Added some safety precautions and added documentation

Stopwatch.lua

@@ -1,51 +1,99 @@
 --luaClasses/Stopwatch.lua
 --Matthew Ellison
 -- Created: 02-01-19
---Modified: 02-06-19
+--Modified: 02-08-19
 --This is a simple class to be used to time runtimes of various things within programs
 
-Stopwatch = {
-	startTime = 0,
-	stopTime = 0
-}
-Stopwatch.__index = Stopwatch
 
+--You need some kind of table to hold the times
+Stopwatch = {}
+Stopwatch.__index = Stopwatch;
+
+--This is needed to create a Stopwatch and link the variables and functions
+--It should be called before anything else when createing a Stopwatch
 function Stopwatch:create()
-	local timer = {}
-	setmetatable(timer, Stopwatch)
-	return timer
+	local timer = {
+		startTime = nil,
+		stopTime = nil
+	};
+	setmetatable(timer, Stopwatch);	--This links the new variable with the functions from the Stopwatch
+	return timer;
 end
 
+--This function gets the start time to simulate actually hitting the button on a stopwatch
 function Stopwatch:start()
-	self.startTime = os.clock()
-	self.stopTime = 0
+	self.stopTime = nil;	--Make sure it knows that the clock is still running
+	--Setting the clock last puts the time closer to the actual start of the thing you are trying to time
+	self.startTime = os.clock();	--Get the current time
 end
 
+--This function gets the stop time to simulate actually hitting the stop button on a stopwatch
 function Stopwatch:stop()
-	self.stopTime = os.clock()
+	--Set the time first, for efficiency sake
+	self.stopTime = os.clock();
+	--Make sure the clock had been started
+	if(startTime == nil) then
+		--If not unset the stop time
+		stopTime = nil;
+	end
 end
 
+--This function resets all the variables. It is used if you want to use the same timer for multiple tests, but it shouldn't be necessary. Use to avoid unforseen bugs
 function Stopwatch:reset()
-	self.startTime = 0
-	self.stopTime = 0
+	self.startTime = nil;
+	self.stopTime = nil;
 end
 
+--Returns the difference in the time at the default time resolution
+--Mostly called from the other get___ functions
 function Stopwatch:getTime()
-	return (self.stopTime - self.startTime)
+	local timeDifference = nil;
+	--If start and stop has been called return the difference
+	if(startTime and stopTime) then
+		timeDifference = endTime - startTime;
+	--If start has been called but stop hasn't make the current time the end time. This simulates looking at a stopwatch while it is still running
+	elseif(startTime and not stopTime) then
+		timeDifference = os.time() - startTime;
+	--Otherwise return -1 as an error
+	else
+		timeDifference = -1;
+	end
+	--Return the number generated
+	return timeDifference;
 end
 
+--This function returns the duration the stopwatch has run in microseconds
 function Stopwatch:getMicroseconds()
-	return math.floor(self:getTime() * 1000000)
+	local timeDifference = self:getTime();	--Get the time that has elapsed
+	--If you did not get an error convert the time to microseconds
+	if(timeDifference >= 0) then
+		timeDifference = timeDifference * 1000000;
+	end
+	return timeDifference;
 end
 
+--This function returns the duration the stopwatch has run in milliseconds
 function Stopwatch:getMilliseconds()
-	return (self:getTime() * 1000)
+	local timeDifference = self:getTime();	--Get the time that has elapsed
+	--If you did not get an error convert the time to milliseconds
+	if(timeDifference >= 0) then
+		timeDifference = timeDifference * 1000;
+	end
+	return timeDifference;
 end
 
+--This function returns the duration the stopwatch has run in seconds
 function Stopwatch:getSeconds()
-	return self:getTime()
+	--The function returns in seconds by default
+	return self:getTime();
 end
 
+--This function returns the duration the stopwatch has run in minutes
 function Stopwatch:getMinutes()
-	return (self:getTime() / 60)
+	local timeDifference = self:getTime();
+	--If you did not get an error conver the time to minutes
+	if(timeDifference >= 0) then
+		timeDifference = timeDifference / 60;
+	end
+	return timeDifference;
 end