// +build linux darwin freebsd

package mount

import (
	"io"
	"sync"

	"bazil.org/fuse"
	fusefs "bazil.org/fuse/fs"
	"github.com/ncw/rclone/fs"
	"golang.org/x/net/context"
)

// ReadFileHandle is an open for read file handle on a File
type ReadFileHandle struct {
	mu         sync.Mutex
	closed     bool // set if handle has been closed
	r          io.ReadCloser
	o          fs.Object
	readCalled bool // set if read has been called
}

func newReadFileHandle(o fs.Object) (*ReadFileHandle, error) {
	r, err := o.Open()
	if err != nil {
		return nil, err
	}
	return &ReadFileHandle{
		r: r,
		o: o,
	}, nil
}

// Check interface satisfied
var _ fusefs.Handle = (*ReadFileHandle)(nil)

// Check interface satisfied
var _ fusefs.HandleReader = (*ReadFileHandle)(nil)

// Read from the file handle
func (fh *ReadFileHandle) Read(ctx context.Context, req *fuse.ReadRequest, resp *fuse.ReadResponse) error {
	fs.Debug(fh.o, "ReadFileHandle.Open")
	if fh.closed {
		fs.ErrorLog(fh.o, "ReadFileHandle.Read error: %v", errClosedFileHandle)
		return errClosedFileHandle
	}
	fh.readCalled = true
	// We don't actually enforce Offset to match where previous read
	// ended. Maybe we should, but that would mean'd we need to track
	// it. The kernel *should* do it for us, based on the
	// fuse.OpenNonSeekable flag.
	//
	// One exception to the above is if we fail to fully populate a
	// page cache page; a read into page cache is always page aligned.
	// Make sure we never serve a partial read, to avoid that.
	buf := make([]byte, req.Size)
	n, err := io.ReadFull(fh.r, buf)
	if err == io.ErrUnexpectedEOF || err == io.EOF {
		err = nil
	}
	resp.Data = buf[:n]
	if err != nil {
		fs.ErrorLog(fh.o, "ReadFileHandle.Open error: %v", err)
	} else {
		fs.Debug(fh.o, "ReadFileHandle.Open OK")
	}
	return err
}

// close the file handle returning errClosedFileHandle if it has been
// closed already.
//
// Must be called with fh.mu held
func (fh *ReadFileHandle) close() error {
	if fh.closed {
		return errClosedFileHandle
	}
	fh.closed = true
	return fh.r.Close()
}

// Check interface satisfied
var _ fusefs.HandleFlusher = (*ReadFileHandle)(nil)

// Flush is called each time the file or directory is closed.
// Because there can be multiple file descriptors referring to a
// single opened file, Flush can be called multiple times.
func (fh *ReadFileHandle) Flush(ctx context.Context, req *fuse.FlushRequest) error {
	fh.mu.Lock()
	defer fh.mu.Unlock()
	fs.Debug(fh.o, "ReadFileHandle.Flush")
	// If Read hasn't been called then ignore the Flush - Release
	// will pick it up
	if !fh.readCalled {
		fs.Debug(fh.o, "ReadFileHandle.Flush ignoring flush on unread handle")
		return nil

	}
	err := fh.close()
	if err != nil {
		fs.ErrorLog(fh.o, "ReadFileHandle.Flush error: %v", err)
		return err
	}
	fs.Debug(fh.o, "ReadFileHandle.Flush OK")
	return nil
}

var _ fusefs.HandleReleaser = (*ReadFileHandle)(nil)

// Release is called when we are finished with the file handle
//
// It isn't called directly from userspace so the error is ignored by
// the kernel
func (fh *ReadFileHandle) Release(ctx context.Context, req *fuse.ReleaseRequest) error {
	fh.mu.Lock()
	defer fh.mu.Unlock()
	if fh.closed {
		fs.Debug(fh.o, "ReadFileHandle.Release nothing to do")
		return nil
	}
	fs.Debug(fh.o, "ReadFileHandle.Release closing")
	err := fh.close()
	if err != nil {
		fs.ErrorLog(fh.o, "ReadFileHandle.Release error: %v", err)
	} else {
		fs.Debug(fh.o, "ReadFileHandle.Release OK")
	}
	return err
}