from nxs import NXfield,NeXusError,napi
import numpy as np

class NXfield_comp(NXfield):
    
    #NOTE: THE CONSTRUCTOR IS OPTIONAL. IF NOT IMPLEMENTED, WE CAN STILL USE THE nxslab_dims PROPERTY
    def __init__(self, value=None, name='field', dtype=None, shape=(), group=None,
                 attrs={}, nxslab_dims=None, **attr):
        NXfield.__init__(self, value=value, name=name, dtype=dtype, shape=shape, group=group,
                 attrs=attrs, **attr)
        self._slab_dims = nxslab_dims
        
    def write(self):
        """
        Write the NXfield, including attributes, to the NeXus file.
        """
        if self.nxfile:
            if self.nxfile.mode == napi.ACC_READ:
                raise NeXusError("NeXus file is readonly")
            if not self.infile:
                shape = self.shape
                if shape == (): shape = (1,)
                with self.nxgroup as path:
                    if self.nxslab_dims is not None:
                    #compress
                        path.compmakedata(self.nxname, self.dtype, shape, 'lzw', 
                                          self.nxslab_dims)
                    else:
                    # Don't use compression
                        path.makedata(self.nxname, self.dtype, shape)
                self._infile = True
            if not self.saved:            
                with self as path:
                    path._writeattrs(self.attrs)
                    value = self.nxdata
                    if value is not None:
                        path.putdata(value)
                self._saved = True
        else:
            raise IOError("Data is not attached to a file")
    
    def _getnxslabdims(self):
        try:
            return self._nxslab_dims
        except:
            slab_dims = None
        #even if slab_dims have not been set, check if the dataset is large 
        shape = self.shape or (1,)
        if np.prod(shape) > 10000:
            slab_dims = np.ones(len(shape),'i')
            slab_dims[-1] = min(shape[-1], 100000)
        return slab_dims
    
    def _setnxslabdims(self, slab_dims):
        self._nxslab_dims = slab_dims
    
    nxslab_dims = property(_getnxslabdims,_setnxslabdims,doc="Slab (a.k.a. chunk) dimensions for compression")