import numpy as np
from ..assign_wcs import niriss



WFSS_EXPTYPES = ['NIS_WFSS', 'NRC_WFSS', 'NRC_GRISM', 'NRC_TSGRISM']


def get_wavelengths(model, exp_type="", order=None):
    """Read or compute wavelengths.

    Parameters
    ----------
    model : `~jwst.datamodels.DataModel`
        The input science data, or a slit from a
        `~jwst.datamodels.MultiSlitModel`.

    exp_type : str
        The exposure type.  This is only needed to check whether the input
        data are WFSS.

    order : int
        Spectral order number, for NIRISS SOSS only.

    Returns
    -------
    wl_array : 2-D ndarray
        An array of wavelengths corresponding to the data in `model`.
    """

    # Use the existing wavelength array, if there is one
    if hasattr(model, "wavelength"):
        wl_array = model.wavelength.copy()
        got_wavelength = True                   # may be reset below
    else:
        wl_array = None
    if (wl_array is None or len(wl_array) == 0 or
        np.nanmin(wl_array) == 0. and np.nanmax(wl_array) == 0.):
            got_wavelength = False
            wl_array = None

    # If no existing wavelength array, compute one
    if hasattr(model.meta, "wcs") and not got_wavelength:

        # Set up an appropriate WCS object
        if hasattr(model.meta, "exposure") and model.meta.exposure.type == "NIS_SOSS":
            wcs = niriss.niriss_soss_set_input(model, order)
        else:
            wcs = model.meta.wcs

        # Evaluate the WCS on the grid of pixel indexes, capturing only the
        # resulting wavelength values
        shape = model.data.shape
        grid = np.indices(shape[-2:], dtype=np.float64)

        if exp_type in WFSS_EXPTYPES:
            # We currently have to loop over pixels for WFSS data.
            wl_array = np.zeros(shape[-2:], dtype=np.float64)
            for j in range(shape[-2]):
                for i in range(shape[-1]):
                    # Keep wavelength; ignore RA and Dec
                    wl_array[..., j, i] = wcs(i, j)[2]
        else:
            wl_array = wcs(grid[1], grid[0])[2]

    return wl_array
