package org.jruby.util.io;

import java.io.Closeable;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.Channel;
import java.nio.channels.Channels;
import java.nio.channels.FileLock;
import java.nio.channels.OverlappingFileLockException;
import java.nio.channels.Pipe;

import jnr.constants.platform.Errno;
import jnr.constants.platform.Fcntl;
import jnr.posix.FileStat;
import jnr.posix.POSIX;

import org.jruby.Ruby;
import org.jruby.ext.fcntl.FcntlLibrary;
import org.jruby.platform.Platform;
import org.jruby.runtime.Helpers;
import org.jruby.util.JRubyFile;
import org.jruby.util.ResourceException;

Representations of as many native posix functions as possible applied to an NIO channel
/**
 * Representations of as many native posix functions as possible applied to an NIO channel
 */
public class PosixShim {
    public static final int LOCK_SH = 1;
    public static final int LOCK_EX = 2;
    public static final int LOCK_NB = 4;
    public static final int LOCK_UN = 8;

    public static final int SEEK_SET = 0;
    public static final int SEEK_CUR = 1;
    public static final int SEEK_END = 2;

    public PosixShim(Ruby runtime) {
        this.runtime = runtime;
        this.posix = runtime.getPosix();
    }
    
    // pseudo lseek(2)
    public long lseek(ChannelFD fd, long offset, int type) {
        clear();

        if (fd.chSeek != null) {
            int adj = 0;
            try {
                switch (type) {
                    case SEEK_SET:
                        return fd.chSeek.position(offset).position();
                    case SEEK_CUR:
                        return fd.chSeek.position(fd.chSeek.position() - adj + offset).position();
                    case SEEK_END:
                        return fd.chSeek.position(fd.chSeek.size() + offset).position();
                    default:
                        setErrno(Errno.EINVAL);
                        return -1;
                }
            } catch (IllegalArgumentException e) {
                setErrno(Errno.EINVAL);
                return -1;
            } catch (IOException ioe) {
                setErrno(Helpers.errnoFromException(ioe));
                return -1;
            }
        } else if (fd.chNative != null) {
            // native channel, use native lseek
            long ret = posix.lseekLong(fd.chNative.getFD(), offset, type);
            if (ret == -1) setErrno(Errno.valueOf(posix.errno()));
            return ret;
        }

        if (fd.chSelect != null) {
            // For other channel types, we can't get at a native descriptor to lseek, and we can't use FileChannel
            // .position, so we have to treat them as unseekable and raise EPIPE
            //
            // TODO: It's perhaps just a coincidence that all the channels for
            // which we should raise are instanceof SelectableChannel, since
            // stdio is not...so this bothers me slightly. -CON
            //
            // Original change made in 66b024fedbb2ee32316ccd9de8387931d07993ec
            setErrno(Errno.EPIPE);
            return -1;
        }

        return 0;
    }

    public int write(ChannelFD fd, byte[] bytes, int offset, int length, boolean nonblock) {
        clear();

        // FIXME: don't allocate every time
        ByteBuffer tmp = ByteBuffer.wrap(bytes, offset, length);
        try {
            if (nonblock) {
                // TODO: figure out what nonblocking writes against atypical streams (files?) actually do
                // If we can't set the channel nonblocking, I'm not sure what we can do to
                // pretend the channel is nonblocking.
            }

            if (fd.chWrite == null) {
                setErrno(Errno.EACCES);
                return -1;
            }
            int written = fd.chWrite.write(tmp);

            if (written == 0 && length > 0) {
                // if it's a nonblocking write against a file and we've hit EOF, do EAGAIN
                if (nonblock) {
                    setErrno(Errno.EAGAIN);
                    return -1;
                }
            }

            return written;
        } catch (IOException ioe) {
            setErrno(Helpers.errnoFromException(ioe));
            error = ioe;
            return -1;
        }
    }

    private static final int NATIVE_EOF = 0;
    private static final int JAVA_EOF = -1;

    public int read(ChannelFD fd, byte[] target, int offset, int length, boolean nonblock) {
        clear();

        try {
            if (nonblock) {
                // need to ensure channels that don't support nonblocking IO at least
                // appear to be nonblocking
                if (fd.chSelect != null) {
                    // ok...we should have set it nonblocking already in setNonblock
                } else {
                    if (fd.chFile != null) {
                        long position = fd.chFile.position();
                        long size = fd.chFile.size();
                        if (position != -1 && size != -1 && position < size) {
                            // there should be bytes available...proceed
                        } else {
                            setErrno(Errno.EAGAIN);
                            return -1;
                        }
                    } else if (fd.chNative != null && fd.isNativeFile) {
                        // it's a native file, so we don't do selection or nonblock
                    } else {
                        setErrno(Errno.EAGAIN);
                        return -1;
                    }
                }
            }

            // FIXME: inefficient to recreate ByteBuffer every time
            ByteBuffer buffer = ByteBuffer.wrap(target, offset, length);
            int read = fd.chRead.read(buffer);

            if (nonblock) {
                if (read == JAVA_EOF) {
                    read = NATIVE_EOF; // still treat EOF as EOF
                } else if (read == 0) {
                    setErrno(Errno.EAGAIN);
                    return -1;
                } else {
                    return read;
                }
            } else {
                // NIO channels will always raise for errors, so -1 only means EOF.
                if (read == JAVA_EOF) read = NATIVE_EOF;
            }

            return read;
        } catch (IOException ioe) {
            setErrno(Helpers.errnoFromException(ioe));
            return -1;
        }
    }

    // rb_thread_flock
    public int flock(ChannelFD fd, int lockMode) {
        // TODO: null channel always succeeds for all locking operations
//        if (descriptor.isNull()) return RubyFixnum.zero(runtime);

        clear();

        int real_fd = fd.realFileno;

        if (posix.isNative() && real_fd != -1 && real_fd < FilenoUtil.FIRST_FAKE_FD && !Platform.IS_SOLARIS) {
            // we have a real fd and not on Solaris...try native flocking
            // see jruby/jruby#3254 and jnr/jnr-posix#60
            int result = posix.flock(real_fd, lockMode);
            if (result < 0) {
                setErrno(Errno.valueOf(posix.errno()));
                return -1;
            }
            return 0;
        }

        if (fd.chFile != null) {
            int ret = checkSharedExclusive(fd, lockMode);
            if (ret < 0) return ret;

            if (!lockStateChanges(fd.currentLock.get(), lockMode)) return 0;

            try {
                synchronized (fd.chFile) {
                    // check again, to avoid unnecessary overhead
                    if (!lockStateChanges(fd.currentLock.get(), lockMode)) return 0;

                    switch (lockMode) {
                        case LOCK_UN:
                        case LOCK_UN | LOCK_NB:
                            return unlock(fd);
                        case LOCK_EX:
                            return lock(fd, true);
                        case LOCK_EX | LOCK_NB:
                            return tryLock(fd, true);
                        case LOCK_SH:
                            return lock(fd, false);
                        case LOCK_SH | LOCK_NB:
                            return tryLock(fd, false);
                    }
                }
            } catch (IOException ioe) {
                setErrno(Helpers.errnoFromException(ioe));
                return -1;
            } catch (OverlappingFileLockException ioe) {
                setErrno(Errno.EINVAL);
                errmsg = "overlapping file locks";
            }
            return lockFailedReturn(lockMode);
        } else {
            // We're not actually a real file, so we can't flock
            // FIXME: This needs to be ENOTSUP
            setErrno(Errno.EINVAL);
            errmsg = "stream is not a file";
            return -1;
        }
    }

    public int dup2(ChannelFD filedes, ChannelFD filedes2) {
        return filedes2.dup2From(posix, filedes);
    }

    public int close(ChannelFD fd) {
        return close((Closeable)fd);
    }

    public int close(Closeable closeable) {
        clear();

        try {
            closeable.close();
            return 0;
        } catch (IOException ioe) {
            Errno errno = Helpers.errnoFromException(ioe);
            if (errno == null) {
                throw new RuntimeException("unknown IOException: " + ioe);
            }
            this.setErrno(errno);
            return -1;
        }
    }

    public Channel[] pipe() {
        clear();
        try {
            Pipe pipe = Pipe.open();
            Channel source = pipe.source(), sink = pipe.sink();

            if (posix.isNative() && !Platform.IS_WINDOWS) {
                // set cloexec if possible
                int read = FilenoUtil.filenoFrom(source);
                int write = FilenoUtil.filenoFrom(sink);
                setCloexec(read, true);
                setCloexec(write, true);
            }

            return new Channel[]{source, sink};
        } catch (IOException ioe) {
            setErrno(Helpers.errnoFromException(ioe));
            return null;
        }
    }

    
The appropriate errno value for the last thrown error, if any.
/**
     * The appropriate errno value for the last thrown error, if any.
     */
    public Errno getErrno() {
        return errno.get();
    }

    public void setErrno(Errno errno) {
        this.errno.set(errno);
    }

    public interface WaitMacros {
        public abstract boolean WIFEXITED(long status);
        public abstract boolean WIFSIGNALED(long status);
        public abstract int WTERMSIG(long status);
        public abstract int WEXITSTATUS(long status);
        public abstract int WSTOPSIG(long status);
        public abstract boolean WIFSTOPPED(long status);
        public abstract boolean WCOREDUMP(long status);
    }

    public static class BSDWaitMacros implements WaitMacros {
        public final long _WSTOPPED = 0177;

        // Only confirmed on Darwin
        public final long WCOREFLAG = 0200;

        public long _WSTATUS(long status) {
            return status & _WSTOPPED;
        }

        public boolean WIFEXITED(long status) {
            return _WSTATUS(status) == 0;
        }

        public boolean WIFSIGNALED(long status) {
            return _WSTATUS(status) != _WSTOPPED && _WSTATUS(status) != 0;
        }

        public int WTERMSIG(long status) {
            return (int)_WSTATUS(status);
        }

        public int WEXITSTATUS(long status) {
            // not confirmed on all platforms
            return (int)((status >>> 8) & 0xFF);
        }

        public int WSTOPSIG(long status) {
            return (int)(status >>> 8);
        }

        public boolean WIFSTOPPED(long status) {
            return _WSTATUS(status) == _WSTOPPED && WSTOPSIG(status) != 0x13;
        }

        public boolean WCOREDUMP(long status) {
            return (status & WCOREFLAG) != 0;
        }
    }

    public static class LinuxWaitMacros implements WaitMacros {
        private int __WAIT_INT(long status) { return (int)status; }

        private int __W_EXITCODE(int ret, int sig) { return (ret << 8) | sig; }
        private int __W_STOPCODE(int sig) { return (sig << 8) | 0x7f; }
        private static int __W_CONTINUED = 0xffff;
        private static int __WCOREFLAG = 0x80;

        /* If WIFEXITED(STATUS), the low-order 8 bits of the status.  */
        private int __WEXITSTATUS(long status) { return (int)((status & 0xff00) >> 8); }

        /* If WIFSIGNALED(STATUS), the terminating signal.  */
        private int __WTERMSIG(long status) { return (int)(status & 0x7f); }

        /* If WIFSTOPPED(STATUS), the signal that stopped the child.  */
        private int __WSTOPSIG(long status) { return __WEXITSTATUS(status); }

        /* Nonzero if STATUS indicates normal termination.  */
        private boolean __WIFEXITED(long status) { return __WTERMSIG(status) == 0; }

        /* Nonzero if STATUS indicates termination by a signal.  */
        private boolean __WIFSIGNALED(long status) {
            return ((status & 0x7f) + 1) >> 1 > 0;
        }

        /* Nonzero if STATUS indicates the child is stopped.  */
        private boolean __WIFSTOPPED(long status) { return (status & 0xff) == 0x7f; }

        /* Nonzero if STATUS indicates the child dumped core.  */
        private boolean __WCOREDUMP(long status) { return (status & __WCOREFLAG) != 0; }

        /* Macros for constructing status values.  */
        public int WEXITSTATUS(long status) { return __WEXITSTATUS (__WAIT_INT (status)); }
        public int WTERMSIG(long status) { return __WTERMSIG(__WAIT_INT(status)); }
        public int WSTOPSIG(long status) { return __WSTOPSIG(__WAIT_INT(status)); }
        public boolean WIFEXITED(long status) { return __WIFEXITED(__WAIT_INT(status)); }
        public boolean WIFSIGNALED(long status) { return __WIFSIGNALED(__WAIT_INT(status)); }
        public boolean WIFSTOPPED(long status) { return __WIFSTOPPED(__WAIT_INT(status)); }
        public boolean WCOREDUMP(long status) { return __WCOREDUMP(__WAIT_INT(status)); }
    }

    public static final WaitMacros WAIT_MACROS;
    static {
        if (Platform.IS_BSD) {
            WAIT_MACROS = new BSDWaitMacros();
        } else {
            // need other platforms
            WAIT_MACROS = new LinuxWaitMacros();
        }
    }

    public int setCloexec(int fd, boolean cloexec) {
        int ret = posix.fcntl(fd, Fcntl.F_GETFD);
        if (ret == -1) {
            setErrno(Errno.valueOf(posix.errno()));
            return -1;
        }
        if (
                (cloexec && (ret & FcntlLibrary.FD_CLOEXEC) == FcntlLibrary.FD_CLOEXEC)
                || (!cloexec && (ret & FcntlLibrary.FD_CLOEXEC) == 0)) {
            return 0;
        }
        ret = cloexec ?
                ret | FcntlLibrary.FD_CLOEXEC :
                ret & ~FcntlLibrary.FD_CLOEXEC;
        ret = posix.fcntlInt(fd, Fcntl.F_SETFD, ret);
        if (ret == -1) setErrno(Errno.valueOf(posix.errno()));
        return ret;
    }

    public int fcntlSetFD(int fd, int flags) {
        int ret = posix.fcntlInt(fd, Fcntl.F_SETFD, flags);
        if (ret == -1) setErrno(Errno.valueOf(posix.errno()));
        return ret;
    }

    public int fcntlGetFD(int fd) {
        int ret = posix.fcntl(fd, Fcntl.F_GETFD);
        if (ret == -1) {
            setErrno(Errno.valueOf(posix.errno()));
        }
        return ret;
    }

    public Channel open(String cwd, String path, int flags, int perm) {
        if (Platform.IS_WINDOWS && (path.equals("/dev/null") || path.equalsIgnoreCase("nul"))) {
            path = "NUL:";
        }

        try {
            return JRubyFile.createResource(runtime, cwd, path).openChannel(flags, perm);
        } catch (ResourceException.FileExists e) {
            setErrno(Errno.EEXIST);
        } catch (ResourceException.FileIsDirectory e) {
            setErrno(Errno.EISDIR);
        } catch (ResourceException.FileIsNotDirectory e) {
            setErrno(Errno.ENOTDIR);
        } catch (ResourceException.NotFound e) {
            setErrno(Errno.ENOENT);
        } catch (ResourceException.PermissionDenied e) {
            setErrno(Errno.EACCES);
        } catch (ResourceException.TooManySymlinks e) {
            setErrno(Errno.ELOOP);
        } catch (ResourceException ex) {
            throw ex.newRaiseException(runtime);
        } catch (IOException ex) {
            throw runtime.newIOErrorFromException(ex);
        }
        return null;
    }

    // no longer used
    public Channel open(String cwd, String path, ModeFlags flags, int perm) {
        return open(cwd, path, flags, perm);
    }

    @Deprecated // special case is already handled with JRubyFile.createResource
    public Channel open(String cwd, String path, ModeFlags flags, int perm, ClassLoader classLoader) {
        if (path.startsWith("classpath:/") && classLoader != null) {
            path = path.substring("classpath:/".length());
            return Channels.newChannel(classLoader.getResourceAsStream(path));
        }

        return open(cwd, path, flags, perm);
    }

    
Joy of POSIX, only way to get the umask is to set the umask,
then set it back. That's unsafe in a threaded program. We
minimize but may not totally remove this race by caching the
obtained or previously set (see umask() above) umask and using
that as the initial set value which, cross fingers, is a
no-op. The cache access is then synchronized. TODO: Better?
/**
     * Joy of POSIX, only way to get the umask is to set the umask,
     * then set it back. That's unsafe in a threaded program. We
     * minimize but may not totally remove this race by caching the
     * obtained or previously set (see umask() above) umask and using
     * that as the initial set value which, cross fingers, is a
     * no-op. The cache access is then synchronized. TODO: Better?
     */
    public static int umask(POSIX posix) {
        synchronized (_umaskLock) {
            final int umask = posix.umask(_cachedUmask);
            if (_cachedUmask != umask ) {
                posix.umask(umask);
                _cachedUmask = umask;
            }
            return umask;
        }
    }

    public static int umask(POSIX posix, int newMask) {
        int oldMask;
        synchronized (_umaskLock) {
            oldMask = posix.umask(newMask);
            _cachedUmask = newMask;
        }
        return oldMask;
    }

    public int ftruncate(ChannelFD fd, long pos) {
        if (fd.chNative != null) {
            int ret = posix.ftruncate(fd.chNative.getFD(), pos);
            if (ret == -1) setErrno(Errno.valueOf(posix.errno()));
            return ret;
        } else if (fd.chFile != null) {
            try {
                fd.chFile.truncate(pos);
            } catch (IOException ioe) {
                setErrno(Helpers.errnoFromException(ioe));
                return -1;
            }
        } else {
            setErrno(Errno.EINVAL);
            return -1;
        }
        return 0;
    }

    public long size(ChannelFD fd) {
        if (fd.chNative != null) { // native fd, use fstat
            FileStat stat = posix.allocateStat();
            int ret = posix.fstat(fd.chNative.getFD(), stat);
            if (ret == -1) {
                setErrno(Errno.valueOf(posix.errno()));
                return -1;
            }
            return stat.st_size();
        } else if (fd.chSeek != null) { // if it is seekable, get size directly
            try {
                return fd.chSeek.size();
            } catch (IOException ioe) {
                setErrno(Helpers.errnoFromException(ioe));
                return -1;
            }
        } else {
            // otherwise just return -1 (should be rare, since size is only defined on File
            setErrno(Errno.EINVAL);
            return -1;
        }
    }

    private void clear() {
        setErrno(null);
        errmsg = null;
    }

    private int checkSharedExclusive(ChannelFD fd, int lockMode) {
        // This logic used to attempt a shared lock instead of an exclusive
        // lock, because LOCK_EX on some systems (as reported in JRUBY-1214)
        // allow exclusively locking a read-only file. However, the JDK
        // APIs do not allow acquiring an exclusive lock on files that are
        // not open for read, and there are other platforms (such as Solaris,
        // see JRUBY-5627) that refuse at an *OS* level to exclusively lock
        // files opened only for read. As a result, this behavior is platform-
        // dependent, and so we will obey the JDK's policy of disallowing
        // exclusive locks on files opened only for read.
        if (fd.chWrite == null && (lockMode & LOCK_EX) > 0) {
            setErrno(Errno.EINVAL);
            errmsg = "cannot acquire exclusive lock on File not opened for write";
            return -1;
        }

        // Likewise, JDK does not allow acquiring a shared lock on files
        // that have not been opened for read. We comply here.
        if (fd.chRead == null && (lockMode & LOCK_SH) > 0) {
            setErrno(Errno.EINVAL);
            errmsg = "cannot acquire shared lock on File not opened for read";
            return -1;
        }

        return 0;
    }

    private static int lockFailedReturn(int lockMode) {
        return (lockMode & LOCK_EX) == 0 ? 0 : -1;
    }

    private static boolean lockStateChanges(FileLock lock, int lockMode) {
        if (lock == null) {
            // no lock, only proceed if we are acquiring
            switch (lockMode & 0xF) {
                case LOCK_UN:
                case LOCK_UN | LOCK_NB:
                    return false;
                default:
                    return true;
            }
        } else {
            // existing lock, only proceed if we are unlocking or changing
            switch (lockMode & 0xF) {
                case LOCK_UN:
                case LOCK_UN | LOCK_NB:
                    return true;
                case LOCK_EX:
                case LOCK_EX | LOCK_NB:
                    return lock.isShared();
                case LOCK_SH:
                case LOCK_SH | LOCK_NB:
                    return !lock.isShared();
                default:
                    return false;
            }
        }
    }

    private int unlock(ChannelFD fd) throws IOException {
        FileLock fileLock = fd.currentLock.get();

        if (fileLock != null) {
            fileLock.release();
            fd.currentLock.remove();

            return 0;
        }
        return -1;
    }

    private int lock(ChannelFD fd, boolean exclusive) throws IOException {
        FileLock fileLock = fd.currentLock.get();

        if (fileLock != null) fileLock.release();

        fileLock = fd.chFile.lock(0L, Long.MAX_VALUE, !exclusive);

        fd.currentLock.set(fileLock);

        if (fileLock != null) {
            return 0;
        }

        return lockFailedReturn(exclusive ? LOCK_EX : LOCK_SH);
    }

    private int tryLock(ChannelFD fd, boolean exclusive) throws IOException {
        FileLock fileLock = fd.currentLock.get();

        if (fileLock != null) fileLock.release();

        fileLock = fd.chFile.tryLock(0L, Long.MAX_VALUE, !exclusive);

        fd.currentLock.set(fileLock);

        if (fileLock != null) {
            return 0;
        }

        return lockFailedReturn(exclusive ? LOCK_EX : LOCK_SH);
    }

    
The last Throwable exception raised by a call.
/**
     * The last Throwable exception raised by a call.
     */
    public Throwable error;

    private ThreadLocal<Errno> errno = new ThreadLocal<>();

    
The recommended error message, if any.
/**
     * The recommended error message, if any.
     */
    public String errmsg;

    
The POSIX instance to use for native calls
/**
     * The POSIX instance to use for native calls
     */
    private final POSIX posix;

    
The current runtime
/**
     * The current runtime
     */
    private final Ruby runtime;

    
An object to synchronize calls to umask
/**
     * An object to synchronize calls to umask
     */
    private static final Object _umaskLock = new Object();

    
The last umask we set
/**
     * The last umask we set
     */
    private static int _cachedUmask = 0;
}