miller/pkg/transformers/gap.go

package transformers

import (
	"fmt"
	"os"
	"strings"

	"github.com/johnkerl/miller/v6/pkg/cli"
	"github.com/johnkerl/miller/v6/pkg/mlrval"
	"github.com/johnkerl/miller/v6/pkg/types"
)

const verbNameGap = "gap"

var gapOptions = []OptionSpec{
	{Flag: "-g", Arg: "{a,b,c}", Type: "csv-list", Desc: "Print a gap whenever values of these fields (e.g. a,b,c) changes."},
	{Flag: "-n", Arg: "{n}", Type: "int", Desc: "Print a gap every n records. Ignored if -g is present."},
}

var GapSetup = TransformerSetup{
	Verb:         verbNameGap,
	UsageFunc:    transformerGapUsage,
	ParseCLIFunc: transformerGapParseCLI,
	IgnoresInput: false,
	Options:      gapOptions,
}

func transformerGapUsage(
	o *os.File,
) {
	fmt.Fprintf(o, "Usage: %s %s [options]\n", "mlr", verbNameGap)
	fmt.Fprint(o, "Emits an empty record every n records, or when certain values change.\n")
	fmt.Fprintf(o, "One of -n or -g is required.\n")
	WriteVerbOptions(o, gapOptions)
}

func transformerGapParseCLI(
	pargi *int,
	argc int,
	args []string,
	_ *cli.TOptions,
	doConstruct bool, // false for first pass of CLI-parse, true for second pass
) (RecordTransformer, error) {

	// Skip the verb name from the current spot in the mlr command line
	argi := *pargi
	verb := args[argi]
	argi++

	gapCount := int64(-1)
	var groupByFieldNames []string = nil

	var err error
	for argi < argc /* variable increment: 1 or 2 depending on flag */ {
		opt := args[argi]
		if !strings.HasPrefix(opt, "-") {
			break // No more flag options to process
		}
		if args[argi] == "--" {
			break // All transformers must do this so main-flags can follow verb-flags
		}
		argi++

		switch opt {
		case "-h", "--help":
			transformerGapUsage(os.Stdout)
			return nil, cli.ErrHelpRequested

		case "-n":
			gapCount, err = cli.VerbGetIntArg(verb, opt, args, &argi, argc)
			if err != nil {
				return nil, err
			}

		case "-g":
			groupByFieldNames, err = cli.VerbGetStringArrayArg(verb, opt, args, &argi, argc)
			if err != nil {
				return nil, err
			}

		default:
			return nil, cli.VerbErrorf(verb, "option \"%s\" not recognized", opt)
		}
	}

	if gapCount == -1 && groupByFieldNames == nil {
		transformerGapUsage(os.Stderr)
		return nil, cli.ErrUsagePrinted
	}

	*pargi = argi
	if !doConstruct { // All transformers must do this for main command-line parsing
		return nil, nil
	}

	transformer, err := NewTransformerGap(
		gapCount,
		groupByFieldNames,
	)
	if err != nil {
		return nil, err
	}

	return transformer, nil
}

type TransformerGap struct {
	// input
	gapCount          int64
	groupByFieldNames []string

	// state
	recordTransformerFunc RecordTransformerFunc
	recordCount           int64
	previousGroupingKey   string
}

func NewTransformerGap(
	gapCount int64,
	groupByFieldNames []string,
) (*TransformerGap, error) {

	tr := &TransformerGap{
		gapCount:          gapCount,
		groupByFieldNames: groupByFieldNames,

		recordCount:         0,
		previousGroupingKey: "",
	}

	if groupByFieldNames == nil {
		tr.recordTransformerFunc = tr.transformUnkeyed
	} else {
		tr.recordTransformerFunc = tr.transformKeyed
	}

	return tr, nil
}

func (tr *TransformerGap) Transform(
	inrecAndContext *types.RecordAndContext,
	outputRecordsAndContexts *[]*types.RecordAndContext, // list of *types.RecordAndContext
	inputDownstreamDoneChannel <-chan bool,
	outputDownstreamDoneChannel chan<- bool,
) error {
	HandleDefaultDownstreamDone(inputDownstreamDoneChannel, outputDownstreamDoneChannel)
	return tr.recordTransformerFunc(inrecAndContext, outputRecordsAndContexts, inputDownstreamDoneChannel, outputDownstreamDoneChannel)
}

func (tr *TransformerGap) transformUnkeyed(
	inrecAndContext *types.RecordAndContext,
	outputRecordsAndContexts *[]*types.RecordAndContext, // list of *types.RecordAndContext
	inputDownstreamDoneChannel <-chan bool,
	outputDownstreamDoneChannel chan<- bool,
) error {
	if !inrecAndContext.EndOfStream {
		if tr.recordCount > 0 && tr.recordCount%tr.gapCount == 0 {
			newrec := mlrval.NewMlrmapAsRecord()
			*outputRecordsAndContexts = append(*outputRecordsAndContexts, types.NewRecordAndContext(newrec, &inrecAndContext.Context))
		}
		*outputRecordsAndContexts = append(*outputRecordsAndContexts, inrecAndContext)

		tr.recordCount++

	} else {
		*outputRecordsAndContexts = append(*outputRecordsAndContexts, inrecAndContext)
	}
	return nil
}

func (tr *TransformerGap) transformKeyed(
	inrecAndContext *types.RecordAndContext,
	outputRecordsAndContexts *[]*types.RecordAndContext, // list of *types.RecordAndContext
	inputDownstreamDoneChannel <-chan bool,
	outputDownstreamDoneChannel chan<- bool,
) error {
	if !inrecAndContext.EndOfStream {
		inrec := inrecAndContext.Record

		groupingKey, ok := inrec.GetSelectedValuesJoined(tr.groupByFieldNames)
		if !ok {
			groupingKey = ""
		}

		if groupingKey != tr.previousGroupingKey && tr.recordCount > 0 {
			newrec := mlrval.NewMlrmapAsRecord()
			*outputRecordsAndContexts = append(*outputRecordsAndContexts, types.NewRecordAndContext(newrec, &inrecAndContext.Context))
		}

		*outputRecordsAndContexts = append(*outputRecordsAndContexts, inrecAndContext)

		tr.previousGroupingKey = groupingKey
		tr.recordCount++

	} else {
		*outputRecordsAndContexts = append(*outputRecordsAndContexts, inrecAndContext)
	}
	return nil
}