res_levis_backend/internal/pkg/model/parser.go

package model

import (
	"bytes"
	"encoding/binary"
	"fmt"
	"sync"
)

type ParserConfig struct {
	Length int    `json:"length"`
	Offset int    `json:"offset"`
	Order  string `json:"order"`
}

type BeaconParser struct {
	Name     string
	CanParse func([]byte) bool
	configs  map[string]ParserConfig
}

type ParserRegistry struct {
	ParserList []BeaconParser
	rw         sync.RWMutex
}

type Config struct {
	Name    string                  `json:"name"`
	Min     int                     `json:"min"`
	Max     int                     `json:"max"`
	Pattern []string                `json:"pattern"`
	Configs map[string]ParserConfig `json:"configs"`
}

func (pc ParserConfig) GetOrder() binary.ByteOrder {
	if pc.Order == "bigendian" {
		return binary.BigEndian
	}

	return binary.LittleEndian
}

func (p *ParserRegistry) Register(name string, c Config) {
	p.rw.Lock()
	defer p.rw.Unlock()

	b := BeaconParser{
		Name: name,
		CanParse: func(ad []byte) bool {
			if len(ad) < 2 {
				return false
			}
			return len(ad) >= c.Min && len(ad) <= c.Max && bytes.HasPrefix(ad[1:], c.GetPatternBytes())
		},
		configs: c.Configs,
	}

	fmt.Printf("registered beacon parser: %+v\n", b)

	p.ParserList = append(p.ParserList, b)
}

func (b *BeaconParser) Parse(ad []byte) (BeaconEvent, bool) {
	flag := false
	event := BeaconEvent{Type: b.Name}
	if cfg, ok := b.configs["battery"]; ok {
		event.Battery = uint32(b.extract(ad, cfg))
		flag = true
	}
	if cfg, ok := b.configs["accX"]; ok {
		event.AccX = int16(b.extract(ad, cfg))
		flag = true
	}
	if cfg, ok := b.configs["accY"]; ok {
		event.AccY = int16(b.extract(ad, cfg))
		flag = true
	}
	if cfg, ok := b.configs["accZ"]; ok {
		event.AccZ = int16(b.extract(ad, cfg))
		flag = true
	}
	return event, flag
}

func (b *BeaconParser) extract(ad []byte, pc ParserConfig) uint16 {
	if len(ad) < pc.Offset+pc.Length {
		return 0
	}
	data := ad[pc.Offset : pc.Offset+pc.Length]

	if pc.Length == 1 {
		return uint16(data[0])
	}

	return pc.GetOrder().Uint16(data)
}

func (c Config) GetPatternBytes() []byte {
	res := make([]byte, len(c.Pattern))
	for i, s := range c.Pattern {
		fmt.Sscanf(s, "0x%02x", &res[i])
	}
	return res
}