import ESMF

import argparse

R0_SCHISM = 6378206.4           # earth radius in meters used by SCHISM


def make_area_file(mesh_in, txt_out):
    schism_mesh = ESMF.Mesh(filename=str(mesh_in), filetype=ESMF.FileFormat.ESMFMESH)
    unit_areas = ESMF.Field(schism_mesh, meshloc=ESMF.MeshLoc.ELEMENT, name='areafield')
    unit_areas.get_area()
    areas_m2 = unit_areas.data[...] * (R0_SCHISM * R0_SCHISM)
    with (open(txt_out, 'w')) as outfile:
        for element in areas_m2:
            outfile.write("{:g}\n".format(element))


def main():
    parser = argparse.ArgumentParser()
    parser.add_argument('mesh_in', type=str, help='Input hgrid.nc file', metavar="hgrid.nc")
    parser.add_argument('txt_out', type=str, help='Output element areas (m^2)', metavar="element_areas.txt")
    args = parser.parse_args()
    make_area_file(args.mesh_in, args.txt_out)


if __name__ == '__main__':
    main()