package net.mattmccutchen.measurements;

public class MeasurementMath {
	public static boolean unitsSame(Measurement a, Measurement b) {
		for (int i = 0; i < Unit.basicUnits.length; i++)
			if (a.unitPowers[i] != b.unitPowers[i])
				return false;
		return true;
	}
	
	public static boolean isPureNumber(Measurement a) {
		for (int i = 0; i < Unit.basicUnits.length; i++)
			if (a.unitPowers[i] != 0)
				return false;
		return true;
	}
	
	public static Measurement neg(Measurement a) {
		if (a == null)
			return null;
		return new Measurement(-a.number, a.uncertainty, a.unitPowers);
	}
	
	public static Measurement add(Measurement a, Measurement b) {
		if (a == null || b == null || !unitsSame(a, b))
			return null;
		return new Measurement(a.number + b.number,
			a.uncertainty + b.uncertainty, a.unitPowers);
	}
	
	public static Measurement sub(Measurement a, Measurement b) {
		if (a == null || b == null || !unitsSame(a, b))
			return null;
		return new Measurement(a.number - b.number,
			a.uncertainty + b.uncertainty, a.unitPowers);
	}
	
	public static Measurement mul(Measurement a, Measurement b) {
		if (a == null || b == null)
			return null;
		int[] up = new int[Unit.basicUnits.length];
		for (int i = 0; i < Unit.basicUnits.length; i++)
			up[i] = a.unitPowers[i] + b.unitPowers[i];
		return new Measurement(a.number * b.number,
			a.uncertainty * Math.abs(b.number)
			+ b.uncertainty * Math.abs(a.number),
			up);
	}
	
	public static Measurement div(Measurement a, Measurement b) {
		if (a == null || b == null)
			return null;
		int[] up = new int[Unit.basicUnits.length];
		for (int i = 0; i < Unit.basicUnits.length; i++)
			up[i] = a.unitPowers[i] - b.unitPowers[i];
		return new Measurement(a.number / b.number,
			// Compare to quotient rule for differentiation
			a.uncertainty / Math.abs(b.number)
			+ Math.abs(a.number) * b.uncertainty / (b.number * b.number),
			up);
	}
	
	public static Measurement powint(Measurement a, int b) {
		if (a == null)
			return null;
		int[] up = new int[Unit.basicUnits.length];
		for (int i = 0; i < Unit.basicUnits.length; i++)
			up[i] = a.unitPowers[i] * b;
		return new Measurement(Math.pow(a.number, b),
			b * a.uncertainty * Math.pow(a.number, b-1),
			up);
	}
	
	public static Measurement pow(Measurement a, Measurement b) {
		if (a == null || !isPureNumber(a) || b == null || !isPureNumber(b))
			return null;
		return new Measurement(Math.pow(a.number, b.number),
			b.number * a.uncertainty * Math.pow(a.number, b.number-1)
			// think: derivative of e^(b ln a) is b' (ln a) e^(b ln a)
			+ b.uncertainty * Math.log(a.number) * Math.pow(a.number, b.number),
			Measurement.pureNumberUnitPowers);
	}
	
	public static double cmp(Measurement a, Measurement b) {
		if (a == null || b == null || !unitsSame(a, b))
			return Double.NaN;
		return (a.number - b.number) / (a.uncertainty + b.uncertainty);
	}
}