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//! A type to hold data for the [`StakeHistory` sysvar][sv].
//!
//! [sv]: https://docs.solana.com/developing/runtime-facilities/sysvars#stakehistory
//!
//! The sysvar ID is declared in [`sysvar::stake_history`].
//!
//! [`sysvar::stake_history`]: crate::sysvar::stake_history

pub use crate::clock::Epoch;
use std::ops::Deref;

pub const MAX_ENTRIES: usize = 512; // it should never take as many as 512 epochs to warm up or cool down

#[derive(Debug, Serialize, Deserialize, PartialEq, Eq, Default, Clone, AbiExample)]
pub struct StakeHistoryEntry {
    pub effective: u64,    // effective stake at this epoch
    pub activating: u64,   // sum of portion of stakes not fully warmed up
    pub deactivating: u64, // requested to be cooled down, not fully deactivated yet
}

impl StakeHistoryEntry {
    pub fn with_effective(effective: u64) -> Self {
        Self {
            effective,
            ..Self::default()
        }
    }

    pub fn with_effective_and_activating(effective: u64, activating: u64) -> Self {
        Self {
            effective,
            activating,
            ..Self::default()
        }
    }

    pub fn with_deactivating(deactivating: u64) -> Self {
        Self {
            effective: deactivating,
            deactivating,
            ..Self::default()
        }
    }
}

impl std::ops::Add for StakeHistoryEntry {
    type Output = StakeHistoryEntry;
    fn add(self, rhs: StakeHistoryEntry) -> Self::Output {
        Self {
            effective: self.effective.saturating_add(rhs.effective),
            activating: self.activating.saturating_add(rhs.activating),
            deactivating: self.deactivating.saturating_add(rhs.deactivating),
        }
    }
}

#[repr(C)]
#[derive(Debug, Serialize, Deserialize, PartialEq, Eq, Default, Clone, AbiExample)]
pub struct StakeHistory(Vec<(Epoch, StakeHistoryEntry)>);

impl StakeHistory {
    pub fn get(&self, epoch: Epoch) -> Option<&StakeHistoryEntry> {
        self.binary_search_by(|probe| epoch.cmp(&probe.0))
            .ok()
            .map(|index| &self[index].1)
    }

    pub fn add(&mut self, epoch: Epoch, entry: StakeHistoryEntry) {
        match self.binary_search_by(|probe| epoch.cmp(&probe.0)) {
            Ok(index) => (self.0)[index] = (epoch, entry),
            Err(index) => (self.0).insert(index, (epoch, entry)),
        }
        (self.0).truncate(MAX_ENTRIES);
    }
}

impl Deref for StakeHistory {
    type Target = Vec<(Epoch, StakeHistoryEntry)>;
    fn deref(&self) -> &Self::Target {
        &self.0
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_stake_history() {
        let mut stake_history = StakeHistory::default();

        for i in 0..MAX_ENTRIES as u64 + 1 {
            stake_history.add(
                i,
                StakeHistoryEntry {
                    activating: i,
                    ..StakeHistoryEntry::default()
                },
            );
        }
        assert_eq!(stake_history.len(), MAX_ENTRIES);
        assert_eq!(stake_history.iter().map(|entry| entry.0).min().unwrap(), 1);
        assert_eq!(stake_history.get(0), None);
        assert_eq!(
            stake_history.get(1),
            Some(&StakeHistoryEntry {
                activating: 1,
                ..StakeHistoryEntry::default()
            })
        );
    }
}