refactor: replace Exec with Consume method in MssqlTransformer; enhance retry handling and streamline transformation logic

internal/app/etl/transformers/process-with-retries.go

@@ -0,0 +1,73 @@
+package transformers
+
+import (
+	"context"
+	"errors"
+	"time"
+
+	"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"
+)
+
+const processBatchCtxCheck = 4096
+
+func ProcessBatchWithRetries(
+	ctx context.Context,
+	batch *models.Batch,
+	transformationPlan []etl.ColumnTransformPlan,
+	retryConfig config.RetryConfig,
+) error {
+	for i, rowValues := range batch.Rows {
+		if i%processBatchCtxCheck == 0 {
+			if err := ctx.Err(); err != nil {
+				return err
+			}
+		}
+
+		for _, task := range transformationPlan {
+			val := rowValues[task.Index]
+			if val == nil {
+				continue
+			}
+
+			var lastErr error
+			success := false
+
+			for attempt := 0; attempt < retryConfig.Attempts; attempt++ {
+				transformed, err := task.Fn(val)
+				if err == nil {
+					rowValues[task.Index] = transformed
+					success = true
+					break
+				}
+
+				lastErr = err
+				if jobError, ok := errors.AsType[*custom_errors.JobError](err); ok {
+					if jobError.ShouldCancelJob {
+						return jobError
+					}
+				}
+
+				if attempt == retryConfig.Attempts-1 {
+					break
+				}
+
+				delay := custom_errors.ComputeBackoffDelay(
+					attempt,
+					retryConfig.BaseDelayMs,
+					retryConfig.MaxDelayMs,
+					retryConfig.MaxJitterMs,
+				)
+				time.Sleep(delay)
+			}
+
+			if !success {
+				return lastErr
+			}
+		}
+	}
+
+	return nil
+}