Darkness coming, snake morph sci fi

I watched this on tv, late at night – I recall it was set on a planet, maybe not earth, but humanoid. A (king?) ruler trying to ready the populace for a time of perpetual night; a woman who turns out to be a snake shapeshifter, who has an tryst out in the desert with a (Mage? Priest?), a love scene by their campfire; the movie ends with darkness encompassing their world. Pretty sure the villain from The Warriors was the Mage/Priest who had the affair with the Snake woman. Not sure how old this is, but I watched it about ten (or more) years ago.

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