//! Optional integration with a locally running Nextcloud desktop client.
//!
//! **Linux desktop only, and strictly optional.** Android has no desktop
//! client, no `XDG_RUNTIME_DIR` socket, and no VFS placeholders, so nothing
//! here exists on the platform that needs it most. Every capability offered by
//! this module is also reachable through [`crate::NextcloudBackend`], which is
//! why it is a convenience rather than a dependency (ARCH §9.0).
//!
//! What it buys where it *is* available: a user whose library already lives in
//! a VFS-synced folder can have DarkRoom ask the client to fetch a file,
//! rather than DarkRoom downloading a second copy over WebDAV and leaving the
//! client's own placeholder state inconsistent.
//!
//! The protocol is newline-delimited `COMMAND:argument` over a Unix socket.
//! Verified against client 4.0.7.

#[cfg(unix)]
use std::io::{BufRead, BufReader, Write};
#[cfg(unix)]
use std::os::unix::net::UnixStream;
use std::path::{Path, PathBuf};
use std::time::Duration;

use dr_sync::RemoteError;

/// How long to wait for the client to acknowledge a command.
const TIMEOUT: Duration = Duration::from_secs(5);

/// A connection to a running desktop client.
/// TRACES: FR-NC-6c | FR-CAT-9
pub struct DesktopClient {
    #[cfg(unix)]
    socket: PathBuf,
}

impl DesktopClient {
    /// Locate a running client, if there is one.
    ///
    /// Returns `None` on Android, where no such client exists, and on any
    /// desktop where the client is not running. Callers treat `None` as
    /// "use the connector", never as an error.
    pub fn detect() -> Option<Self> {
        #[cfg(all(unix, not(target_os = "android")))]
        {
            let runtime = std::env::var_os("XDG_RUNTIME_DIR")?;
            let socket = PathBuf::from(runtime).join("Nextcloud/socket");
            socket.exists().then_some(Self { socket })
        }
        #[cfg(not(all(unix, not(target_os = "android"))))]
        {
            None
        }
    }

    /// Ask the client to download a placeholder.
    ///
    /// Hydration is **whole-file**, so this is appropriate for the original
    /// tier — opening an image in develop, or exporting it — and never for
    /// browsing. Filling a grid this way would download the entire library,
    /// which is exactly what range extraction exists to avoid (FR-NC-3).
    ///
    /// Returns once the command is accepted, not once the download completes;
    /// callers poll for the materialised path.
    pub fn make_available_locally(&self, path: &Path) -> Result<(), RemoteError> {
        self.send("MAKE_AVAILABLE_LOCALLY", path)
    }

    /// Ask the client to dehydrate a file back to a placeholder, freeing disk.
    pub fn make_online_only(&self, path: &Path) -> Result<(), RemoteError> {
        self.send("MAKE_ONLINE_ONLY", path)
    }

    #[cfg(unix)]
    fn send(&self, command: &str, path: &Path) -> Result<(), RemoteError> {
        let mut stream = UnixStream::connect(&self.socket)
            .map_err(|e| RemoteError::Network(format!("desktop client socket: {e}")))?;
        stream
            .set_read_timeout(Some(TIMEOUT))
            .and_then(|_| stream.set_write_timeout(Some(TIMEOUT)))
            .map_err(|e| RemoteError::Network(e.to_string()))?;

        writeln!(stream, "{command}:{}", path.display())
            .map_err(|e| RemoteError::Network(e.to_string()))?;
        stream
            .flush()
            .map_err(|e| RemoteError::Network(e.to_string()))?;

        // The client greets with REGISTER_PATH lines; reading one confirms it
        // is speaking the protocol rather than silently discarding input.
        let mut line = String::new();
        BufReader::new(&stream)
            .read_line(&mut line)
            .map_err(|e| RemoteError::Network(e.to_string()))?;

        log::debug!("desktop client: {command} -> {}", line.trim());
        Ok(())
    }

    #[cfg(not(unix))]
    fn send(&self, _command: &str, _path: &Path) -> Result<(), RemoteError> {
        Err(RemoteError::Unsupported(
            "desktop client integration is Linux-only",
        ))
    }
}

/// Whether a path names a VFS placeholder — a file the user has remotely but
/// not locally.
pub fn is_placeholder(path: &Path) -> bool {
    path.file_name()
        .map(|n| n.to_string_lossy().ends_with(dr_types::PLACEHOLDER_SUFFIX))
        .unwrap_or(false)
}

/// The path a placeholder will occupy once hydrated.
///
/// Suffix-mode VFS renames on hydration, so the materialised file appears
/// under a *different* path than the stub. Callers polling for completion must
/// watch this one, not the original.
pub fn hydrated_path(placeholder: &Path) -> PathBuf {
    let s = placeholder.to_string_lossy();
    PathBuf::from(
        s.strip_suffix(dr_types::PLACEHOLDER_SUFFIX)
            .unwrap_or(&s)
            .to_string(),
    )
}

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

    #[test]
    fn placeholders_are_recognised_by_suffix() {
        assert!(is_placeholder(Path::new("/x/IMG_4130.CR2.nextcloud")));
        assert!(!is_placeholder(Path::new("/x/IMG_4130.CR2")));
        assert!(!is_placeholder(Path::new("/x")));
    }

    #[test]
    fn hydration_changes_the_path() {
        // Suffix mode renames rather than filling in place, so polling the
        // original path would wait forever.
        assert_eq!(
            hydrated_path(Path::new("/x/IMG_4130.CR2.nextcloud")),
            PathBuf::from("/x/IMG_4130.CR2")
        );
    }

    #[test]
    fn hydrated_path_is_idempotent() {
        // Calling it on an already-materialised path must not truncate it.
        assert_eq!(
            hydrated_path(Path::new("/x/IMG_4130.CR2")),
            PathBuf::from("/x/IMG_4130.CR2")
        );
    }

    #[test]
    fn detection_returns_none_rather_than_failing() {
        // Absence is the normal case — Android always, desktop whenever the
        // client is not running — so it must never be an error.
        let _ = DesktopClient::detect();
    }
}

/// TRACES: FR-NC-6c
/// The desktop client's placeholder convention, as a
/// [`Vfs`](dr_sync_folder::Vfs).
///
/// This is what turns a folder the client syncs into a library DarkRoom can
/// open: the folder connector handles every filesystem operation, and this
/// answers the three questions it cannot — what is a stub, what is the
/// photograph called, and can the content be fetched and given back.
///
/// **Linux suffix mode only**, which is the only mode Linux supports
/// (ARCH §9.0). A dehydrated `IMG.CR2` exists solely as `IMG.CR2.nextcloud`
/// holding one byte.
pub struct NextcloudVfs {
    /// `None` where no client is running. The folder still lists and reads
    /// correctly; it simply cannot fetch what is not there, which the backend
    /// reports as `Materialisation::Placeholders`.
    client: Option<DesktopClient>,
}

impl NextcloudVfs {
    /// Attach to a running client, if there is one.
    ///
    /// Absence is the ordinary state — Android always, desktop whenever the
    /// client is not running — and never an error.
    pub fn detect() -> Self {
        Self {
            client: DesktopClient::detect(),
        }
    }

    /// Whether a directory looks like one this client syncs.
    ///
    /// Used to decide whether to apply this convention at all. Deliberately
    /// cheap and deliberately not authoritative: the client's own database
    /// would answer properly, but it is a private schema, and being wrong here
    /// costs one extra `stat` per read rather than anything correctness
    /// depends on.
    pub fn looks_synced(root: &Path) -> bool {
        std::fs::read_dir(root)
            .map(|entries| {
                entries.flatten().any(|e| {
                    let name = e.file_name();
                    let name = name.to_string_lossy();
                    // The client's per-folder journal sits at the sync root,
                    // and a stub anywhere beneath it is equally conclusive.
                    name.starts_with("._sync_") && name.ends_with(".db")
                        || name.ends_with(dr_types::PLACEHOLDER_SUFFIX)
                })
            })
            .unwrap_or(false)
    }
}

impl dr_sync_folder::Vfs for NextcloudVfs {
    fn name(&self) -> &'static str {
        "Nextcloud"
    }

    fn is_placeholder(&self, on_disk: &str) -> bool {
        on_disk.ends_with(dr_types::PLACEHOLDER_SUFFIX)
    }

    fn real_name<'a>(&self, on_disk: &'a str) -> &'a str {
        on_disk
            .strip_suffix(dr_types::PLACEHOLDER_SUFFIX)
            .unwrap_or(on_disk)
    }

    fn placeholder_name(&self, name: &str) -> std::borrow::Cow<'_, str> {
        std::borrow::Cow::Owned(format!("{name}{}", dr_types::PLACEHOLDER_SUFFIX))
    }

    fn can_materialise(&self) -> bool {
        self.client.is_some()
    }

    fn materialise(&self, local: &Path) -> Result<(), RemoteError> {
        self.client
            .as_ref()
            .ok_or(RemoteError::Unsupported(
                "no Nextcloud desktop client is running to fetch this",
            ))?
            .make_available_locally(local)
    }

    fn dematerialise(&self, local: &Path) -> Result<(), RemoteError> {
        self.client
            .as_ref()
            .ok_or(RemoteError::Unsupported(
                "no Nextcloud desktop client is running to release this",
            ))?
            .make_online_only(local)
    }
}

#[cfg(test)]
mod vfs_tests {
    use super::*;
    use dr_sync_folder::Vfs as _;

    #[test]
    fn a_stub_is_recognised_and_reports_the_photographs_name() {
        let v = NextcloudVfs { client: None };
        assert!(v.is_placeholder("IMG_4130.CR2.nextcloud"));
        assert!(!v.is_placeholder("IMG_4130.CR2"));
        // The name the catalog records, so identity survives a download.
        assert_eq!(v.real_name("IMG_4130.CR2.nextcloud"), "IMG_4130.CR2");
        assert_eq!(v.real_name("IMG_4130.CR2"), "IMG_4130.CR2");
        assert_eq!(v.placeholder_name("IMG_4130.CR2"), "IMG_4130.CR2.nextcloud");
    }

    #[test]
    fn without_a_client_it_refuses_rather_than_pretending() {
        // The folder still works; it just cannot fetch. Silently doing nothing
        // would make a borrow think it had the content.
        let v = NextcloudVfs { client: None };
        assert!(!v.can_materialise());
        assert!(v.materialise(Path::new("/x/a.CR2.nextcloud")).is_err());
        assert!(v.dematerialise(Path::new("/x/a.CR2")).is_err());
    }

    #[test]
    fn an_ordinary_folder_is_not_mistaken_for_a_synced_one() {
        let d = std::env::temp_dir().join("dr-vfs-detect");
        let _ = std::fs::remove_dir_all(&d);
        std::fs::create_dir_all(&d).unwrap();
        std::fs::write(d.join("a.CR2"), b"raw").unwrap();
        assert!(!NextcloudVfs::looks_synced(&d));

        std::fs::write(d.join("b.CR2.nextcloud"), [0u8]).unwrap();
        assert!(NextcloudVfs::looks_synced(&d));
        let _ = std::fs::remove_dir_all(&d);
    }
}