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use bitcoin::{OutPoint, TxOut, Txid};

use crate::{Anchor, COINBASE_MATURITY};

/// Represents the observed position of some chain data.
///
/// The generic `A` should be a [`Anchor`] implementation.
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, core::hash::Hash)]
#[cfg_attr(
    feature = "serde",
    derive(serde::Deserialize, serde::Serialize),
    serde(bound(
        deserialize = "A: Ord + serde::Deserialize<'de>",
        serialize = "A: Ord + serde::Serialize",
    ))
)]
pub enum ChainPosition<A> {
    /// The chain data is seen as confirmed, and in anchored by `A`.
    Confirmed(A),
    /// The chain data is not confirmed and last seen in the mempool at this timestamp.
    Unconfirmed(u64),
}

impl<A> ChainPosition<A> {
    /// Returns whether [`ChainPosition`] is confirmed or not.
    pub fn is_confirmed(&self) -> bool {
        matches!(self, Self::Confirmed(_))
    }
}

impl<A: Clone> ChainPosition<&A> {
    /// Maps a [`ChainPosition<&A>`] into a [`ChainPosition<A>`] by cloning the contents.
    pub fn cloned(self) -> ChainPosition<A> {
        match self {
            ChainPosition::Confirmed(a) => ChainPosition::Confirmed(a.clone()),
            ChainPosition::Unconfirmed(last_seen) => ChainPosition::Unconfirmed(last_seen),
        }
    }
}

impl<A: Anchor> ChainPosition<A> {
    /// Determines the upper bound of the confirmation height.
    pub fn confirmation_height_upper_bound(&self) -> Option<u32> {
        match self {
            ChainPosition::Confirmed(a) => Some(a.confirmation_height_upper_bound()),
            ChainPosition::Unconfirmed(_) => None,
        }
    }
}

/// A `TxOut` with as much data as we can retrieve about it
#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord)]
pub struct FullTxOut<A> {
    /// The position of the transaction in `outpoint` in the overall chain.
    pub chain_position: ChainPosition<A>,
    /// The location of the `TxOut`.
    pub outpoint: OutPoint,
    /// The `TxOut`.
    pub txout: TxOut,
    /// The txid and chain position of the transaction (if any) that has spent this output.
    pub spent_by: Option<(ChainPosition<A>, Txid)>,
    /// Whether this output is on a coinbase transaction.
    pub is_on_coinbase: bool,
}

impl<A: Anchor> FullTxOut<A> {
    /// Whether the `txout` is considered mature.
    ///
    /// Depending on the implementation of [`confirmation_height_upper_bound`] in [`Anchor`], this
    /// method may return false-negatives. In other words, interpreted confirmation count may be
    /// less than the actual value.
    ///
    /// [`confirmation_height_upper_bound`]: Anchor::confirmation_height_upper_bound
    pub fn is_mature(&self, tip: u32) -> bool {
        if self.is_on_coinbase {
            let tx_height = match &self.chain_position {
                ChainPosition::Confirmed(anchor) => anchor.confirmation_height_upper_bound(),
                ChainPosition::Unconfirmed(_) => {
                    debug_assert!(false, "coinbase tx can never be unconfirmed");
                    return false;
                }
            };
            let age = tip.saturating_sub(tx_height);
            if age + 1 < COINBASE_MATURITY {
                return false;
            }
        }

        true
    }

    /// Whether the utxo is/was/will be spendable with chain `tip`.
    ///
    /// This method does not take into account the lock time.
    ///
    /// Depending on the implementation of [`confirmation_height_upper_bound`] in [`Anchor`], this
    /// method may return false-negatives. In other words, interpreted confirmation count may be
    /// less than the actual value.
    ///
    /// [`confirmation_height_upper_bound`]: Anchor::confirmation_height_upper_bound
    pub fn is_confirmed_and_spendable(&self, tip: u32) -> bool {
        if !self.is_mature(tip) {
            return false;
        }

        let confirmation_height = match &self.chain_position {
            ChainPosition::Confirmed(anchor) => anchor.confirmation_height_upper_bound(),
            ChainPosition::Unconfirmed(_) => return false,
        };
        if confirmation_height > tip {
            return false;
        }

        // if the spending tx is confirmed within tip height, the txout is no longer spendable
        if let Some((ChainPosition::Confirmed(spending_anchor), _)) = &self.spent_by {
            if spending_anchor.anchor_block().height <= tip {
                return false;
            }
        }

        true
    }
}

#[cfg(test)]
mod test {
    use bdk_core::ConfirmationBlockTime;

    use crate::BlockId;

    use super::*;

    #[test]
    fn chain_position_ord() {
        let unconf1 = ChainPosition::<ConfirmationBlockTime>::Unconfirmed(10);
        let unconf2 = ChainPosition::<ConfirmationBlockTime>::Unconfirmed(20);
        let conf1 = ChainPosition::Confirmed(ConfirmationBlockTime {
            confirmation_time: 20,
            block_id: BlockId {
                height: 9,
                ..Default::default()
            },
        });
        let conf2 = ChainPosition::Confirmed(ConfirmationBlockTime {
            confirmation_time: 15,
            block_id: BlockId {
                height: 12,
                ..Default::default()
            },
        });

        assert!(unconf2 > unconf1, "higher last_seen means higher ord");
        assert!(unconf1 > conf1, "unconfirmed is higher ord than confirmed");
        assert!(
            conf2 > conf1,
            "confirmation_height is higher then it should be higher ord"
        );
    }
}