1. Core Structure Sui’s object-centric model requires:

Pool Object: Stores reserves, LP token data, and config.

LP Token: A Coin-like asset tracking ownership.

move
module dex::amm {  
    use sui::balance;  
    use sui::coin;  
    use sui::math;  
    use sui::tx_context;  

    struct Pool<phantom X, phantom Y> has key {  
        id: UID,  
        reserve_x: Balance<X>,  
        reserve_y: Balance<Y>,  
        lp_supply: Balance<LP<X, Y>>,  
        fee_bps: u64, // e.g., 30 = 0.3%  
    }  

    struct LP<phantom X, phantom Y> has store {} // LP token type  

2. Deposit Logic (Adding Liquidity) Key steps:

Take input tokens.

Mint LP tokens proportionally.

Update reserves atomically.

move
public fun add_liquidity<X, Y>(  
    pool: &mut Pool<X, Y>,  
    x: Coin<X>,  
    y: Coin<Y>,  
    ctx: &mut TxContext  
): Coin<LP<X, Y>> {  
    let x_val = coin::value(&x);  
    let y_val = coin::value(&y);  
    assert!(x_val > 0 && y_val > 0, EINVALID_AMOUNT);  

    // Calculate LP tokens to mint (geometric mean)  
    let lp_amount = if (balance::supply(&pool.lp_supply) == 0) {  
        math::sqrt(x_val * y_val) // Initial mint  
    } else {  
        min(  
            (x_val * balance::supply(&pool.lp_supply)) / balance::value(&pool.reserve_x),  
            (y_val * balance::supply(&pool.lp_supply)) / balance::value(&pool.reserve_y)  
        )  
    };  

    // Update reserves  
    balance::join(&mut pool.reserve_x, coin::into_balance(x));  
    balance::join(&mut pool.reserve_y, coin::into_balance(y));  

    // Mint LP tokens  
    balance::increase_supply(&mut pool.lp_supply, lp_amount)  
}  

3. Swap Logic (With Fees)

move
public fun swap_x_to_y<X, Y>(  
    pool: &mut Pool<X, Y>,  
    dx: Coin<X>,  
    min_dy: u64,  
    ctx: &mut TxContext  
): Coin<Y> {  
    let dx_val = coin::value(&dx);  
    let fee = dx_val * pool.fee_bps / 10_000;  
    let dx_after_fee = dx_val - fee;  

    // Constant product formula  
    let dy_val = (dx_after_fee * balance::value(&pool.reserve_y)) /  
                 (balance::value(&pool.reserve_x) + dx_after_fee);  
    assert!(dy_val >= min_dy, EINSUFFICIENT_OUTPUT);  

    // Update reserves  
    balance::join(&mut pool.reserve_x, coin::into_balance(dx));  
    balance::withdraw(&mut pool.reserve_y, dy_val)  
}  

4. Key Optimizations Sui Advantages:

No reentrancy: Move’s ownership model prevents it.

Batch transactions: Use entry functions for multi-step ops.

Dynamic Fields: Store extra data (e.g., TWAP oracles) on the pool object.

5. Common Pitfalls & Fixes Overflow: Use math::checked_* functions for arithmetic.

LP rounding: Store fractional amounts via u128 internally.

Frontrunning:

Require min_dy in swaps (set by frontend).

Use TxContext::epoch() for deadline checks.