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1. Client computes nullifier = hash(secret, context)
2. Client fetches validity proof for derived address (proves it does not exist)
3. Client calls create_nullifier with nullifier values and proof
4. Program derives address from nullifier, creates compressed account via CPI
5. Light system program rejects CPI if address already exists

#[derive(Clone, Debug, Default, BorshSerialize, BorshDeserialize, LightDiscriminator)]
pub struct NullifierAccount {}

pub const NULLIFIER_PREFIX: &[u8] = b"nullifier";

let (address, address_seed) = derive_address(
    &[NULLIFIER_PREFIX, nullifier.as_slice()],  // seeds
    &address_tree_pubkey,                        // address tree
    &program_id,                                 // program ID
);

#[derive(Clone, Debug, AnchorSerialize, AnchorDeserialize)]
pub struct NullifierInstructionData {
    pub proof: ValidityProof,           // ZK proof that addresses don't exist
    pub address_tree_info: PackedAddressTreeInfo,
    pub output_state_tree_index: u8,
    pub system_accounts_offset: u8,
}

pub fn create_nullifiers<'info>(
    nullifiers: &[[u8; 32]],
    data: NullifierInstructionData,
    signer: &AccountInfo<'info>,
    remaining_accounts: &[AccountInfo<'info>],
) -> Result<()> {
    let light_cpi_accounts = CpiAccounts::new(
        signer,
        &remaining_accounts[data.system_accounts_offset as usize..],
        LIGHT_CPI_SIGNER,
    );

    let address_tree_pubkey = data
        .address_tree_info
        .get_tree_pubkey(&light_cpi_accounts)
        .map_err(|_| ErrorCode::AccountNotEnoughKeys)?;

    let mut cpi_builder = LightSystemProgramCpi::new_cpi(LIGHT_CPI_SIGNER, data.proof);
    let mut new_address_params: Vec<NewAddressParamsAssignedPacked> =
        Vec::with_capacity(nullifiers.len());

    for (i, nullifier) in nullifiers.iter().enumerate() {
        let (address, address_seed) = derive_address(
            &[NULLIFIER_PREFIX, nullifier.as_slice()],
            &address_tree_pubkey,
            &crate::ID,
        );

        let nullifier_account = LightAccount::<NullifierAccount>::new_init(
            &crate::ID,
            Some(address),
            data.output_state_tree_index,
        );

        cpi_builder = cpi_builder.with_light_account(nullifier_account)?;
        new_address_params.push(
            data.address_tree_info
                .into_new_address_params_assigned_packed(address_seed, Some(i as u8)),
        );
    }

    cpi_builder
        .with_new_addresses(&new_address_params)
        .invoke(light_cpi_accounts)?;

    Ok(())
}

#[program]
pub mod nullifier {
    pub fn create_nullifier<'info>(
        ctx: Context<'_, '_, '_, 'info, CreateNullifierAccounts<'info>>,
        data: NullifierInstructionData,
        nullifiers: Vec<[u8; 32]>,
    ) -> Result<()> {
        // Verify your ZK proof here. Use nullifiers as public inputs.
        // Example:
        // let public_inputs = [...nullifiers, ...your_other_inputs];
        // Groth16Verifier::new(...).verify()?;

        create_nullifiers(
            &nullifiers,
            data,
            ctx.accounts.signer.as_ref(),
            ctx.remaining_accounts,
        )
    }
}

#[derive(Accounts)]
pub struct CreateNullifierAccounts<'info> {
    #[account(mut)]
    pub signer: Signer<'info>,
}

const NULLIFIER_PREFIX = Buffer.from("nullifier");
const addressTree = new web3.PublicKey(batchAddressTree);

// Derive addresses for each nullifier
const addressesWithTree = nullifiers.map((nullifier) => {
    const seed = deriveAddressSeedV2([NULLIFIER_PREFIX, nullifier]);
    const address = deriveAddressV2(seed, addressTree, programId);
    return { tree: addressTree, queue: addressTree, address: bn(address.toBytes()) };
});

// Get validity proof (proves addresses don't exist)
const proofResult = await rpc.getValidityProofV0([], addressesWithTree);

// Build remaining accounts
const remainingAccounts = new PackedAccounts();
remainingAccounts.addSystemAccountsV2(SystemAccountMetaConfig.new(programId));
const addressMerkleTreeIndex = remainingAccounts.insertOrGet(addressTree);
const outputStateTreeIndex = remainingAccounts.insertOrGet(outputStateTree);

// Build instruction data
const data = {
    proof: { 0: proofResult.compressedProof },
    addressTreeInfo: {
        addressMerkleTreePubkeyIndex: addressMerkleTreeIndex,
        addressQueuePubkeyIndex: addressMerkleTreeIndex,
        rootIndex: proofResult.rootIndices[0],
    },
    outputStateTreeIndex,
    systemAccountsOffset: systemStart,
};

// Call program
const ix = await program.methods
    .createNullifier(data, nullifiers.map((n) => Array.from(n)))
    .accounts({ signer: signer.publicKey })
    .remainingAccounts(remainingAccounts)
    .instruction();

use light_sdk::address::v2::derive_address;

let address_tree_info = rpc.get_address_tree_v2();

// Derive addresses
let address_with_trees: Vec<AddressWithTree> = nullifiers
    .iter()
    .map(|n| {
        let (address, _) = derive_address(
            &[NULLIFIER_PREFIX, n.as_slice()],
            &address_tree_info.tree,
            &program_id,
        );
        AddressWithTree {
            address,
            tree: address_tree_info.tree,
        }
    })
    .collect();

// Get validity proof (empty hashes = non-inclusion proof)
let rpc_result = rpc
    .get_validity_proof(vec![], address_with_trees, None)
    .await?
    .value;

// Build accounts
let mut remaining_accounts = PackedAccounts::default();
let config = SystemAccountMetaConfig::new(program_id);
remaining_accounts.add_system_accounts_v2(config)?;

let packed_address_tree_accounts = rpc_result
    .pack_tree_infos(&mut remaining_accounts)
    .address_trees;

let output_state_tree_index = rpc
    .get_random_state_tree_info()?
    .pack_output_tree_index(&mut remaining_accounts)?;