How would I make a shader that has 100% opacity cel-shading, except for around the outlines?

I'm planning on creating a game that uses a shader very similar to animations by the Zeurel, specifically TomSka's "War". Mathematically, I know what I'll need to do to accomplish this, but I have never messed around with custom shaders. I want to have solid black cel-shading, but there would be a wide invisible edge detection effect that only erases shadows that it covers, and then on top of that there would be a thinner edge detection effect to serve as the outlines.