A decentralized prediction market platform built on Stacks blockchain using Clarity, enabling users to create and participate in harvest outcome predictions.

Overview

This smart contract allows users to create prediction markets for agricultural harvest outcomes and place bets using STX tokens. Markets can predict yield levels (high, medium, low) or crop failure, with winners receiving proportional rewards from the total pool.

Features

• Market Creation: Create time-bound prediction markets with custom descriptions
• Four Outcome Types: High yield, Medium yield, Low yield, Crop failure
• Proportional Rewards: Winners share the total pool based on their contribution
• Platform Fees: Configurable 2% fee on total pools
• Market Lifecycle: Open → Closed → Resolved states with validation
• Duplicate Prevention: Users can only predict once per market
• Input Validation: All user inputs are validated to prevent errors

Contract Functions

Public Functions

create-market

(create-market (description (string-ascii 256)) (duration-blocks uint))

Creates a new prediction market. Duration must be between 144 blocks (~1 day) and 52,560 blocks (~1 year).

Returns: Market ID (uint)

place-prediction

(place-prediction (market-id uint) (outcome uint) (amount uint))

Place a prediction on a market outcome (1-4). Minimum bet: 1,000,000 micro-STX (1 STX).

Outcomes:

• 1: High yield
• 2: Medium yield
• 3: Low yield
• 4: Crop failure

close-market

(close-market (market-id uint))

Closes a market after end-block is reached. Only callable by contract owner.

resolve-market

(resolve-market (market-id uint) (winning-outcome uint))

Resolves a closed market with the winning outcome. Only callable by contract owner.

claim-reward

(claim-reward (market-id uint))

Winners claim their proportional share of the total pool minus platform fee.

Reward Formula: (user-amount * total-pool * 98) / (winning-pool * 100)

Read-Only Functions

get-market

(get-market (market-id uint))

Returns complete market details including all pool amounts and state.

get-prediction

(get-prediction (market-id uint) (predictor principal))

Returns a user's prediction details for a specific market.

calculate-potential-reward

(calculate-potential-reward (market-id uint) (predictor principal))

Calculates potential reward if the user's prediction wins.

get-platform-fee-rate

(get-platform-fee-rate)

Returns current platform fee rate (default: 200 = 2%).

Data Structures

Market

{
  creator: principal,
  description: (string-ascii 256),
  end-block: uint,
  total-pool: uint,
  outcome-1-pool: uint,
  outcome-2-pool: uint,
  outcome-3-pool: uint,
  outcome-4-pool: uint,
  is-resolved: bool,
  winning-outcome: (optional uint),
  state: uint  ;; 1=open, 2=closed, 3=resolved
}

Prediction

{
  outcome: uint,
  amount: uint,
  claimed: bool
}

Error Codes

Code	Constant	Description
100	ERR-NOT-AUTHORIZED	Caller not authorized
101	ERR-MARKET-NOT-FOUND	Market doesn't exist
102	ERR-MARKET-CLOSED	Market already closed
103	ERR-MARKET-NOT-CLOSED	Market still open
104	ERR-INVALID-OUTCOME	Invalid outcome (must be 1-4)
105	ERR-ALREADY-PREDICTED	User already predicted
106	ERR-INSUFFICIENT-AMOUNT	Amount below minimum
107	ERR-MARKET-NOT-RESOLVED	Market not resolved yet
108	ERR-REWARD-CLAIMED	Reward already claimed
109	ERR-NOT-WINNER	User didn't predict winning outcome
110	ERR-INVALID-DURATION	Duration outside valid range
111	ERR-INVALID-DESCRIPTION	Description too short

Usage Example

;; 1. Create a market (as contract owner)
(contract-call? .harvest-prediction-market create-market 
  "Will corn yield exceed 180 bushels/acre in Iowa 2024?" 
  u10000)  ;; ~70 days

;; 2. Place predictions (as users)
(contract-call? .harvest-prediction-market place-prediction 
  u1           ;; market-id
  u1           ;; outcome: high yield
  u5000000)    ;; 5 STX

;; 3. Close market after end-block (as owner)
(contract-call? .harvest-prediction-market close-market u1)

;; 4. Resolve with winning outcome (as owner)
(contract-call? .harvest-prediction-market resolve-market u1 u1)

;; 5. Winners claim rewards
(contract-call? .harvest-prediction-market claim-reward u1)

Deployment

1. Install Clarinet: npm install -g @hirosystems/clarinet
2. Create new project: clarinet new harvest-market
3. Add contract to contracts/ directory
4. Test: clarinet test
5. Deploy: clarinet deploy --testnet or --mainnet

Security Considerations

• Owner Privileges: Market resolution requires trusted owner/oracle
• No Refunds: Predictions are final once placed
• Block Timing: Market duration based on block height, not timestamps
• Fee Collection: Platform fees accumulate in contract balance
• Reentrancy Safe: Uses Clarity's built-in transfer functions

Testing Checklist

• Create market with valid/invalid durations
• Place predictions on all outcomes
• Attempt duplicate predictions
• Close market before/after end-block
• Resolve with each outcome type
• Claim rewards as winner/loser
• Verify fee calculations
• Test edge cases (zero pool, single predictor)