AMM Swap: Executing a Swap

Challenge: The Swap Math

Implement the swap logic.

Step 1: Calculate Output

You must calculate the output amount using curve math. If the user deposits amount_in of Token A, how much Token B do they get so that x * y = k is respected? (Hint: don't forget to subtract your protocol fee first!)

Step 2: Transfer In

Use a standard CPI to transfer Token A from the user to vault_a.

Step 3: Transfer Out (PDA Signer)

Use CpiContext::new_with_signer to transfer Token B from vault_b back to the user. Because the vault is owned by the PDA, the PDA must "sign" the transaction.

let seeds = &[
    b"amm".as_ref(),
    // ... other seeds
    &[bump],
];
let signer_seeds = &[&seeds[..]];

let cpi_ctx = CpiContext::new_with_signer(cpi_program, cpi_accounts, signer_seeds);
token::transfer(cpi_ctx, amount_out)?;