refactor: streamline error handling and processing in GenericExtractor; implement partition processing with retries

internal/app/etl/extractors/main.go

@@ -1,7 +1,11 @@
 package extractors
 
 import (
+	"context"
+
 	dbwrapper "git.ksdemosapps.com/kylesoda/go-migrate/internal/app/db-wrapper"
+	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/models"
+	"github.com/google/uuid"
 )
 
 type GenericExtractor struct {
@@ -11,3 +15,28 @@ type GenericExtractor struct {
 func NewExtractor(db dbwrapper.DbWrapper) GenericExtractor {
 	return GenericExtractor{db: db}
 }
+
+func sendBatch(ctx context.Context, chBatchesOut chan<- models.Batch, batch models.Batch) error {
+	select {
+	case chBatchesOut <- batch:
+		return nil
+	case <-ctx.Done():
+		return ctx.Err()
+	}
+}
+
+func flush(
+	ctx context.Context,
+	partition *models.Partition,
+	batchSize int,
+	batchRows []models.UnknownRowValues,
+	chBatchesOut chan<- models.Batch,
+) error {
+	if len(batchRows) == 0 {
+		return nil
+	}
+
+	batch := models.Batch{Id: uuid.New(), PartitionId: partition.Id, Rows: batchRows}
+	batchRows = make([]models.UnknownRowValues, 0, batchSize)
+	return sendBatch(ctx, chBatchesOut, batch)
+}