#![doc = "Physical State Anchor layout and exact fuse-overlayfs mount lifecycle."]

use std::ffi::OsString;
use std::fmt;
use std::fs::File;
use std::io::{self, Write};
use std::os::fd::{AsFd, AsRawFd, OwnedFd};
use std::os::unix::ffi::{OsStrExt, OsStringExt};
use std::path::{Component, Path, PathBuf};
use std::sync::atomic::{AtomicU64, Ordering};
use std::thread;
use std::time::{Duration, Instant};

use lazaret_core::configuration::{ConfinedPathPlan, ResolvedDomainConfiguration};
use lazaret_core::identity::{
    DeviceId, HostPath, InodeId, MountIdentity, NamespaceIdentity, PreparedArtifactId,
};
use lazaret_core::records::{
    HostProcessOwnershipSlot, PersistedHostProcessOwnership, PreparedArtifact,
    ProcessOwnershipCommitAck, StagedProcessOwnership, StateAnchorOwnership,
};
use lazaret_linux::filesystem::{mount_identity, namespace_identity};
use lazaret_linux::ipc::{
    private_seqpacket_pair, receive_descriptors, receive_packet, send_descriptors, send_packet,
};
use lazaret_linux::process::{
    ProcessOwnershipContext, RetainedProcess, TargetCommand, child_broker, require_pidfs_magic,
};
use rustix::fs::{
    AtFlags, FileType, Mode, OFlags, RawDir, RenameFlags, ResolveFlags, mkdirat, openat2, renameat,
    renameat_with, statat, unlinkat,
};
use rustix::io::dup;
use rustix::thread::{ThreadNameSpaceType, move_into_thread_name_spaces};
use storage::{
    atomic_replace_at, create_directory, create_regular_file, descriptor_child_path,
    descriptor_path, host_path, inspect_directory, move_all_entries, move_selected_entries,
    open_directory, open_exact_directory_path, open_mounted_directory, open_or_create_quarantine,
    open_regular_file, path_from_host, remove_directory_contents,
    require_directory_descriptor_identity, require_maintenance_work_shape, require_same_descriptor,
    validate_relative_path,
};

const MOUNT_TIMEOUT: Duration = Duration::from_secs(5);
const MOUNT_POLL_INTERVAL: Duration = Duration::from_millis(2);
pub const PRIVATE_STATE_ANCHOR_RECOVERY_ROLE: &str = "--lazaret-private-state-anchor-recovery";
static TEMPORARY_SEQUENCE: AtomicU64 = AtomicU64::new(0);
pub const PROTECTED_RUNTIME_FILES: [&str; 3] = ["resolv.conf", "hosts", "hostname"];
const RESET_QUARANTINE: &str = "reset-quarantine";

pub struct ProtectedRuntimeFiles<'a> {
    pub resolv_conf: &'a [u8],
    pub hosts: &'a [u8],
    pub hostname: &'a [u8],
}

#[derive(Debug)]
pub enum StateAnchorError {
    Io(io::Error),
    InvalidLayout(&'static str),
    MountTimeout,
    DaemonExited,
    OwnershipMismatch,
}

impl fmt::Display for StateAnchorError {
    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::Io(error) => write!(formatter, "State Anchor I/O failed: {error}"),
            Self::InvalidLayout(detail) => {
                write!(formatter, "invalid State Anchor layout: {detail}")
            }
            Self::MountTimeout => formatter.write_str("fuse-overlayfs mount timed out"),
            Self::DaemonExited => formatter.write_str("fuse-overlayfs exited before mounting"),
            Self::OwnershipMismatch => formatter.write_str("State Anchor mount identity mismatch"),
        }
    }
}

impl std::error::Error for StateAnchorError {
    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
        match self {
            Self::Io(error) => Some(error),
            Self::InvalidLayout(_)
            | Self::MountTimeout
            | Self::DaemonExited
            | Self::OwnershipMismatch => None,
        }
    }
}

impl From<io::Error> for StateAnchorError {
    fn from(error: io::Error) -> Self {
        Self::Io(error)
    }
}

#[derive(Debug)]
pub struct StateAnchorLayout<'configuration> {
    persistent_plan: &'configuration ConfinedPathPlan,
    runtime_plan: &'configuration ConfinedPathPlan,
    persistent_root: OwnedFd,
    runtime_root: OwnedFd,
    persistent_anchor: OwnedFd,
    runtime_anchor: OwnedFd,
    upper_descriptor: OwnedFd,
    work_descriptor: OwnedFd,
    merged_descriptor: OwnedFd,
    runtime_files_descriptor: OwnedFd,
    upper: PathBuf,
    work: PathBuf,
    merged: PathBuf,
    runtime_files: PathBuf,
    upper_label: PathBuf,
    work_label: PathBuf,
    merged_label: PathBuf,
    persistent_destinations: Vec<PathBuf>,
}

impl<'configuration> StateAnchorLayout<'configuration> {
    /// Creates the fixed layout beneath retained, revalidated Domain authorities.
    ///
    /// # Errors
    /// Refuses changed roots, non-directory fixed paths, and unsafe persistent destinations.
    pub fn create(
        configuration: &'configuration ResolvedDomainConfiguration,
    ) -> Result<Self, StateAnchorError> {
        let persistent_root = configuration
            .persistent_domain_root()
            .open_authority()
            .map_err(|_| StateAnchorError::InvalidLayout("persistent Domain authority changed"))?;
        let runtime_root = configuration
            .runtime_domain_root()
            .open_authority()
            .map_err(|_| StateAnchorError::InvalidLayout("runtime Domain authority changed"))?;
        create_directory(&persistent_root, "state-anchor")?;
        let persistent_anchor = open_directory(&persistent_root, Path::new("state-anchor"))?;
        for name in ["upper", "work"] {
            create_directory(&persistent_anchor, name)?;
        }
        create_directory(&runtime_root, "state-anchor")?;
        let runtime_anchor = open_directory(&runtime_root, Path::new("state-anchor"))?;
        for name in ["merged", "runtime-files"] {
            create_directory(&runtime_anchor, name)?;
        }
        let upper_descriptor = open_directory(&persistent_anchor, Path::new("upper"))?;
        let work_descriptor = open_directory(&persistent_anchor, Path::new("work"))?;
        let merged_descriptor = open_directory(&runtime_anchor, Path::new("merged"))?;
        let runtime_files_descriptor = open_directory(&runtime_anchor, Path::new("runtime-files"))?;
        for name in PROTECTED_RUNTIME_FILES {
            create_regular_file(&runtime_files_descriptor, name)?;
        }
        rustix::fs::fsync(&runtime_anchor).map_err(io::Error::from)?;
        rustix::fs::fsync(&persistent_anchor).map_err(io::Error::from)?;
        let persistent_base =
            path_from_host(configuration.persistent_domain_root().canonical_label());
        let runtime_base = path_from_host(configuration.runtime_domain_root().canonical_label());
        let persistent_destinations = configuration
            .fingerprint_record()
            .persistent_dirs
            .iter()
            .map(|destination| PathBuf::from(destination.strip_prefix('/').unwrap_or(destination)))
            .collect();
        Ok(Self {
            persistent_plan: configuration.persistent_domain_root(),
            runtime_plan: configuration.runtime_domain_root(),
            persistent_root,
            runtime_root,
            upper: descriptor_child_path(&persistent_anchor, "upper"),
            work: descriptor_child_path(&persistent_anchor, "work"),
            merged: descriptor_child_path(&runtime_anchor, "merged"),
            runtime_files: descriptor_child_path(&runtime_anchor, "runtime-files"),
            persistent_anchor,
            runtime_anchor,
            upper_descriptor,
            work_descriptor,
            merged_descriptor,
            runtime_files_descriptor,
            upper_label: persistent_base.join("state-anchor/upper"),
            work_label: persistent_base.join("state-anchor/work"),
            merged_label: runtime_base.join("state-anchor/merged"),
            persistent_destinations,
        })
    }

    #[must_use]
    pub fn upper(&self) -> &Path {
        &self.upper
    }

    #[must_use]
    pub fn work(&self) -> &Path {
        &self.work
    }

    #[must_use]
    pub fn merged(&self) -> &Path {
        &self.merged
    }

    /// Returns the ordinary host path used as the merged mount label.
    #[must_use]
    pub fn merged_label(&self) -> &Path {
        &self.merged_label
    }

    #[must_use]
    pub fn runtime_files(&self) -> &Path {
        &self.runtime_files
    }

    #[must_use]
    pub fn persistent_destinations(&self) -> &[PathBuf] {
        &self.persistent_destinations
    }

    /// Revalidates every fixed directory through the retained Domain authorities.
    ///
    /// # Errors
    /// Refuses replacement, symlink, mount crossing, or a non-directory fixed path.
    pub fn revalidate(&self) -> Result<(), StateAnchorError> {
        self.revalidate_authorities()?;
        let merged = open_directory(&self.runtime_anchor, Path::new("merged"))?;
        require_same_descriptor(&merged, &self.merged_descriptor)
    }

    fn revalidate_authorities(&self) -> Result<(), StateAnchorError> {
        let persistent_root = self
            .persistent_plan
            .open_authority()
            .map_err(|_| StateAnchorError::InvalidLayout("persistent Domain authority changed"))?;
        let runtime_root = self
            .runtime_plan
            .open_authority()
            .map_err(|_| StateAnchorError::InvalidLayout("runtime Domain authority changed"))?;
        require_same_descriptor(&persistent_root, &self.persistent_root)?;
        require_same_descriptor(&runtime_root, &self.runtime_root)?;
        let persistent_anchor = open_directory(&self.persistent_root, Path::new("state-anchor"))?;
        let runtime_anchor = open_directory(&self.runtime_root, Path::new("state-anchor"))?;
        require_same_descriptor(&persistent_anchor, &self.persistent_anchor)?;
        require_same_descriptor(&runtime_anchor, &self.runtime_anchor)?;
        for (name, expected) in [
            ("upper", &self.upper_descriptor),
            ("work", &self.work_descriptor),
        ] {
            let observed = open_directory(&self.persistent_anchor, Path::new(name))?;
            require_same_descriptor(&observed, expected)?;
        }
        let runtime_files = open_directory(&self.runtime_anchor, Path::new("runtime-files"))?;
        require_same_descriptor(&runtime_files, &self.runtime_files_descriptor)?;
        for name in PROTECTED_RUNTIME_FILES {
            drop(open_regular_file(&self.runtime_files_descriptor, name)?);
        }
        Ok(())
    }

    fn current_merged_identity(&self) -> Result<MountIdentity, StateAnchorError> {
        self.revalidate_authorities()?;
        let merged = open_mounted_directory(&self.runtime_anchor, Path::new("merged"))?;
        mount_identity(&merged).map_err(StateAnchorError::from)
    }

    fn require_mounted(&self, expected: MountIdentity) -> Result<(), StateAnchorError> {
        if self.current_merged_identity()? == expected {
            Ok(())
        } else {
            Err(StateAnchorError::OwnershipMismatch)
        }
    }

    fn require_unmounted(&self) -> Result<(), StateAnchorError> {
        self.revalidate()
    }

    /// Atomically replaces sandbox runtime files in host-private transient storage.
    ///
    /// # Errors
    /// Refuses changed layout and incomplete durable replacement.
    pub fn replace_protected_runtime_files(
        &self,
        files: &ProtectedRuntimeFiles<'_>,
    ) -> Result<(), StateAnchorError> {
        self.revalidate_authorities()?;
        for (name, bytes) in [
            ("resolv.conf", files.resolv_conf),
            ("hosts", files.hosts),
            ("hostname", files.hostname),
        ] {
            atomic_replace_at(&self.runtime_files_descriptor, name, bytes)?;
        }
        self.revalidate_authorities()
    }

    #[must_use]
    pub fn ownership_intent(&self, artifact_id: PreparedArtifactId) -> StateAnchorOwnership {
        StateAnchorOwnership {
            lower_artifact_id: Some(artifact_id),
            upper_path: Some(host_path(&self.upper_label)),
            work_path: Some(host_path(&self.work_label)),
            merged_path: Some(host_path(&self.merged_label)),
            daemon: PersistedHostProcessOwnership::unassigned(),
            user_namespace: None,
            mount_namespace: None,
            mount: None,
        }
    }

    #[must_use]
    pub fn matches_recorded_paths(&self, ownership: &StateAnchorOwnership) -> bool {
        ownership.upper_path.as_ref() == Some(&host_path(&self.upper_label))
            && ownership.work_path.as_ref() == Some(&host_path(&self.work_label))
            && ownership.merged_path.as_ref() == Some(&host_path(&self.merged_label))
    }

    /// Verifies inactive structural authority and returns content-free upper-layer metadata.
    ///
    /// # Errors
    /// Refuses changed roots, mounts, fixed-path links, orphan quarantine, and unsupported entries.
    pub fn inspect_state(&self) -> Result<StateAnchorInspection, StateAnchorError> {
        self.require_maintenance_ready()?;
        let mut entries = Vec::new();
        inspect_directory(&self.upper_descriptor, Path::new(""), &mut entries)?;
        entries.sort_by(|left, right| left.path.cmp(&right.path));
        Ok(StateAnchorInspection { entries })
    }

    /// Completes the physical half of one durable reset intent.
    ///
    /// # Errors
    /// Refuses changed authority, mounts, unsupported scope, collisions, links in authority paths,
    /// or incomplete durable cleanup.
    pub fn complete_state_reset(
        &self,
        scope: StateAnchorResetScope<'_>,
    ) -> Result<(), StateAnchorError> {
        self.require_maintenance_ready_allowing_quarantine()?;
        let selected = match scope {
            StateAnchorResetScope::All => None,
            StateAnchorResetScope::Selected(destination) => {
                Some(self.selected_relative(destination)?)
            }
        };
        let quarantine = open_or_create_quarantine(&self.persistent_anchor)?;
        if let Some(relative) = selected {
            move_selected_entries(&self.upper_descriptor, &quarantine, &relative)?;
        } else {
            move_all_entries(&self.upper_descriptor, &quarantine)?;
        }
        remove_directory_contents(&quarantine)?;
        rustix::fs::fsync(&quarantine).map_err(io::Error::from)?;
        unlinkat(
            self.persistent_anchor.as_fd(),
            RESET_QUARANTINE,
            AtFlags::REMOVEDIR,
        )
        .map_err(io::Error::from)?;
        rustix::fs::fsync(&self.persistent_anchor).map_err(io::Error::from)?;
        Ok(())
    }

    /// Refuses a physical quarantine that lacks a matching durable reset intent.
    ///
    /// # Errors
    /// Returns an error for changed layout or an orphan quarantine.
    pub fn require_no_reset_quarantine(&self) -> Result<(), StateAnchorError> {
        self.revalidate_authorities()?;
        match open_directory(&self.persistent_anchor, Path::new(RESET_QUARANTINE)) {
            Ok(_) => Err(StateAnchorError::InvalidLayout(
                "State Anchor reset quarantine has no durable intent",
            )),
            Err(StateAnchorError::Io(error)) if error.kind() == io::ErrorKind::NotFound => Ok(()),
            Err(error) => Err(error),
        }
    }

    fn selected_relative(&self, destination: &Path) -> Result<PathBuf, StateAnchorError> {
        if !self
            .persistent_destinations
            .iter()
            .any(|configured| configured == destination.strip_prefix("/").unwrap_or(destination))
        {
            return Err(StateAnchorError::InvalidLayout(
                "reset target is not a configured persistent path",
            ));
        }
        let relative = destination.strip_prefix("/").unwrap_or(destination);
        validate_relative_path(relative)?;
        Ok(relative.to_path_buf())
    }

    fn require_maintenance_ready(&self) -> Result<(), StateAnchorError> {
        self.require_maintenance_ready_allowing_quarantine()?;
        self.require_no_reset_quarantine()
    }

    fn require_maintenance_ready_allowing_quarantine(&self) -> Result<(), StateAnchorError> {
        self.require_unmounted()?;
        require_maintenance_work_shape(&self.work_descriptor)
    }
}

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum StateAnchorEntryKind {
    Directory,
    RegularFile,
    Symlink,
    Whiteout,
}

#[derive(Clone, Debug, Eq, PartialEq)]
pub struct StateAnchorEntry {
    pub path: Vec<u8>,
    pub kind: StateAnchorEntryKind,
    pub mode: u32,
    pub uid: u32,
    pub gid: u32,
    pub size: u64,
}

#[derive(Clone, Debug, Eq, PartialEq)]
pub struct StateAnchorInspection {
    pub entries: Vec<StateAnchorEntry>,
}

#[derive(Clone, Copy, Debug)]
pub enum StateAnchorResetScope<'a> {
    All,
    Selected(&'a Path),
}

/// Proves that no physical State Anchor exists under either retained Domain authority.
///
/// # Errors
/// Refuses changed authority, links, inaccessible paths, or any persistent or runtime anchor.
pub fn require_state_anchor_absent(
    configuration: &ResolvedDomainConfiguration,
) -> Result<(), StateAnchorError> {
    for plan in [
        configuration.persistent_domain_root(),
        configuration.runtime_domain_root(),
    ] {
        let root = plan
            .open_authority()
            .map_err(|_| StateAnchorError::InvalidLayout("Domain authority changed"))?;
        match open_directory(&root, Path::new("state-anchor")) {
            Ok(_) => {
                return Err(StateAnchorError::InvalidLayout(
                    "State Anchor exists without Domain Store authority",
                ));
            }
            Err(StateAnchorError::Io(error)) if error.kind() == io::ErrorKind::NotFound => {}
            Err(error) => return Err(error),
        }
    }
    Ok(())
}

/// Refuses an orphan reset quarantine without opening transient mount paths.
///
/// # Errors
/// Refuses changed persistent authority, fixed-path links, and orphan quarantine.
pub fn require_no_orphan_reset_quarantine(
    configuration: &ResolvedDomainConfiguration,
) -> Result<(), StateAnchorError> {
    let root = configuration
        .persistent_domain_root()
        .open_authority()
        .map_err(|_| StateAnchorError::InvalidLayout("persistent Domain authority changed"))?;
    let anchor = match open_directory(&root, Path::new("state-anchor")) {
        Ok(anchor) => anchor,
        Err(StateAnchorError::Io(error)) if error.kind() == io::ErrorKind::NotFound => {
            return Ok(());
        }
        Err(error) => return Err(error),
    };
    match open_directory(&anchor, Path::new(RESET_QUARANTINE)) {
        Ok(_) => Err(StateAnchorError::InvalidLayout(
            "State Anchor reset quarantine has no durable intent",
        )),
        Err(StateAnchorError::Io(error)) if error.kind() == io::ErrorKind::NotFound => Ok(()),
        Err(error) => Err(error),
    }
}

/// Pins the exact mounted and lower authorities until the view is dropped before unmount.
#[derive(Debug)]
pub struct StateAnchorSandboxView<'layout, 'configuration> {
    layout: &'layout StateAnchorLayout<'configuration>,
    lower_descriptor: OwnedFd,
    merged_descriptor: OwnedFd,
    lower: PathBuf,
    lower_identity: (u64, u64),
    merged: PathBuf,
    mount: MountIdentity,
    runtime_files: PathBuf,
    persistent_destinations: Vec<PathBuf>,
}

impl<'layout, 'configuration> StateAnchorSandboxView<'layout, 'configuration> {
    /// Binds a serviceable State Anchor view to exact prepared-lower and mount evidence.
    ///
    /// # Errors
    /// Refuses changed layout, prepared lower, or mount identity.
    pub fn from_mounted(
        layout: &'layout StateAnchorLayout<'configuration>,
        artifact: &PreparedArtifact,
        mount: MountIdentity,
    ) -> Result<Self, StateAnchorError> {
        let lower_descriptor = open_exact_directory_path(
            &path_from_host(&artifact.path),
            (artifact.device.get(), artifact.inode.get()),
        )?;
        layout.require_mounted(mount)?;
        let merged_descriptor =
            open_mounted_directory(&layout.runtime_anchor, Path::new("merged"))?;
        let view = Self {
            layout,
            lower: descriptor_path(&lower_descriptor),
            lower_identity: (artifact.device.get(), artifact.inode.get()),
            merged: descriptor_path(&merged_descriptor),
            mount,
            runtime_files: descriptor_path(&layout.runtime_files_descriptor),
            persistent_destinations: layout.persistent_destinations.clone(),
            lower_descriptor,
            merged_descriptor,
        };
        view.revalidate()?;
        Ok(view)
    }

    /// Revalidates the immutable lower, exact overlay mount, and host-private runtime files.
    ///
    /// # Errors
    /// Refuses replacement or unreadable physical evidence.
    pub fn revalidate(&self) -> Result<(), StateAnchorError> {
        self.layout.require_mounted(self.mount)?;
        require_directory_descriptor_identity(&self.lower_descriptor, self.lower_identity)?;
        if mount_identity(&self.merged_descriptor)? != self.mount {
            return Err(StateAnchorError::OwnershipMismatch);
        }
        for name in PROTECTED_RUNTIME_FILES {
            drop(open_regular_file(
                &self.layout.runtime_files_descriptor,
                name,
            )?);
        }
        Ok(())
    }

    #[must_use]
    pub fn lower(&self) -> &Path {
        &self.lower
    }

    pub fn persistent_mounts(&self) -> impl Iterator<Item = (PathBuf, PathBuf)> + '_ {
        self.persistent_destinations.iter().map(|destination| {
            (
                self.merged.join(destination),
                Path::new("/").join(destination),
            )
        })
    }

    pub fn protected_runtime_mounts(&self) -> impl Iterator<Item = (PathBuf, PathBuf)> + '_ {
        PROTECTED_RUNTIME_FILES
            .into_iter()
            .map(|name| (self.runtime_files.join(name), Path::new("/etc").join(name)))
    }
}

#[path = "lib/authority.rs"]
mod authority;
#[path = "lib/mount.rs"]
mod mount;
#[path = "lib/storage.rs"]
mod storage;

pub use authority::{
    RuntimeStateAnchorAbsenceAuthority, RuntimeStateAnchorAuthority, RuntimeStateAnchorInherited,
    RuntimeStateAnchorMount, StateAnchorAcquisition, StateAnchorLaunchAuthority,
    VerifiedStateAnchorReadiness,
};
pub use mount::{
    FuseOverlayfsMount, dispatch_private_state_anchor_recovery, recover_private_state_anchor_mount,
    unmount_after_coordinator_loss,
};
pub use storage::{observe_mount_absence, require_mount_absent};

#[cfg(test)]
#[path = "lib/tests.rs"]
mod tests;