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// Descriptor wallet library extending bitcoin & miniscript functionality
// by LNP/BP Association (https://lnp-bp.org)
// Written in 2020-2021 by
//     Dr. Maxim Orlovsky <orlovsky@pandoracore.com>
//
// To the extent possible under law, the author(s) have dedicated all
// copyright and related and neighboring rights to this software to
// the public domain worldwide. This software is distributed without
// any warranty.
//
// You should have received a copy of the Apache-2.0 License
// along with this software.
// If not, see <https://opensource.org/licenses/Apache-2.0>.

use bitcoin::{TxOut, Txid};

use crate::Psbt;

/// Errors happening when PSBT or other resolver information does not match the
/// structure of bitcoin transaction
#[derive(
    Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, Display, Error,
)]
#[display(doc_comments)]
pub enum MatchError {
    /// No `witness_utxo` and `non_witness_utxo` is provided for input {0}
    NoInputTx(usize),

    /// Provided `non_witness_utxo` {1} does not match transaction input {0}
    NoTxidMatch(usize, Txid),

    /// Number of transaction inputs does not match number of the provided PSBT
    /// input data for input {0}
    UnmatchingInputNumber(usize),

    /// Transaciton has less than {0} inputs
    WrongInputNo(usize),
}

/// API for accessing previous transaction output data
pub trait InputPreviousTxo {
    /// Returns [`TxOut`] reference returned by resolver, if any, or reports
    /// specific matching error prevented from getting the output
    fn input_previous_txo(&self, index: usize) -> Result<&TxOut, MatchError>;
}

/// Errors happening during fee computation
#[derive(
    Clone,
    Copy,
    PartialEq,
    Eq,
    PartialOrd,
    Ord,
    Hash,
    Debug,
    Display,
    Error,
    From,
)]
#[display(doc_comments)]
pub enum FeeError {
    /// No input source information found because of wrong or incomplete PSBT
    /// structure
    #[from]
    MatchError(MatchError),

    /// Sum of inputs is less than sum of outputs
    InputsLessThanOutputs,
}

/// Fee computing resolver
pub trait Fee {
    /// Returns fee for a transaction, or returns error reporting resolver
    /// problem or wrong transaction structure
    fn fee(&self) -> Result<u64, FeeError>;
}

impl InputPreviousTxo for Psbt {
    fn input_previous_txo(&self, index: usize) -> Result<&TxOut, MatchError> {
        if let (Some(input), Some(txin)) = (
            self.inputs.get(index),
            self.global.unsigned_tx.input.get(index),
        ) {
            let txid = txin.previous_output.txid;
            input
                .witness_utxo
                .as_ref()
                .ok_or(MatchError::NoInputTx(index))
                .or_else(|_| {
                    input
                        .non_witness_utxo
                        .as_ref()
                        .ok_or(MatchError::NoInputTx(index))
                        .and_then(|tx| {
                            if txid != tx.txid() {
                                Err(MatchError::NoTxidMatch(index, txid))
                            } else {
                                tx.output
                                    .get(txin.previous_output.vout as usize)
                                    .ok_or(MatchError::UnmatchingInputNumber(
                                        index,
                                    ))
                            }
                        })
                })
        } else {
            Err(MatchError::WrongInputNo(index))
        }
    }
}

impl Fee for Psbt {
    fn fee(&self) -> Result<u64, FeeError> {
        let mut input_sum = 0;
        for index in 0..self.global.unsigned_tx.input.len() {
            input_sum += self.input_previous_txo(index)?.value;
        }

        let output_sum = self
            .global
            .unsigned_tx
            .output
            .iter()
            .map(|txout| txout.value)
            .sum();

        if input_sum < output_sum {
            Err(FeeError::InputsLessThanOutputs)
        } else {
            Ok(input_sum - output_sum)
        }
    }
}