// Let's make `parseManifest` accept a callback that takes a `ManifestEntry` (very javascript =).
// It just processes lines into manifest entries and hands them off.

func parseManifest(ctx context.Context, manifestBody string, processEntry func(ManifestEntry)) error {
	dec := json.NewDecoder(strings.NewReader(manifestBody))
	
	for {
		var e ManifestEntry
		if err := dec.Decode(&e); err == io.EOF {
			break
		} else if err != nil {
			return fmt.Errorf("failed to decode manifest entry: %w", err)
		}

		processEntry(e)
	}
	
	return nil
}

// In handler, update parseManifest
// Use a waitgroup and goroutines to process each file -> csv conversion and upload separately
// Something like:

var wg sync.WaitGroup

err := parseManifest(ctx, manifest, func(entry ManifestEntry) {
	wg.Add(1)
	go func(e ManifestEntry) {
		defer wg.Done()
		
	 	// download file and convert to csv (could potentially be separate operations ...?)
		csv, err := getExportDataFile(ctx, e.DataFileS3Key)
		if err != nil {
			log.Printf("Failed to get export data for %s: %v", e.DataFileS3Key, err)
			return // probs need to handle an issue better
		}
    
	    	// do something for filename ...
	    	filename := fmt.Sprintf("export_%s.csv", extractFileID(e.DataFileS3Key))
	    	// preferably upload without writing to disk first ...
	    	if err := uploadCSV(filename, csv); err != nil {
	      	log.Printf("Failed to upload CSV for %s: %v", e.DataFileS3Key, err)
			return // probs need to handle an issue better
	    	}
		
		log.Printf("Successfully processed %s", e.DataFileS3Key)
	}(entry)
})

wg.Wait()