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: simple_group_by.go
    path of file: ./repos/octosql/execution/nodes
    
    the code of the file until where you have to start completion: package nodes

import (
	"fmt"
	"time"

	"github.com/zyedidia/generic/hashmap"

	. "github.com/cube2222/octosql/execution"
	"github.com/cube2222/octosql/octosql"
)

// SimpleGroupBy is a special group by that's much faster than the CustomTriggerGroupBy but only works with no custom triggers.
type SimpleGroupBy struct {
	aggregatePrototypes []func() Aggregate
	aggregateExprs      []Expression
	keyExprs            []Expression
	source              Node
}

func NewSimpleGroupBy(
	aggregatePrototypes []func() Aggregate,
	aggregateExprs []Expression,
	keyExprs []Expression,
	source Node,
) *SimpleGroupBy {
	return &SimpleGroupBy{
		aggregatePrototypes: aggregatePrototypes,
		aggregateExprs:      aggregateExprs,
		keyExprs:            keyExprs,
		source:              source,
	}
}

type hashmapAggregatesItem struct {
	Aggregates []Aggregate

	// AggregatedSetSize omits NULL inputs.
	AggregatedSetSize []int

	// OverallRecordCount counts all records minus retractions.
	OverallRecordCount int
}

func (g *SimpleGroupBy) Run(ctx ExecutionContext, produce ProduceFn, metaSend MetaSendFn) error {
	aggregates := hashmap.New[GroupKey, *hashmapAggregatesItem](BTreeDefaultDegree, func(a, b GroupKey) bool {
		for i := range a {
			if a[i].Compare(b[i]) != 0 {
				return false
			}
		}
		return true
	}, func(k GroupKey) uint64 {
		return octosql.HashManyValues(k)
	})

	if err := g.source.Run(ctx, func(produceCtx ProduceContext, record Record) error {
		ctx := ctx.WithRecord(record)

		key := make(GroupKey, len(g.keyExprs))
		for i, expr := range g.keyExprs {
			value, err := expr.Evaluate(ctx)
			if err != nil {
				return fmt.Errorf("couldn't evaluate %d group by key expression: %w", i, err)
			}
			key[i] = value
		}

		{
			itemTyped, ok := aggregates.Get(key)

			if !ok {
				newAggregates := make([]Aggregate, len(g.aggregatePrototypes))
				for i := range g.aggregatePrototypes {
					newAggregates[i] = g.aggregatePrototypes[i]()
				}

				itemTyped = &hashmapAggregatesItem{Aggregates: newAggregates, AggregatedSetSize: make([]int, len(g.aggregatePrototypes))}
				aggregates.Put(key, itemTyped)
			}

			if !record.Retraction {
				itemTyped.OverallRecordCount++
			} else {
				itemTyped.OverallRecordCount--
			}
			for i, expr := range g.aggregateExprs {
				aggregateInput, err := expr.Evaluate(ctx)
				if err != nil {
					return fmt.Errorf("couldn't evaluate %d aggregate expression: %w", i, err)
				}

				if aggregateInput.TypeID !
    
func (g *SimpleGroupBy) Run(ctx ExecutionContext, produce ProduceFn, metaSend MetaSendFn) error {
	aggregates := hashmap.New[GroupKey, *hashmapAggregatesItem](BTreeDefaultDegree, func(a, b GroupKey) bool {
		for i := range a {
			if a[i].Compare(b[i]) != 0 {
				return false
			}
		}
		return true
	}, func(k GroupKey) uint64 {
		return octosql.HashManyValues(k)
	})

	if err := g.source.Run(ctx, func(produceCtx ProduceContext, record Record) error {
		ctx := ctx.WithRecord(record)

		key := make(GroupKey, len(g.keyExprs))
		for i, expr := range g.keyExprs {
			value, err := expr.Evaluate(ctx)
			if err != nil {
				return fmt.Errorf("couldn't evaluate %d group by key expression: %w", i, err)
			}
			key[i] = value
		}

		{
			itemTyped, ok := aggregates.Get(key)

			if !ok {
				newAggregates := make([]Aggregate, len(g.aggregatePrototypes))
				for i := range g.aggregatePrototypes {
					newAggregates[i] = g.aggregatePrototypes[i]()
				}

				itemTyped = &hashmapAggregatesItem{Aggregates: newAggregates, AggregatedSetSize: make([]int, len(g.aggregatePrototypes))}
				aggregates.Put(key, itemTyped)
			}

			if !record.Retraction {
				itemTyped.OverallRecordCount++
			} else {
				itemTyped.OverallRecordCount--
			}
			for i, expr := range g.aggregateExprs {
				aggregateInput, err := expr.Evaluate(ctx)
				if err != nil {
					return fmt.Errorf("couldn't evaluate %d aggregate expression: %w", i, err)
				}

				if aggregateInput.TypeID != octosql.TypeIDNull {
					if !record.Retraction {
						itemTyped.AggregatedSetSize[i]++
					} else {
						itemTyped.AggregatedSetSize[i]--
					}
					itemTyped.Aggregates[i].Add(record.Retraction, aggregateInput)
				}
			}

			if itemTyped.OverallRecordCount == 0 {
				aggregates.Remove(key)
			}
		}

		return nil
	}, func(ctx ProduceContext, msg MetadataMessage) error {
		return metaSend(ctx, msg)
	}); err != nil {
		return fmt.Errorf("couldn't run source: %w", err)
	}

	var err error
	func() {
		type stopEach struct{}
		defer func() {
			msg := recover()
			if msg == nil {
				return
			}
			if _, ok := msg.(stopEach); ok {
				return
			}
			panic(msg)
		}()
		aggregates.Each(func(key GroupKey, itemTyped *hashmapAggregatesItem) {
			outputValues := make([]octosql.Value, len(key)+len(g.aggregateExprs))
			copy(outputValues, key)

			for i := range itemTyped.Aggregates {
				if itemTyped.AggregatedSetSize[i] > 0 {
					outputValues[len(key)+i] = itemTyped.Aggregates[i].Trigger()
				} else {
					outputValues[len(key)+i] = octosql.NewNull()
				}
			}

			if err = produce(ProduceFromExecutionContext(ctx), NewRecord(outputValues, false, time.Time{})); err != nil {
				panic(stopEach{})
			}
		})
	}()

	return err
}