turash/bugulma/backend/internal/geospatial/bounding_box.go

package geospatial

import (
	"math"
)

// BoundingBoxCalculatorImpl implements BoundingBoxCalculator interface
type BoundingBoxCalculatorImpl struct {
	config *Config
}

// NewBoundingBoxCalculator creates a new bounding box calculator
func NewBoundingBoxCalculator(config *Config) BoundingBoxCalculator {
	return &BoundingBoxCalculatorImpl{
		config: config,
	}
}

// CalculateBoundingBox calculates the bounding box that contains all given points
func (bbc *BoundingBoxCalculatorImpl) CalculateBoundingBox(points []Point) (*BoundingBox, error) {
	if len(points) == 0 {
		return nil, ErrEmptyPointList
	}

	minLat := points[0].Latitude
	maxLat := points[0].Latitude
	minLon := points[0].Longitude
	maxLon := points[0].Longitude

	for _, point := range points {
		if err := validatePoint(point); err != nil {
			return nil, err
		}

		if point.Latitude < minLat {
			minLat = point.Latitude
		}
		if point.Latitude > maxLat {
			maxLat = point.Latitude
		}
		if point.Longitude < minLon {
			minLon = point.Longitude
		}
		if point.Longitude > maxLon {
			maxLon = point.Longitude
		}
	}

	return &BoundingBox{
		NorthEast: Point{
			Latitude:  maxLat,
			Longitude: maxLon,
		},
		SouthWest: Point{
			Latitude:  minLat,
			Longitude: minLon,
		},
	}, nil
}

// ExpandBoundingBox expands a bounding box by a specified distance in kilometers
func (bbc *BoundingBoxCalculatorImpl) ExpandBoundingBox(bbox BoundingBox, expansionKm float64) (*BoundingBox, error) {
	if err := bbc.ValidateBoundingBox(bbox); err != nil {
		return nil, err
	}

	// Convert expansion from km to approximate degrees
	// At equator: 1 degree latitude ≈ 111 km
	// Longitude varies by latitude: 1 degree ≈ 111 km * cos(latitude)
	latExpansion := expansionKm / 111.0
	avgLat := (bbox.NorthEast.Latitude + bbox.SouthWest.Latitude) / 2
	lonExpansion := expansionKm / (111.0 * math.Cos(avgLat*math.Pi/180))

	expanded := BoundingBox{
		NorthEast: Point{
			Latitude:  math.Min(bbox.NorthEast.Latitude+latExpansion, 90),
			Longitude: math.Min(bbox.NorthEast.Longitude+lonExpansion, 180),
		},
		SouthWest: Point{
			Latitude:  math.Max(bbox.SouthWest.Latitude-latExpansion, -90),
			Longitude: math.Max(bbox.SouthWest.Longitude-lonExpansion, -180),
		},
	}

	return &expanded, nil
}

// IsPointInBoundingBox checks if a point is within a bounding box
func (bbc *BoundingBoxCalculatorImpl) IsPointInBoundingBox(point Point, bbox BoundingBox) bool {
	if err := validatePoint(point); err != nil {
		return false
	}
	if err := bbc.ValidateBoundingBox(bbox); err != nil {
		return false
	}

	return point.Latitude >= bbox.SouthWest.Latitude &&
		point.Latitude <= bbox.NorthEast.Latitude &&
		point.Longitude >= bbox.SouthWest.Longitude &&
		point.Longitude <= bbox.NorthEast.Longitude
}

// BoundingBoxArea calculates the area of a bounding box in square kilometers
func (bbc *BoundingBoxCalculatorImpl) BoundingBoxArea(bbox BoundingBox) (float64, error) {
	if err := bbc.ValidateBoundingBox(bbox); err != nil {
		return 0, err
	}

	// Calculate area using spherical approximation
	latDiff := (bbox.NorthEast.Latitude - bbox.SouthWest.Latitude) * math.Pi / 180
	avgLat := (bbox.NorthEast.Latitude + bbox.SouthWest.Latitude) / 2 * math.Pi / 180
	lonDiff := (bbox.NorthEast.Longitude - bbox.SouthWest.Longitude) * math.Pi / 180

	// Area = R² * lat_diff * lon_diff * cos(avg_lat)
	area := bbc.config.EarthRadiusKm * bbc.config.EarthRadiusKm * latDiff * lonDiff * math.Cos(avgLat)

	return math.Abs(area), nil
}

// ValidateBoundingBox validates a bounding box
func (bbc *BoundingBoxCalculatorImpl) ValidateBoundingBox(bbox BoundingBox) error {
	if err := validatePoint(bbox.NorthEast); err != nil {
		return err
	}
	if err := validatePoint(bbox.SouthWest); err != nil {
		return err
	}

	if bbox.NorthEast.Latitude < bbox.SouthWest.Latitude {
		return ErrInvalidBoundingBox
	}

	// Handle longitude wrap-around (e.g., -180 to 180)
	if bbox.NorthEast.Longitude < bbox.SouthWest.Longitude {
		// This is valid if the box crosses the date line
		// For simplicity, we'll allow it but note it requires special handling
	}

	return nil
}