package user

import "math"

// Activity level multipliers (Mifflin-St Jeor).
var activityMultiplier = map[string]float64{
	"low":      1.375,
	"moderate": 1.55,
	"high":     1.725,
}

// Goal adjustments in kcal.
var goalAdjustment = map[string]float64{
	"lose":     -500,
	"maintain": 0,
	"gain":     300,
}

// CalculateDailyCalories computes the daily calorie target using the
// Mifflin-St Jeor equation. Returns nil if any required parameter is missing.
func CalculateDailyCalories(heightCM *int, weightKG *float64, age *int, gender, activity, goal *string) *int {
	if heightCM == nil || weightKG == nil || age == nil || gender == nil || activity == nil || goal == nil {
		return nil
	}

	// BMR = 10 * weight(kg) + 6.25 * height(cm) - 5 * age
	bmr := 10**weightKG + 6.25*float64(*heightCM) - 5*float64(*age)

	switch *gender {
	case "male":
		bmr += 5
	case "female":
		bmr -= 161
	default:
		return nil
	}

	mult, ok := activityMultiplier[*activity]
	if !ok {
		return nil
	}

	adj, ok := goalAdjustment[*goal]
	if !ok {
		return nil
	}

	tdee := bmr * mult
	result := int(math.Round(tdee + adj))
	return &result
}