use anyhow::{Context, Result};
use chrono::{DateTime, Utc};
use serde::{Deserialize, Serialize};
use std::fs::{File, OpenOptions};
use std::io::Write;
use std::os::unix::io::AsRawFd;
use std::path::{Path, PathBuf};

/// A single project tracked by claw-store. Persisted as a row in the
/// manifest at `/var/lib/claw-store/projects.toml`.
///
/// `pinned` (added v0.2.0): operator intent flag — when true, GC skips
/// this project for both stale-eviction (`gc_stale_targets`) and LRU
/// eviction (`gc_by_space`). Defaults to `false` via `#[serde(default)]`
/// so older manifests written by the v0.1.x line still parse cleanly.
#[derive(Debug, Clone, Deserialize, Serialize)]
pub struct Project {
    pub name: String, // "org/repo" e.g. "quantumclaw/quantum-pulse"
    pub warm_path: PathBuf,
    pub hot_target_path: PathBuf,
    pub last_build: Option<DateTime<Utc>>,
    pub last_active: Option<DateTime<Utc>>,
    pub last_sync: Option<DateTime<Utc>>,
    #[serde(default)]
    pub pinned: bool,
}

#[derive(Debug, Clone, Deserialize, Serialize, Default)]
pub struct Manifest {
    pub projects: Vec<Project>,
}

impl Manifest {
    /// Read the manifest under a shared (read) flock. Returns
    /// `Self::default()` if the file is missing — the old daemon
    /// behavior on first boot — but propagates parse errors instead
    /// of silently masking them like the pre-v0.2 `unwrap_or_default`
    /// pattern at call sites did.
    pub fn load(path: &Path) -> Result<Self> {
        if !path.exists() {
            return Ok(Self::default());
        }
        let _guard = lock_path(path, LockMode::Shared)
            .with_context(|| format!("flock(LOCK_SH) on {}", path.display()))?;
        let s = std::fs::read_to_string(path)
            .with_context(|| format!("reading manifest at {}", path.display()))?;
        // An empty file is treated as "no projects yet" (matches the
        // not-exists fallthrough above). Bare-init shell ops or a
        // half-written tempfile that crashed pre-rename would otherwise
        // hard-fail the daemon on next startup.
        if s.trim().is_empty() {
            return Ok(Self::default());
        }
        toml::from_str(&s).context("parsing manifest")
    }

    /// Backward-compatible save. Now writes go through a sibling
    /// tempfile + rename so a crash mid-write can't leave a corrupt
    /// half-written TOML where the next reader silently sees an empty
    /// manifest. Takes EX flock on the lock sidecar so a concurrent
    /// writer doesn't race the rename. Prefer `update()` for any
    /// load-then-mutate path — `save()` alone re-introduces the
    /// lost-update window that `update()` closes.
    pub fn save(&self, path: &Path) -> Result<()> {
        if let Some(parent) = path.parent() {
            std::fs::create_dir_all(parent)
                .with_context(|| format!("mkdir -p {}", parent.display()))?;
        }
        let _guard = lock_path(path, LockMode::Exclusive)
            .with_context(|| format!("flock(LOCK_EX) on {}", path.display()))?;
        write_atomic(path, self).context("writing manifest")
    }

    /// Locked load → mutate → save in one transaction.
    ///
    /// Replaces the v0.1 pattern of `let mut m = load(); m.x(); m.save();`
    /// at call sites — that triple was unsafe under any concurrency
    /// (daemon's 5-min poll tick, plus the dashboard shelling out to
    /// `claw-store activate` which itself did load/mutate/save). Two
    /// such triples interleaved would silently drop one writer's
    /// changes.
    ///
    /// Takes an EX flock for the whole transaction, reloads from disk
    /// AFTER acquiring the lock (so we always operate on the latest
    /// state), runs the closure, and atomically renames the resulting
    /// tempfile over the destination. All three steps are inside the
    /// lock so no other writer can race.
    pub fn update(
        path: &Path,
        f: impl FnOnce(&mut Manifest) -> Result<()>,
    ) -> Result<Manifest> {
        if let Some(parent) = path.parent() {
            std::fs::create_dir_all(parent)
                .with_context(|| format!("mkdir -p {}", parent.display()))?;
        }
        let _guard = lock_path(path, LockMode::Exclusive)
            .with_context(|| format!("flock(LOCK_EX) on {}", path.display()))?;
        let mut m = if path.exists() {
            let s = std::fs::read_to_string(path)
                .with_context(|| format!("reading manifest at {}", path.display()))?;
            if s.trim().is_empty() {
                Manifest::default()
            } else {
                toml::from_str(&s).context("parsing manifest")?
            }
        } else {
            Manifest::default()
        };
        f(&mut m)?;
        write_atomic(path, &m).context("writing manifest")?;
        Ok(m)
    }

    pub fn get(&self, name: &str) -> Option<&Project> {
        self.projects.iter().find(|p| p.name == name)
    }

    pub fn get_mut(&mut self, name: &str) -> Option<&mut Project> {
        self.projects.iter_mut().find(|p| p.name == name)
    }

    pub fn upsert(&mut self, project: Project) {
        if let Some(p) = self.get_mut(&project.name.clone()) {
            *p = project;
        } else {
            self.projects.push(project);
        }
    }

    /// Field finding 2026-07-12 (Pi deploy on vision-02): the old
    /// hardcoded `/var/lib/claw-store/projects.toml` broke under
    /// `ProtectSystem=strict` in the user-mode systemd unit because
    /// /var is read-only. Follow the XDG Base Directory spec so a
    /// user-mode install writes under `$HOME/.local/state`, and only
    /// root installs land in `/var/lib`.
    ///
    /// Precedence:
    ///   1. `$XDG_STATE_HOME/claw-store/projects.toml` (per spec)
    ///   2. `$HOME/.local/state/claw-store/projects.toml` (XDG default)
    ///   3. `/var/lib/claw-store/projects.toml` (system fallback)
    pub fn default_path() -> PathBuf {
        if let Ok(xdg) = std::env::var("XDG_STATE_HOME") {
            if !xdg.is_empty() {
                return PathBuf::from(xdg)
                    .join("claw-store")
                    .join("projects.toml");
            }
        }
        if let Ok(home) = std::env::var("HOME") {
            if !home.is_empty() {
                return PathBuf::from(home)
                    .join(".local/state/claw-store/projects.toml");
            }
        }
        PathBuf::from("/var/lib/claw-store/projects.toml")
    }
}

// ── flock + atomic rename helpers ────────────────────────────────────────────

enum LockMode {
    Shared,
    Exclusive,
}

/// RAII flock guard — releases the lock on drop.
struct FlockGuard(File);

impl Drop for FlockGuard {
    fn drop(&mut self) {
        // Best-effort unlock. The kernel releases automatically on
        // close anyway when File drops; we just hint it sooner. Errors
        // here are not actionable.
        unsafe {
            libc::flock(self.0.as_raw_fd(), libc::LOCK_UN);
        }
    }
}

/// Lock a sidecar `.lock` file (so the data file can be replaced by
/// atomic rename without invalidating the lock). Returns a guard that
/// releases on drop.
fn lock_path(target: &Path, mode: LockMode) -> Result<FlockGuard> {
    let lock_path = sidecar_lock_path(target);
    if let Some(parent) = lock_path.parent() {
        std::fs::create_dir_all(parent)?;
    }
    let f = OpenOptions::new()
        .create(true)
        .write(true)
        .truncate(false)
        .open(&lock_path)
        .with_context(|| format!("opening lock {}", lock_path.display()))?;
    let flag = match mode {
        LockMode::Shared => libc::LOCK_SH,
        LockMode::Exclusive => libc::LOCK_EX,
    };
    let rc = unsafe { libc::flock(f.as_raw_fd(), flag) };
    if rc != 0 {
        return Err(std::io::Error::last_os_error()).context("flock");
    }
    Ok(FlockGuard(f))
}

fn sidecar_lock_path(target: &Path) -> PathBuf {
    let mut p = target.as_os_str().to_owned();
    p.push(".lock");
    PathBuf::from(p)
}

/// Atomic write: serialize → write to sibling tempfile in the same dir
/// → fsync → rename(2) into place. The rename is POSIX-atomic on the
/// same filesystem, so a reader sees either the old contents or the
/// new contents, never a torn half-written TOML.
fn write_atomic(path: &Path, manifest: &Manifest) -> Result<()> {
    let s = toml::to_string_pretty(manifest).context("serialising manifest")?;
    let parent = path.parent().unwrap_or_else(|| Path::new("."));
    let mut tmp = tempfile::Builder::new()
        .prefix(".projects.toml.")
        .suffix(".new")
        .tempfile_in(parent)
        .with_context(|| format!("tempfile in {}", parent.display()))?;
    tmp.write_all(s.as_bytes()).context("write tempfile")?;
    tmp.as_file().sync_all().context("fsync tempfile")?;
    tmp.persist(path).map_err(|e| anyhow::anyhow!("rename: {e}"))?;
    Ok(())
}

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

    #[test]
    fn default_path_honours_xdg_state_home() {
        // Field finding 2026-07-12: precedence XDG_STATE_HOME →
        // $HOME/.local/state → /var/lib. Guard: an env-set XDG wins
        // over HOME; empty XDG is treated as unset.
        // NOTE: env mutation is process-global, so this test does its
        // own setup/teardown and doesn't run in parallel with another
        // that touches the same vars.
        let saved_xdg = std::env::var("XDG_STATE_HOME").ok();
        let saved_home = std::env::var("HOME").ok();

        // Case 1: XDG_STATE_HOME wins.
        std::env::set_var("XDG_STATE_HOME", "/tmp/xdg-fake");
        std::env::set_var("HOME", "/tmp/home-fake");
        assert_eq!(
            Manifest::default_path(),
            PathBuf::from("/tmp/xdg-fake/claw-store/projects.toml")
        );

        // Case 2: XDG unset → HOME/.local/state.
        std::env::remove_var("XDG_STATE_HOME");
        assert_eq!(
            Manifest::default_path(),
            PathBuf::from("/tmp/home-fake/.local/state/claw-store/projects.toml")
        );

        // Case 3: empty XDG treated as unset.
        std::env::set_var("XDG_STATE_HOME", "");
        assert_eq!(
            Manifest::default_path(),
            PathBuf::from("/tmp/home-fake/.local/state/claw-store/projects.toml")
        );

        // Restore.
        match saved_xdg {
            Some(v) => std::env::set_var("XDG_STATE_HOME", v),
            None => std::env::remove_var("XDG_STATE_HOME"),
        }
        match saved_home {
            Some(v) => std::env::set_var("HOME", v),
            None => std::env::remove_var("HOME"),
        }
    }

    #[test]
    fn test_roundtrip_manifest() {
        let mut m = Manifest::default();
        m.projects.push(Project {
            name: "kitchen-cash".into(),
            warm_path: "/slab/projects/kitchen-cash".into(),
            hot_target_path: "/hot/targets/kitchen-cash".into(),
            last_build: None,
            last_active: None,
            last_sync: None,
            pinned: false,
        });
        let f = NamedTempFile::new().unwrap();
        m.save(f.path()).unwrap();
        let loaded = Manifest::load(f.path()).unwrap();
        assert_eq!(loaded.projects.len(), 1);
        assert_eq!(loaded.projects[0].name, "kitchen-cash");
    }

    #[test]
    fn test_get_project() {
        let mut m = Manifest::default();
        m.projects.push(Project {
            name: "zeroclaw".into(),
            warm_path: "/slab/projects/zeroclaw".into(),
            hot_target_path: "/hot/targets/zeroclaw".into(),
            last_build: None,
            last_active: None,
            last_sync: None,
            pinned: false,
        });
        assert!(m.get("zeroclaw").is_some());
        assert!(m.get("nonexistent").is_none());
    }

    #[test]
    fn legacy_toml_without_pinned_field_parses() {
        // Manifest written by v0.1.x. Must still load — pinned defaults
        // to false via #[serde(default)]. Without this we'd break every
        // existing deployment on upgrade.
        let legacy = r#"
            [[projects]]
            name = "old/repo"
            warm_path = "/slab/projects/old/repo"
            hot_target_path = "/hot/targets/old/repo"
        "#;
        let f = tempfile::NamedTempFile::new().unwrap();
        std::fs::write(f.path(), legacy).unwrap();
        let m = Manifest::load(f.path()).unwrap();
        assert_eq!(m.projects.len(), 1);
        assert!(!m.projects[0].pinned);
    }

    #[test]
    fn update_serializes_two_sequential_writers() {
        let f = tempfile::NamedTempFile::new().unwrap();
        // Seed.
        Manifest::update(f.path(), |m| {
            m.upsert(Project {
                name: "alpha".into(),
                warm_path: "/w/alpha".into(),
                hot_target_path: "/h/alpha".into(),
                last_build: None,
                last_active: None,
                last_sync: None,
                pinned: false,
            });
            Ok(())
        })
        .unwrap();

        // Two sequential updates — each should see the previous
        // committed state. With the broken v0.1 load/mutate/save
        // pattern these would race; here they serialize via flock.
        Manifest::update(f.path(), |m| {
            m.upsert(Project {
                name: "beta".into(),
                warm_path: "/w/beta".into(),
                hot_target_path: "/h/beta".into(),
                last_build: None,
                last_active: None,
                last_sync: None,
                pinned: true,
            });
            Ok(())
        })
        .unwrap();
        Manifest::update(f.path(), |m| {
            if let Some(p) = m.get_mut("alpha") {
                p.pinned = true;
            }
            Ok(())
        })
        .unwrap();

        let m = Manifest::load(f.path()).unwrap();
        assert_eq!(m.projects.len(), 2);
        assert!(m.projects.iter().all(|p| p.pinned));
    }
}