refactor: implement bidirectional transformation support with PostgreSQL integration

internal/app/etl/transformers/postgres.go

@@ -0,0 +1,72 @@
+package transformers
+
+import (
+	"context"
+	"sync"
+
+	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/config"
+	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/custom_errors"
+	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/etl"
+	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/models"
+)
+
+type PostgresTransformer struct {
+	sourceTable config.SourceTableInfo
+}
+
+func NewPostgresTransformer(sourceTable config.SourceTableInfo) etl.Transformer {
+	return &PostgresTransformer{sourceTable: sourceTable}
+}
+
+func (pgTr *PostgresTransformer) Consume(
+	ctx context.Context,
+	columns []models.ColumnType,
+	retryConfig config.RetryConfig,
+	batchSize int,
+	chBatchesIn <-chan models.Batch,
+	chBatchesOut chan<- models.Batch,
+	chJobErrorsOut chan<- custom_errors.JobError,
+	wgActiveBatches *sync.WaitGroup,
+) {
+	transformationPlan := computePostgresTransformationPlan(columns)
+
+	acc := &batchAccumulator{batchSize: batchSize}
+
+	for {
+		select {
+		case <-ctx.Done():
+			return
+
+		case batch, ok := <-chBatchesIn:
+			if !ok {
+				acc.flush(ctx, chBatchesOut, wgActiveBatches)
+				return
+			}
+
+			if len(transformationPlan) > 0 {
+				if err := ProcessBatchWithRetries(ctx, &batch, transformationPlan, retryConfig); err != nil {
+					sendTransformError(ctx, err, chJobErrorsOut)
+					return
+				}
+			}
+
+			if batchSize <= 0 {
+				wgActiveBatches.Add(1)
+				select {
+				case chBatchesOut <- batch:
+				case <-ctx.Done():
+					wgActiveBatches.Done()
+					return
+				}
+				continue
+			}
+
+			acc.add(batch)
+			if acc.ready() {
+				if !acc.flush(ctx, chBatchesOut, wgActiveBatches) {
+					return
+				}
+			}
+		}
+	}
+}