window-keeper util class

.vimrc

@@ -1,3 +1,4 @@
 map \d :w<C-m>:!clear;echo Building ...; echo; make mlr<C-m>
 map \f :w<C-m>:!clear;echo Building ...; echo; make ut<C-m>
 map \r :w<C-m>:!clear;echo Building ...; echo; make ut-scan ut-mlv<C-m>
+map \t :w<C-m>:!clear;go test github.com/johnkerl/miller/internal/pkg/transformers/...<C-m>

internal/pkg/transformers/utils/window-keeper.go

@@ -0,0 +1,70 @@
+package utils
+
+import (
+	"github.com/johnkerl/miller/internal/pkg/lib"
+)
+
+// WindowKeeper is a sliding-window container, nominally for use by mlr step,
+// for holding a number of records before the current one, the current one, and
+// a number of records after. The payload is interface{}, not *mlrval.Mlrmap,
+// for ease of unit-testing -- as well as since nothing here inspects the
+// payload, so this code could be repurposed.
+type WindowKeeper struct {
+	numBackward int
+	numForward  int
+
+	recordsBackward []interface{}
+	currentRecord   interface{}
+	recordsForward  []interface{}
+}
+
+func NewWindowKeeper(
+	numBackward int,
+	numForward int,
+) *WindowKeeper {
+	return &WindowKeeper{
+		numBackward: numBackward,
+		numForward:  numForward,
+
+		recordsBackward: make([]interface{}, numBackward),
+		currentRecord:   nil,
+		recordsForward:  make([]interface{}, numForward),
+	}
+}
+
+func (wk *WindowKeeper) IngestRecord(
+	inrec interface{},
+) {
+	for i := wk.numBackward - 1; i > 0; i-- {
+		wk.recordsBackward[i] = wk.recordsBackward[i-1]
+	}
+	if wk.numBackward > 0 {
+		wk.recordsBackward[0] = wk.currentRecord
+	}
+	if wk.numForward > 0 {
+		wk.currentRecord = wk.recordsForward[0]
+		for i := 0; i < wk.numForward-1; i++ {
+			wk.recordsForward[i] = wk.recordsForward[i+1]
+		}
+		wk.recordsForward[wk.numForward-1] = inrec
+	} else {
+		wk.currentRecord = inrec
+	}
+}
+
+// GetRecord maps a user-visible indexing ..., -3, -2, -1, 0, 1, 2, 3, ...
+// into this struct's zero-index array storage.
+func (wk *WindowKeeper) GetRecord(
+	index int,
+) interface{} {
+	if index == 0 {
+		return wk.currentRecord
+	} else if index > 0 {
+		lib.InternalCodingErrorIf(index > wk.numForward)
+		return wk.recordsForward[index-1]
+	} else {
+		index = -index
+		lib.InternalCodingErrorIf(index > wk.numBackward)
+		return wk.recordsBackward[index-1]
+	}
+}

internal/pkg/transformers/utils/window_keeper_test.go

@@ -0,0 +1,157 @@
+package utils
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func Test00(t *testing.T) {
+	wk := NewWindowKeeper(0, 0)
+
+	wk.IngestRecord("a")
+	assert.Equal(t, "a", wk.GetRecord(0).(string))
+
+	wk.IngestRecord("b")
+	assert.Equal(t, "b", wk.GetRecord(0).(string))
+}
+
+func Test10(t *testing.T) {
+	wk := NewWindowKeeper(1, 0)
+
+	wk.IngestRecord("a")
+	assert.Equal(t, "a", wk.GetRecord(0).(string))
+	assert.Equal(t, nil, wk.GetRecord(-1))
+
+	wk.IngestRecord("b")
+	assert.Equal(t, "b", wk.GetRecord(0).(string))
+	assert.Equal(t, "a", wk.GetRecord(-1).(string))
+
+	wk.IngestRecord("c")
+	assert.Equal(t, "c", wk.GetRecord(0).(string))
+	assert.Equal(t, "b", wk.GetRecord(-1).(string))
+}
+
+func Test20(t *testing.T) {
+	wk := NewWindowKeeper(2, 0)
+
+	wk.IngestRecord("a")
+	assert.Equal(t, "a", wk.GetRecord(0).(string))
+	assert.Equal(t, nil, wk.GetRecord(-1))
+	assert.Equal(t, nil, wk.GetRecord(-2))
+
+	wk.IngestRecord("b")
+	assert.Equal(t, "b", wk.GetRecord(0).(string))
+	assert.Equal(t, "a", wk.GetRecord(-1).(string))
+	assert.Equal(t, nil, wk.GetRecord(-2))
+
+	wk.IngestRecord("c")
+	assert.Equal(t, "c", wk.GetRecord(0).(string))
+	assert.Equal(t, "b", wk.GetRecord(-1).(string))
+	assert.Equal(t, "a", wk.GetRecord(-2).(string))
+
+	wk.IngestRecord("d")
+	assert.Equal(t, "d", wk.GetRecord(0).(string))
+	assert.Equal(t, "c", wk.GetRecord(-1).(string))
+	assert.Equal(t, "b", wk.GetRecord(-2).(string))
+}
+
+func Test01(t *testing.T) {
+	wk := NewWindowKeeper(0, 1)
+
+	wk.IngestRecord("a")
+	assert.Equal(t, "a", wk.GetRecord(1).(string))
+	assert.Equal(t, nil, wk.GetRecord(0))
+
+	wk.IngestRecord("b")
+	assert.Equal(t, "b", wk.GetRecord(1).(string))
+	assert.Equal(t, "a", wk.GetRecord(0).(string))
+
+	wk.IngestRecord("c")
+	assert.Equal(t, "c", wk.GetRecord(1).(string))
+	assert.Equal(t, "b", wk.GetRecord(0).(string))
+}
+
+func Test02(t *testing.T) {
+	wk := NewWindowKeeper(0, 2)
+
+	wk.IngestRecord("a")
+	assert.Equal(t, "a", wk.GetRecord(2).(string))
+	assert.Equal(t, nil, wk.GetRecord(1))
+	assert.Equal(t, nil, wk.GetRecord(0))
+
+	wk.IngestRecord("b")
+	assert.Equal(t, "b", wk.GetRecord(2).(string))
+	assert.Equal(t, "a", wk.GetRecord(1).(string))
+	assert.Equal(t, nil, wk.GetRecord(0))
+
+	wk.IngestRecord("c")
+	assert.Equal(t, "c", wk.GetRecord(2).(string))
+	assert.Equal(t, "b", wk.GetRecord(1).(string))
+	assert.Equal(t, "a", wk.GetRecord(0).(string))
+
+	wk.IngestRecord("d")
+	assert.Equal(t, "d", wk.GetRecord(2).(string))
+	assert.Equal(t, "c", wk.GetRecord(1).(string))
+	assert.Equal(t, "b", wk.GetRecord(0).(string))
+}
+
+func Test32(t *testing.T) {
+	wk := NewWindowKeeper(3, 2)
+
+	wk.IngestRecord("a")
+	assert.Equal(t, "a", wk.GetRecord(2).(string))
+	assert.Equal(t, nil, wk.GetRecord(1))
+	assert.Equal(t, nil, wk.GetRecord(0))
+	assert.Equal(t, nil, wk.GetRecord(-1))
+	assert.Equal(t, nil, wk.GetRecord(-2))
+	assert.Equal(t, nil, wk.GetRecord(-3))
+
+	wk.IngestRecord("b")
+	assert.Equal(t, "b", wk.GetRecord(2).(string))
+	assert.Equal(t, "a", wk.GetRecord(1).(string))
+	assert.Equal(t, nil, wk.GetRecord(0))
+	assert.Equal(t, nil, wk.GetRecord(-1))
+	assert.Equal(t, nil, wk.GetRecord(-2))
+	assert.Equal(t, nil, wk.GetRecord(-3))
+
+	wk.IngestRecord("c")
+	assert.Equal(t, "c", wk.GetRecord(2).(string))
+	assert.Equal(t, "b", wk.GetRecord(1).(string))
+	assert.Equal(t, "a", wk.GetRecord(0).(string))
+	assert.Equal(t, nil, wk.GetRecord(-1))
+	assert.Equal(t, nil, wk.GetRecord(-2))
+	assert.Equal(t, nil, wk.GetRecord(-3))
+
+	wk.IngestRecord("d")
+	assert.Equal(t, "d", wk.GetRecord(2).(string))
+	assert.Equal(t, "c", wk.GetRecord(1).(string))
+	assert.Equal(t, "b", wk.GetRecord(0).(string))
+	assert.Equal(t, "a", wk.GetRecord(-1).(string))
+	assert.Equal(t, nil, wk.GetRecord(-2))
+	assert.Equal(t, nil, wk.GetRecord(-3))
+
+	wk.IngestRecord("e")
+	assert.Equal(t, "e", wk.GetRecord(2).(string))
+	assert.Equal(t, "d", wk.GetRecord(1).(string))
+	assert.Equal(t, "c", wk.GetRecord(0).(string))
+	assert.Equal(t, "b", wk.GetRecord(-1).(string))
+	assert.Equal(t, "a", wk.GetRecord(-2).(string))
+	assert.Equal(t, nil, wk.GetRecord(-3))
+
+	wk.IngestRecord("f")
+	assert.Equal(t, "f", wk.GetRecord(2).(string))
+	assert.Equal(t, "e", wk.GetRecord(1).(string))
+	assert.Equal(t, "d", wk.GetRecord(0).(string))
+	assert.Equal(t, "c", wk.GetRecord(-1).(string))
+	assert.Equal(t, "b", wk.GetRecord(-2).(string))
+	assert.Equal(t, "a", wk.GetRecord(-3).(string))
+
+	wk.IngestRecord("g")
+	assert.Equal(t, "g", wk.GetRecord(2).(string))
+	assert.Equal(t, "f", wk.GetRecord(1).(string))
+	assert.Equal(t, "e", wk.GetRecord(0).(string))
+	assert.Equal(t, "d", wk.GetRecord(-1).(string))
+	assert.Equal(t, "c", wk.GetRecord(-2).(string))
+	assert.Equal(t, "b", wk.GetRecord(-3).(string))
+}