mecha-core 0.1.3

//! `~/.mecha/work/<producer>/` — where a run's generated output goes.
//!
//! Two directories, and they mean opposite things:
//!
//! ```text
//! ~/.mecha/work/<producer>/     generated · mutable · disposable · cleanable
//! ~/.mecha/bundles/<id>/<ver>/  published · immutable · versioned · never deleted
//! ```
//!
//! A *producer* is whatever made the output: a trigger's name, or `chat`, or a
//! session id. The directory is **stable across runs of the same producer**,
//! which is the whole point — yesterday's briefing is an ordinary file in
//! today's run rather than something that has to be fetched back from
//! somewhere. It is also the run's workspace, and that fixes three things at
//! once:
//!
//! - **The jail default.** A trigger with no explicit workspace fell through to
//!   `std::env::current_dir()`, and the daemon's unit sets
//!   `WorkingDirectory=%h`. So an unattended run with filesystem tools was
//!   path-jailed to `$HOME`, which contains `~/.mecha/` — the mail OAuth
//!   tokens, every session transcript, the learning store. Rooting it here
//!   roots it somewhere holding nothing sensitive. (The interactive half of
//!   that hazard is [`ensure_outside_mecha_home`].)
//! - **Cross-run read-back**, as above.
//! - **`notify`.** The shipped morning trigger ended with
//!   `mkdir -p ~/.mecha/briefings && cat > …` — a shell redirect into a
//!   directory it created on the way past, outside every path jail, so no
//!   later run could read it. That existed only because there was no
//!   designated place to write.
//!
//! **Retention is a policy, not an intention.** Anything without one becomes a
//! pile nobody opens, so [`clean`] keeps the last *N* entries per producer and
//! says what it removed. One hard rule: it never removes anything a published
//! bundle names as a source, because "regenerate last week's report" must not
//! silently lose its input.

use anyhow::{Context, Result};
use std::collections::BTreeSet;
use std::path::{Path, PathBuf};

/// How many entries per producer survive a [`clean`] that does not say.
///
/// Enough to hold a week and a half of a daily producer, so "what did
/// yesterday's run say" and "what changed since Monday" are both still on
/// disk. A placeholder in the honest sense: it wants a week of real output to
/// tune, and `[work] keep` in config is where that tuning goes.
pub const DEFAULT_KEEP: usize = 10;

/// `~/.mecha`, or `$MECHA_HOME`.
///
/// The override exists for tests and for anyone running two mechas side by
/// side; nothing in a normal install sets it.
pub fn mecha_home() -> Result<PathBuf> {
    if let Ok(dir) = std::env::var("MECHA_HOME") {
        if !dir.is_empty() {
            return Ok(PathBuf::from(dir));
        }
    }
    let home = dirs::home_dir().context("cannot determine home directory")?;
    Ok(home.join(".mecha"))
}

/// `~/.mecha/work`.
pub fn root() -> Result<PathBuf> {
    Ok(mecha_home()?.join("work"))
}

/// `~/.mecha/bundles` — the published mirror. Written by the publisher, read
/// here only to find out what [`clean`] must not remove.
pub fn bundles_root() -> Result<PathBuf> {
    Ok(mecha_home()?.join("bundles"))
}

/// A producer name is a directory name, a CLI argument and a log line. Keep it
/// to what is unambiguous in all three — the same rule trigger names follow,
/// because a trigger name *is* a producer name.
pub fn valid_producer(name: &str) -> Result<()> {
    anyhow::ensure!(!name.is_empty(), "a producer needs a name");
    anyhow::ensure!(
        name.len() <= 64,
        "producer name `{name}` is too long (64 characters max)"
    );
    anyhow::ensure!(
        name.chars()
            .all(|c| c.is_ascii_lowercase() || c.is_ascii_digit() || c == '-' || c == '_'),
        "producer name `{name}` may only contain lowercase letters, digits, `-` and `_`"
    );
    Ok(())
}

/// The directory for one producer, without creating it.
pub fn producer_dir(producer: &str) -> Result<PathBuf> {
    valid_producer(producer)?;
    Ok(root()?.join(producer))
}

/// The directory for one producer, created if absent.
///
/// Owner-only like every other directory under `~/.mecha`: a run's scratch
/// output is as private as the transcript it came from.
pub fn ensure(producer: &str) -> Result<PathBuf> {
    let dir = producer_dir(producer)?;
    crate::create_private_dir(&dir).with_context(|| format!("creating {}", dir.display()))?;
    Ok(dir)
}

/// Refuse a workspace that **contains** the mecha home.
///
/// `$HOME` contains `~/.mecha`, so a run started there is jailed over the mail
/// OAuth tokens, every session transcript and the learning store — which is
/// close to no jail at all, and is the silently-degrading-sandbox shape this
/// project keeps naming. The interlock is still a backstop (reading a token
/// arms `private_data`, and exfiltration needs an `external_send` it refuses),
/// but a backstop is not a boundary.
///
/// Note the direction. A workspace *inside* the mecha home is fine and is in
/// fact the new default — `~/.mecha/work/morning/` holds nothing sensitive.
/// What is refused is a workspace the mecha home sits *under*.
pub fn ensure_outside_mecha_home(workspace: &Path) -> Result<()> {
    let home = mecha_home()?;
    // The home may not exist yet on a first run, and a path that cannot be
    // canonicalized is compared as written — over-refusing a workspace is
    // recoverable, under-refusing one is the bug.
    let home = home.canonicalize().unwrap_or(home);
    let workspace_c = workspace.canonicalize();
    let ws = workspace_c.as_deref().unwrap_or(workspace);
    if home.starts_with(ws) {
        anyhow::bail!(
            "workspace {} contains the mecha home ({}), so the path jail would \
             cover the mail tokens, every session transcript and the learning \
             store.\n\
             Run from a project directory instead, or name one explicitly with \
             `--workspace <dir>`.",
            ws.display(),
            home.display()
        );
    }
    Ok(())
}

/// One producer's directory, as [`list`] reports it.
#[derive(Debug, Clone)]
pub struct Producer {
    pub name: String,
    pub path: PathBuf,
    /// Top-level entries, newest first.
    pub entries: Vec<Entry>,
    pub bytes: u64,
}

/// One top-level entry in a producer's directory. A run's output may be a file
/// or a directory (a rendered bundle is a directory), so retention counts
/// entries rather than files.
#[derive(Debug, Clone)]
pub struct Entry {
    pub path: PathBuf,
    pub modified: std::time::SystemTime,
    pub bytes: u64,
    pub is_dir: bool,
}

/// Every producer with a directory, alphabetically.
pub fn list() -> Result<Vec<Producer>> {
    let root = root()?;
    if !root.is_dir() {
        return Ok(Vec::new());
    }
    let mut out = Vec::new();
    for dir_entry in std::fs::read_dir(&root)? {
        let path = dir_entry?.path();
        if !path.is_dir() {
            continue;
        }
        let name = match path.file_name().and_then(|n| n.to_str()) {
            Some(n) => n.to_string(),
            None => continue,
        };
        let entries = entries_of(&path)?;
        let bytes = entries.iter().map(|e| e.bytes).sum();
        out.push(Producer {
            name,
            path,
            entries,
            bytes,
        });
    }
    out.sort_by(|a, b| a.name.cmp(&b.name));
    Ok(out)
}

/// A producer's top-level entries, newest first.
fn entries_of(dir: &Path) -> Result<Vec<Entry>> {
    let mut out = Vec::new();
    for entry in std::fs::read_dir(dir)? {
        let entry = entry?;
        let path = entry.path();
        let meta = entry.metadata()?;
        let is_dir = meta.is_dir();
        out.push(Entry {
            modified: meta.modified().unwrap_or(std::time::UNIX_EPOCH),
            bytes: if is_dir { dir_bytes(&path) } else { meta.len() },
            path,
            is_dir,
        });
    }
    // Newest first, with the path as a tiebreak so a `clean` is deterministic
    // when two entries share a timestamp — which they will, since a single run
    // writes them.
    out.sort_by(|a, b| b.modified.cmp(&a.modified).then(a.path.cmp(&b.path)));
    Ok(out)
}

fn dir_bytes(dir: &Path) -> u64 {
    let mut total = 0;
    let Ok(read) = std::fs::read_dir(dir) else {
        return 0;
    };
    for entry in read.flatten() {
        let Ok(meta) = entry.metadata() else { continue };
        total += if meta.is_dir() {
            dir_bytes(&entry.path())
        } else {
            meta.len()
        };
    }
    total
}

/// Paths a published bundle names as its source, which [`clean`] must never
/// remove.
///
/// The contract with the publisher, and it is deliberately one field of data
/// rather than a shared type: a mirrored version directory
/// (`~/.mecha/bundles/<id>/<ver>/`) may carry a `bundle.json` with a
/// `"sources": ["<absolute path>", …]` array naming what it was rendered from.
/// Anything else in that file is the publisher's business. A mirror that does
/// not exist yet — which is every install until `mecha-factory-publish` is
/// wired — protects nothing, and that is correct rather than a stub.
pub fn protected_sources() -> Result<BTreeSet<PathBuf>> {
    let mut out = BTreeSet::new();
    let root = bundles_root()?;
    if !root.is_dir() {
        return Ok(out);
    }
    for bundle in std::fs::read_dir(&root)?.flatten() {
        let Ok(versions) = std::fs::read_dir(bundle.path()) else {
            continue;
        };
        for version in versions.flatten() {
            let manifest = version.path().join("bundle.json");
            let Ok(text) = std::fs::read_to_string(&manifest) else {
                continue;
            };
            let Ok(value) = serde_json::from_str::<serde_json::Value>(&text) else {
                tracing::warn!("unreadable bundle manifest {}", manifest.display());
                continue;
            };
            let Some(sources) = value.get("sources").and_then(|s| s.as_array()) else {
                continue;
            };
            for source in sources.iter().filter_map(|s| s.as_str()) {
                let path = PathBuf::from(source);
                out.insert(path.canonicalize().unwrap_or(path));
            }
        }
    }
    Ok(out)
}

/// What a [`clean`] did, or would do.
#[derive(Debug, Default)]
pub struct CleanReport {
    pub removed: Vec<Entry>,
    /// Entries that were past the keep window but survive because a published
    /// bundle names them. Reported rather than silent — an unexplained
    /// survivor reads as a bug in the retention.
    pub protected: Vec<Entry>,
    pub dry_run: bool,
}

impl CleanReport {
    pub fn bytes_removed(&self) -> u64 {
        self.removed.iter().map(|e| e.bytes).sum()
    }
}

/// Keep the `keep` most recent entries in each producer's directory and remove
/// the rest.
///
/// `only` restricts it to one producer. The producer directories themselves are
/// never removed: a producer with nothing left in it is an empty directory, not
/// an absence, and deleting it would make tomorrow's run recreate it.
pub fn clean(keep: usize, only: Option<&str>, dry_run: bool) -> Result<CleanReport> {
    let protected = protected_sources()?;
    let mut report = CleanReport {
        dry_run,
        ..Default::default()
    };
    for producer in list()? {
        if only.is_some_and(|name| name != producer.name) {
            continue;
        }
        for entry in producer.entries.into_iter().skip(keep) {
            let canonical = entry
                .path
                .canonicalize()
                .unwrap_or_else(|_| entry.path.clone());
            if protected.contains(&canonical) {
                report.protected.push(entry);
                continue;
            }
            if !dry_run {
                let removed = if entry.is_dir {
                    std::fs::remove_dir_all(&entry.path)
                } else {
                    std::fs::remove_file(&entry.path)
                };
                removed.with_context(|| format!("removing {}", entry.path.display()))?;
            }
            report.removed.push(entry);
        }
    }
    Ok(report)
}

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

    /// `MECHA_HOME` is process-global, so the tests that set it hold one lock
    /// and restore it. Cheaper than threading a root parameter through an API
    /// whose whole job is to know where the mecha home is.
    static ENV: std::sync::Mutex<()> = std::sync::Mutex::new(());

    struct HomeGuard {
        _lock: std::sync::MutexGuard<'static, ()>,
        previous: Option<String>,
        dir: PathBuf,
    }

    impl HomeGuard {
        fn new() -> Self {
            let lock = ENV.lock().unwrap_or_else(|e| e.into_inner());
            let previous = std::env::var("MECHA_HOME").ok();
            let dir = std::env::temp_dir().join(format!("mecha-work-{}", uuid::Uuid::new_v4()));
            std::fs::create_dir_all(&dir).unwrap();
            std::env::set_var("MECHA_HOME", &dir);
            HomeGuard {
                _lock: lock,
                previous,
                dir,
            }
        }
    }

    impl Drop for HomeGuard {
        fn drop(&mut self) {
            match &self.previous {
                Some(v) => std::env::set_var("MECHA_HOME", v),
                None => std::env::remove_var("MECHA_HOME"),
            }
            let _ = std::fs::remove_dir_all(&self.dir);
        }
    }

    /// Write a file with a modification time `age` seconds in the past, so the
    /// ordering under test is the one being asserted rather than whatever the
    /// filesystem's timestamp granularity happened to record for four writes
    /// in the same millisecond.
    fn write_aged(dir: &Path, name: &str, age: i64) {
        use std::os::unix::ffi::OsStrExt;
        let path = dir.join(name);
        std::fs::write(&path, name).unwrap();
        let c = std::ffi::CString::new(path.as_os_str().as_bytes()).unwrap();
        let when = libc::timeval {
            tv_sec: 1_700_000_000 - age,
            tv_usec: 0,
        };
        let times = [when, when];
        // SAFETY: a valid NUL-terminated path and a two-element timeval array,
        // which is exactly what utimes(2) takes.
        assert_eq!(unsafe { libc::utimes(c.as_ptr(), times.as_ptr()) }, 0);
    }

    #[test]
    fn a_producer_directory_is_stable_and_private() {
        let home = HomeGuard::new();
        let first = ensure("morning").unwrap();
        let second = ensure("morning").unwrap();
        assert_eq!(first, second, "the same producer gets the same directory");
        assert_eq!(first, home.dir.join("work").join("morning"));
        #[cfg(unix)]
        {
            use std::os::unix::fs::PermissionsExt;
            let mode = std::fs::metadata(&first).unwrap().permissions().mode();
            assert_eq!(mode & 0o777, 0o700, "owner-only, like every ~/.mecha leaf");
        }
    }

    #[test]
    fn a_producer_name_that_is_not_a_safe_directory_name_is_refused() {
        let _home = HomeGuard::new();
        for bad in ["", "../escape", "has space", "Upper", "a/b"] {
            assert!(
                producer_dir(bad).is_err(),
                "`{bad}` should not be a producer name"
            );
        }
        assert!(producer_dir("morning-brief_2").is_ok());
    }

    /// The bug this whole module exists to close: a workspace that contains
    /// `~/.mecha` jails over the mail tokens and the transcripts. Fails on the
    /// old behaviour, which accepted any directory that existed.
    #[test]
    fn a_workspace_containing_the_mecha_home_is_refused() {
        let home = HomeGuard::new();
        let parent = home.dir.parent().unwrap();

        let err = ensure_outside_mecha_home(parent).unwrap_err().to_string();
        assert!(
            err.contains("contains the mecha home"),
            "unexpected message: {err}"
        );
        assert!(
            err.contains("--workspace"),
            "the message names the fix: {err}"
        );

        // The home itself contains itself, and holds the secrets directly.
        assert!(ensure_outside_mecha_home(&home.dir).is_err());
    }

    /// And the direction that must stay allowed, or the new default workspace
    /// would refuse itself.
    #[test]
    fn a_workspace_inside_the_mecha_home_is_allowed() {
        let _home = HomeGuard::new();
        let work = ensure("morning").unwrap();
        ensure_outside_mecha_home(&work).unwrap();
    }

    #[test]
    fn clean_keeps_the_newest_n_per_producer_and_reports_what_it_removed() {
        let _home = HomeGuard::new();
        let morning = ensure("morning").unwrap();
        let evening = ensure("evening").unwrap();
        for (i, name) in ["a.md", "b.md", "c.md", "d.md"].iter().enumerate() {
            write_aged(&morning, name, i as i64 * 100);
            write_aged(&evening, name, i as i64 * 100);
        }

        let preview = clean(2, None, true).unwrap();
        assert_eq!(preview.removed.len(), 4, "two producers, two stale each");
        assert!(
            morning.join("d.md").exists(),
            "a dry run removes nothing at all"
        );

        let report = clean(2, Some("morning"), false).unwrap();
        let removed: Vec<_> = report
            .removed
            .iter()
            .map(|e| e.path.file_name().unwrap().to_str().unwrap())
            .collect();
        assert_eq!(removed, ["c.md", "d.md"], "the two oldest, newest kept");
        assert!(morning.join("a.md").exists());
        assert!(morning.join("b.md").exists());
        assert!(
            evening.join("d.md").exists(),
            "`--producer` restricts the sweep"
        );
        assert!(morning.is_dir(), "the producer directory itself survives");
    }

    /// The one hard rule: an input a published bundle names is not scratch,
    /// however old it is.
    #[test]
    fn clean_never_removes_a_published_bundles_source() {
        let home = HomeGuard::new();
        let work = ensure("morning").unwrap();
        for (i, name) in ["new.md", "old.md"].iter().enumerate() {
            write_aged(&work, name, i as i64 * 100);
        }
        let source = work.join("old.md").canonicalize().unwrap();

        let version = home.dir.join("bundles").join("brief").join("3");
        std::fs::create_dir_all(&version).unwrap();
        std::fs::write(
            version.join("bundle.json"),
            serde_json::json!({ "sources": [source] }).to_string(),
        )
        .unwrap();

        let report = clean(1, None, false).unwrap();
        assert!(
            report.removed.is_empty(),
            "nothing was eligible but the source"
        );
        assert_eq!(report.protected.len(), 1);
        assert!(work.join("old.md").exists());
    }

    /// A mirror that does not exist protects nothing, and must not be an error
    /// — that is every install until the publisher is wired.
    #[test]
    fn no_bundle_mirror_means_no_protected_sources() {
        let _home = HomeGuard::new();
        assert!(protected_sources().unwrap().is_empty());
    }
}