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use crate::{
    db_state::ScndIdxNum,
    lsm::{
        entryset::CommittedEntrySet,
        unit::{
            CommitDataType, CommitInfo, CommitVer, CompactedUnit, ReplacementNum, StagingUnit,
            UnitDir,
        },
    },
};
use anyhow::Result;
use pancake_engine_common::{fs_utils, ReadonlyMemLog, SSTable};
use pancake_types::{
    serde::OptDatum,
    types::{PKShared, PVShared, SVPKShared},
};
use std::collections::HashMap;

pub struct CommittedUnit {
    pub prim: Option<CommittedEntrySet<PKShared, OptDatum<PVShared>>>,
    pub scnds: HashMap<ScndIdxNum, CommittedEntrySet<SVPKShared, OptDatum<PVShared>>>,
    pub dir: UnitDir,
    pub commit_info: CommitInfo,
}

impl CommittedUnit {
    /// Cost:
    /// - There is no cost converting each `WritableMemLog` to `ReadonlyMemLog`.
    /// - There *is* a cost of serializing a [`CommitInfo`].
    pub fn from_staging(stg: StagingUnit, commit_ver: CommitVer) -> Result<Self> {
        let prim: ReadonlyMemLog<PKShared, OptDatum<PVShared>> = stg.prim.into();
        let prim = CommittedEntrySet::RMemLog(prim);

        let scnds = stg
            .scnds
            .into_iter()
            .map(|(scnd_idx_num, w_memlog)| {
                let r_memlog: ReadonlyMemLog<SVPKShared, OptDatum<PVShared>> = w_memlog.into();
                let entryset = CommittedEntrySet::RMemLog(r_memlog);
                (scnd_idx_num, entryset)
            })
            .collect::<HashMap<_, _>>();

        let commit_info = CommitInfo {
            commit_ver_hi_incl: commit_ver,
            commit_ver_lo_incl: commit_ver,
            replacement_num: ReplacementNum::FOR_NEW_COMMIT_VER_INTERVAL,
            data_type: CommitDataType::MemLog,
        };
        let commit_info_path = stg.dir.format_commit_info_file_path();
        commit_info.ser(commit_info_path)?;

        Ok(Self {
            prim: Some(prim),
            scnds,
            dir: stg.dir,
            commit_info,
        })
    }

    /// Cost:
    /// - This constructor serializes CommitInfo. The caller shouldn't do it before.
    pub fn from_compacted(compacted: CompactedUnit, commit_info: CommitInfo) -> Result<Self> {
        let prim = compacted.prim.map(CommittedEntrySet::SSTable);

        let scnds = compacted
            .scnds
            .into_iter()
            .map(|(si_num, sstable)| (si_num, CommittedEntrySet::SSTable(sstable)))
            .collect::<HashMap<_, _>>();

        let commit_info_path = compacted.dir.format_commit_info_file_path();
        commit_info.ser(commit_info_path)?;

        Ok(Self {
            prim,
            scnds,
            dir: compacted.dir,
            commit_info,
        })
    }

    pub fn load(dir: UnitDir, commit_info: CommitInfo) -> Result<Self> {
        let prim_path = dir.format_prim_file_path();
        let prim = if prim_path.exists() {
            let entryset = match commit_info.data_type() {
                CommitDataType::MemLog => {
                    CommittedEntrySet::RMemLog(ReadonlyMemLog::load(prim_path)?)
                }
                CommitDataType::SSTable => CommittedEntrySet::SSTable(SSTable::load(prim_path)?),
            };
            Some(entryset)
        } else {
            None
        };

        let mut scnds = HashMap::new();
        for res in dir.list_scnd_file_paths()? {
            let (scnd_path, si_num) = res?;
            let entryset = match commit_info.data_type() {
                CommitDataType::MemLog => {
                    CommittedEntrySet::RMemLog(ReadonlyMemLog::load(scnd_path)?)
                }
                CommitDataType::SSTable => CommittedEntrySet::SSTable(SSTable::load(scnd_path)?),
            };
            scnds.insert(si_num, entryset);
        }

        Ok(Self {
            prim,
            scnds,
            dir,
            commit_info,
        })
    }

    pub fn remove_dir(self) -> Result<()> {
        fs_utils::remove_dir_all(self.dir.path())?;
        Ok(())
    }
}