Native VRF Randomness

Block N:   Player bets → Chooses "High"
Block N+1: Miner sees bet → Can manipulate block hash
           by choosing which transactions to include
           until hash favors the house

VRF Solution:
- Verifiable: Anyone can verify correctness
- Unpredictable: No one knows result before generation
- Unmanipulable: Generator cannot choose the output

Block N:   User places bet + requests VRF
Block N+1: Validators generate VRF random number
Block N+1: Contract reads result and settles

Advantages:
- Miner cannot predict or manipulate
- Cryptographically secure

Use for: High-stakes gambling, important lotteries, NFT reveals

Block N: User places bet + gets instant random + settles

Advantages:
- Immediate result, better UX
- Suitable for low-value operations

Use for: Small bets, game item drops, casual gaming

pub mod VRFSystem {
    /// Request random number (generated in next block)
    /// Returns: request_id for later retrieval
    pub fn request_random(seed: Hash) -> u64;
 
    /// Get random result
    /// Returns: Some(VRFOutput) if ready, None if pending
    pub fn get_random(request_id: u64) -> Option<VRFOutput>;
 
    /// Verify random number
    pub fn verify_random(output: &VRFOutput) -> bool;
 
    /// Instant random (current block, lower security)
    pub fn instant_random(seed: Hash) -> Hash;
 
    /// Batch request multiple random numbers
    pub fn request_random_batch(seeds: Vec<Hash>) -> Vec<u64>;
}

pub struct VRFOutput {
    /// 32-byte random value
    pub random: Hash,
 
    /// Cryptographic proof
    pub proof: VRFProof,
 
    /// Block when requested
    pub request_block: u64,
 
    /// Block when generated
    pub fulfill_block: u64,
 
    /// Requester address
    pub requester: Address,
 
    /// Input seed
    pub seed: Hash,
}
 
pub struct VRFProof {
    pub gamma: [u8; 32],
    pub c: [u8; 32],
    pub s: [u8; 32],
}

use tako_sdk::*;
 
/// Place bet with VRF
fn place_bet(player: Address, amount: u64, choice: u8) {
    // Lock player funds
    lock_funds(player, amount);
 
    // Generate unique seed
    let seed = blake3_hash(player, amount, choice, get_block_number());
 
    // Request VRF random
    let request_id = vrf_request_random(seed);
 
    // Store bet info
    store_bet(Bet {
        request_id,
        player,
        amount,
        choice, // 0 = Low, 1 = High
        timestamp: get_timestamp(),
    });
}
 
/// Settle bet (anyone can call after VRF ready)
fn settle_bet(request_id: u64) {
    let bet = get_bet(request_id)?;
    let vrf = vrf_get_random(request_id)?;
 
    // Verify VRF proof
    assert!(vrf_verify(&vrf));
 
    // Calculate result: 0-49 = Low, 50-99 = High
    let result = vrf.random[0] % 100;
    let win = (result < 50 && bet.choice == 0) ||
              (result >= 50 && bet.choice == 1);
 
    if win {
        // 1.95x payout
        let payout = bet.amount * 195 / 100;
        transfer(&bet.player, payout);
    }
 
    delete_bet(request_id);
}

/// Instant lottery (low value)
fn lottery(player: Address) {
    let ticket_price = 1_000000; // 1 USDT
 
    // Deduct ticket
    deduct(&player, ticket_price);
 
    // Get instant random
    let seed = blake3_hash(player, get_block_number(), get_timestamp());
    let random = vrf_instant_random(seed);
 
    // ~1.2% chance to win 100 USDT
    let roll = random[0];
    if roll < 3 {
        transfer(&player, 100_000000);
        emit_event("BigWin", player, 100_000000);
    }
}

/// Open mystery box
fn open_mystery_box(player: Address, box_id: u64) {
    // Verify ownership and burn box
    require!(owns_box(&player, box_id));
    burn_box(box_id);
 
    // Request VRF
    let seed = blake3_hash(player, box_id, get_block_number());
    let request_id = vrf_request_random(seed);
 
    store_pending_reveal(request_id, player, box_id);
}
 
/// Reveal box contents (after VRF ready)
fn reveal_mystery_box(request_id: u64) {
    let pending = get_pending_reveal(request_id)?;
    let vrf = vrf_get_random(request_id)?;
 
    // Determine rarity from random
    let roll = u32::from_be_bytes(vrf.random[0..4].try_into().unwrap()) % 10000;
 
    let rarity = match roll {
        0..=49 => Rarity::Legendary,    // 0.5%
        50..=499 => Rarity::Epic,       // 4.5%
        500..=1999 => Rarity::Rare,     // 15%
        _ => Rarity::Common,            // 80%
    };
 
    // Mint NFT with determined rarity
    mint_nft(&pending.player, rarity);
 
    delete_pending_reveal(request_id);
}