res_levis_backend/internal/pkg/common/utils/beacons.go

package utils

import (
	"github.com/AFASystems/presence/internal/pkg/common/appcontext"
	"github.com/AFASystems/presence/internal/pkg/model"
)

// ParseADFast efficiently parses Advertising Data structures
// Returns slice of [startIndex, endIndex] pairs for each AD structure
func ParseADFast(b []byte) [][2]int {
	var res [][2]int
	i := 0

	for i < len(b) {
		l := int(b[i])
		if l == 0 || i+1+l > len(b) {
			break
		}

		res = append(res, [2]int{i, i + 1 + l})

		i += 1 + l
	}

	return res
}

// RemoveFlagBytes removes Bluetooth advertising flag bytes if present
// Some beacons include flag bytes as the first AD structure
func RemoveFlagBytes(b []byte) []byte {
	if len(b) > 1 && b[1] == 0x01 {
		l := int(b[0])
		if 1+l <= len(b) {
			return b[1+l:]
		}
	}
	return b
}

// Generate event based on the Beacon type
func LoopADStructures(b []byte, i [][2]int, id string, parserRegistry *model.ParserRegistry) appcontext.BeaconEvent {
	be := appcontext.BeaconEvent{}
	for _, r := range i {
		ad := b[r[0]:r[1]]
		if !isValidADStructure(ad) {
			break
		}
		for name, parser := range parserRegistry.ParserList {
			if parser.CanParse(ad) {
				event, ok := parser.Parse(name, ad)
				if ok {
					event.ID = id
					event.Name = id
					return event
				}
			}
		}
	}

	return be
}

// IsValidADStructure validates if an AD structure is well-formed
func isValidADStructure(data []byte) bool {
	if len(data) < 2 {
		return false
	}

	length := int(data[0])
	return length > 0 && int(length)+1 <= len(data)
}