You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: decoder.go
    path of file: ./repos/syft/syft/format/cyclonedxjson
    
    the code of the file until where you have to start completion: package cyclonedxjson

import (
	"encoding/json"
	"fmt"
	"io"

	"github.com/CycloneDX/cyclonedx-go"

	"github.com/anchore/syft/internal/log"
	"github.com/anchore/syft/syft/format/internal/cyclonedxutil"
	"github.com/anchore/syft/syft/format/internal/cyclonedxutil/helpers"
	"github.com/anchore/syft/syft/format/internal/stream"
	"github.com/anchore/syft/syft/sbom"
)

var _ sbom.FormatDecoder = (*decoder)(nil)

type decoder struct {
	decoder cyclonedxutil.Decoder
}

func NewFormatDecoder() sbom.FormatDecoder {
	return decoder{
		decoder: cyclonedxutil.NewDecoder(cyclonedx.BOMFileFormatJSON),
	}
}

func (d decoder) Decod
    
func (d decoder) Identify(r io.Reader) (sbom.FormatID, string) {
	reader, err := stream.SeekableReader(r)
	if err != nil {
		return "", ""
	}

	if _, err := reader.Seek(0, io.SeekStart); err != nil {
		log.Debugf("unable to seek to start of CycloneDX JSON SBOM: %+v", err)
		return "", ""
	}

	type Document struct {
		JSONSchema  string `json:"$schema"`
		BOMFormat   string `json:"bomFormat"`
		SpecVersion string `json:"specVersion"`
	}

	dec := json.NewDecoder(reader)

	var doc Document
	if err = dec.Decode(&doc); err != nil {
		// maybe not json? maybe not valid? doesn't matter, we won't process it.
		return "", ""
	}

	id, version := getFormatInfo(doc.BOMFormat, doc.SpecVersion)
	if version == "" || id != ID {
		// not a cyclonedx json document that we support
		return "", ""
	}

	return id, version
}