/// <summary>
/// Calculates the area above the top limit for two blood sugar points.
/// </summary>
/// <param name="glucoseValue1">The first blood sugar glucose value.</param>
/// <param name="timestamp1">The timestamp of the first blood sugar.</param>
/// <param name="glucoseValue2">The second blood sugar glucose value.</param>
/// <param name="timestamp2">The timestamp of the second blood sugar.</param>
/// <param name="inclusiveTopLimit">The inclusive limit of good blood sugar.</param>
/// <returns>The area above the top limit (seconds * mmol/L).</returns>
private static decimal calculateAreaAboveRange(decimal glucoseValue1, DateTime timestamp1, decimal glucoseValue2, DateTime timestamp2, decimal inclusiveTopLimit)
{
//Both values are BELOW the limit.
if (glucoseValue1 <= inclusiveTopLimit && glucoseValue2 <= inclusiveTopLimit)
{
return(0);
}
//Both values are ABOVE the limit.
else if (glucoseValue1 > inclusiveTopLimit && glucoseValue2 > inclusiveTopLimit)
{
var hoursBetween = calculateTimeDifferenceInHours(timestamp1, timestamp2);
var minValue = Math.Min(glucoseValue1, glucoseValue2);
var area = (minValue - inclusiveTopLimit) * hoursBetween;
var maxValue = Math.Max(glucoseValue1, glucoseValue2);
var triangleArea = (maxValue - minValue) * hoursBetween / 2;
area += triangleArea;
if (area < 0)
{
throw new ConstraintException("The area calculated was a negative value.");
}
return(area);
}
//One value is above the limit and the other is below.
else
{
//Find the line traversing the blood sugar values.
var hoursBetween = calculateTimeDifferenceInHours(timestamp1, timestamp2);
var p1 = new PointF(0, (float)(glucoseValue1));
var p2 = new PointF((float)hoursBetween, (float)(glucoseValue2));
var line = new MathLine(p1, p2);
//Find where the line crosses the top limit.
var topLimitLine = new MathLine(0, (float)inclusiveTopLimit);
var intersection = MathLine.GetIntersectionPoint(line, topLimitLine);
//Calculate the area above the top limit.
var highestPoint = p1.Y > p2.Y ? p1 : p2;
var triangleBase = Math.Abs(intersection.X - highestPoint.X);
var triangleHeight = highestPoint.Y - (float)inclusiveTopLimit;
var triangleArea = triangleBase * triangleHeight / 2;
//Return the area above the top limit.
if (triangleArea < 0)
{
throw new ConstraintException("The area calculated was a negative value.");
}
return(Convert.ToDecimal(triangleArea));
}
}
/// <summary>
/// Gets the point in which two lines intersect.
/// </summary>
/// <param name="lineA">The first line.</param>
/// <param name="lineB">The second line.</param>
/// <returns>The point in which the two lines intersect.</returns>
public static PointF GetIntersectionPoint(MathLine lineA, MathLine lineB)
{
//Implemented according to:
//https://en.wikipedia.org/w/index.php?title=Line%E2%80%93line_intersection&oldid=815048738#Given_the_equations_of_the_lines
if (lineA.Slope == lineB.Slope)
{
throw new ConstraintException("The slopes are identical, meaning the lines are parallel and has no intersection point!");
}
float x = (lineB.Offset - lineA.Offset) / (lineA.Slope - lineB.Slope); //Will never be division by zero due to the exception above.
float y = lineA.GetY(x);
PointF intersection = new PointF(x, y);
return(intersection);
}
