res_levis_backend/internal/pkg/model/parser.go

package model

import (
	"bytes"
	"encoding/binary"
	"fmt"
	"log/slog"
	"sync"

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

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

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

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

type Config struct {
	Name    string                  `json:"name" gorm:"primaryKey" validate:"required"`
	Min     int                     `json:"min" validate:"gte=0,ltefield=Max"`
	Max     int                     `json:"max" validate:"gte=0"`
	Pattern []string                `json:"pattern" gorm:"serializer:json" validate:"required,min=1,dive,required"`
	Configs map[string]ParserConfig `json:"configs" gorm:"serializer:json"`
}

type KafkaParser struct {
	ID     string
	Name   string
	Config Config
}

func (pc ParserConfig) GetOrder() any {
	if pc.Order == "fixedpoint" {
		return "fixedpoint"
	}
	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{
		CanParse: func(ad []byte) bool {
			if len(ad) < 2 {
				msg := "Beacon advertisement is too short"
				slog.Error(msg)
				return false
			}
			return len(ad) >= c.Min && len(ad) <= c.Max && bytes.HasPrefix(ad[1:], c.GetPatternBytes())
		},
		configs: c.Configs,
	}

	p.ParserList[name] = b
}

func (p *ParserRegistry) Unregister(name string) {
	p.rw.Lock()
	delete(p.ParserList, name)
	p.rw.Unlock()
}

// TODO: change this to be dynamic, maybe event is interface with no predefined properties
// or types

func (b *BeaconParser) Parse(name string, ad []byte) (appcontext.BeaconEvent, bool) {
	flag := false
	event := appcontext.BeaconEvent{Type: name}
	if cfg, ok := b.configs["battery"]; ok {
		event.Battery = uint32(b.extract(ad, cfg).(uint16))
		flag = true
	}
	if cfg, ok := b.configs["accX"]; ok {
		val := b.extract(ad, cfg).(float64)
		event.AccX = int16(val)
		flag = true
	}
	if cfg, ok := b.configs["accY"]; ok {
		val := b.extract(ad, cfg).(float64)
		event.AccY = int16(val)
		flag = true
	}
	if cfg, ok := b.configs["accZ"]; ok {
		val := b.extract(ad, cfg).(float64)
		event.AccZ = int16(val)
		flag = true
	}
	if cfg, ok := b.configs["temperature"]; ok {
		val := b.extract(ad, cfg).(float64)
		event.Temperature = uint16(val)
		flag = true
	}

	return event, flag
}

func (b *BeaconParser) extract(ad []byte, pc ParserConfig) any {
	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])
	}

	order := pc.GetOrder()
	if order == "fixedpoint" {
		val := int16(data[0])<<8 | int16(data[1])
		return float64(val) / 256.0
	}

	o := order.(binary.ByteOrder)
	return o.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
}