//! The engine seam.
//!
//! Everything ClamAV-specific (version probe, signature freshness, the
//! `clamscan` subprocess + output parsing, `freshclam`) lives behind
//! [`ScanEngine`]. The daemon's `status` / `scan` / `update` RPCs are
//! defined against the trait, so a native Rust engine later — ours or a
//! rewritten ClamAV — plugs in by implementing four methods and flipping
//! the const at the bottom. Nothing on the wire, in the CLI, or in the
//! GUI needs to change.
//!
//! The wire API is deliberately engine-agnostic: `Status.engine`
//! identifies the implementation, and DB freshness travels as a file
//! name + timestamp (any signature store has those two facts).

use anyhow::{Context, Result};
use hound_api::{DbFile, ScanResult};
use std::fs;
use std::process::Command;
use std::sync::OnceLock;

/// What an engine implementation must answer.
///
/// `Send + Sync` because the daemon holds exactly one engine for its
/// whole life and hands it to every connection thread and to the
/// real-time monitor.
pub trait ScanEngine: Send + Sync {
    /// Stable id for the wire (`Status.engine`): "clamav" today, e.g.
    /// "hound-native" when the Rust engine ships.
    fn name(&self) -> &'static str;

    /// Presence + signature-DB freshness. `present` is the tray's
    /// "engine online/offline" signal.
    fn probe(&self) -> (bool, String, Option<DbFile>);

    /// How many detection rules are actually compiled and live.
    ///
    /// The self-check needs this to tell "scanned and found nothing" apart
    /// from "scanned with no rules loaded", which look identical from the
    /// outside and mean opposite things.
    fn rule_count(&self) -> usize {
        0
    }

    /// Scan `path` (canonicalize first) and return per-file findings.
    fn scan(&self, path: &str, recursive: bool) -> Result<ScanResult>;

    /// Refresh the signature store. Returns (success, command label,
    /// combined stdout+stderr tail) for the last attempt made.
    fn update(&self) -> Result<(bool, String, String)>;

    /// Scan bytes already in hand, returning a detection name.
    ///
    /// This exists for the execution gate, which is handed an open
    /// descriptor and must never re-open the path: an `open()` on a
    /// watched mount queues a permission event behind the one being
    /// answered and deadlocks the daemon against itself. Engines that
    /// can only scan paths return `None` and are simply not usable
    /// behind the gate.
    fn scan_bytes(&self, _bytes: &[u8]) -> Option<String> {
        None
    }

    /// Whether a detection may move the file, rather than only report it.
    ///
    /// Defaults to `false`. An engine that does not model this — or a
    /// detection name it does not recognise — must not destroy anything.
    fn may_quarantine(&self, _detection: &str) -> bool {
        false
    }

    /// Answer from memory alone, without reading the file.
    ///
    /// `Some(verdict)` means we have judged this exact file version
    /// before; `None` means it must be scanned. The execution gate uses
    /// this to answer repeat executions without waking a worker, which is
    /// most of the traffic on a machine that is actually doing something.
    fn cached_verdict(&self, _md: &std::fs::Metadata) -> Option<Option<String>> {
        None
    }
}

/// The ClamAV-backed engine: `clamscan` + `freshclam` over their
/// well-behaved text interfaces.
pub struct ClamAvEngine;

impl ScanEngine for ClamAvEngine {
    fn name(&self) -> &'static str {
        "clamav"
    }

    fn probe(&self) -> (bool, String, Option<DbFile>) {
        let version = Command::new("clamscan")
            .arg("--version")
            .output()
            .map(|o| String::from_utf8_lossy(&o.stdout).trim().to_string())
            .unwrap_or_default();
        if version.is_empty() {
            return (false, String::new(), None);
        }
        // freshclam's DB files live in /var/lib/clamav; report the newest.
        let mut newest: Option<(String, std::time::SystemTime)> = None;
        for entry in fs::read_dir("/var/lib/clamav")
            .into_iter()
            .flatten()
            .flatten()
        {
            let path = entry.path();
            if !path
                .extension()
                .is_some_and(|ext| ext == "cld" || ext == "ndb")
            {
                continue;
            }
            let Ok(mtime) = entry.metadata().and_then(|m| m.modified()) else {
                continue;
            };
            let name = path
                .file_name()
                .map(|f| f.to_string_lossy().into_owned())
                .unwrap_or_default();
            let replace = match &newest {
                None => true,
                Some((_, cur)) => mtime > *cur,
            };
            if replace {
                newest = Some((name, mtime));
            }
        }
        match newest {
            Some((file, t)) => {
                let days = std::time::SystemTime::now()
                    .duration_since(t)
                    .map(|d| d.as_secs() / 86_400)
                    .unwrap_or(0);
                (
                    true,
                    format!("signatures updated {days}d ago ({file}) [clamav {version}]"),
                    Some(DbFile {
                        file,
                        updated_at: to_rfc3339(t),
                    }),
                )
            }
            None => (
                true,
                format!("no signature DB found (run: sudo freshclam) [clamav {version}]"),
                None,
            ),
        }
    }

    fn scan(&self, path: &str, recursive: bool) -> Result<ScanResult> {
        let path = fs::canonicalize(path).with_context(|| format!("no such path: {path}"))?;
        let mut cmd = Command::new("clamscan");
        cmd.arg("--no-summary")
            .arg("--stdout")
            .arg("--max-filesize=100M")
            .arg("--max-scansize=250M");
        if recursive {
            cmd.arg("-r");
        }
        cmd.arg("--allmatch").arg(path);

        let out = cmd
            .output()
            .context("running clamscan (is ClamAV installed?)")?;

        Ok(parse_clamscan(
            &out.stdout,
            out.status.code().unwrap_or(-1),
        )?)
    }

    fn update(&self) -> Result<(bool, String, String)> {
        let attempts: [(&str, &[&str]); 2] = [
            ("sudo freshclam", &["sudo", "freshclam", "--no-dns"]),
            ("freshclam", &["freshclam", "--no-dns"]),
        ];

        let (ok, label, out) = if std::env::var_os("HOUNDD_NO_SUDO").is_some() {
            // Daemon already running as root: skip sudo (it would prompt).
            let (label, argv) = attempts[1];
            let (label, out) = run_cmd(label, argv)?;
            (out.status.success(), label, out)
        } else {
            let (label, argv) = attempts[0];
            let (label, out) = run_cmd(label, argv)?;
            if out.status.success() {
                (true, label, out)
            } else {
                // Plain user without group perms: report the honest reason.
                let (label2, argv2) = attempts[1];
                let (label2, out2) = run_cmd(label2, argv2)?;
                (out2.status.success(), label2, out2)
            }
        };

        let mut combined = String::from_utf8_lossy(&out.stdout).to_string();
        if !out.stderr.is_empty() {
            combined.push_str(&String::from_utf8_lossy(&out.stderr));
        }
        Ok((ok, label.to_string(), combined))
    }
}

fn run_cmd(label: &str, argv: &[&str]) -> Result<(String, std::process::Output)> {
    let out = Command::new(argv[0])
        .args(&argv[1..])
        .output()
        .with_context(|| format!("running {label} failed (installed?)"))?;
    Ok((label.to_string(), out))
}

/// Parse `clamscan --stdout` output into findings.
///
/// Every file ClamAV looks at emits exactly one line:
///
/// ```text
/// /abs/path: OK
/// /abs/path: VirusName FOUND
/// /abs/path: INCOMPLETE
/// ```
///
/// We parse those lines (not `--json`) because the text format is stable
/// across ClamAV 0.103 → 1.x while `--json` fields have churned.
/// `--allmatch` reports *every* signature a file matches (EICAR trips 3),
/// so each path is counted once for the scanned total and reported once
/// as a finding.
pub fn parse_clamscan(stdout: &[u8], exit_code: i32) -> Result<ScanResult> {
    use hound_api::Found;
    use std::collections::HashSet;

    let text = String::from_utf8_lossy(stdout);
    let mut found: Vec<Found> = Vec::new();
    let mut seen_files: HashSet<String> = HashSet::new();
    let mut reported: HashSet<String> = HashSet::new();

    for line in text.lines() {
        // A per-file result line starts with the path then ": ".
        let Some(idx) = line.find(": ") else { continue };
        let file = line[..idx].trim();
        if !file.starts_with('/') || file.is_empty() {
            continue;
        }
        seen_files.insert(file.to_string());
        let body = &line[idx + 2..];
        if let Some(end) = body.rfind(" FOUND") {
            let key = file.to_string();
            if reported.insert(key.clone()) {
                found.push(Found {
                    path: key,
                    virus: body[..end].to_string(),
                });
            }
        }
    }

    // 0 = no infections, 1 = infections found, >1 = real error.
    if !(exit_code == 0 || exit_code == 1) {
        anyhow::bail!("clamscan exited {exit_code}");
    }

    let scanned = seen_files.len() as u64;
    let infected = found.len() as u64;
    let clean = scanned.saturating_sub(infected);

    Ok(ScanResult {
        scanned,
        clean,
        infected,
        // clamscan does not tell us what it skipped for size.
        skipped: 0,
        found,
    })
}

/// Format a `SystemTime` as RFC3339 UTC for the wire.
pub fn to_rfc3339(t: std::time::SystemTime) -> String {
    use time::format_description::well_known::Rfc3339;
    let Ok(d) = t.duration_since(std::time::UNIX_EPOCH) else {
        return "unknown".into();
    };
    let Ok(dt) = time::OffsetDateTime::from_unix_timestamp(d.as_secs() as i64) else {
        return "unknown".into();
    };
    dt.format(&Rfc3339).unwrap_or_else(|_| "unknown".into())
}

/// The active engine, chosen once at daemon startup.
///
/// Default is [`HoundEngine`](crate::native::HoundEngine) — yara-x in
/// process. `HOUNDD_ENGINE` overrides it:
///
/// * `clamav` — the legacy `clamscan` subprocess path. Kept so the two
///   can be compared directly, and because it still owns the Windows
///   malware corpus that our own rules deliberately do not cover.
/// * `fake`   — the synthetic engine the E2E test drives, so a full
///   daemon lifecycle can run without ClamAV or a real rule pack.
///
/// The whole point of the trait is that this is the only place the
/// daemon decides *which* engine it serves.
pub fn engine() -> &'static dyn ScanEngine {
    // Selection is per call — one getenv — so the choice stays live and
    // two tests in one process cannot contaminate each other. Only the
    // expensive engine is memoised, below.
    match std::env::var("HOUNDD_ENGINE").as_deref() {
        Ok("fake") => {
            static FAKE: FakeEngine = FakeEngine;
            &FAKE
        }
        Ok("clamav") => {
            static CLAMAV: ClamAvEngine = ClamAvEngine;
            &CLAMAV
        }
        _ => native_engine(),
    }
}

/// The native engine, built exactly once. Compiling the ruleset is the
/// one genuinely expensive thing the daemon does at startup, so it must
/// never happen twice.
fn native_engine() -> &'static dyn ScanEngine {
    static ENGINE: OnceLock<Box<dyn ScanEngine>> = OnceLock::new();
    ENGINE
        .get_or_init(|| match crate::native::HoundEngine::new() {
            Ok(e) => Box::new(e) as Box<dyn ScanEngine>,
            Err(e) => {
                // Losing detection entirely is worse than falling back to
                // the slow path, so say so loudly and carry on.
                eprintln!("engine: rules failed to compile ({e}) — falling back to clamav");
                Box::new(ClamAvEngine)
            }
        })
        .as_ref()
}

/// Test engine: reports itself present, scans anything whose name
/// contains "EICAR" or ".eicar" as infected, and updates cleanly.
/// Lets the E2E test exercise the full wire without ClamAV installed.
pub struct FakeEngine;

impl ScanEngine for FakeEngine {
    fn name(&self) -> &'static str {
        "fake"
    }

    fn probe(&self) -> (bool, String, Option<DbFile>) {
        (
            true,
            "signatures: synthetic [fake]".to_string(),
            Some(DbFile {
                file: "fake.cld".to_string(),
                updated_at: to_rfc3339(std::time::SystemTime::now()),
            }),
        )
    }

    fn scan(&self, path: &str, _recursive: bool) -> Result<ScanResult> {
        use hound_api::Found;
        let path = fs::canonicalize(path).with_context(|| format!("no such path: {path}"))?;
        let infected = path
            .to_string_lossy()
            .to_ascii_lowercase()
            .contains("eicar");
        let found = if infected {
            vec![Found {
                path: path.to_string_lossy().to_string(),
                virus: "Fake-Eicar".to_string(),
            }]
        } else {
            Vec::new()
        };
        let scanned: u64 = 1;
        let infected_u: u64 = if infected { 1 } else { 0 };
        Ok(ScanResult {
            scanned,
            clean: scanned - infected_u,
            infected: infected_u,
            skipped: 0,
            found,
        })
    }

    fn update(&self) -> Result<(bool, String, String)> {
        Ok((
            true,
            "fake update".to_string(),
            "OK: fake DB refreshed\n".to_string(),
        ))
    }
}

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

    #[test]
    fn parses_clean_scan() {
        let out = br"/tmp/a.txt: OK
/tmp/b.txt: OK
";
        let r = parse_clamscan(out, 0).unwrap();
        assert_eq!(r.scanned, 2);
        assert_eq!(r.clean, 2);
        assert_eq!(r.infected, 0);
        assert!(r.found.is_empty());
        assert!(r.is_clean());
    }

    #[test]
    fn parses_infected_scan_dedup_allmatch() {
        // --allmatch: one EICAR file trips several signatures, one line each.
        let out = br"/tmp/eicar.com: Eicar-Test-Signature FOUND\n\
                    /tmp/eicar.com: Test.Virus TWO FOUND\n\
                    /tmp/clean.txt: OK\n";
        let r = parse_clamscan(out, 1).unwrap();
        assert_eq!(r.scanned, 2, "two unique files, not three lines");
        assert_eq!(r.infected, 1, "EICAR must count as one threat");
        assert_eq!(r.clean, 1);
        assert_eq!(r.found.len(), 1);
        assert_eq!(r.found[0].path, "/tmp/eicar.com");
        assert_eq!(r.found[0].virus, "Eicar-Test-Signature");
    }

    #[test]
    fn incomplete_lines_counted_not_infected() {
        let out = br"/tmp/big.bin: INCOMPLETE
/tmp/x: OK
";
        let r = parse_clamscan(out, 0).unwrap();
        assert_eq!(r.scanned, 2);
        assert_eq!(r.infected, 0);
    }

    #[test]
    fn nonzero_exit_is_error() {
        let r = parse_clamscan(b"", 7);
        assert!(r.is_err());
        assert!(r.unwrap_err().to_string().contains("7"));
    }

    #[test]
    fn e2e_eicar_via_real_clamscan() {
        // Skips itself when ClamAV isn't installed (CI boxes).
        let which = Command::new("clamscan").arg("--version").output();
        if which.as_ref().is_err() {
            return;
        }
        let tmp = std::env::temp_dir().join(format!("houndd-engine-test-{}", std::process::id()));
        let _ = fs::create_dir_all(&tmp);
        std::fs::write(
            tmp.join("eicar.bin"),
            "X5O!P%@AP[4\\PZX54(P^)7CC)7}$EICAR-STANDARD-ANTIVIRUS-TEST-FILE!$H+H*",
        )
        .unwrap();
        let engine = ClamAvEngine;
        let r = engine.scan(tmp.to_str().unwrap(), true).unwrap();
        assert_eq!(r.scanned, 1);
        assert_eq!(r.infected, 1);
        assert_eq!(r.found[0].virus, "Eicar-Test-Signature");
        let _ = fs::remove_dir_all(&tmp);
    }

    #[test]
    fn probe_reports_present() {
        let (present, _summary, _db) = ClamAvEngine.probe();
        // CI boxes without ClamAV: presence is whatever the OS says.
        let via_cmd = Command::new("clamscan").arg("--version").output();
        assert_eq!(
            present,
            via_cmd.map(|o| o.status.success()).unwrap_or(false)
        );
    }

    #[test]
    fn trait_is_object_safe() {
        fn take(_e: &dyn ScanEngine) {}
        take(engine());
    }
}