feat: add shared unstable listing classifier

packages/core/src/index.ts

@@ -41,3 +41,4 @@ export * from "./utils/cookies";
 export * from "./utils/delay";
 export * from "./utils/format";
 export * from "./utils/http";
+export * from "./utils/unstable";

packages/core/src/types/common.ts

@@ -18,3 +18,12 @@ export interface ListingDetails {
   address?: string | null;
   creationDate?: string;
 }
+
+export interface UnstableListingBuckets<T> {
+  results: T[];
+  unstableResults: T[];
+}
+
+export interface UnstableListingModeOptions {
+  hideUnstableResults?: boolean;
+}

packages/core/src/utils/unstable.ts

@@ -0,0 +1,46 @@
+import type { ListingDetails, UnstableListingBuckets } from "../types/common";
+
+function getMedian(values: number[]): number {
+  const middleIndex = Math.floor(values.length / 2);
+
+  if (values.length % 2 === 0) {
+    return (values[middleIndex - 1] + values[middleIndex]) / 2;
+  }
+
+  return values[middleIndex];
+}
+
+export function classifyUnstableListings<T extends ListingDetails>(
+  listings: T[],
+): UnstableListingBuckets<T> {
+  const validPrices = listings
+    .map((listing) => listing.listingPrice.cents)
+    .filter((price) => Number.isFinite(price) && price > 0)
+    .sort((left, right) => left - right);
+
+  if (validPrices.length < 2) {
+    return {
+      results: [...listings],
+      unstableResults: [],
+    };
+  }
+
+  const threshold = getMedian(validPrices) * 0.8;
+  const buckets: UnstableListingBuckets<T> = {
+    results: [],
+    unstableResults: [],
+  };
+
+  for (const listing of listings) {
+    const price = listing.listingPrice.cents;
+
+    if (Number.isFinite(price) && price > 0 && price < threshold) {
+      buckets.unstableResults.push(listing);
+      continue;
+    }
+
+    buckets.results.push(listing);
+  }
+
+  return buckets;
+}