pipecircuit 0.0.20

Correct. Robust. Fast. Portable. Pick four.
Documentation 
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use super::blocks::SlotLocation;
use super::key::checked_ordered_word;
use super::{RangeIndex, RangeIndexInconsistency, RangeIndexKey};
use crate::storage::warp_table::secondary_index::StableSlot;

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum RangeIndexRemoveError<Key> {
    OrderedWordOutsideWidth {
        key: Key,
        ordered_word: u64,
        bits: u32,
    },
    Inconsistent {
        key: Key,
        slot: StableSlot,
        reason: RangeIndexInconsistency,
    },
}

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
#[must_use]
pub enum RangeIndexRemoveOutcome<Key> {
    Removed { key: Key, slot: StableSlot },
}

pub struct PreparedRangeIndexRemove<'index, Key: RangeIndexKey> {
    member_count: &'index mut u64,
    key: Key,
    word: u64,
    slot: StableSlot,
    location: SlotLocation<'index>,
    previous_member_count: u64,
    committed: bool,
}

impl<Key: RangeIndexKey> RangeIndex<Key> {
    pub fn try_prepare_remove(
        &mut self,
        key: Key,
        slot: StableSlot,
    ) -> Result<PreparedRangeIndexRemove<'_, Key>, RangeIndexRemoveError<Key>> {
        let word = checked_ordered_word(key).map_err(|outside| {
            RangeIndexRemoveError::OrderedWordOutsideWidth {
                key: outside.key,
                ordered_word: outside.ordered_word,
                bits: outside.bits,
            }
        })?;
        let (mut location, member_count) = self
            .validate_stored_word(word, slot)
            .map_err(|reason| inconsistent(key, slot, reason))?;
        let previous_member_count = *member_count;
        let Some(next_member_count) = previous_member_count.checked_sub(1) else {
            return Err(inconsistent(
                key,
                slot,
                RangeIndexInconsistency::MemberCountMismatch {
                    members: previous_member_count,
                },
            ));
        };
        location.write(false, 0);
        *member_count = next_member_count;
        Ok(PreparedRangeIndexRemove {
            member_count,
            key,
            word,
            slot,
            location,
            previous_member_count,
            committed: false,
        })
    }

    pub(super) fn validate_stored_word(
        &mut self,
        expected: u64,
        slot: StableSlot,
    ) -> Result<(SlotLocation<'_>, &mut u64), RangeIndexInconsistency> {
        let words_per_block = self.validated_words_per_block()?;
        let (location, member_count) = self.locate_slot(slot, words_per_block)?;
        if !location.member() {
            return Err(RangeIndexInconsistency::MemberAbsent);
        }
        let actual = location.word();
        if actual != expected {
            return Err(RangeIndexInconsistency::StoredWordMismatch { expected, actual });
        }
        Ok((location, member_count))
    }
}

impl<Key: RangeIndexKey> PreparedRangeIndexRemove<'_, Key> {
    pub fn commit(mut self) -> RangeIndexRemoveOutcome<Key> {
        self.committed = true;
        RangeIndexRemoveOutcome::Removed {
            key: self.key,
            slot: self.slot,
        }
    }
}

impl<Key: RangeIndexKey> Drop for PreparedRangeIndexRemove<'_, Key> {
    fn drop(&mut self) {
        if !self.committed {
            self.location.write(true, self.word);
            *self.member_count = self.previous_member_count;
        }
    }
}

pub(super) fn inconsistent<Key>(
    key: Key,
    slot: StableSlot,
    reason: RangeIndexInconsistency,
) -> RangeIndexRemoveError<Key> {
    RangeIndexRemoveError::Inconsistent { key, slot, reason }
}