && depth <= params.referenceChainLimit) {
+      for (const { postId: citedPostId, weight } of post.citations) {
+        const citedPost = this.getPost(citedPostId);
+        let outboundAmount = weight * increment;
+        // If this is a negative citation, it must not bring the target below zero value.
+        if (outboundAmount < 0) {
+          const citedPostTotalCitationWeight = citedPost.citations.reduce((t, { weight: w }) => t += w, 0);
+          const citedPostCapacity = citedPost.value / (1 - citedPostTotalCitationWeight);
+          outboundAmount = Math.max(outboundAmount, -citedPostCapacity);
+        }
+        totalOutboundAmount += outboundAmount;
+        await this.propagateValue(rewardsAccumulator, post, citedPost, outboundAmount, depth + 1);
+      }
     }
 
     // Apply leaching value
-    const incrementAfterLeaching = increment - (totalOutboundAmount - refundFromOutbound) * params.leachingValue;
-
-    // Prevent value from decreasing below zero
-    const rawNewValue = post.value + incrementAfterLeaching;
-    const newValue = Math.max(0, rawNewValue);
-    // We "refund" the amount that could not be applied.
-    // Note that this will always be a negative quantity, because this situation only arises when increment is negative.
-    const refundToInbound = rawNewValue - newValue;
-    const appliedIncrement = newValue - post.value;
+    const incrementAfterLeaching = increment - totalOutboundAmount * params.leachingValue;
 
     // Award reputation to post author
-    rewardsAccumulator.set(post.tokenId, appliedIncrement);
+    rewardsAccumulator.set(post.tokenId, incrementAfterLeaching);
 
     // Increment the value of the post
-    await this.setPostValue(post, newValue);
-
-    return refundToInbound;
+    await this.setPostValue(post, post.value + incrementAfterLeaching);
   }
 }