package koboldsim

import (
	"math"

	"golang.org/x/exp/constraints"
)

// Generic helper functions not directly attached to Card Sim Engine mechanics.

// Mean calculates the mathematical mean of its arguments (the sum, divided
// by the number of elements). If it is called with no arguments, it returns
// NaN ("not a number"). If there are contradictory infinities among the
// arguments, it also returns NaN. Overflowing or underflowing can create an
// infinity.
func Mean(vals ...float64) float64 {
	if len(vals) == 0 {
		return math.NaN()
	}

	total := 0.0
	for _, x := range vals {
		total += x
	}
	return total / float64(len(vals))
}

// clamp returns the middle of the three provided values. It doesn't
// matter which order the values are in. This function is known as `mid` in
// Pico-8's library, among others. It is usually used to clamp a value to a
// range, and it doesn't care which order the range is written in.
func clamp[T constraints.Ordered](a, b, c T) T {
	if a <= b && a <= c {
		// `a` is least; mid is lower of `b` or `c`
		if b <= c {
			return b
		}
		return c
	}
	if a >= b && a >= c {
		// `a` is most; mid is greater of `b` or `c`
		if b >= c {
			return b
		}
		return c
	}
	// `a` is neither most nor least; therefore, `a` is mid
	return a
}