Drafting Software Recommendation

I am looking for simple, logical, programmatically powerful drafting software to draw floor plans. Ideally it would be online or open source. I don't have a windows computer at this time, so unless I want to get one I need to use something that is capable of running on older unix / linux or online.

I tried Canva to reproduce a pen and ink sketch I made but so far I have a found it lacking. It is slow to use and illogical. Point and click and drag sucks relative to being able to enter the parameters that define a geometric object in a simple command line interface (if such an interface exists).

For example in Cnva when you draw lines by hand they do not automatically snap to 90 degree corners. You have to fight with the mouse to make a 90 degree corner. How many buildings have 78 or 89 degree corners between interior walls as planned! It would be just as well to use a MS paint like program at this point.

I would like a program that has a scale. That you can draw straight perpendicular lines in. There would be two primary classes of line. Horizontal and vertical. Imagine that. Each line would have a label like AA. If line AA was near to line BB you would have the the option to make a corner. There would be stock symbols for windows, doors, electrical and plumbing fixtures. Positions of everything would be in feet or meters (selectable according to an origin) or relative to other elements. The origin would be at the lower left corner of the canvas. The output would be SVG or convertible to PDF.

For example under the programmatic description of a line it could look like AA:(0,0,24,v) for a line that starts at the origin, is vertical, and extends 24 feet from the origin.

Then if you wanted to draw another line relative to AA you could have BB:(r,d[AA],24,h). The 'r' parameter signals to the program that the position of line BB is relative to the distal end of line AA, it extends 24 feet, and is horizontal. If I wanted BB to start at the origin I could write BB:(r,p[AA],24,h), i.e. starting from the proximal end or AA. Proximal is defined as lower, left most end of an element, while distal is the upper, right most end. Alternatively the command BB:(0,0,24,h) draws the same line.