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package transformers
import (
"container/list"
"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 verbNameRemoveEmptyColumns = "remove-empty-columns"
var RemoveEmptyColumnsSetup = TransformerSetup{
Verb: verbNameRemoveEmptyColumns,
UsageFunc: transformerRemoveEmptyColumnsUsage,
ParseCLIFunc: transformerRemoveEmptyColumnsParseCLI,
IgnoresInput: false,
}
func transformerRemoveEmptyColumnsUsage(
o *os.File,
) {
fmt.Fprintf(o, "Usage: %s %s [options]\n", "mlr", verbNameRemoveEmptyColumns)
fmt.Fprintf(o, "Omits fields which are empty on every input row. Non-streaming.\n")
fmt.Fprintf(o, "Options:\n")
fmt.Fprintf(o, "-h|--help Show this message.\n")
}
func transformerRemoveEmptyColumnsParseCLI(
pargi *int,
argc int,
args []string,
_ *cli.TOptions,
doConstruct bool, // false for first pass of CLI-parse, true for second pass
) IRecordTransformer {
// Skip the verb name from the current spot in the mlr command line
argi := *pargi
argi++
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++
if opt == "-h" || opt == "--help" {
transformerRemoveEmptyColumnsUsage(os.Stdout)
os.Exit(0)
} else {
transformerRemoveEmptyColumnsUsage(os.Stderr)
os.Exit(1)
}
}
*pargi = argi
if !doConstruct { // All transformers must do this for main command-line parsing
return nil
}
transformer, err := NewTransformerRemoveEmptyColumns()
if err != nil {
fmt.Fprintln(os.Stderr, err)
os.Exit(1)
}
return transformer
}
// ----------------------------------------------------------------
type TransformerRemoveEmptyColumns struct {
recordsAndContexts *list.List
namesWithNonEmptyValues map[string]bool
}
func NewTransformerRemoveEmptyColumns() (*TransformerRemoveEmptyColumns, error) {
tr := &TransformerRemoveEmptyColumns{
recordsAndContexts: list.New(),
namesWithNonEmptyValues: make(map[string]bool),
}
return tr, nil
}
// ---------------------------------------------------------------
func (tr *TransformerRemoveEmptyColumns) Transform(
inrecAndContext *types.RecordAndContext,
outputRecordsAndContexts *list.List, // list of *types.RecordAndContext
inputDownstreamDoneChannel <-chan bool,
outputDownstreamDoneChannel chan<- bool,
) {
HandleDefaultDownstreamDone(inputDownstreamDoneChannel, outputDownstreamDoneChannel)
if !inrecAndContext.EndOfStream {
inrec := inrecAndContext.Record
tr.recordsAndContexts.PushBack(inrecAndContext)
for pe := inrec.Head; pe != nil; pe = pe.Next {
if !pe.Value.IsVoid() {
tr.namesWithNonEmptyValues[pe.Key] = true
}
}
} else { // end of record stream
for e := tr.recordsAndContexts.Front(); e != nil; e = e.Next() {
outrecAndContext := e.Value.(*types.RecordAndContext)
outrec := outrecAndContext.Record
newrec := mlrval.NewMlrmapAsRecord()
for pe := outrec.Head; pe != nil; pe = pe.Next {
_, ok := tr.namesWithNonEmptyValues[pe.Key]
if ok {
// Transferring ownership from old record to new record; no copy needed
newrec.PutReference(pe.Key, pe.Value)
}
}
outputRecordsAndContexts.PushBack(types.NewRecordAndContext(newrec, &outrecAndContext.Context))
}
outputRecordsAndContexts.PushBack(inrecAndContext) // Emit the stream-terminating null record
}
}
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