import datetime

import h5py


def write_nexus_file(fname, image, md={}):
    """
    write the image to a NeXus HDF5 data file

    Parameters
    ----------
    fname : str
            name of the file (relative or absolute) to be written
    image : numpy array
            the image data
    md : dictionary
            key: value where value is something that can be written by h5py
                     (such as str, int, float, numpy array, ...)
    """
    nexus = h5py.File(fname, "w")
    nexus.attrs["filename"] = fname
    nexus.attrs["file_time"] = datetime.datetime.now().astimezone().isoformat()
    nexus.attrs["creator"] = "write_nexus_file()"
    nexus.attrs["H5PY_VERSION"] = h5py.__version__

    # /entry
    nxentry = nexus.create_group("entry")
    nxentry.attrs["NX_class"] = "NXentry"
    nexus.attrs["default"] = nxentry.name

    # /entry/instrument
    nxinstrument = nxentry.create_group("instrument")
    nxinstrument.attrs["NX_class"] = "NXinstrument"

    # /entry/instrument/detector
    nxdetector = nxinstrument.create_group("detector")
    nxdetector.attrs["NX_class"] = "NXdetector"

    # /entry/instrument/detector/image
    ds = nxdetector.create_dataset("image", data=image, compression="gzip")
    ds.attrs["units"] = "counts"
    ds.attrs["target"] = "/entry/instrument/detector/image"

    # /entry/data
    nxdata = nxentry.create_group("data")
    nxdata.attrs["NX_class"] = "NXdata"
    nxentry.attrs["default"] = nxdata.name

    # /entry/data/data --> /entry/instrument/detector/image
    nxdata["data"] = nexus["/entry/instrument/detector/image"]
    nxdata.attrs["signal"] = "data"

    if len(md) > 0:
        # /entry/instrument/metadata (optional, for metadata)
        metadata = nxinstrument.create_group("metadata")
        metadata.attrs["NX_class"] = "NXcollection"
        for k, v in md.items():
            try:
                metadata.create_dataset(k, data=v)
            except Exception:
                metadata.create_dataset(k, data=str(v))

    nexus.close()


if __name__ == "__main__":
    """demonstrate how to use this code"""
    import epics

    prefix = "13SIM1:"
    img = epics.caget(prefix + "image1:ArrayData")
    size_x = epics.caget(prefix + "cam1:ArraySizeX_RBV")
    size_y = epics.caget(prefix + "cam1:ArraySizeY_RBV")
    # edit the full image for just the binned data
    img = img[: size_x * size_y].reshape((size_x, size_y))

    extra_information = dict(
        unique_id=epics.caget(prefix + "image1:UniqueId_RBV"),
        size_x=size_x,
        size_y=size_y,
        detector_state=epics.caget(prefix + "cam1:DetectorState_RBV"),
        bitcoin_value="15000",
    )
    write_nexus_file("example.h5", img, md=extra_information)