s01e02/internal/domain/location.go

package domain

import (
	"context"
	"encoding/json"
	"fmt"
	"io"
	"math"
	"net/http"
	"time"
)

// Location represents a location with coordinates
type Location struct {
	Name      string  `json:"name"`
	Latitude  float64 `json:"lat"`
	Longitude float64 `json:"lon"`
}

// PersonLocation represents a person's location
type PersonLocation struct {
	Name      string  `json:"name"`
	Surname   string  `json:"surname"`
	Latitude  float64 `json:"lat"`
	Longitude float64 `json:"lon"`
}

// DistanceResult represents the distance calculation result
type DistanceResult struct {
	Person       string  `json:"person"`
	Location     string  `json:"location"`
	DistanceKm   float64 `json:"distance_km"`
}

// Haversine calculates the distance between two points on Earth (in kilometers)
// using the Haversine formula
func Haversine(lat1, lon1, lat2, lon2 float64) float64 {
	const earthRadiusKm = 6371.0

	// Convert degrees to radians
	lat1Rad := lat1 * math.Pi / 180
	lat2Rad := lat2 * math.Pi / 180
	deltaLat := (lat2 - lat1) * math.Pi / 180
	deltaLon := (lon2 - lon1) * math.Pi / 180

	// Haversine formula
	a := math.Sin(deltaLat/2)*math.Sin(deltaLat/2) +
		math.Cos(lat1Rad)*math.Cos(lat2Rad)*
			math.Sin(deltaLon/2)*math.Sin(deltaLon/2)

	c := 2 * math.Atan2(math.Sqrt(a), math.Sqrt(1-a))

	return earthRadiusKm * c
}

// CalculateDistance calculates distance between person and location
func CalculateDistance(person PersonLocation, location Location) DistanceResult {
	distance := Haversine(person.Latitude, person.Longitude, location.Latitude, location.Longitude)

	return DistanceResult{
		Person:     person.Name + " " + person.Surname,
		Location:   location.Name,
		DistanceKm: distance,
	}
}

// FindClosestLocation finds the closest location to a person
func FindClosestLocation(person PersonLocation, locations []Location) *DistanceResult {
	if len(locations) == 0 {
		return nil
	}

	var closest *DistanceResult
	minDistance := math.MaxFloat64

	for _, loc := range locations {
		result := CalculateDistance(person, loc)
		if result.DistanceKm < minDistance {
			minDistance = result.DistanceKm
			closest = &result
		}
	}

	return closest
}

// NominatimResponse represents OpenStreetMap Nominatim API response
type NominatimResponse struct {
	Lat string `json:"lat"`
	Lon string `json:"lon"`
}

// GetPlantGeolocation fetches accurate coordinates for a city using geocoding API
func GetPlantGeolocation(ctx context.Context, cityName string) (float64, float64, error) {
	url := fmt.Sprintf("https://nominatim.openstreetmap.org/search?city=%s&country=Poland&format=json&limit=1", cityName)

	req, err := http.NewRequestWithContext(ctx, "GET", url, nil)
	if err != nil {
		return 0, 0, fmt.Errorf("creating request: %w", err)
	}

	// OpenStreetMap requires User-Agent header
	req.Header.Set("User-Agent", "PersonProcessor/1.0")

	client := &http.Client{
		Timeout: 10 * time.Second,
	}

	resp, err := client.Do(req)
	if err != nil {
		return 0, 0, fmt.Errorf("making request: %w", err)
	}
	defer resp.Body.Close()

	body, err := io.ReadAll(resp.Body)
	if err != nil {
		return 0, 0, fmt.Errorf("reading response: %w", err)
	}

	var results []NominatimResponse
	if err := json.Unmarshal(body, &results); err != nil {
		return 0, 0, fmt.Errorf("parsing JSON: %w", err)
	}

	if len(results) == 0 {
		return 0, 0, fmt.Errorf("no results found for city: %s", cityName)
	}

	// Parse coordinates
	var lat, lon float64
	if _, err := fmt.Sscanf(results[0].Lat, "%f", &lat); err != nil {
		return 0, 0, fmt.Errorf("parsing latitude: %w", err)
	}
	if _, err := fmt.Sscanf(results[0].Lon, "%f", &lon); err != nil {
		return 0, 0, fmt.Errorf("parsing longitude: %w", err)
	}

	return lat, lon, nil
}

// NearestPointResult represents result of finding nearest point
type NearestPointResult struct {
	Latitude   float64 `json:"latitude"`
	Longitude  float64 `json:"longitude"`
	DistanceKm float64 `json:"distance_km"`
	Index      int     `json:"index"`
}

// FindNearestPoint finds the nearest point from a list to a reference point
func FindNearestPoint(referenceLat, referenceLon float64, points [][]float64) *NearestPointResult {
	if len(points) == 0 {
		return nil
	}

	var nearest *NearestPointResult
	minDistance := math.MaxFloat64

	for i, point := range points {
		if len(point) < 2 {
			continue // Skip invalid points
		}

		lat := point[0]
		lon := point[1]

		distance := Haversine(referenceLat, referenceLon, lat, lon)

		if distance < minDistance {
			minDistance = distance
			nearest = &NearestPointResult{
				Latitude:   lat,
				Longitude:  lon,
				DistanceKm: distance,
				Index:      i,
			}
		}
	}

	return nearest
}