//! Filesystem APIs for GDB, vFile

use bitflags::bitflags;
use std::io::{self, prelude::*};

/// Errno values for Host I/O operations.
#[derive(Debug)]
pub enum HostErrno {
    /// Operation not permitted (POSIX.1-2001).
    EPERM = 1,
    /// No such file or directory (POSIX.1-2001).
    ///
    /// Typically, this error results when a specified pathname does not exist,
    /// or one of the components in the directory prefix of a pathname does not
    /// exist, or the specified pathname is a dangling symbolic link.
    ENOENT = 2,
    /// Interrupted function call (POSIX.1-2001); see signal(7).
    EINTR = 4,
    /// Bad file descriptor (POSIX.1-2001).
    EBADF = 9,
    /// Permission denied (POSIX.1-2001).
    EACCES = 13,
    /// Bad address (POSIX.1-2001).
    EFAULT = 14,
    /// Device or resource busy (POSIX.1-2001).
    EBUSY = 16,
    /// File exists (POSIX.1-2001).
    EEXIST = 17,
    /// No such device (POSIX.1-2001).
    ENODEV = 19,
    /// Not a directory (POSIX.1-2001).
    ENOTDIR = 20,
    /// Is a directory (POSIX.1-2001).
    EISDIR = 21,
    /// Invalid argument (POSIX.1-2001).
    EINVAL = 22,
    /// Too many open files in system (POSIX.1-2001). On Linux, this is probably
    /// a result of encountering the /proc/sys/fs/file-max limit (see proc(5)).
    ENFILE = 23,
    /// Too many open files (POSIX.1-2001). Commonly caused by exceeding the
    /// RLIMIT_NOFILE resource limit described in getrlimit(2).
    EMFILE = 24,
    /// File too large (POSIX.1-2001).
    EFBIG = 27,
    /// No space left on device (POSIX.1-2001).
    ENOSPC = 28,
    /// Invalid seek (POSIX.1-2001).
    ESPIPE = 29,
    /// Read-only filesystem (POSIX.1-2001).
    EROFS = 30,
    /// Filename too long (POSIX.1-2001).
    ENAMETOOLONG = 91,
    /// Unknown errno - there may not be a GDB mapping for this value
    EUNKNOWN = 9999,
}

/// The result type for host I/O operations.  Return error if the operation
/// in question is not implemented.  Otherwise, the success type indicates
/// whether the operation succeeded, with `HostErrno` values for failure.
pub type IOResult<T> = Result<Result<T, HostErrno>, ()>;

bitflags! {
    /// Host file permissions.
    pub struct HostMode: u32 {
        /// A regular file.
        const S_IFREG = 0o100000;
        /// A directory.
        const S_IFDIR = 0o40000;
        /// User read permissions.
        const S_IRUSR = 0o400;
        /// User write permissions.
        const S_IWUSR = 0o200;
        /// User execute permissions.
        const S_IXUSR = 0o100;
        /// Group read permissions.
        const S_IRGRP = 0o40;
        /// Group write permissions
        const S_IWGRP = 0o20;
        /// Group execute permissions.
        const S_IXGRP = 0o10;
        /// World read permissions.
        const S_IROTH = 0o4;
        /// World write permissions
        const S_IWOTH = 0o2;
        /// World execute permissions.
        const S_IXOTH = 0o1;
    }
}

bitflags! {
    // The read/write flags below may look a little weird, but that is the way
    // they are defined in the protocol.
    /// Host flags for opening files.
    pub struct HostOpenFlags: u32 {
        /// A read-only file.
        const O_RDONLY = 0x0;
        /// A write-only file.
        const O_WRONLY = 0x1;
        /// A read-write file.
        const O_RDWR = 0x2;
        /// Append to an existing file.
        const O_APPEND = 0x8;
        /// Create a non-existent file.
        const O_CREAT = 0x200;
        /// Truncate an existing file.
        const O_TRUNC = 0x400;
        /// Exclusive access.
        const O_EXCL = 0x800;
    }
}

/// Data returned by a host fstat request.  The members of this structure are
/// specified by the remote protocol; conversion of actual host stat
/// information into this structure may therefore require truncation of some
/// members.
#[derive(Debug)]
pub struct HostStat {
    /// The device.
    pub st_dev: u32,
    /// The inode.
    pub st_ino: u32,
    /// Protection bits.
    pub st_mode: HostMode,
    /// The number of hard links.
    pub st_nlink: u32,
    /// The user id of the owner.
    pub st_uid: u32,
    /// The group id of the owner.
    pub st_gid: u32,
    /// The device type, if an inode device.
    pub st_rdev: u32,
    /// The size of the file in bytes.
    pub st_size: u64,
    /// The blocksize for the filesystem.
    pub st_blksize: u64,
    /// The number of blocks allocated.
    pub st_blocks: u64,
    /// The last time the file was accessed, in seconds since the epoch.
    pub st_atime: u32,
    /// The last time the file was modified, in seconds since the epoch.
    pub st_mtime: u32,
    /// The last time the file was changed, in seconds since the epoch.
    pub st_ctime: u32,
}

// Having to write out all the fields for these two operations is annoying,
// but the alternatives are even more annoying.  For instance, we could
// represent HostStat as a big array, with fields at appropriate offsets, but
// we'd have to write a bunch of accessor methods.  Note that #[repr(C)]
// isn't quite good enough, since that might introduce C-mandated padding
// into the structure.
pub fn write_stat<W>(writer: &mut W, stat: HostStat) -> io::Result<()>
where
    W: Write,
{
    use byteorder::{BigEndian, WriteBytesExt};

    writer.write_u32::<BigEndian>(stat.st_dev)?;
    writer.write_u32::<BigEndian>(stat.st_ino)?;
    writer.write_u32::<BigEndian>(stat.st_mode.bits())?;
    writer.write_u32::<BigEndian>(stat.st_nlink)?;
    writer.write_u32::<BigEndian>(stat.st_uid)?;
    writer.write_u32::<BigEndian>(stat.st_gid)?;
    writer.write_u32::<BigEndian>(stat.st_rdev)?;
    writer.write_u64::<BigEndian>(stat.st_size)?;
    writer.write_u64::<BigEndian>(stat.st_blksize)?;
    writer.write_u64::<BigEndian>(stat.st_blocks)?;
    writer.write_u32::<BigEndian>(stat.st_atime)?;
    writer.write_u32::<BigEndian>(stat.st_mtime)?;
    writer.write_u32::<BigEndian>(stat.st_ctime)
}

#[allow(dead_code)]
pub fn read_stat(v: &[u8]) -> io::Result<HostStat> {
    use byteorder::{BigEndian, ReadBytesExt};
    use std::io::Cursor;

    let mut r = Cursor::new(v);
    let st_dev = r.read_u32::<BigEndian>()?;
    let st_ino = r.read_u32::<BigEndian>()?;
    let st_mode = HostMode::from_bits_truncate(r.read_u32::<BigEndian>()?);
    let st_nlink = r.read_u32::<BigEndian>()?;
    let st_uid = r.read_u32::<BigEndian>()?;
    let st_gid = r.read_u32::<BigEndian>()?;
    let st_rdev = r.read_u32::<BigEndian>()?;
    let st_size = r.read_u64::<BigEndian>()?;
    let st_blksize = r.read_u64::<BigEndian>()?;
    let st_blocks = r.read_u64::<BigEndian>()?;
    let st_atime = r.read_u32::<BigEndian>()?;
    let st_mtime = r.read_u32::<BigEndian>()?;
    let st_ctime = r.read_u32::<BigEndian>()?;

    Ok(HostStat {
        st_dev,
        st_ino,
        st_mode,
        st_nlink,
        st_uid,
        st_gid,
        st_rdev,
        st_size,
        st_blksize,
        st_blocks,
        st_atime,
        st_mtime,
        st_ctime,
    })
}

/// TODO: doc
pub trait FileSystem {
    /// Open a file on the remote stub's current filesystem.
    fn host_open(&self, _filename: Vec<u8>, _flags: HostOpenFlags, _mode: HostMode) -> IOResult<u64> {
        Err(())
    }

    /// Close a file opened with `host_open`.
    fn host_close(&self, _fd: u64) -> IOResult<()> {
        Err(())
    }

    /// Read data from an open file at the given offset.
    fn host_pread(&self, _fd: u64, _count: u64, _offset: u64) -> IOResult<Vec<u8>> {
        Err(())
    }

    /// Write data to an open file at the given offset.
    fn host_pwrite(&self, _fd: u64, _offset: u64, _data: Vec<u8>) -> IOResult<u64> {
        Err(())
    }

    /// Return a `HostStat` describing the attributes of the given open file.
    fn host_fstat(&self, _fd: u64) -> IOResult<HostStat> {
        Err(())
    }

    /// Remove a file from the remote stub's current filesystem.
    fn host_unlink(&self, _filename: Vec<u8>) -> IOResult<()> {
        Err(())
    }

    /// Read the contents of a symbolic link on the remote stub's current filesystem.
    fn host_readlink(&self, _filename: Vec<u8>) -> IOResult<Vec<u8>> {
        Err(())
    }

    /// Set the current filesystem for subsequent host I/O requests.  If the
    /// given pid is 0, select the filesystem of the remote stub.  Otherwise,
    /// select the filesystem as seen by the process with the given pid.
    fn host_setfs(&self, _pid: u64) -> IOResult<()> {
        Err(())
    }
}

#[test]
fn stat_size() {
    // See https://sourceware.org/gdb/onlinedocs/gdb/struct-stat.html#struct-stat
    // 10 int  fields (32 bits, 4 bytes)
    // 3  long fields (64 bits, 8 bytes)
    use std::mem;
    assert_eq!(mem::size_of::<HostStat>(), 4 * 10 + 8 * 3);
}