feat: initialize asin-check project with Bun

- Add README.md with installation and usage instructions.
- Create bun.lock for dependency management.
- Add package.json to define project metadata and dependencies.
- Implement caching with Redis in cache.ts for ASIN data.
- Configure environment variables in config.ts for API keys and Redis URL.
- Develop main application logic in index.ts to read products, fetch data, and analyze results.
- Integrate Keepa API for product data retrieval in keepa.ts.
- Create LLM analysis functionality in llm.ts for product viability assessment.
- Implement product reading from Excel files in reader.ts.
- Stub SP-API integration in sp-api.ts for future implementation.
- Define TypeScript types in types.ts for product and analysis data structures.
- Write results to console and CSV in writer.ts.
- Configure TypeScript settings in tsconfig.json for project compilation.

src/keepa.ts

@@ -0,0 +1,111 @@
+import { config } from "./config.ts";
+import type { KeepaData } from "./types.ts";
+
+const KEEPA_BASE = "https://api.keepa.com";
+const MAX_ASINS_PER_REQUEST = 100;
+
+// Token-based rate limiting: Keepa Pro = 1 token/min regeneration.
+// Each product request costs 1 token regardless of ASIN count (up to 100).
+// The API response includes tokensLeft and refillRate — we use those to pace.
+let tokensLeft = 1; // Conservative start; updated from API response
+let refillRate = 1; // tokens per minute, updated from API response
+let lastRequestTime = 0;
+
+async function waitForToken(): Promise<void> {
+  if (tokensLeft > 0) return;
+
+  const elapsed = (Date.now() - lastRequestTime) / 60_000; // minutes
+  const regenerated = Math.floor(elapsed * refillRate);
+  if (regenerated > 0) {
+    tokensLeft += regenerated;
+    return;
+  }
+
+  // Wait until we regenerate at least 1 token
+  const waitMs = Math.ceil((1 / refillRate) * 60_000) - (Date.now() - lastRequestTime);
+  if (waitMs > 0) {
+    console.log(`Keepa tokens exhausted. Waiting ${Math.ceil(waitMs / 1000)}s for token regeneration...`);
+    await new Promise((r) => setTimeout(r, waitMs));
+  }
+  tokensLeft = 1;
+}
+
+export async function fetchKeepaDataBatch(asins: string[]): Promise<Map<string, KeepaData>> {
+  const results = new Map<string, KeepaData>();
+
+  // Split into chunks of MAX_ASINS_PER_REQUEST
+  for (let i = 0; i < asins.length; i += MAX_ASINS_PER_REQUEST) {
+    const chunk = asins.slice(i, i + MAX_ASINS_PER_REQUEST);
+    await waitForToken();
+
+    const asinParam = chunk.join(",");
+    const url = `${KEEPA_BASE}/product?key=${config.keepaApiKey}&domain=1&asin=${asinParam}&stats=90`;
+
+    console.log(`Keepa: fetching ${chunk.length} ASINs (tokens left: ${tokensLeft})...`);
+
+    const res = await fetch(url);
+    lastRequestTime = Date.now();
+
+    if (!res.ok) {
+      const text = await res.text();
+      throw new Error(`Keepa API error ${res.status}: ${text}`);
+    }
+
+    const data = (await res.json()) as {
+      products?: Record<string, any>[];
+      tokensLeft?: number;
+      refillRate?: number;
+    };
+
+    // Update token state from API response
+    if (data.tokensLeft != null) tokensLeft = data.tokensLeft;
+    if (data.refillRate != null) refillRate = data.refillRate;
+
+    console.log(`Keepa: ${data.products?.length ?? 0} products returned, ${tokensLeft} tokens remaining (refill: ${refillRate}/min)`);
+
+    if (data.products) {
+      for (const product of data.products) {
+        const asin = product.asin;
+        if (!asin) continue;
+        results.set(asin, parseKeepaProduct(product));
+      }
+    }
+  }
+
+  return results;
+}
+
+function parseKeepaProduct(product: Record<string, any>): KeepaData {
+  const stats = product.stats;
+  const csv = product.csv;
+
+  return {
+    currentPrice: extractCurrentPrice(csv),
+    avgPrice90: stats?.avg?.[0] != null ? stats.avg[0] / 100 : null,
+    minPrice90: stats?.min?.[0] != null ? stats.min[0] / 100 : null,
+    maxPrice90: stats?.max?.[0] != null ? stats.max[0] / 100 : null,
+    salesRank: stats?.current?.[3] ?? null,
+    salesRankAvg90: stats?.avg?.[3] ?? null,
+    salesRankDrops30: product.salesRankDrops30 ?? null,
+    salesRankDrops90: product.salesRankDrops90 ?? null,
+    sellerCount: stats?.current?.[11] ?? null,
+    buyBoxSeller: product.buyBoxSellerId ?? null,
+    buyBoxPrice: stats?.current?.[18] != null ? stats.current[18] / 100 : null,
+    monthlySold: product.monthlySold ?? null,
+    categoryTree: product.categoryTree?.map((c: { name: string }) => c.name) ?? [],
+  };
+}
+
+function extractCurrentPrice(csv: number[][] | undefined): number | null {
+  if (!csv) return null;
+
+  // csv[0] = Amazon price history, csv[1] = Marketplace new price history
+  // Each is [time, price, time, price, ...] — last value is most recent
+  for (const series of [csv[0], csv[1]]) {
+    if (series && series.length >= 2) {
+      const lastPrice = series[series.length - 1]!;
+      if (lastPrice > 0) return lastPrice / 100;
+    }
+  }
+  return null;
+}