sn_transfers 0.11.11

// Copyright 2023 MaidSafe.net limited.
//
// This SAFE Network Software is licensed to you under The General Public License (GPL), version 3.
// Unless required by applicable law or agreed to in writing, the SAFE Network Software distributed
// under the GPL Licence is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied. Please review the Licences for the specific language governing
// permissions and limitations relating to use of the SAFE Network Software.

use super::{Error, Inputs, Result, SpendRequest, TransferOutputs};

use sn_dbc::{
    random_derivation_index, rng, Dbc, DerivationIndex, DerivedKey, FeeOutput, Hash, Input,
    PublicAddress, Token, TransactionBuilder,
};

use std::collections::BTreeMap;

/// A function for creating an offline transfer of tokens.
/// This is done by creating new dbcs to the recipients (and a change dbc if any)
/// by selecting from the available input dbcs, and creating the necessary
/// spends to do so.
///
/// Those signed spends are found in each new dbc, and must be uploaded to the network
/// for the transaction to take effect.
/// The peers will validate each signed spend they receive, before accepting it.
/// Once enough peers have accepted all the spends of the transaction, and serve
/// them upon request, the transaction will be completed.
pub fn create_offline_transfer(
    available_dbcs: Vec<(Dbc, DerivedKey)>,
    recipients: Vec<(Token, PublicAddress, DerivationIndex)>,
    change_to: PublicAddress,
    reason_hash: Hash,
) -> Result<TransferOutputs> {
    let total_output_amount = recipients
        .iter()
        .try_fold(Token::zero(), |total, (amount, _, _)| {
            total.checked_add(*amount)
        })
        .ok_or_else(|| {
            Error::DbcReissueFailed(
                "Overflow occurred while summing the amounts for the recipients.".to_string(),
            )
        })?;

    // We need to select the necessary number of dbcs from those that we were passed.
    let (dbcs_to_spend, change_amount) = select_inputs(available_dbcs, total_output_amount)?;

    let selected_inputs = Inputs {
        dbcs_to_spend,
        recipients,
        change: (change_amount, change_to),
    };

    create_transfer_with(selected_inputs, reason_hash, None)
}

/// Select the necessary number of dbcs from those that we were passed.
fn select_inputs(
    available_dbcs: Vec<(Dbc, DerivedKey)>,
    total_output_amount: Token,
) -> Result<(Vec<(Dbc, DerivedKey)>, Token)> {
    let mut dbcs_to_spend = Vec::new();
    let mut total_input_amount = Token::zero();
    let mut change_amount = total_output_amount;

    for (dbc, derived_key) in available_dbcs {
        let input_key = dbc.id();

        let dbc_balance = match dbc.token() {
            Ok(token) => token,
            Err(err) => {
                warn!("Ignoring input Dbc (id: {input_key:?}) due to missing an output: {err:?}");
                continue;
            }
        };

        // Add this Dbc as input to be spent.
        dbcs_to_spend.push((dbc, derived_key));

        // Input amount increases with the amount of the dbc.
        total_input_amount = total_input_amount.checked_add(dbc_balance)
            .ok_or_else(|| {
                Error::DbcReissueFailed(
                    "Overflow occurred while increasing total input amount while trying to cover the output DBCs."
                    .to_string(),
            )
            })?;

        // If we've already combined input DBCs for the total output amount, then stop.
        match change_amount.checked_sub(dbc_balance) {
            Some(pending_output) => {
                change_amount = pending_output;
                if change_amount.as_nano() == 0 {
                    break;
                }
            }
            None => {
                change_amount = Token::from_nano(dbc_balance.as_nano() - change_amount.as_nano());
                break;
            }
        }
    }

    // Make sure total input amount gathered with input DBCs are enough for the output amount
    if total_output_amount > total_input_amount {
        return Err(Error::NotEnoughBalance(
            total_input_amount,
            total_output_amount,
        ));
    }

    Ok((dbcs_to_spend, change_amount))
}

/// The tokens of the input dbcs will be transfered to the
/// new dbcs (and a change dbc if any), which are returned from this function.
/// This does not register the transaction in the network.
/// To do that, the `signed_spends` of each new dbc, has to be uploaded
/// to the network. When those same signed spends can be retrieved from
/// enough peers in the network, the transaction will be completed.
fn create_transfer_with(
    selected_inputs: Inputs,
    reason_hash: Hash,
    fee: Option<FeeOutput>,
) -> Result<TransferOutputs> {
    let Inputs {
        change: (change, change_to),
        ..
    } = selected_inputs;

    let mut inputs = vec![];
    let mut src_txs = BTreeMap::new();
    for (dbc, derived_key) in selected_inputs.dbcs_to_spend {
        let token = match dbc.token() {
            Ok(token) => token,
            Err(err) => {
                warn!("Ignoring dbc, as it didn't have the correct derived key: {err}");
                continue;
            }
        };
        let input = Input {
            dbc_id: dbc.id(),
            token,
        };
        inputs.push((input, derived_key, dbc.src_tx.clone()));
        let _ = src_txs.insert(dbc.id(), dbc.src_tx);
    }

    let mut tx_builder = TransactionBuilder::default()
        .add_inputs(inputs)
        .add_outputs(selected_inputs.recipients);

    if let Some(fee_output) = fee {
        tx_builder = tx_builder.set_fee_output(fee_output);
    }

    let mut rng = rng::thread_rng();
    let derivation_index = random_derivation_index(&mut rng);
    let change_id = change_to.new_dbc_id(&derivation_index);
    if !change.is_zero() {
        tx_builder = tx_builder.add_output(change, change_to, derivation_index);
    }

    // Finalize the tx builder to get the dbc builder.
    let dbc_builder = tx_builder
        .build(reason_hash)
        .map_err(Box::new)
        .map_err(Error::Dbcs)?;

    let tx = dbc_builder.spent_tx.clone();

    let signed_spends: BTreeMap<_, _> = dbc_builder
        .signed_spends()
        .into_iter()
        .map(|spend| (spend.dbc_id(), spend))
        .collect();

    // We must have a source transaction for each signed spend (i.e. the tx where the dbc was created).
    // These are required to upload the spends to the network.
    if !signed_spends
        .iter()
        .all(|(dbc_id, _)| src_txs.contains_key(*dbc_id))
    {
        return Err(Error::DbcReissueFailed(
            "Not all signed spends could be matched to a source dbc transaction.".to_string(),
        ));
    }

    let mut all_spend_requests = vec![];
    for (dbc_id, signed_spend) in signed_spends.into_iter() {
        let parent_tx = src_txs.get(dbc_id).ok_or(Error::DbcReissueFailed(format!(
            "Missing source dbc tx of {dbc_id:?}!"
        )))?;

        let spend_requests = SpendRequest {
            signed_spend: signed_spend.clone(),
            parent_tx: parent_tx.clone(),
        };

        all_spend_requests.push(spend_requests);
    }

    // Perform validations of input tx and signed spends,
    // as well as building the output DBCs.
    let mut created_dbcs: Vec<_> = dbc_builder
        .build()
        .map_err(Box::new)
        .map_err(Error::Dbcs)?
        .into_iter()
        .map(|(dbc, _)| dbc)
        .collect();

    let mut change_dbc = None;
    created_dbcs.retain(|created| {
        if created.id() == change_id {
            change_dbc = Some(created.clone());
            false
        } else {
            true
        }
    });

    Ok(TransferOutputs {
        tx,
        created_dbcs,
        change_dbc,
        all_spend_requests,
    })
}