tankstopp-app/internal/handlers/dashboard.go

package handlers

import (
	"log"
	"net/http"

	"tankstopp/internal/models"
	"tankstopp/internal/views/pages"
)

// HomeHandler serves the main dashboard page
func (h *Handler) HomeHandler(w http.ResponseWriter, r *http.Request) {
	userID, username := h.getCurrentUser(r)
	if userID == 0 {
		http.Redirect(w, r, "/login", http.StatusSeeOther)
		return
	}

	// Get the user object
	user, err := h.db.GetUserByID(userID)
	if err != nil {
		log.Printf("Error getting user: %v", err)
		http.Error(w, "Internal server error", http.StatusInternalServerError)
		return
	}

	// Get fuel stops for the user
	stops, err := h.db.GetFuelStops(userID)
	if err != nil {
		log.Printf("Error getting fuel stops: %v", err)
		http.Error(w, "Internal server error", http.StatusInternalServerError)
		return
	}

	// Get fuel stop statistics
	stats, err := h.db.GetFuelStopStats(userID)
	if err != nil {
		log.Printf("Error getting fuel stop stats: %v", err)
		http.Error(w, "Internal server error", http.StatusInternalServerError)
		return
	}

	// Get vehicles for the user
	vehicles, err := h.db.GetVehicles(userID)
	if err != nil {
		log.Printf("Error getting vehicles: %v", err)
		http.Error(w, "Internal server error", http.StatusInternalServerError)
		return
	}

	// Calculate dashboard statistics
	totalStops := len(stops)
	totalCost := stats.TotalSpent

	// Calculate detailed consumption statistics
	avgConsumption, _, _ := h.calculateConsumptionStats(stops)
	if avgConsumption == 0 {
		avgConsumption = stats.AverageConsumption // Fallback to basic stats
	}

	var lastFillUp *models.FuelStop
	if len(stops) > 0 {
		lastFillUp = &stops[0]
	}

	// Render dashboard using templ
	component := pages.DashboardPage(user, username, stops, vehicles, totalStops, totalCost, avgConsumption, lastFillUp)

	w.Header().Set("Content-Type", "text/html")
	err = component.Render(r.Context(), w)
	if err != nil {
		log.Printf("Error rendering template: %v", err)
		http.Error(w, "Internal server error", http.StatusInternalServerError)
	}
}

// calculateConsumptionStats calculates consumption-related statistics
func (h *Handler) calculateConsumptionStats(stops []models.FuelStop) (float64, float64, float64) {
	if len(stops) == 0 {
		return 0, 0, 0
	}

	var totalLiters, totalKm float64
	var consumptionReadings []float64

	for _, stop := range stops {
		totalLiters += stop.Liters

		if stop.TripLength > 0 {
			totalKm += stop.TripLength

			// Calculate consumption for this stop (L/100km)
			consumption := (stop.Liters / stop.TripLength) * 100
			if consumption > 0 && consumption < 50 { // Filter out unrealistic values
				consumptionReadings = append(consumptionReadings, consumption)
			}
		}
	}

	// Average consumption from individual readings
	var avgConsumption float64
	if len(consumptionReadings) > 0 {
		var sum float64
		for _, consumption := range consumptionReadings {
			sum += consumption
		}
		avgConsumption = sum / float64(len(consumptionReadings))
	}

	// Overall consumption from totals
	var overallConsumption float64
	if totalKm > 0 {
		overallConsumption = (totalLiters / totalKm) * 100
	}

	return avgConsumption, overallConsumption, totalKm
}

// calculateEfficiencyTrend calculates fuel efficiency trend over time
func (h *Handler) calculateEfficiencyTrend(stops []models.FuelStop) string {
	if len(stops) < 2 {
		return "insufficient_data"
	}

	// Get consumption for recent stops (last 5) vs older stops
	recentStops := stops[:min(5, len(stops))]
	olderStops := stops[min(5, len(stops)):]

	recentAvg, _, _ := h.calculateConsumptionStats(recentStops)
	olderAvg, _, _ := h.calculateConsumptionStats(olderStops)

	if recentAvg == 0 || olderAvg == 0 {
		return "insufficient_data"
	}

	diff := recentAvg - olderAvg
	if diff < -0.5 {
		return "improving" // Lower consumption is better
	} else if diff > 0.5 {
		return "worsening"
	}
	return "stable"
}

// min helper function
func min(a, b int) int {
	if a < b {
		return a
	}
	return b
}