#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct VerifiedStateAnchorReadiness {
    staged: StagedProcessOwnership,
    mount: MountIdentity,
}

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct StateAnchorAcquisition<'path> {
    pub lower: &'path Path,
    pub expected_lower: (u64, u64),
    pub expected_parent: lazaret_core::identity::PidfsProcessIdentityV1,
    pub ownership: ProcessOwnershipContext,
}

pub struct StateAnchorLaunchAuthority {
    lower: OwnedFd,
    lower_label: PathBuf,
    persistent_root: OwnedFd,
    persistent_anchor: OwnedFd,
    persistent_anchor_label: PathBuf,
    runtime_root: OwnedFd,
    runtime_anchor: OwnedFd,
    runtime_anchor_label: PathBuf,
    expected_lower: (u64, u64),
    persistent_destinations: Vec<PathBuf>,
}

impl StateAnchorLaunchAuthority {
    /// Captures exact directory authorities for inheritance by the Runtime Supervisor.
    ///
    /// # Errors
    /// Refuses a changed layout or prepared lower.
    pub fn capture(
        layout: &StateAnchorLayout<'_>,
        artifact: &PreparedArtifact,
    ) -> Result<Self, StateAnchorError> {
        layout.revalidate()?;
        let expected_lower = (artifact.device.get(), artifact.inode.get());
        let lower = open_exact_directory_path(&path_from_host(&artifact.path), expected_lower)?;
        Self::capture_open(
            layout,
            expected_lower,
            path_from_host(&artifact.path),
            lower,
        )
    }

    /// Captures an already-confined prepared-lower authority for inheritance.
    ///
    /// # Errors
    /// Refuses a changed layout or prepared-lower descriptor.
    pub fn capture_retained(
        layout: &StateAnchorLayout<'_>,
        artifact: &PreparedArtifact,
        lower_label: &Path,
        lower: impl AsFd,
    ) -> Result<Self, StateAnchorError> {
        layout.revalidate()?;
        let expected_lower = (artifact.device.get(), artifact.inode.get());
        require_directory_descriptor_identity(&lower, expected_lower)?;
        Self::capture_open(layout, expected_lower, lower_label.to_owned(), lower)
    }

    fn capture_open(
        layout: &StateAnchorLayout<'_>,
        expected_lower: (u64, u64),
        lower_label: PathBuf,
        lower: impl AsFd,
    ) -> Result<Self, StateAnchorError> {
        Ok(Self {
            lower: inherit_for_exec(lower)?,
            lower_label,
            persistent_root: inherit_for_exec(&layout.persistent_root)?,
            persistent_anchor: inherit_for_exec(&layout.persistent_anchor)?,
            persistent_anchor_label: layout
                .upper_label
                .parent()
                .ok_or(StateAnchorError::InvalidLayout(
                    "upper label has no State Anchor parent",
                ))?
                .to_owned(),
            runtime_root: inherit_for_exec(&layout.runtime_root)?,
            runtime_anchor: inherit_for_exec(&layout.runtime_anchor)?,
            runtime_anchor_label: layout
                .merged_label
                .parent()
                .ok_or(StateAnchorError::InvalidLayout(
                    "merged label has no State Anchor parent",
                ))?
                .to_owned(),
            expected_lower,
            persistent_destinations: layout.persistent_destinations.clone(),
        })
    }

    #[must_use]
    pub fn lower_fd(&self) -> i32 {
        self.lower.as_raw_fd()
    }

    #[must_use]
    pub fn persistent_anchor_fd(&self) -> i32 {
        self.persistent_anchor.as_raw_fd()
    }

    #[must_use]
    pub fn persistent_root_fd(&self) -> i32 {
        self.persistent_root.as_raw_fd()
    }

    #[must_use]
    pub fn runtime_anchor_fd(&self) -> i32 {
        self.runtime_anchor.as_raw_fd()
    }

    #[must_use]
    pub fn runtime_root_fd(&self) -> i32 {
        self.runtime_root.as_raw_fd()
    }

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

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

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

    #[must_use]
    pub const fn expected_lower(&self) -> (u64, u64) {
        self.expected_lower
    }

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

pub struct RuntimeStateAnchorAuthority {
    lower: OwnedFd,
    persistent_anchor: OwnedFd,
    runtime_anchor: OwnedFd,
    merged_label: PathBuf,
    merged_descriptor: OwnedFd,
}

#[derive(Clone, Copy)]
pub struct RuntimeStateAnchorInherited<'a> {
    pub lower_fd: i32,
    pub lower_label: &'a Path,
    pub persistent_root_fd: i32,
    pub persistent_anchor_fd: i32,
    pub persistent_anchor_label: &'a Path,
    pub runtime_root_fd: i32,
    pub runtime_anchor_fd: i32,
    pub runtime_anchor_label: &'a Path,
    pub expected_lower: (u64, u64),
}

impl RuntimeStateAnchorAuthority {
    /// Reopens inherited authorities without falling back to ambient configured paths.
    ///
    /// # Errors
    /// Refuses missing, replaced, or incorrectly typed descriptors and fixed children.
    pub fn from_inherited(
        inherited: RuntimeStateAnchorInherited<'_>,
    ) -> Result<Self, StateAnchorError> {
        let retained_lower = reopen_inherited_directory(inherited.lower_fd)?;
        require_directory_descriptor_identity(&retained_lower, inherited.expected_lower)?;
        if !inherited.lower_label.is_absolute() {
            return Err(StateAnchorError::InvalidLayout(
                "prepared lower label is not absolute",
            ));
        }
        let lower = open_exact_directory_path(inherited.lower_label, inherited.expected_lower)?;
        let persistent_root = reopen_inherited_directory(inherited.persistent_root_fd)?;
        let retained_persistent_anchor =
            reopen_inherited_directory(inherited.persistent_anchor_fd)?;
        if !inherited.persistent_anchor_label.is_absolute() {
            return Err(StateAnchorError::InvalidLayout(
                "persistent State Anchor label is not absolute",
            ));
        }
        let retained_persistent =
            rustix::fs::fstat(&retained_persistent_anchor).map_err(io::Error::from)?;
        let confined_persistent_anchor =
            open_directory(&persistent_root, Path::new("state-anchor"))?;
        require_directory_descriptor_identity(
            &confined_persistent_anchor,
            (retained_persistent.st_dev, retained_persistent.st_ino),
        )?;
        let persistent_anchor = open_exact_directory_path(
            inherited.persistent_anchor_label,
            (retained_persistent.st_dev, retained_persistent.st_ino),
        )?;
        let runtime_root = reopen_inherited_directory(inherited.runtime_root_fd)?;
        let retained_runtime_anchor = reopen_inherited_directory(inherited.runtime_anchor_fd)?;
        if !inherited.runtime_anchor_label.is_absolute() {
            return Err(StateAnchorError::InvalidLayout(
                "runtime State Anchor label is not absolute",
            ));
        }
        let confined_runtime_anchor = open_directory(&runtime_root, Path::new("state-anchor"))?;
        let retained = rustix::fs::fstat(&retained_runtime_anchor).map_err(io::Error::from)?;
        require_directory_descriptor_identity(
            &confined_runtime_anchor,
            (retained.st_dev, retained.st_ino),
        )?;
        let runtime_anchor = open_exact_directory_path(
            inherited.runtime_anchor_label,
            (retained.st_dev, retained.st_ino),
        )?;
        for name in ["upper", "work"] {
            drop(open_directory(&persistent_anchor, Path::new(name))?);
        }
        let merged_descriptor = open_directory(&runtime_anchor, Path::new("merged"))?;
        let merged_label = inherited.runtime_anchor_label.join("merged");
        Ok(Self {
            lower,
            persistent_anchor,
            runtime_anchor,
            merged_label,
            merged_descriptor,
        })
    }

    /// Mounts the exact inherited prepared lower and anchors under RS child ownership.
    ///
    /// # Errors
    /// Refuses acquisition, acknowledgment, readiness, or authority failures.
    pub fn acquire<Stage, Acknowledge, Ready>(
        self,
        expected_parent: lazaret_core::identity::PidfsProcessIdentityV1,
        ownership: ProcessOwnershipContext,
        stage: Stage,
        acknowledge: Acknowledge,
        ready: Ready,
    ) -> Result<RuntimeStateAnchorMount, StateAnchorError>
    where
        Stage: FnOnce(StagedProcessOwnership) -> io::Result<()>,
        Acknowledge: FnOnce(StagedProcessOwnership) -> io::Result<ProcessOwnershipCommitAck>,
        Ready: FnOnce(VerifiedStateAnchorReadiness) -> io::Result<()>,
    {
        if ownership.slot != HostProcessOwnershipSlot::StateAnchorDaemon {
            return Err(StateAnchorError::InvalidLayout(
                "process slot is not State Anchor daemon",
            ));
        }
        let baseline = mount_identity(&self.merged_descriptor)?;
        let lower_launch = inherit_for_exec(&self.lower)?;
        let persistent_launch = inherit_for_exec(&self.persistent_anchor)?;
        let target = TargetCommand::new("fuse-overlayfs")
            .argument("-f")
            .argument("-o")
            .argument(overlay_options(
                &descriptor_path(&lower_launch),
                &descriptor_child_path(&persistent_launch, "upper"),
                &descriptor_child_path(&persistent_launch, "work"),
            ))
            .argument(&self.merged_label);
        let process =
            child_broker().acquire(expected_parent, ownership, &target, stage, acknowledge)?;
        let staged = StagedProcessOwnership::v1(
            ownership.domain_id,
            ownership.generation_id,
            ownership.coordinator_id,
            ownership.slot,
            process.identity(),
        );
        let deadline = Instant::now() + MOUNT_TIMEOUT;
        loop {
            if process.has_exited()? {
                child_broker().reap(process)?;
                return Err(StateAnchorError::DaemonExited);
            }
            let mounted = open_mounted_directory(&self.runtime_anchor, Path::new("merged"))?;
            let observed = mount_identity(&mounted)?;
            if observed.mount_id != baseline.mount_id {
                let readiness = VerifiedStateAnchorReadiness {
                    staged,
                    mount: observed,
                };
                if let Err(error) = ready(readiness) {
                    process.send_signal(rustix::process::Signal::KILL)?;
                    while !process.has_exited()? {
                        thread::yield_now();
                    }
                    let _ = rootless_unmount_path(&self.merged_label);
                    child_broker().reap(process)?;
                    return Err(error.into());
                }
                return Ok(RuntimeStateAnchorMount {
                    authority: self,
                    process,
                    mount: observed,
                    merged: mounted,
                });
            }
            if Instant::now() >= deadline {
                process.send_signal(rustix::process::Signal::KILL)?;
                while !process.has_exited()? {
                    thread::yield_now();
                }
                let merged = open_mounted_directory(&self.runtime_anchor, Path::new("merged"))?;
                let observed = mount_identity(&merged)?;
                if observed.mount_id != baseline.mount_id {
                    let _ = rootless_unmount_path(&self.merged_label);
                }
                child_broker().reap(process)?;
                return Err(StateAnchorError::MountTimeout);
            }
            thread::sleep(MOUNT_POLL_INTERVAL);
        }
    }
}

pub struct RuntimeStateAnchorMount {
    authority: RuntimeStateAnchorAuthority,
    process: RetainedProcess,
    mount: MountIdentity,
    merged: OwnedFd,
}

pub struct RuntimeStateAnchorAbsenceAuthority {
    runtime_anchor: OwnedFd,
    mount: MountIdentity,
}

impl RuntimeStateAnchorAbsenceAuthority {
    /// Reopens the exact runtime anchor to produce a fresh post-unmount observation.
    ///
    /// # Errors
    /// Refuses an unreadable anchor or the continued presence of the retired mount.
    pub fn observe_absence(
        &self,
        expected_mount: MountIdentity,
    ) -> Result<MountIdentity, StateAnchorError> {
        if expected_mount != self.mount {
            return Err(StateAnchorError::OwnershipMismatch);
        }
        let observed = mount_identity(&open_directory(&self.runtime_anchor, Path::new("merged"))?)?;
        if observed == self.mount {
            Err(StateAnchorError::OwnershipMismatch)
        } else {
            Ok(observed)
        }
    }
}

impl RuntimeStateAnchorMount {
    #[must_use]
    pub const fn mount_identity(&self) -> MountIdentity {
        self.mount
    }

    /// Validates configured persistent subpaths beneath the exact mounted view.
    ///
    /// # Errors
    /// Refuses missing paths, symlinks, nested mounts, or mount replacement.
    pub fn require_persistent_destinations(
        &self,
        destinations: &[PathBuf],
    ) -> Result<(), StateAnchorError> {
        if mount_identity(&self.merged)? != self.mount {
            return Err(StateAnchorError::OwnershipMismatch);
        }
        for destination in destinations {
            if destination.as_os_str().is_empty()
                || destination
                    .components()
                    .any(|component| !matches!(component, std::path::Component::Normal(_)))
            {
                return Err(StateAnchorError::InvalidLayout(
                    "persistent destination is not normalized and relative",
                ));
            }
            let descriptor = openat2(
                &self.merged,
                destination,
                OFlags::PATH | OFlags::DIRECTORY | OFlags::CLOEXEC | OFlags::NOFOLLOW,
                Mode::empty(),
                ResolveFlags::BENEATH
                    | ResolveFlags::NO_MAGICLINKS
                    | ResolveFlags::NO_SYMLINKS
                    | ResolveFlags::NO_XDEV,
            )
            .map_err(io::Error::from)?;
            if !FileType::from_raw_mode(
                rustix::fs::fstat(&descriptor)
                    .map_err(io::Error::from)?
                    .st_mode,
            )
            .is_dir()
            {
                return Err(StateAnchorError::InvalidLayout(
                    "persistent destination is not a directory",
                ));
            }
        }
        Ok(())
    }

    /// Unmounts and reaps only the retained exact RS-owned State Anchor.
    ///
    /// # Errors
    /// Refuses mount replacement, unmount failure, or exact child cleanup failure.
    pub fn unmount(self) -> Result<RuntimeStateAnchorAbsenceAuthority, StateAnchorError> {
        let Self {
            authority,
            process,
            mount,
            merged,
        } = self;
        let observed = mount_identity(&merged)?;
        if observed != mount {
            return Err(StateAnchorError::OwnershipMismatch);
        }
        drop(merged);
        rootless_unmount_path(&authority.merged_label)?;
        let after = mount_identity(&open_directory(
            &authority.runtime_anchor,
            Path::new("merged"),
        )?)?;
        if after == mount {
            return Err(StateAnchorError::OwnershipMismatch);
        }
        child_broker().reap(process)?;
        Ok(RuntimeStateAnchorAbsenceAuthority {
            runtime_anchor: authority.runtime_anchor,
            mount,
        })
    }
}

impl VerifiedStateAnchorReadiness {
    #[must_use]
    pub const fn from_parts(staged: StagedProcessOwnership, mount: MountIdentity) -> Self {
        Self { staged, mount }
    }

    #[must_use]
    pub const fn staged(self) -> StagedProcessOwnership {
        self.staged
    }

    #[must_use]
    pub const fn mount(self) -> MountIdentity {
        self.mount
    }
}