package user

import (
	"math"
	"time"
)

// 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,
}

// AgeFromDOB computes age in years from a "YYYY-MM-DD" string. Returns nil on error.
func AgeFromDOB(dob *string) *int {
	if dob == nil {
		return nil
	}
	t, err := time.Parse("2006-01-02", *dob)
	if err != nil {
		return nil
	}
	now := time.Now()
	years := now.Year() - t.Year()
	if now.Month() < t.Month() || (now.Month() == t.Month() && now.Day() < t.Day()) {
		years--
	}
	return &years
}

// 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
}