res_levis_backend/internal/pkg/decoder/process.go

package decoder

import (
	"bytes"
	"context"
	"encoding/hex"
	"fmt"
	"log/slog"
	"strings"

	"github.com/AFASystems/presence/internal/pkg/common/appcontext"
	"github.com/AFASystems/presence/internal/pkg/common/utils"
	"github.com/AFASystems/presence/internal/pkg/model"
	"github.com/segmentio/kafka-go"
)

// AlertWriter writes decoded beacon events (e.g. to alertbeacons topic).
type AlertWriter interface {
	WriteMessages(ctx context.Context, msgs ...kafka.Message) error
}

// ProcessIncoming decodes a beacon advertisement and writes the event to the writer if it changed.
func ProcessIncoming(adv model.BeaconAdvertisement, appState *appcontext.AppState, writer AlertWriter, registry *model.ParserRegistry) {
	if err := DecodeBeacon(adv, appState, writer, registry); err != nil {
		slog.Error("decoding beacon", "err", err, "id", adv.ID)
	}
}

// DecodeBeacon hex-decodes the payload, runs the parser registry, dedupes by event hash, and writes to writer.
func DecodeBeacon(adv model.BeaconAdvertisement, appState *appcontext.AppState, writer AlertWriter, registry *model.ParserRegistry) error {
	beacon := strings.TrimSpace(adv.Data)
	id := adv.ID
	if beacon == "" {
		return nil
	}

	b, err := hex.DecodeString(beacon)
	if err != nil {
		return err
	}

	b = utils.RemoveFlagBytes(b)
	indices := utils.ParseADFast(b)
	event := utils.LoopADStructures(b, indices, id, registry)

	if event.ID == "" {
		return nil
	}

	prevEvent, ok := appState.GetBeaconEvent(id)
	appState.UpdateBeaconEvent(id, event)

	if event.Type == "iBeacon" {
		event.BtnPressed = true
	}

	if ok && bytes.Equal(prevEvent.Hash(), event.Hash()) {
		return nil
	}

	eMsg, err := event.ToJSON()
	if err != nil {
		return err
	}

	if err := writer.WriteMessages(context.Background(), kafka.Message{Value: eMsg}); err != nil {
		return fmt.Errorf("write alert: %w", err)
	}

	return nil
}