mushroomdb-storage 0.4.2

use std::fs::{File, OpenOptions};
use std::io::{Read, Write};
use std::path::PathBuf;

#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum FileId {
    Wal,
    Snapshot,
    /// Backup of the previous snapshot, kept until the next clean open at
    /// the current format version. Written before any migration to preserve
    /// the original bytes if the migration step fails.
    SnapshotBak,
    /// RBAC role definitions sidecar. Written atomically by `apply_schema`
    /// when roles change; loaded at open. Never part of WAL/snapshot format.
    Roles,
}

impl FileId {
    fn name(self) -> &'static str {
        match self {
            FileId::Wal => "wal.bin",
            FileId::Snapshot => "snapshot.bin",
            FileId::SnapshotBak => "snapshot.bin.bak",
            FileId::Roles => "roles.json",
        }
    }
}

pub trait Fs {
    fn append(&mut self, file: FileId, data: &[u8]) -> std::io::Result<()>;
    fn sync(&mut self, file: FileId) -> std::io::Result<()>;
    fn read(&self, file: FileId) -> std::io::Result<Vec<u8>>;
    fn write_atomic(&mut self, file: FileId, data: &[u8]) -> std::io::Result<()>;
    /// Return the on-disk path of the snapshot file, if any.
    ///
    /// `Some` for `RealFs` (used by `MappedBase::map` for true file mmap).
    /// `None` for `SimFs` and other in-memory implementations (falls back to
    /// `MappedBase::from_bytes`).
    fn snapshot_path(&self) -> Option<std::path::PathBuf> {
        None
    }
    /// Read at most `n` bytes from the beginning of `file` without loading
    /// the full contents.
    ///
    /// Used by the open path to sniff the 6-byte magic+version header before
    /// deciding whether to mmap (V8) or full-read (legacy V5-V7).
    ///
    /// The default implementation calls `read()` and truncates; override in
    /// `RealFs` for a true partial read.
    fn read_prefix(&self, file: FileId, n: usize) -> std::io::Result<Vec<u8>> {
        let mut bytes = self.read(file)?;
        bytes.truncate(n);
        Ok(bytes)
    }

    // ── WAL archive methods (Task 4: history-preserving snapshots) ─────────────

    /// List all WAL archive identifiers, sorted ascending (oldest first).
    ///
    /// Each archive created by [`archive_wal`] with commit-seq `N` appears as `N`.
    /// Returns an empty list when no archives exist.
    ///
    /// Default: no archive support — returns empty.
    fn list_archives(&self) -> std::io::Result<Vec<u64>> {
        Ok(vec![])
    }

    /// Read the byte contents of WAL archive `n`.
    ///
    /// Returns an empty `Vec` when the archive does not exist.
    ///
    /// Default: no archive support — returns empty.
    fn read_archive(&self, _n: u64) -> std::io::Result<Vec<u8>> {
        Ok(vec![])
    }

    /// Atomically rename the current WAL to `wal.<n>.archive` (same directory,
    /// same filesystem — the rename is guaranteed atomic at the OS level).
    ///
    /// The caller ensures the snapshot has been durably written before calling
    /// this method.  After a successful rename the old WAL no longer exists as
    /// `wal.bin`; a subsequent [`write_atomic`] on `FileId::Wal` creates a new
    /// empty WAL.
    ///
    /// Returns `Err` if the operation is not supported or fails.
    fn archive_wal(&mut self, _n: u64) -> std::io::Result<()> {
        Err(std::io::Error::other(
            "archive_wal not supported by this Fs implementation",
        ))
    }

    /// Delete archive `n`.  No-op if it does not exist.
    ///
    /// Retention pruning (inside `snapshot_with`) is the only call site.
    ///
    /// Default: no-op.
    fn delete_archive(&mut self, _n: u64) -> std::io::Result<()> {
        Ok(())
    }

    /// Return the persisted horizon floor — the global frame index of the
    /// first commit that is still reachable through surviving archives.
    ///
    /// Defaults to `0` (all history reachable / no pruning ever performed).
    fn read_horizon_floor(&self) -> std::io::Result<u64> {
        Ok(0)
    }

    /// Atomically persist `floor` so that a subsequent [`read_horizon_floor`]
    /// after reopen returns the same value.
    ///
    /// Default: no-op (in-memory only; override in durable implementations).
    fn write_horizon_floor(&mut self, _floor: u64) -> std::io::Result<()> {
        Ok(())
    }

    /// Return `true` when the `wal.genesis` marker file is present.
    ///
    /// The marker signals that the surviving archive chain forms a complete,
    /// uninterrupted WAL history starting from the store's first-ever commit
    /// (the genesis chain).  When absent, archive-resident commits are not
    /// safe to replay from empty state and `open_at` must refuse them.
    ///
    /// Default: `false` (no genesis chain / no archive support).
    fn has_genesis_marker(&self) -> bool {
        false
    }

    /// Durably create the `wal.genesis` marker file.
    ///
    /// Written exactly once, when the first WAL archive is taken from a store
    /// that has never undergone a WAL-truncating snapshot.
    ///
    /// Default: no-op.
    fn write_genesis_marker(&mut self) -> std::io::Result<()> {
        Ok(())
    }

    /// Remove the `wal.genesis` marker file.
    ///
    /// Called when the genesis chain is broken: either by archive pruning
    /// (floor advances past 0) or by a WAL-truncating snapshot taken after
    /// archives already exist.  No-op if the marker is absent.
    ///
    /// Default: no-op.
    fn delete_genesis_marker(&mut self) -> std::io::Result<()> {
        Ok(())
    }
}

pub trait FsIntrospect {
    fn total_appended(&self) -> usize;
    fn sync_count(&self) -> usize {
        0
    }
}

#[derive(Debug)]
pub struct RealFs {
    dir: PathBuf,
}

impl RealFs {
    pub fn new(dir: &std::path::Path) -> std::io::Result<Self> {
        std::fs::create_dir_all(dir)?;
        Ok(Self {
            dir: dir.to_path_buf(),
        })
    }

    /// The database directory this filesystem is rooted at.
    pub fn dir(&self) -> &std::path::Path {
        &self.dir
    }

    fn path(&self, file: FileId) -> PathBuf {
        self.dir.join(file.name())
    }
}

impl Fs for RealFs {
    fn append(&mut self, file: FileId, data: &[u8]) -> std::io::Result<()> {
        let mut f = OpenOptions::new()
            .create(true)
            .append(true)
            .open(self.path(file))?;
        f.write_all(data)
    }

    fn sync(&mut self, file: FileId) -> std::io::Result<()> {
        let f = File::open(self.path(file))?;
        full_sync(&f)
    }

    fn read(&self, file: FileId) -> std::io::Result<Vec<u8>> {
        match File::open(self.path(file)) {
            Ok(mut f) => {
                let mut buf = Vec::new();
                f.read_to_end(&mut buf)?;
                Ok(buf)
            }
            Err(e) if e.kind() == std::io::ErrorKind::NotFound => Ok(Vec::new()),
            Err(e) => Err(e),
        }
    }

    fn write_atomic(&mut self, file: FileId, data: &[u8]) -> std::io::Result<()> {
        let tmp = self.dir.join(format!("{}.tmp", file.name()));
        {
            let mut f = File::create(&tmp)?;
            f.write_all(data)?;
            full_sync(&f)?;
        }
        std::fs::rename(&tmp, self.path(file))?;
        sync_dir(&self.dir)
    }

    fn snapshot_path(&self) -> Option<std::path::PathBuf> {
        Some(self.path(FileId::Snapshot))
    }

    fn read_prefix(&self, file: FileId, n: usize) -> std::io::Result<Vec<u8>> {
        use std::io::Read as _;
        match File::open(self.path(file)) {
            Ok(mut f) => {
                let mut buf = vec![0u8; n];
                let read = f.read(&mut buf)?;
                buf.truncate(read);
                Ok(buf)
            }
            Err(e) if e.kind() == std::io::ErrorKind::NotFound => Ok(Vec::new()),
            Err(e) => Err(e),
        }
    }

    fn list_archives(&self) -> std::io::Result<Vec<u64>> {
        let mut ns = Vec::new();
        for entry in std::fs::read_dir(&self.dir)? {
            let entry = entry?;
            let name = entry.file_name();
            let s = name.to_string_lossy();
            if let Some(mid) = s
                .strip_prefix("wal.")
                .and_then(|r| r.strip_suffix(".archive"))
            {
                if let Ok(n) = mid.parse::<u64>() {
                    ns.push(n);
                }
            }
        }
        ns.sort_unstable();
        Ok(ns)
    }

    fn read_archive(&self, n: u64) -> std::io::Result<Vec<u8>> {
        let path = self.dir.join(format!("wal.{n}.archive"));
        match std::fs::read(&path) {
            Ok(b) => Ok(b),
            Err(e) if e.kind() == std::io::ErrorKind::NotFound => Ok(vec![]),
            Err(e) => Err(e),
        }
    }

    fn archive_wal(&mut self, n: u64) -> std::io::Result<()> {
        let wal_path = self.path(FileId::Wal);
        let archive_path = self.dir.join(format!("wal.{n}.archive"));
        std::fs::rename(&wal_path, &archive_path)?;
        sync_dir(&self.dir)
    }

    fn delete_archive(&mut self, n: u64) -> std::io::Result<()> {
        let path = self.dir.join(format!("wal.{n}.archive"));
        match std::fs::remove_file(&path) {
            Ok(()) => sync_dir(&self.dir),
            Err(e) if e.kind() == std::io::ErrorKind::NotFound => Ok(()),
            Err(e) => Err(e),
        }
    }

    fn read_horizon_floor(&self) -> std::io::Result<u64> {
        let path = self.dir.join("wal.floor");
        match std::fs::read(&path) {
            Ok(b) if b.len() >= 8 => Ok(u64::from_le_bytes([
                b[0], b[1], b[2], b[3], b[4], b[5], b[6], b[7],
            ])),
            Ok(_) => Ok(0),
            Err(e) if e.kind() == std::io::ErrorKind::NotFound => Ok(0),
            Err(e) => Err(e),
        }
    }

    fn write_horizon_floor(&mut self, floor: u64) -> std::io::Result<()> {
        let tmp = self.dir.join("wal.floor.tmp");
        {
            let mut f = File::create(&tmp)?;
            f.write_all(&floor.to_le_bytes())?;
            full_sync(&f)?;
        }
        std::fs::rename(&tmp, self.dir.join("wal.floor"))?;
        sync_dir(&self.dir)
    }

    fn has_genesis_marker(&self) -> bool {
        self.dir.join("wal.genesis").exists()
    }

    fn write_genesis_marker(&mut self) -> std::io::Result<()> {
        let path = self.dir.join("wal.genesis");
        {
            let mut f = File::create(&path)?;
            f.write_all(b"")?;
            full_sync(&f)?;
        }
        sync_dir(&self.dir)
    }

    fn delete_genesis_marker(&mut self) -> std::io::Result<()> {
        match std::fs::remove_file(self.dir.join("wal.genesis")) {
            Ok(()) => sync_dir(&self.dir),
            Err(e) if e.kind() == std::io::ErrorKind::NotFound => Ok(()),
            Err(e) => Err(e),
        }
    }
}

fn full_sync(file: &File) -> std::io::Result<()> {
    #[cfg(target_os = "macos")]
    {
        use std::os::unix::io::AsRawFd;
        let fd = file.as_raw_fd();
        let rc = unsafe { libc::fcntl(fd, libc::F_FULLFSYNC) };
        if rc == -1 {
            return Err(std::io::Error::last_os_error());
        }
        Ok(())
    }
    #[cfg(not(target_os = "macos"))]
    {
        file.sync_all()
    }
}

/// Sync the WAL file at `dir/wal.bin` to persistent storage without
/// requiring a `&mut Fs`.  Used by the group-commit drain thread to fsync
/// outside the exclusive write-lock window (reducing reader-visible latency).
///
/// On macOS, uses `F_FULLFSYNC` for true durability.  On other platforms,
/// falls back to `fdatasync` / `fsync`.  Returns `Ok(())` if the WAL file
/// does not exist (nothing to sync).
pub fn sync_wal_at(dir: &std::path::Path) -> std::io::Result<()> {
    let path = dir.join(FileId::Wal.name());
    let f = match std::fs::File::open(&path) {
        Ok(f) => f,
        Err(e) if e.kind() == std::io::ErrorKind::NotFound => return Ok(()),
        Err(e) => return Err(e),
    };
    full_sync(&f)
}

/// Truncate the WAL file at `dir/wal.bin` to exactly `len` bytes and fsync
/// the truncation to persistent storage.
///
/// Used by the group-commit drain thread when a group fsync fails: truncating
/// the WAL back to the last known-good synced offset removes the unsynced
/// frames, ensuring a crash-then-replay cannot silently make the failed group
/// durable via a later successful fsync flushing the whole inode.
///
/// Returns `Ok(())` if the file does not exist (nothing to truncate).
pub fn truncate_wal_at(dir: &std::path::Path, len: u64) -> std::io::Result<()> {
    let path = dir.join(FileId::Wal.name());
    let f = match OpenOptions::new().write(true).open(&path) {
        Ok(f) => f,
        Err(e) if e.kind() == std::io::ErrorKind::NotFound => return Ok(()),
        Err(e) => return Err(e),
    };
    f.set_len(len)?;
    f.sync_all() // plain sync_all is sufficient for a truncation barrier
}

fn sync_dir(dir: &std::path::Path) -> std::io::Result<()> {
    let d = File::open(dir)?;
    d.sync_all()
}

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

    fn tmp() -> std::path::PathBuf {
        let d = std::env::temp_dir().join(format!("graphdb-fs-{}", std::process::id()));
        let _ = std::fs::remove_dir_all(&d);
        d
    }

    #[test]
    fn append_read_and_atomic_write() {
        let mut fs = RealFs::new(&tmp()).unwrap();
        assert_eq!(fs.read(FileId::Wal).unwrap(), Vec::<u8>::new()); // absent = empty
        fs.append(FileId::Wal, b"ab").unwrap();
        fs.append(FileId::Wal, b"cd").unwrap();
        fs.sync(FileId::Wal).unwrap();
        assert_eq!(fs.read(FileId::Wal).unwrap(), b"abcd");
        fs.write_atomic(FileId::Snapshot, b"snap1").unwrap();
        fs.write_atomic(FileId::Snapshot, b"snap2").unwrap(); // replaces
        assert_eq!(fs.read(FileId::Snapshot).unwrap(), b"snap2");
        fs.write_atomic(FileId::Wal, b"").unwrap(); // truncation path
        assert_eq!(fs.read(FileId::Wal).unwrap(), Vec::<u8>::new());
    }

    #[test]
    fn write_atomic_replaces_and_still_readable() {
        // existing append_read_and_atomic_write already covers replace;
        // keep it; dir-sync is best-effort observable only via crash tests.
        // Do not fake F_FULLFSYNC in SimFs.
        let d = std::env::temp_dir().join(format!("graphdb-fs-atomic-{}", std::process::id()));
        let _ = std::fs::remove_dir_all(&d);
        let mut fs = RealFs::new(&d).unwrap();
        fs.write_atomic(FileId::Snapshot, b"snap1").unwrap();
        fs.write_atomic(FileId::Snapshot, b"snap2").unwrap();
        assert_eq!(fs.read(FileId::Snapshot).unwrap(), b"snap2");
    }
}