//! Helpers more than one op family uses: agent-name validation and the
//! `h-` container prefix, the credential-name charset, and [`StagedFile`],
//! the no-follow write-then-rename every root-side file write goes through.

use std::os::fd::{AsRawFd as _, FromRawFd as _, OwnedFd};
use std::path::{Path, PathBuf};

use anyhow::{Context as _, Result, bail};
use hive_priv_sock::AGENT_PREFIX;

/// Return the system container name for a logical agent name.
/// All agents (including the manager) use the `h-` prefix.
///
/// **This prefix is what confines the lifecycle verbs to agent containers** —
/// not their name validation, which only checks characters. A caller cannot
/// name `hive-forge` and reach it: it becomes `h-hive-forge`. No lifecycle
/// verb takes a sibling name: the forge and matrix are swarm services a hive
/// does not start or stop, and the gateway is reached through
/// [`hive_priv_sock::PrivRequest::ControlInfraContainer`] and the
/// [`hive_priv_sock::InfraContainer`] enum.
pub(crate) fn container_system_name(name: &str) -> String {
    format!("{AGENT_PREFIX}{name}")
}

/// Validate a logical agent name (the name hive-c0re uses internally,
/// before the `h-` container prefix is applied).
pub(crate) fn validate_agent_name(name: &str) -> Result<()> {
    validate_name_chars(name)?;
    Ok(())
}

pub(crate) fn validate_name_chars(name: &str) -> Result<()> {
    if name.is_empty()
        || !name
            .chars()
            .all(|c| c.is_ascii_lowercase() || c.is_ascii_digit() || c == '-')
    {
        bail!("invalid name {name:?}: must be non-empty lowercase ascii + digits + hyphens");
    }
    Ok(())
}

/// A systemd credential id must be a short token — restrict to
/// `[A-Za-z0-9_-]` (no `.`) so it can't inject extra `--load-credential`
/// argv or break the `name:path` shape. `.` is deliberately excluded, not
/// just a bare `..`: this name gets interpolated into filesystem paths
/// (snapshot labels) and there's no legitimate need for a dot in either a
/// systemd credential id or a `hive-`-prefixed snapshot label — we're
/// defining this token format from scratch, so keep it maximally strict
/// rather than allow-then-patch each traversal-adjacent character
/// (mara: "we are making up the rules here, lets go strict").
pub(crate) fn validate_credential_name(name: &str) -> Result<()> {
    if name.is_empty()
        || !name
            .bytes()
            .all(|b| b.is_ascii_alphanumeric() || matches!(b, b'_' | b'-'))
    {
        bail!("invalid credential name {name:?}: must be non-empty [A-Za-z0-9_-]");
    }
    Ok(())
}

/// A leaf safe to join onto an agent-owned directory: one plain component, so
/// it can neither climb out of the directory nor name the directory itself.
pub(crate) fn ensure_plain_filename(who: &str, filename: &str) -> Result<()> {
    if filename.is_empty() || filename == "." || filename == ".." || filename.contains('/') {
        bail!("{who}: refusing non-plain filename {filename:?}");
    }
    Ok(())
}

/// Name the content is written under before being renamed onto `filename`,
/// unique per call so two concurrent writes of one file never share a temp.
///
/// The leading dot and the `.partial` suffix are load-bearing: a reader
/// globbing on a published name's prefix, or systemd reading `*.conf` out of
/// `tmpfiles.d` and drop-in dirs, cannot pick up a half-written temp.
fn partial_name(filename: &str) -> String {
    use std::sync::atomic::{AtomicU64, Ordering};
    static SEQ: AtomicU64 = AtomicU64::new(0);
    let n = SEQ.fetch_add(1, Ordering::Relaxed);
    format!(".{filename}.{}-{n}.partial", std::process::id())
}

/// Open `path` as a directory fd for [`StagedFile`] to work relative to.
pub(crate) fn open_dir(path: &Path) -> Result<std::fs::File> {
    use std::os::unix::fs::OpenOptionsExt as _;
    std::fs::OpenOptions::new()
        .read(true)
        .custom_flags(libc::O_DIRECTORY)
        .open(path)
        .with_context(|| format!("open directory {}", path.display()))
}

/// A file written under a [`partial_name`] in its destination directory and
/// then renamed onto its final name, so a reader sees either the old file or
/// the complete new one, never a partial or wrong-mode one. Mode, and owner
/// when the caller `fchown`s [`file`](Self::file), are on the inode before the
/// rename makes it visible.
///
/// Every step is relative to the `dir` fd, so it is safe in a directory an
/// agent or container controls: the temp is created `O_EXCL|O_NOFOLLOW`, which
/// refuses any entry already planted at its name, and `rename` replaces
/// whatever sits at the final name without following it.
///
/// Dropped without [`publish`](Self::publish), it unlinks the temp, so a
/// failure between the two leaves the old file untouched and no residue.
pub(crate) struct StagedFile<'a> {
    dir: &'a std::fs::File,
    tmp: std::ffi::CString,
    dest: std::ffi::CString,
    dest_path: PathBuf,
    file: std::fs::File,
    published: bool,
}

impl<'a> StagedFile<'a> {
    /// Create the temp at `mode` and write `content` to it. The mode is set
    /// again on the fd after the write, so the umask cannot change it.
    pub(crate) fn write(
        dir: &'a std::fs::File,
        dir_path: &Path,
        filename: &str,
        content: &[u8],
        mode: u32,
    ) -> Result<Self> {
        use std::io::Write as _;
        use std::os::unix::fs::PermissionsExt as _;

        ensure_plain_filename("StagedFile::write", filename)?;
        let dest_path = dir_path.join(filename);
        let tmp_name = partial_name(filename);
        let tmp = std::ffi::CString::new(tmp_name.as_str())
            .with_context(|| format!("NUL in filename {filename:?}"))?;
        let dest = std::ffi::CString::new(filename)
            .with_context(|| format!("NUL in filename {filename:?}"))?;
        // SAFETY: `dir` is an open directory fd and `tmp` is NUL-terminated;
        // the result is checked before it is wrapped.
        let fd = unsafe {
            libc::openat(
                dir.as_raw_fd(),
                tmp.as_ptr(),
                libc::O_WRONLY | libc::O_CREAT | libc::O_EXCL | libc::O_NOFOLLOW | libc::O_CLOEXEC,
                mode,
            )
        };
        if fd < 0 {
            return Err(std::io::Error::last_os_error())
                .with_context(|| format!("create {}", dir_path.join(&tmp_name).display()));
        }
        // SAFETY: `fd` is a fresh, valid fd that nothing else owns.
        let file = std::fs::File::from(unsafe { OwnedFd::from_raw_fd(fd) });
        let mut staged = Self {
            dir,
            tmp,
            dest,
            dest_path,
            file,
            published: false,
        };
        staged
            .file
            .write_all(content)
            .with_context(|| format!("write {}", staged.dest_path.display()))?;
        staged
            .file
            .set_permissions(std::fs::Permissions::from_mode(mode))
            .with_context(|| format!("chmod {mode:o} {}", staged.dest_path.display()))?;
        Ok(staged)
    }

    /// The temp's open fd, for an `fchown` that must land before publishing.
    pub(crate) fn file(&self) -> &std::fs::File {
        &self.file
    }

    /// Flush the content, rename the temp onto the final name, and flush the
    /// directory: without the last step a crash can lose the rename itself.
    pub(crate) fn publish(mut self) -> Result<()> {
        self.file
            .sync_all()
            .with_context(|| format!("fsync {}", self.dest_path.display()))?;
        let fd = self.dir.as_raw_fd();
        // SAFETY: `fd` is an open directory fd; both names are NUL-terminated.
        if unsafe { libc::renameat(fd, self.tmp.as_ptr(), fd, self.dest.as_ptr()) } != 0 {
            return Err(std::io::Error::last_os_error())
                .with_context(|| format!("publishing {}", self.dest_path.display()));
        }
        self.published = true;
        self.dir
            .sync_all()
            .with_context(|| format!("fsync directory of {}", self.dest_path.display()))
    }
}

impl Drop for StagedFile<'_> {
    fn drop(&mut self) {
        if self.published {
            return;
        }
        // SAFETY: `self.dir` is an open directory fd; `self.tmp` is
        // NUL-terminated.
        if unsafe { libc::unlinkat(self.dir.as_raw_fd(), self.tmp.as_ptr(), 0) } != 0 {
            tracing::warn!(
                dest = %self.dest_path.display(),
                error = %std::io::Error::last_os_error(),
                "failed to remove unpublished temp"
            );
        }
    }
}

/// Scratch-directory helpers shared by every module's tests. One counter for
/// the whole crate, so no two tests get the same directory.
#[cfg(test)]
pub(crate) mod test_support {
    use std::path::PathBuf;
    use std::sync::atomic::{AtomicU32, Ordering};

    /// Unique scratch dir per test, no external tempfile dep.
    pub(crate) fn scratch() -> PathBuf {
        static CTR: AtomicU32 = AtomicU32::new(0);
        let n = CTR.fetch_add(1, Ordering::Relaxed);
        let dir = std::env::temp_dir().join(format!(
            "hive-priv-nofollow-test-{}-{n}",
            std::process::id()
        ));
        std::fs::create_dir_all(&dir).unwrap();
        dir
    }

    /// Names in `dir`, sorted — the residue check every publish test ends on.
    pub(crate) fn entries(dir: &PathBuf) -> Vec<String> {
        let mut v: Vec<String> = std::fs::read_dir(dir)
            .unwrap()
            .map(|e| e.unwrap().file_name().to_string_lossy().into_owned())
            .collect();
        v.sort();
        v
    }
}

#[cfg(test)]
mod tests {
    use super::test_support::{entries, scratch};
    use super::{
        StagedFile, ensure_plain_filename, open_dir, partial_name, validate_credential_name,
    };

    /// The temp name is the whole reason the rename is safe to watch: a
    /// `systemd.path` unit globbing `matrix-token*` would fire on a temp that
    /// merely suffixed the real name, on exactly the empty file the rename
    /// exists to hide.
    #[test]
    fn a_temp_cannot_match_a_glob_on_the_name_it_publishes() {
        for real in ["matrix-token", "matrix-token-alice", "forge-token"] {
            let tmp = partial_name(real);
            assert!(
                !tmp.starts_with(real),
                "{tmp:?} matches a `{real}*` path unit while half-written"
            );
            assert!(!tmp.contains('/'), "temp must stay in the same directory");
        }
    }

    /// Any failure between staging and publishing drops the `StagedFile`.
    /// Until the rename a reader sees only the old file, and afterwards the
    /// old file is still whole and the temp is gone.
    #[test]
    fn a_failed_write_leaves_the_old_file_intact() {
        let dir = scratch();
        let dest = dir.join("hyperhive-limits.conf");
        std::fs::write(&dest, "OLD").unwrap();
        let dir_fd = open_dir(&dir).unwrap();

        let staged =
            StagedFile::write(&dir_fd, &dir, "hyperhive-limits.conf", b"NEW", 0o644).unwrap();
        assert_eq!(std::fs::read_to_string(&dest).unwrap(), "OLD");
        assert_eq!(
            entries(&dir).len(),
            2,
            "control: the temp exists while staged"
        );
        drop(staged);

        assert_eq!(std::fs::read_to_string(&dest).unwrap(), "OLD");
        assert_eq!(entries(&dir), ["hyperhive-limits.conf"], "temp left behind");
        std::fs::remove_dir_all(&dir).ok();
    }

    /// Two overlapping writes of one file each own a temp, so whichever
    /// publishes last lands whole — never the other's bytes, never a mix.
    #[test]
    fn overlapping_writes_of_one_file_never_share_a_temp() {
        let dir = scratch();
        let dir_fd = open_dir(&dir).unwrap();
        let name = "hyperhive-agents.conf";

        let first = StagedFile::write(&dir_fd, &dir, name, b"roster A\n", 0o644).unwrap();
        let second = StagedFile::write(&dir_fd, &dir, name, b"roster B, longer\n", 0o644).unwrap();
        second.publish().unwrap();
        first.publish().unwrap();

        assert_eq!(
            std::fs::read_to_string(dir.join(name)).unwrap(),
            "roster A\n"
        );
        assert_eq!(entries(&dir), [name], "temp left behind");
        std::fs::remove_dir_all(&dir).ok();
    }

    /// The only gate on the root-privileged socket for a `--load-credential`
    /// name. The doc comment is explicit that `.` is excluded on purpose
    /// ("this name gets interpolated into filesystem paths") — a future
    /// "let's allow dots for version numbers" loosening must fail this,
    /// not just the `/` case below.
    #[test]
    fn validate_credential_name_rejects_dot_slash_and_empty_but_allows_the_charset() {
        assert!(
            validate_credential_name("").is_err(),
            "empty must be rejected"
        );
        assert!(validate_credential_name("valid-name_123").is_ok());
        assert!(
            validate_credential_name("bad.name").is_err(),
            "dot must be rejected — see the fn's doc comment"
        );
        assert!(validate_credential_name("bad/name").is_err());
    }

    /// `ensure_plain_filename` is the gate between an agent-writable
    /// directory and a root-privileged file write. `.`/`..` would resolve
    /// to the directory itself or its parent; any `/` climbs into a path
    /// component the caller never named.
    #[test]
    fn ensure_plain_filename_rejects_dot_dotdot_and_any_slash() {
        assert!(ensure_plain_filename("test", ".").is_err());
        assert!(ensure_plain_filename("test", "..").is_err());
        assert!(ensure_plain_filename("test", "sub/dir").is_err());
        assert!(ensure_plain_filename("test", "matrix-token").is_ok());
    }
}