Web Backend Development Skill

This skill provides guidance for developing backend services and API routes in the /web project for CRAN/E.

Tech Stack

• TypeScript for type safety
• React Router v7 server-side capabilities (Vite SSR)
• Supabase for database access with generated types
• Zod for runtime validation
• TTLCache (@isaacs/ttlcache) for caching
• AI SDK (@ai-sdk/google) for embeddings
• MCP (Model Context Protocol) server implementation

Architecture Principles

Service Layer Pattern

All data access is organized into service classes with static methods:

• PackageService (app/data/package.service.ts) - CRAN package operations
• AuthorService (app/data/author.service.ts) - Author/maintainer operations
• SearchService (app/data/search.service.ts) - Universal search
• PackageInsightService (app/data/package-insight.service.server.ts) - Download stats, trends
• ArticleService (app/data/article.service.server.ts) - Press/blog content
• PageInsightService (app/data/page-insight.service.ts) - Analytics

Generated Database Types

Always use the generated Supabase types from app/data/supabase.types.generated.ts:

import { Database, Tables } from "./supabase.types.generated";

// Type a specific table
type Package = Tables<"cran_packages">;
type Author = Tables<"authors">;

// Type the database client
import { createClient } from "@supabase/supabase-js";
export const supabase = createClient<Database>(url, key);

Regenerate types when schema changes:

npm run db.types  # Requires Supabase CLI + credentials

Supabase Client Pattern

Single shared client instance (app/data/supabase.server.ts):

import { createClient } from "@supabase/supabase-js";
import { Database } from "./supabase.types.generated";

export const supabase = createClient<Database>(
  process.env.SUPABASE_URL,
  process.env.SUPABASE_ANON_KEY,
);

Always:

• Use typed queries with from() and typed table names
• Handle errors explicitly with .error checks
• Use .maybeSingle() for nullable results, .single() for required results
• Use .select("*") or specific columns for type safety

Example query:

const result = await supabase
  .from("cran_packages")
  .select("*")
  .eq("name", packageName)
  .maybeSingle();

if (result.error || !result.data) {
  return null;
}

return result.data;

Validation with Zod

Define schemas in *.shape.ts files:

import { z } from "zod";

export const packageNameSchema = z.string().min(1).max(300);
export const packageIdSchema = z.number().int().positive().min(1);
export type PackageSlug = z.infer<typeof packageNameSchema>;

Validate inputs at service boundaries:

static async getPackageByName(name: string) {
  packageNameSchema.parse(name);  // Throws if invalid
  // ... proceed with query
}

Caching Strategy

Use TTLCache for expensive operations:

import TTLCache from "@isaacs/ttlcache";
import { hoursToMilliseconds, minutesToMilliseconds } from "date-fns";

class PackageService {
  private static cache = new TTLCache<CacheKey, CacheValue>({
    ttl: hoursToMilliseconds(6),
    max: 1000,
  });

  static async getData(key: string) {
    const cached = this.cache.get(key);
    if (cached) return cached;

    const data = await fetchData();
    this.cache.set(key, data);
    return data;
  }
}

Cache keys: Use string literals or union types for type safety.

TTL guidelines:

• Sitemap/metadata: 6 hours
• Search results: 5 minutes
• Download stats: 6 hours
• Dynamic content: 1-5 minutes

Service Class Structure

export class ExampleService {
  // Private static cache
  private static cache = new TTLCache<CacheKey, CacheValue>({
    ttl: hoursToMilliseconds(6),
  });

  // Static methods only (stateless)
  static async getById(id: number) {
    // 1. Validate input
    idSchema.parse(id);

    // 2. Check cache
    const cached = this.cache.get(`id:${id}`);
    if (cached) return cached;

    // 3. Query database
    const result = await supabase
      .from("table_name")
      .select("*")
      .eq("id", id)
      .maybeSingle();

    // 4. Handle errors
    if (result.error) {
      slog.error("Query failed", { error: result.error, id });
      return null;
    }

    // 5. Cache and return
    if (result.data) {
      this.cache.set(`id:${id}`, result.data);
    }
    return result.data;
  }
}

API Route Patterns

Action-based API (POST)

File: app/routes/api.search._index.ts

import { ActionFunction } from "react-router";
import { SearchService } from "../data/search.service";

export const action: ActionFunction = async ({ request }) => {
  const formData = await request.formData();
  const intent = formData.get("intent");

  if (intent === "all") {
    const query = String(formData.get("q")).slice(0, 100);
    const result = await SearchService.searchUniversal(query);
    return Response.json(result);
  }

  throw new Error("Invalid intent");
};

Use for:

• Search operations
• Mutations
• Form submissions

Loader-based API (GET)

export const loader: LoaderFunction = async ({ params, request }) => {
  const { packageName } = params;
  const data = await PackageService.getPackageByName(packageName);

  if (!data) {
    throw data(null, { status: 404 });
  }

  return data(data, {
    headers: {
      "Cache-Control": "public, max-age=3600",
    },
  });
};

Use for:

• Page data loading
• Read-only operations
• SSR data fetching

MCP Server Endpoint

File: app/routes/api.mcp.ts

Singleton transport pattern for stateful MCP connections:

let transport: WebStandardStreamableHTTPServerTransport | null = null;

function getTransport() {
  if (!transport) {
    transport = new WebStandardStreamableHTTPServerTransport({});
    const server = getMcpServer();
    server.connect(transport);
  }
  return transport;
}

export async function loader({ request }: LoaderFunctionArgs) {
  return getTransport().handleRequest(request);
}

Error Handling

Use structured logging (app/modules/observability.server.ts):

import { slog } from "../modules/observability.server";

try {
  const result = await someOperation();
} catch (error) {
  slog.error("Operation failed", {
    error,
    context: { userId, action },
  });
  throw error;
}

Log levels:

• slog.info() - Informational events
• slog.warn() - Warning conditions
• slog.error() - Error conditions

Type Patterns

Tables Type Helper

import { Tables } from "../data/supabase.types.generated";

type Pkg = Tables<"cran_packages">;
type Author = Tables<"authors"> & { roles: string[] };

Custom Types

Define in app/data/types.ts:

export type PackageRelationshipType =
  | "depends"
  | "imports"
  | "suggests"
  | "linking_to"
  | "enhances"
  | "reverse_depends"
  | "reverse_imports"
  | "reverse_suggests"
  | "reverse_enhances"
  | "reverse_linking_to";

export type PackageDependency = {
  relationship_type: PackageRelationshipType;
  version: string | null;
  related_package: { id: number; name: string };
};

Loader Data Types

type LoaderData = {
  item: Tables<"cran_packages">;
  relations: Partial<Record<PackageRelationshipType, PackageDependency[]>>;
  authors: Author[];
  maintainer: Author;
  // ... other fields
};

export const loader: LoaderFunction = async ({ params }) => {
  const data: LoaderData = await buildLoaderData(params);
  return data(data);
};

External API Integration

Example: CRAN Logs API (PackageInsightService)

class PackageInsightService {
  private static readonly CRAN_LOGS_URL = "https://cranlogs.r-pkg.org";

  private static async fetchFromCRAN<T>(path: string): Promise<T | null> {
    try {
      const response = await fetch(`${this.CRAN_LOGS_URL}${path}`);
      if (!response.ok) return null;
      return await response.json();
    } catch (error) {
      slog.error("CRAN API fetch failed", { error, path });
      return null;
    }
  }

  static async getTopDownloadedPackages(period: string, count: number) {
    const cached = this.cache.get(`/top/${period}/${count}`);
    if (cached) return cached;

    const data = await this.fetchFromCRAN<TopDownloadsResponse>(
      `/top/${period}/${count}`
    );

    if (data) this.cache.set(`/top/${period}/${count}`, data);
    return data || [];
  }
}

Async Operations

Use Promise.allSettled() for parallel operations with error handling:

const [packages, authors] = await Promise.allSettled([
  PackageService.searchPackages(query),
  AuthorService.searchAuthors(query),
]);

if (packages.status === "rejected") {
  slog.error("Package search failed", { error: packages.reason });
}

const packageHits =
  packages.status === "fulfilled"
    ? packages.value
    : { combined: [], isSemanticPreferred: false };

Environment Variables

Define in app/data/env.ts with Zod validation:

import { z } from "zod";

const envSchema = z.object({
  SUPABASE_URL: z.string().url(),
  SUPABASE_ANON_KEY: z.string().min(1),
  // ... other vars
});

export const env = envSchema.parse(process.env);

Access: import { env } from "./data/env";

Database Query Patterns

Simple Select

const packages = await supabase
  .from("cran_packages")
  .select("id, name, title")
  .limit(10);

With Filters

const result = await supabase
  .from("cran_packages")
  .select("*")
  .eq("name", packageName)
  .maybeSingle();

With Joins (via foreign keys)

const result = await supabase
  .from("package_relations")
  .select(`
    relationship_type,
    version,
    related_package:related_package_id (
      id,
      name
    )
  `)
  .eq("package_id", packageId);

Full-text Search

const results = await supabase
  .from("cran_packages")
  .select("name, title, description")
  .textSearch("name", query, { type: "websearch" })
  .limit(50);

Vector/Embedding Search

const embeddings = await supabase.rpc("match_package_embeddings", {
  query_embedding: embedding,
  match_threshold: 0.5,
  match_count: 10,
});

Performance Best Practices

1. Always limit queries: Use .limit() to prevent over-fetching
2. Select specific columns: Avoid SELECT * when possible
3. Cache expensive operations: Use TTLCache for repeated queries
4. Parallel fetching: Use Promise.all() or Promise.allSettled()
5. Deduplicate results: Use uniqBy() from es-toolkit
6. Lazy load heavy data: Split large queries into smaller chunks

Utility Functions

Use es-toolkit for data manipulation:

import { groupBy, uniqBy, omit } from "es-toolkit";

const grouped = groupBy(items, (item) => item.type);
const unique = uniqBy(items, (item) => item.id);
const cleaned = omit(obj, ["sensitiveField"]);

Use date-fns for date operations:

import {
  format,
  formatRelative,
  subDays,
  hoursToMilliseconds,
  minutesToSeconds,
} from "date-fns";

AI Integration

Embeddings for semantic search:

import { google } from "@ai-sdk/google";
import { embed } from "ai";

const { embedding } = await embed({
  model: google.textEmbeddingModel("text-embedding-004"),
  value: query,
});

File Organization

• Service classes: /web/app/data/.service.ts or .service.server.ts
• Type definitions: /web/app/data/.shape.ts (Zod), .types.generated.ts (Supabase)
• Custom types: /web/app/data/types.ts
• API routes: /web/app/routes/api.*.ts
• Server utilities: /web/app/modules/*.server.ts

Server-Only Code

Files with .server.ts suffix are excluded from client bundles. Use for:

• Supabase client initialization
• Environment variable access
• External API calls
• Logging/observability
• MCP server logic

Testing Strategy

• Typecheck: npm run typecheck catches type errors
• Build: npm run build validates server code compiles
• Lint: npm run lint enforces code quality
• No unit tests; rely on TypeScript + runtime validation

Common Pitfalls to Avoid

1. Don't instantiate service classes - Use static methods only
2. Don't bypass Zod validation - Always validate at service boundaries
3. Don't ignore Supabase errors - Check .error property
4. Don't skip caching - Cache expensive DB/API calls
5. Don't use any types - Leverage generated Supabase types
6. Don't forget .server.ts suffix - Keep server code out of client bundle
7. Don't hardcode URLs - Use environment variables

Environment

• Node >= 20 (v23.3.0 recommended)
• npm with legacy-peer-deps = true
• Required env vars: SUPABASEURL, SUPABASEANON_KEY
• Optional: GOOGLEGENERATIVEAIAPIKEY for embeddings