Pre-Implementation Checklist (MANDATORY)

⚠️ STOP! Before writing ANY code, complete this checklist.

This skill enforces the DRY principle and ensures you search for existing patterns before creating new ones. Skipping this checklist leads to code duplication and inconsistency.

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✅ MANDATORY CHECKLIST (Complete Before Coding)

Step 1: Search for Existing Patterns

Before creating ANYTHING new, search the codebase:

# Search by concept name
grep -r "slug validation" --include="*.ts" --include="*.tsx"
grep -r "price format" --include="*.ts" --include="*.tsx"

# Search by function name patterns
grep -r "isValid" --include="*.ts" utils/
grep -r "format" --include="*.ts" utils/
grep -r "build" --include="*.ts" utils/
grep -r "use[A-Z]" --include="*.ts" components/hooks/

# Search by literal values (regex, constants)
grep -r "YOUR_REGEX_PATTERN" --include="*.ts"

Report findings BEFORE proposing implementation:

• ✅ "Found isValidCategorySlugFormat in utils/category-mapping.ts - will reuse"
• ✅ "Found similar hook useImageRetry in components/hooks/ - will extend"
• ✅ "No existing pattern found - will create new utility"

Step 2: Check Canonical Locations

What You're Creating	Where to Search First
Type/Interface	types/ directory, check types/README.md
Validation function	utils/ for isValid*, validate*
Helper/Utility	utils/, lib/
Constant/Config	utils/constants.ts, config/
Component	components/ui/
Hook	components/hooks/
API call	lib/api/

Step 3: Verify No Duplication

Check these specific files for existing patterns:

types/common.ts          → NavigationItem, SocialLinks, shared types
types/props.ts           → Reusable component props
types/api/*.ts           → DTOs (CitySummaryResponseDTO, etc.)
utils/constants.ts       → Shared constants (dates, distances, labels)
utils/api-helpers.ts     → buildEventsQuery, buildNewsQuery, getInternalApiUrl
config/filters.ts        → Filter configurations

Step 4: Propose Plan (No Code Yet)

After searching, propose a 2-4 step plan:

Plan:
1. Reuse `isValidSlug` from utils/validation.ts
2. Create new `PriceFilter` component in components/ui/filters/
3. Add type to types/filters.ts (extending existing FilterConfig)
4. Update tests in test/filter-system.test.ts

Wait for user confirmation before implementing.

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🚫 ANTI-PATTERNS (Stop Immediately If You're Doing This)

❌ Writing Code First, Searching Later

// WRONG: Implementing inline, then searching
const isValidSlug = (slug: string) => /^[a-z0-9-]+$/.test(slug);
// "Oh wait, let me check if this exists..."

// CORRECT: Search first, then decide
// "Searching for 'isValid.*Slug' in utils/..."
// "Found isValidCategorySlugFormat in utils/category-mapping.ts - reusing"

❌ Creating Types Outside /types

// WRONG: Inline type in component
type ButtonProps = { variant: string; size: string };

// CORRECT: Define in types/props.ts
// types/props.ts
export interface ButtonProps {
  variant: ButtonVariant;
  size: ButtonSize;
}

❌ Duplicating Constants

// WRONG: Hardcoded values
const DEFAULT_DISTANCE = 50;
const DATE_OPTIONS = ["avui", "dema", "setmana"];

// CORRECT: Import from constants
import { DEFAULT_DISTANCE, DATE_OPTIONS } from "@utils/constants";

❌ Creating Helper Used Only Once

// WRONG: Over-abstraction
const formatEventTitle = (title: string) => title.trim();
// Only used in one place

// CORRECT: Inline simple logic, abstract only when reused
<h1>{event.title.trim()}</h1>;

❌ Creating Barrel Files (index.ts) for Component Folders

// WRONG: Barrel re-exports "use client" components from different routes
// components/ui/sponsor/index.ts
export { default as SponsorBannerSlot } from "./SponsorBannerSlot";
export { default as CheckoutButton } from "./CheckoutButton";
export { default as PricingSectionClient } from "./PricingSectionClient";

// Any route importing SponsorBannerSlot from the barrel
// also leaks CheckoutButton + PricingSectionClient into its manifest!
import { SponsorBannerSlot } from "@components/ui/sponsor";

// CORRECT: Always use direct file imports
import SponsorBannerSlot from "@components/ui/sponsor/SponsorBannerSlot";

Why: In Next.js RSC, every "use client" module re-exported from a barrel gets registered in the client-reference-manifest of every route that imports from that barrel. This caused 24 KB of bloat on /[place] (Feb 2026). optimizePackageImports only works for npm packages.

❌ Time-Dependent Conditional Rendering in Server Components Without connection()

// WRONG: new Date() drives tree structure in a cached server component
const status = computeTemporalStatus(event.startDate); // uses new Date()
return (
  <>
    {status.state !== "past" && <EventWeather />}  // tree shape changes over time!
    {status.state === "past" && <PastEventBanner />}
  </>
);

// CORRECT: call connection() first to opt out of component caching
import { connection } from "next/server";

await connection(); // signals dynamic rendering
const status = computeTemporalStatus(event.startDate);
// Now the conditional tree is safe — no stale cache replay

Why: With cacheComponents: true, React caches the RSC payload. If new Date() produces a different tree shape on replay (e.g., event went from "upcoming" to "past"), React throws "Couldn't find all resumable slots" and falls back to full client rendering — killing SSR performance and SEO. This caused repeated errors in production (Apr 2026). Content-only date usage (formatting text) is fine without connection().

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📋 Decision Tree: Should I Create New Code?

┌─────────────────────────────────────────┐
│ Need to implement something new?        │
└─────────────────┬───────────────────────┘
                  │
                  ▼
┌─────────────────────────────────────────┐
│ Did you search for existing patterns?   │
│ (grep, semantic_search, file_search)    │
├─────────────────┬───────────────────────┤
│ NO              │ YES                   │
│ ↓               │ ↓                     │
│ STOP!           │ Continue              │
│ Search first    │                       │
└─────────────────┴───────────────────────┘
                  │
                  ▼
┌─────────────────────────────────────────┐
│ Found existing pattern?                 │
├─────────────────┬───────────────────────┤
│ YES             │ NO                    │
│ ↓               │ ↓                     │
│ REUSE or        │ Create new, but:      │
│ EXTEND it       │ - Place in canonical  │
│                 │   location            │
│                 │ - Follow conventions  │
│                 │ - Add tests           │
└─────────────────┴───────────────────────┘

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📍 Canonical Locations Reference

Types (MUST go in /types)

types/
├── common.ts           # Shared UI types (NavigationItem, SocialLinks)
├── props.ts            # Component props (ButtonProps, CardProps)
├── event.ts            # Event domain types
├── filters.ts          # Filter types (FilterConfig, FilterState)
├── api/
│   ├── event.ts        # EventDTO, EventResponseDTO
│   ├── news.ts         # NewsDTO, NewsResponseDTO
│   ├── city.ts         # CitySummaryResponseDTO
│   └── ...
└── README.md           # Type organization guide

Utilities (Check before creating)

utils/
├── constants.ts        # Shared constants (CHECK FIRST!)
├── api-helpers.ts      # API query builders
├── url-filters.ts      # URL building
├── url-parsing.ts      # URL parsing
├── date-helpers.ts     # Date formatting
├── category-mapping.ts # Category validation
└── ...

Components (Feature folders)

components/
├── ui/
│   ├── filters/        # Filter components
│   ├── events/         # Event cards, lists
│   ├── forms/          # Form components
│   └── ...
├── hooks/              # Custom hooks (useXxx)
└── partials/           # Layout partials

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✅ Verification Checklist (Before PR)

• Searched for existing patterns using grep/semantic_search
• Reported findings before implementing
• All types defined in /types directory
• No inline type definitions in components
• Constants imported from utils/constants.ts
• Reused existing utilities where possible
• No helper functions used only once
• No barrel files (index.ts) re-exporting "use client" components from different routes
• All component imports use direct file paths (not barrel re-exports)
• Followed canonical location for new files
• Ran yarn typecheck && yarn lint && yarn test

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🔧 Quick Search Commands

# Find existing types
grep -r "interface\|type " types/ --include="*.ts"

# Find existing hooks
ls components/hooks/

# Find existing utilities
ls utils/

# Find constants
grep -r "export const" utils/constants.ts

# Find validation functions
grep -r "isValid\|validate" utils/ --include="*.ts"

# Find formatters
grep -r "format\|Format" utils/ --include="*.ts"

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Remember: 5 minutes of searching saves 30 minutes of refactoring.

Last Updated: January 15, 2026