  We present the SuperNova Explosion Code (SNEC), an open-source Lagrangian
code for the hydrodynamics and equilibrium-diffusion radiation transport in the
expanding envelopes of supernovae. Given a model of a progenitor star, an
explosion energy, and an amount and distribution of radioactive nickel, SNEC
generates the bolometric light curve, as well as the light curves in different
broad bands assuming black body emission. As a first application of SNEC, we
consider the explosions of a grid of 15 Msun (at zero-age main sequence) stars
whose hydrogen envelopes are stripped to different extents and at different
points in their evolution. The resulting light curves exhibit plateaus with
durations of ~20-100 days if >~1.5-2 Msun of hydrogen-rich material is left and
no plateau if less hydrogen-rich material is left. If these shorter plateau
lengths are not seen for Type IIP supernovae in nature, it suggests that, at
least for zero-age main sequence masses <~ 20 Msun, hydrogen mass loss occurs
as an all or nothing process. This perhaps points to the important role binary
interactions play in generating the observed mass-stripped supernovae (i.e.,
Type Ib/c events). These light curves are also unlike what is typically seen
for Type IIL supernovae, arguing that simply varying the amount of mass loss
cannot explain these events. The most stripped models begin to show
double-peaked light curves similar to what is often seen for Type IIb
supernovae, confirming previous work that these supernovae can come from
progenitors that have a small amount of hydrogen and a radius of ~500 Rsun.
