WTB Market

Each message is normalized before matching (punctuation, regional suffixes, special characters stripped), then split into rows and tokenized. Matching fans out with p-limit (10 parallel workers) inside a serialized PQueue, matching one message at a time while processing ten users in parallel. Notifications go through a Bottleneck rate limiter at 40 req/s that zeroes and restores its reservoir on a rateLimited event.

• ·Unknown guild members are migrated to an archive collection.
• ·Zero-match senders receive a DM with formatting tips.
• ·Webhook failures fall back to a direct DM.
• ·All ping events are persisted to a log collection for audit.

External APIs often return incomplete or inconsistent data. I handle lookups through a fallback chain: provider API → MongoDB cache → provider slug lookup. The result is saved in the cache to prevent repeated misses.

• ·Items without a retail price are defaulted to 0 rather than null to keep the response shape consistent.
• ·Identifier is sanitized before all comparisons to avoid mismatches from scraped data.
• ·Cache auto-population is logged with the query string so new items added at runtime are auditable.

Stores and user lists are fetched in parallel, then merged in a single pass using a Map keyed by normalized slugs. This replaced a previous Array.find loop that scanned ~6.9M entries at 4300 items. Identity fields are attached during processing for ensuring correctmapping on frontend.

• ·Different size are normalized before the merge.
• ·Freemium restrictions are enforced at the data layer, not on the client.
• ·The count field reflects total sources (stores + lists) so sorting stays consistent.

Before each mutation, a reverse payload is created from the original data and time bounded. The undo action re-enters thesame mutation pipeline, reusing the same validation, error handling and API normalization.

• ·Undo is blocked if the user has hit their quota limit between the original action and the reversal attempt.
• ·If the undo fails, a new second error toast surfaces without replacing or dismissing the original.
• ·Bulk operations generate individual reverse payloads per row, so partial undos remain possible.