context.go

package types

import (
	"bytes"
	"container/list"
	"strconv"

	"github.com/johnkerl/miller/internal/pkg/mlrval"
)

// Since Go is concurrent, the context struct (AWK-like variables such as
// FILENAME, NF, NR, FNR, etc.) needs to be duplicated and passed through the
// channels along with each record.
//
// Strings to be printed from put/filter DSL print/dump/etc statements are
// passed along to the output channel via this OutputString rather than
// fmt.Println directly in the put/filter handlers since we want all print
// statements and record-output to be in the same goroutine, for deterministic
// output ordering.

type RecordAndContext struct {
	Record       *mlrval.Mlrmap
	Context      Context
	OutputString string
	EndOfStream  bool
}

func NewRecordAndContext(
	record *mlrval.Mlrmap,
	context *Context,
) *RecordAndContext {
	return &RecordAndContext{
		Record: record,
		// Since Go is concurrent, the context struct needs to be duplicated and
		// passed through the channels along with each record. Here is where
		// the copy happens, via the '*' in *context.
		Context:      *context,
		OutputString: "",
		EndOfStream:  false,
	}
}

// For the record-readers to update their initial context as each new record is read.
func (rac *RecordAndContext) Copy() *RecordAndContext {
	if rac == nil {
		return nil
	}
	recordCopy := rac.Record.Copy()
	contextCopy := rac.Context
	return &RecordAndContext{
		Record:       recordCopy,
		Context:      contextCopy,
		OutputString: "",
		EndOfStream:  false,
	}
}

// For print/dump/etc to insert strings sequenced into the record-output
// stream.  This avoids race conditions between different goroutines printing
// to stdout: we have a single designated goroutine printing to stdout. This
// makes output more predictable and intuitive for users; it also makes our
// regression tests run reliably the same each time.
func NewOutputString(
	outputString string,
	context *Context,
) *RecordAndContext {
	return &RecordAndContext{
		Record:       nil,
		Context:      *context,
		OutputString: outputString,
		EndOfStream:  false,
	}
}

// For the record-readers to update their initial context as each new record is read.
func NewEndOfStreamMarker(context *Context) *RecordAndContext {
	return &RecordAndContext{
		Record:       nil,
		Context:      *context,
		OutputString: "",
		EndOfStream:  true,
	}
}

// TODO: comment
// For the record-readers to update their initial context as each new record is read.
func NewEndOfStreamMarkerList(context *Context) *list.List {
	ell := list.New()
	ell.PushBack(NewEndOfStreamMarker(context))
	return ell
}

// ----------------------------------------------------------------
type Context struct {
	FILENAME string
	FILENUM  int64

	// This is computed dynammically from the current record's field-count
	// NF int
	NR  int64
	FNR int64
}

// TODO: comment: Remember command-line values to pass along to CST evaluators.
// The options struct-pointer can be nil when invoked by non-DSL verbs such as
// join or seqgen.
func NewContext() *Context {
	context := &Context{
		FILENAME: "(stdin)",
		FILENUM:  0,
		NR:       0,
		FNR:      0,
	}

	return context
}

// TODO: comment: Remember command-line values to pass along to CST evaluators.
// The options struct-pointer can be nil when invoked by non-DSL verbs such as
// join or seqgen.
func NewNilContext() *Context { // TODO: rename
	context := &Context{
		FILENAME: "(stdin)",
		FILENUM:  0,
		NR:       0,
		FNR:      0,
	}

	return context
}

// For the record-readers to update their initial context as each new file is opened.
func (context *Context) UpdateForStartOfFile(filename string) {
	context.FILENAME = filename
	context.FILENUM++
	context.FNR = 0
}

// For the record-readers to update their initial context as each new record is read.
func (context *Context) UpdateForInputRecord() {
	context.NR++
	context.FNR++
}

func (context *Context) Copy() *Context {
	other := *context
	return &other
}

func (context *Context) GetStatusString() string {

	var buffer bytes.Buffer // stdio is non-buffered in Go, so buffer for speed increase
	buffer.WriteString("FILENAME=\"")
	buffer.WriteString(context.FILENAME)

	buffer.WriteString("\",FILENUM=")
	buffer.WriteString(strconv.FormatInt(context.FILENUM, 10))

	buffer.WriteString(",NR=")
	buffer.WriteString(strconv.FormatInt(context.NR, 10))

	buffer.WriteString(",FNR=")
	buffer.WriteString(strconv.FormatInt(context.FNR, 10))

	return buffer.String()
}