package staffing

import "github.com/shopspring/decimal"

// The portfolio optimizer maximizes total assignment value. The value of assigning a candidate to a
// requirement is a stated function of the frozen engine fit and the requirement priority:
//
//	value(i, j) = engineTotal(i, j) * priorityMultiplier(j)
//
// where engineTotal is the deterministic 0 to 100 score and priorityMultiplier maps the requirement's
// backing opportunity dollar value into a bounded multiplier. The value is then scaled to an int64 so the
// minimum cost flow solve is integer exact and FIPS clean (no float in the objective). Scoring stays
// decimal in the engine; only this objective is an integer, and it is allocation, not scoring.

// PriorityMultiplier maps an opportunity dollar value to a bounded multiplier in [minM, maxM]:
//
//	minM + clamp(value / reference, 0, maxM - minM)
//
// With the defaults (reference 5,000,000, min 1, max 3): a 5,000,000 dollar opportunity maps to 2x, a
// 10,000,000 or larger to the 3x cap, a tiny opportunity to just above 1x, and a zero or negative value to
// 1x. A non positive reference disables the dollar weighting (every requirement gets the minimum
// multiplier), which keeps fit the sole driver rather than dividing by zero.
func PriorityMultiplier(value, reference, minM, maxM decimal.Decimal) decimal.Decimal {
	if reference.LessThanOrEqual(decimal.Zero) {
		return minM
	}
	span := maxM.Sub(minM)
	if span.LessThan(decimal.Zero) {
		span = decimal.Zero
	}
	add := value.Div(reference)
	if add.LessThan(decimal.Zero) {
		add = decimal.Zero
	}
	if add.GreaterThan(span) {
		add = span
	}
	return minM.Add(add)
}

// ScaledValue computes the int64 objective value for one candidate requirement pair:
//
//	round( engineTotal * priorityMultiplier * scale )
//
// shopspring rounds half away from zero, which is deterministic, so identical inputs yield byte identical
// integers across runs and machines. engineTotal is in [0,100] and the multiplier in [1,3], so with the
// default scale of 1,000,000 the result is at most 3e8, far inside int64.
func ScaledValue(engineTotal, multiplier decimal.Decimal, scale int64) int64 {
	return engineTotal.Mul(multiplier).Mul(decimal.NewFromInt(scale)).Round(0).IntPart()
}