Mac Book Pro Rretina (2014) will not charge I accidently drained my mac book pro retina battery and now it will not charge.  The power source is adequate and there does not appear to be any debris concerning the magnetic connector.
I have left my computer plugged in for days on end.  Have I ruined the battery?
I strongly doubt you've ruined the battery.

Here are some steps to try:
1) https://support.apple.com/en-us/HT201295 - reset the SMC as someone else suggested also

2) unplug your power adapter from the wall for over 2 minutes. There is breaker-like circuitry that triggers when there is a fault with the power adapter (usually thermal, like if it was lying on the carpet and overheated). Unplugging for 2 minutes resets this

3) sometimes rarely, something weird happens and the battery just needs to be unplugged/re-plugged. Don't do this yourself unless you know what you are doing. The battery in these laptops can be actually dangerous (think boom) without the right equipment. Take it to the Apple store along with the power adapter and just tell them "it stopped getting power, please help." Diagnostics are free even if the thing is out of warranty. You don't have to lie about what happened if they ask - leaving your laptop un-powered for a few days is not a crime nor warranty-voiding if you have a warranty.