GeoGacha

GeoGacha is a Web3-powered exploration app that turns the real world into a loot map. Users walk to GPS-based locations, check in, and trigger onchain randomized rewards secured by onchain randomness on Flow . Designed for outdoor adventurers, brand activations, and gamified tourism, GeoGacha blends physical movement with provably fair digital rewards.

How GeoGacha Was Built

Core Stack:

• Frontend: Next.js 15 + TypeScript + Tailwind CSS for a mobile-first PWA experience
• Web3: Ethers.js connecting to Flow EVM Testnet (Chain ID: 545)
• Smart Contract: Solidity contract using Flow's Cadence Random Consumer for true on-chain randomness
• UI: Shadcn/UI components with custom animations and responsive design

Architecture Flow:

1. GPS Simulation → Mock location data triggers proximity detection
2. Wallet Connection → Auto-detects MetaMask, switches to Flow EVM, handles network addition
3. Contract Calls → Two-step randomness: getRandomNumber() for rarity, selectRandomItem() for specific rewards
4. Fallback System → Graceful degradation when contract calls fail

Partner Tech Benefits:

• Flow EVM: Ethereum compatibility with Flow's performance and native randomness
• Cadence Random Consumer: Eliminates need for external oracles like Chainlink VRF

Notable Hacks:

• Dual Randomness Strategy: Contract-first with local fallback ensures 100% uptime
• Network Auto-Switching: Automatically adds Flow EVM Testnet to MetaMask if missing
• GPS Proximity Simulation: Uses percentage-based positioning for demo without requiring actual GPS
• Weighted Rarity System: Single contract call determines rarity (5% legendary, 20% rare, 75% common) then selects from appropriate pool

Clever Implementation: The app calls your deployed randomness contract for authentic blockchain-based rewards while maintaining smooth UX through optimistic UI updates and error handling.