use btlib::{
    blocktree::{Blocktree, ModeAuthorizer},
    crypto::{
        tpm::{TpmCredStore, TpmCreds},
        CredStore,
    },
};
use fuse_backend_rs::{
    api::server::Server,
    transport::{Error, FuseSession},
};
use log::error;
use std::{
    ffi::{c_char, CString},
    fs::{self, File},
    io,
    os::fd::FromRawFd,
    os::{raw::c_int, unix::ffi::OsStrExt},
    path::{Path, PathBuf},
    str::FromStr,
    sync::mpsc::Sender,
};
use tss_esapi::{
    tcti_ldr::{TabrmdConfig, TctiNameConf},
    Context,
};

const DEFAULT_TABRMD: &str = "bus_type=session";
const MOUNT_OPTIONS: &str = "default_permissions";
const FSNAME: &str = "btfuse";
const FSTYPE: &str = "bt";

trait PathExt {
    fn try_create_dir(&self) -> io::Result<()>;
}

impl<T: AsRef<Path>> PathExt for T {
    fn try_create_dir(&self) -> io::Result<()> {
        match fs::create_dir(self) {
            Ok(_) => Ok(()),
            Err(err) => match err.kind() {
                io::ErrorKind::AlreadyExists => Ok(()),
                _ => Err(err),
            },
        }
    }
}

#[link(name = "fuse3")]
extern "C" {
    /// Opens a channel to the kernel.
    fn fuse_open_channel(mountpoint: *const c_char, options: *const c_char) -> c_int;
}

/// Calls into libfuse3 to mount this file system at the given path. The file descriptor to use
/// to communicate with the kernel is returned.
fn mount_at<P: AsRef<Path>>(mnt_point: P) -> File {
    let mountpoint = CString::new(mnt_point.as_ref().as_os_str().as_bytes()).unwrap();
    let options = CString::new(MOUNT_OPTIONS).unwrap();
    let raw_fd = unsafe { fuse_open_channel(mountpoint.as_ptr(), options.as_ptr()) };
    unsafe { File::from_raw_fd(raw_fd) }
}

/// A fuse daemon process.
struct FuseDaemon<'a> {
    /// The path of the directory to store all file system information in.
    path: &'a Path,
    /// The configuration string to use to connect to a Tabrmd instance.
    tabrmd_config: &'a str,
    /// An optional [Sender] which is called when this daemon has finished starting up.
    started_signal: Option<Sender<()>>,
}

impl<'a> FuseDaemon<'a> {
    fn new(path: &'a Path, tabrmd_config: &'a str) -> FuseDaemon<'_> {
        FuseDaemon {
            path,
            tabrmd_config,
            started_signal: None,
        }
    }

    fn tpm_state_path<P: AsRef<Path>>(path: P) -> PathBuf {
        path.as_ref().join("tpm_state")
    }

    fn mnt_path<P: AsRef<Path>>(path: P) -> PathBuf {
        path.as_ref().join("mnt")
    }

    fn server<P: AsRef<Path>>(&self, mnt_path: P) -> Server<Blocktree<TpmCreds, ModeAuthorizer>> {
        let empty = fs::read_dir(&mnt_path)
            .expect("failed to read mountdir")
            .next()
            .is_none();
        let context = Context::new(TctiNameConf::Tabrmd(
            TabrmdConfig::from_str(self.tabrmd_config).expect("failed to parse Tabrmd config"),
        ))
        .expect("failed to connect to Tabrmd");
        let cred_store = TpmCredStore::new(context, Self::tpm_state_path(self.path))
            .expect("failed to create TpmCredStore");
        let node_creds = cred_store
            .node_creds()
            .expect("failed to retrieve node creds");
        let bt_path = self.path.join("bt");
        bt_path
            .try_create_dir()
            .expect("failed to create blocktree directory");
        let fs = if empty {
            Blocktree::new_empty(bt_path, 0, node_creds, ModeAuthorizer {})
        } else {
            Blocktree::new_existing(bt_path, node_creds, ModeAuthorizer {})
        }
        .expect("failed to create blocktree");

        Server::new(fs)
    }

    fn fuse_session<P: AsRef<Path>>(&self, mnt_path: P) -> FuseSession {
        self.path
            .try_create_dir()
            .expect("failed to create main directory");
        let mut session = FuseSession::new(mnt_path.as_ref(), FSNAME, FSTYPE, false)
            .expect("failed to create FUSE session");
        session.set_fuse_file(mount_at(mnt_path));

        session
    }

    fn start(&self) {
        let mnt_path = Self::mnt_path(self.path);
        mnt_path
            .try_create_dir()
            .expect("failed to create mount directory");
        let server = self.server(&mnt_path);
        let session = self.fuse_session(&mnt_path);
        drop(mnt_path);
        let mut channel = session
            .new_channel()
            .expect("failed to create FUSE channel");
        if let Some(tx) = self.started_signal.as_ref() {
            tx.send(()).expect("failed to send started signal");
        }

        loop {
            match channel.get_request() {
                Ok(Some((reader, writer))) => {
                    if let Err(err) = server.handle_message(reader, writer.into(), None, None) {
                        error!("error while handling FUSE message: {err}");
                    }
                }
                Ok(None) => break,
                Err(err) => {
                    match err {
                        // Occurs when the file system is unmounted.
                        Error::SessionFailure(_) => break,
                        _ => error!("{err}"),
                    }
                }
            }
        }
    }
}

fn main() {
    env_logger::init();
    let main_dir = std::env::args().nth(1).expect("no mount point given");
    let main_dir =
        PathBuf::from_str(main_dir.as_str()).expect("failed to convert mount point to PathBuf");
    let tabrmd_string = std::env::var("BT_TABRMD").ok();
    let tabrmd_str = tabrmd_string
        .as_ref()
        .map_or(DEFAULT_TABRMD, |s| s.as_str());
    let daemon = FuseDaemon::new(&main_dir, tabrmd_str);
    daemon.start();
}

#[cfg(test)]
mod test {
    use std::{
        ffi::{OsStr, OsString},
        fs::{
            create_dir, hard_link, metadata, read, read_dir, remove_dir, remove_file,
            set_permissions, write, Permissions, ReadDir,
        },
        os::unix::fs::PermissionsExt,
        sync::mpsc::{channel, Receiver},
        thread::JoinHandle,
        time::Duration,
    };

    use btlib::{crypto::Creds, log::BuilderExt, Epoch, Principaled};
    use swtpm_harness::SwtpmHarness;
    use tempdir::TempDir;

    use super::*;

    /// Unmounts the file system at the given path.
    fn unmount<P: AsRef<Path>>(mnt_path: P) {
        const PROG: &str = "fusermount";
        let mnt_path = mnt_path
            .as_ref()
            .as_os_str()
            .to_str()
            .expect("failed to convert mnt_path to `str`");
        let code = std::process::Command::new(PROG)
            .args(["-u", mnt_path])
            .status()
            .expect("waiting for exit status failed")
            .code()
            .expect("code returned None");
        if code != 0 {
            panic!("{PROG} exited with a non-zero status: {code}");
        }
    }

    fn file_names(read_dir: ReadDir) -> impl Iterator<Item = OsString> {
        read_dir.map(|entry| entry.unwrap().file_name())
    }

    struct TestCase {
        temp_path_rx: Receiver<PathBuf>,
        mnt_path: Option<PathBuf>,
        handle: Option<JoinHandle<()>>,
    }

    impl TestCase {
        const ROOT_PASSWD: &str = "Gnurlingwheel";

        fn new() -> TestCase {
            let (tx, rx) = channel();
            let (started_tx, started_rx) = channel();
            let handle = std::thread::spawn(move || {
                let dir = TempDir::new("btfuse").expect("failed to create TempDir");
                tx.send(dir.path().to_owned()).expect("send failed");
                let swtpm = SwtpmHarness::new().expect("failed to start swtpm");
                {
                    let context = swtpm.context().expect("failed to create TPM context");
                    let cred_store =
                        TpmCredStore::new(context, FuseDaemon::tpm_state_path(dir.path()))
                            .expect("failed to create TpmCredStore");
                    let root_creds = cred_store
                        .gen_root_creds(Self::ROOT_PASSWD)
                        .expect("failed to gen root creds");
                    let mut node_creds = cred_store.node_creds().expect("failed to get node creds");
                    let expires = Epoch::now() + Duration::from_secs(3600);
                    let writecap = root_creds
                        .issue_writecap(node_creds.principal(), vec![], expires)
                        .expect("failed to issue writecap to node creds");
                    cred_store
                        .assign_node_writecap(&mut node_creds, writecap)
                        .expect("failed to assign writecap");
                }
                let mut daemon = FuseDaemon::new(dir.path(), swtpm.tabrmd_config());
                daemon.started_signal = Some(started_tx);
                daemon.start()
            });
            started_rx
                .recv_timeout(Duration::from_secs(1))
                .expect("failed to received started signal from `FuseDaemon`");
            println!("sent started signal");
            TestCase {
                temp_path_rx: rx,
                mnt_path: None,
                handle: Some(handle),
            }
        }

        fn mnt_path(&mut self) -> &PathBuf {
            self.mnt_path.get_or_insert_with(|| {
                let temp_path = self
                    .temp_path_rx
                    .recv_timeout(Duration::from_secs(1))
                    .expect("receive failed");
                FuseDaemon::mnt_path(temp_path)
            })
        }

        fn wait(&mut self) {
            if let Some(handle) = self.handle.take() {
                handle.join().expect("join failed");
            }
        }

        fn unmount_and_wait(&mut self) {
            // If `handle` has already been taken that means `wait` has already been called. If
            // this thread called `wait` and subsequently became unblocked, we know that the FUSE
            // thread halted, which only happens when the file system is unmounted. Hence
            // we don't have to unmount it, nor wait for the FUSE thread.
            if self.handle.is_none() {
                return;
            }
            let mnt_path = self.mnt_path();
            unmount(mnt_path);
            self.wait();
        }
    }

    impl Drop for TestCase {
        fn drop(&mut self) {
            self.unmount_and_wait();
        }
    }

    /// Creates a new file system and mounts it at `/tmp/btfuse.<random>/mnt` so it can be
    /// tested manually.
    //#[test]
    #[allow(dead_code)]
    fn manual_test() {
        std::env::set_var("RUST_LOG", "debug");
        env_logger::Builder::from_default_env().btformat().init();
        let mut case = TestCase::new();
        case.wait();
    }

    /// Tests if the file system can be mount then unmounted successfully.
    #[test]
    fn mount_then_unmount() {
        let _ = TestCase::new();
    }

    #[test]
    fn write_read() {
        const EXPECTED: &[u8] =
            b"The paths to failure are uncountable, yet to success there is but one.";
        let mut case = TestCase::new();
        let file_path = case.mnt_path().join("file");

        write(&file_path, EXPECTED).expect("write failed");

        let actual = read(&file_path).expect("read failed");
        assert_eq!(EXPECTED, actual);
    }

    #[test]
    fn create_file_then_readdir() {
        const DATA: &[u8] = b"Au revoir Shoshanna!";
        let file_name = OsStr::new("landa_dialog.txt");
        let expected = [file_name];
        let mut case = TestCase::new();
        let mnt_path = case.mnt_path();
        let file_path = mnt_path.join(file_name);

        write(&file_path, DATA).expect("write failed");

        let first = file_names(read_dir(&mnt_path).expect("read_dir failed"));
        assert!(first.eq(expected));
        let second = file_names(read_dir(&mnt_path).expect("read_dir failed"));
        assert!(second.eq(expected));
    }

    #[test]
    fn create_then_delete_file() {
        const DATA: &[u8] = b"The universe is hostile, so impersonal. Devour to survive";
        let file_name = OsStr::new("tool_lyrics.txt");
        let mut case = TestCase::new();
        let mnt_path = case.mnt_path();
        let file_path = mnt_path.join(file_name);
        write(&file_path, DATA).expect("write failed");

        remove_file(&file_path).expect("remove_file failed");

        let expected: [&OsStr; 0] = [];
        assert!(file_names(read_dir(&mnt_path).expect("read_dir failed")).eq(expected))
    }

    #[test]
    fn hard_link_then_remove() {
        const EXPECTED: &[u8] = b"And the lives we've reclaimed";
        let name1 = OsStr::new("refugee_lyrics.txt");
        let name2 = OsStr::new("rise_against_lyrics.txt");
        let mut case = TestCase::new();
        let mnt_path = case.mnt_path();
        let path1 = mnt_path.join(name1);
        let path2 = mnt_path.join(name2);
        write(&path1, EXPECTED).expect("write failed");

        hard_link(&path1, &path2).expect("hard_link failed");
        remove_file(&path1).expect("remove_file failed");

        let actual = read(&path2).expect("read failed");
        assert_eq!(EXPECTED, actual);
    }

    #[test]
    fn hard_link_then_remove_both() {
        const EXPECTED: &[u8] = b"And the lives we've reclaimed";
        let name1 = OsStr::new("refugee_lyrics.txt");
        let name2 = OsStr::new("rise_against_lyrics.txt");
        let mut case = TestCase::new();
        let mnt_path = case.mnt_path();
        let path1 = mnt_path.join(name1);
        let path2 = mnt_path.join(name2);
        write(&path1, EXPECTED).expect("write failed");

        hard_link(&path1, &path2).expect("hard_link failed");
        remove_file(&path1).expect("remove_file on path1 failed");
        remove_file(&path2).expect("remove_file on path2 failed");

        let expected: [&OsStr; 0] = [];
        assert!(file_names(read_dir(&mnt_path).expect("read_dir failed")).eq(expected));
    }

    #[test]
    fn set_mode_bits() {
        const EXPECTED: u32 = libc::S_IFREG | 0o777;
        let mut case = TestCase::new();
        let file_path = case.mnt_path().join("bagobits");
        write(&file_path, []).expect("write failed");
        let original = metadata(&file_path)
            .expect("metadata failed")
            .permissions()
            .mode();
        assert_ne!(EXPECTED, original);

        set_permissions(&file_path, Permissions::from_mode(EXPECTED))
            .expect("set_permissions failed");

        let actual = metadata(&file_path)
            .expect("metadata failed")
            .permissions()
            .mode();
        assert_eq!(EXPECTED, actual);
    }

    #[test]
    fn create_directory() {
        const EXPECTED: &str = "etc";
        let mut case = TestCase::new();
        let mnt_path = case.mnt_path();
        let dir_path = mnt_path.join(EXPECTED);

        create_dir(&dir_path).expect("create_dir failed");

        let actual = file_names(read_dir(mnt_path).expect("read_dir failed"));
        assert!(actual.eq([EXPECTED]));
    }

    #[test]
    fn create_file_under_new_directory() {
        const DIR_NAME: &str = "etc";
        const FILE_NAME: &str = "file";
        let mut case = TestCase::new();
        let mnt_path = case.mnt_path();
        let dir_path = mnt_path.join(DIR_NAME);
        let file_path = dir_path.join(FILE_NAME);

        create_dir(&dir_path).expect("create_dir failed");
        write(&file_path, []).expect("write failed");

        let actual = file_names(read_dir(dir_path).expect("read_dir failed"));
        assert!(actual.eq([FILE_NAME]));
    }

    #[test]
    fn create_then_remove_directory() {
        const DIR_NAME: &str = "etc";
        let mut case = TestCase::new();
        let mnt_path = case.mnt_path();
        let dir_path = mnt_path.join(DIR_NAME);

        create_dir(&dir_path).expect("create_dir failed");
        remove_dir(&dir_path).expect("remove_dir failed");

        let actual = file_names(read_dir(&mnt_path).expect("read_dir failed"));
        const EMPTY: [&str; 0] = [""; 0];
        assert!(actual.eq(EMPTY));
    }

    #[test]
    fn read_only_dir_cant_create_subdir() {
        const DIR_NAME: &str = "etc";
        let mut case = TestCase::new();
        let dir_path = case.mnt_path().join(DIR_NAME);
        create_dir(&dir_path).expect("create_dir failed");
        set_permissions(&dir_path, Permissions::from_mode(libc::S_IFDIR | 0o444))
            .expect("set_permissions failed");

        let result = create_dir(dir_path.join("sub"));

        let err = result.err().expect("create_dir returned `Ok`");
        let os_err = err.raw_os_error().expect("raw_os_error was empty");
        assert_eq!(os_err, libc::EACCES);
    }

    #[test]
    fn read_only_dir_cant_remove_subdir() {
        const DIR_NAME: &str = "etc";
        let mut case = TestCase::new();
        let dir_path = case.mnt_path().join(DIR_NAME);
        let sub_path = dir_path.join("sub");
        create_dir(&dir_path).expect("create_dir failed");
        create_dir(&sub_path).expect("create_dir failed");
        set_permissions(&dir_path, Permissions::from_mode(libc::S_IFDIR | 0o444))
            .expect("set_permissions failed");

        let result = remove_dir(&sub_path);

        let err = result.err().expect("remove_dir returned `Ok`");
        let os_err = err.raw_os_error().expect("raw_os_error was empty");
        assert_eq!(os_err, libc::EACCES);
    }
}