BitDCA — Dollar Cost Averaging on Bitcoin L1

Automated DCA into any OP20 token, powered by OPNet smart contracts on Bitcoin.

BitDCA lets users deposit tokens and configure recurring swaps via MotoSwap. A keeper bot monitors positions and triggers executions at configured intervals, delivering purchased tokens directly to the user's wallet.

Architecture

bitdca/
├── contracts/     AssemblyScript smart contract (DCAVault)
├── frontend/      React + Vite dashboard
└── keeper/        Node.js keeper bot

Smart Contract (contracts/)

• DCAVault — On-chain position management with reentrancy protection
• Users deposit OP20 tokens and set amount, interval, and target token
• Keeper-triggered swaps via MotoSwap router with slippage protection
• Position top-up, cancellation with refund, auto-deactivation when exhausted
• Uses TransferHelper / OP20Utils from btc-runtime for correct SHA256 selectors
• Emergency pause by deployer

Frontend (frontend/)

• React 19 + TypeScript + Vite + TailwindCSS
• @btc-vision/walletconnect for native OPNet wallet integration
• Real-time position monitoring with block countdown timers
• Create, top-up, and cancel positions
• Uses increaseAllowance (not approve) per OP20 ATK-05

Keeper Bot (keeper/)

• Polls all active positions every 30s
• Fetches MotoSwap quotes for slippage calculation
• Simulates then sends execution transactions
• Configurable via environment variables

Quick Start

Prerequisites

• Node.js 18+
• An OPNet wallet (e.g., OPWallet browser extension)

Install & Build

# Install all dependencies
cd contracts && npm install && cd ..
cd frontend && npm install && cd ..
cd keeper && npm install && cd ..

# Build the smart contract (WASM)
cd contracts && npm run build

# Build the frontend
cd frontend && npm run build

# Build the keeper
cd keeper && npm run build

Run Frontend (Development)

cd frontend
npm run dev

Run Keeper Bot

cd keeper
DCA_VAULT_ADDRESS=0x... KEEPER_MNEMONIC="your words here" npm start

Environment Variables

Keeper

Variable	Default	Description
RPC_URL	https://testnet.opnet.org	OPNet RPC endpoint
NETWORK	testnet	Network: regtest, testnet, mainnet
DCA_VAULT_ADDRESS	—	Deployed DCAVault hex address
ROUTER_ADDRESS	MotoSwap regtest	MotoSwap router hex address
KEEPER_MNEMONIC	dev mnemonic	BIP39 mnemonic for keeper wallet
POLL_INTERVAL_MS	30000	How often to scan positions
SLIPPAGE_PERCENT	5	Max slippage tolerance
MAX_SATS_PER_TX	50000	Max sats per execution TX
FEE_RATE	10	Fee rate (sat/vB)

Contract Deployment

Deploy with the OPNet CLI:

cd contracts
npx opnet-cli deploy --wasm build/dca.wasm \
  --abi abis/DCAVault.abi.json \
  --args ROUTER_ADDRESS,KEEPER_ADDRESS

After deployment, update DCA_VAULT_ADDRESS in:

• frontend/src/config/contracts.ts
• Keeper's environment variable

Key Design Decisions

1. SHA256 selectors — OPNet uses SHA256 (not keccak256) for function selectors. All cross-contract calls use encodeSelector() from btc-runtime.

2. increaseAllowance over approve — Prevents the ERC20 approval race condition (ATK-05).

3. Balance-diff pattern for swaps — MotoSwap's swapExactTokensForTokensSupportingFeeOnTransferTokens returns void, so we snapshot balances before/after to measure output.

4. Reentrancy guard — DCAVault extends ReentrancyGuard with STANDARD level protection.

5. State-before-interaction — All state updates happen before external calls (CEI pattern).

Tech Stack

• Smart Contract: AssemblyScript + @btc-vision/btc-runtime
• Frontend: React 19 + Vite + TailwindCSS + @btc-vision/walletconnect
• Keeper: Node.js + TypeScript + opnet SDK
• DEX: MotoSwap (on-chain AMM)
• Network: OPNet (Bitcoin L1 smart contracts)

License

MIT