Function calcUsageMonthlyCost

internal/estimate/estimator.go:696–721

calcUsageMonthlyCost computes the monthly cost for a usage-based resource given a monthly quantity. It uses the OnDemand entry's tiers when available, otherwise falls back to the flat rate.

(entries []resources.PriceEntry, monthlyQty float64)

// given a monthly quantity. It uses the OnDemand entry's tiers when available,
// otherwise falls back to the flat rate.
func calcUsageMonthlyCost(entries []resources.PriceEntry, monthlyQty float64) decimal.Decimal {
	// Find the OnDemand entry.
	var target *resources.PriceEntry
	for i := range entries {
		if entries[i].IsCurrent {
			target = &entries[i]
			break
		}
	}
	if target == nil && len(entries) > 0 {
		target = &entries[0]
	}
	if target == nil {
		return decimal.Zero
	}

	qty := decimal.NewFromFloat(monthlyQty)

	if len(target.Tiers) == 0 {
		// Flat rate: price per unit × quantity.
		return target.RatePerHr.Mul(qty)
	}

	// Tiered pricing: walk through tiers and accumulate cost.
	return calcTieredCost(target.Tiers, qty)
}

// calcTieredCost applies volume-tiered pricing to a total quantity.
// Each tier covers [startRange, endRange) units at its price.