CSVQueueable.java

public class CSVQueueable implements Queueable, Database.AllowsCallouts {
  // Read in the CSV to a List<CSVRow> 
  // Persist the execution state across Async Queuable and Batch
  private CSVState state;

  // Count of Unique Policy Numbers to aggregate from the CSV
  private Integer csvChunkSize;
  
  public CSVQueueable (CSVState state) {
    this(state, 1000);
  }
  
  public CSVQueueable (CSVState state, Integer chunkSize) {
    this.state = state;
    this.csvChunkSize = chunkSize;
  }
  
  public void execute (BatchableContext ctx) {
    state.next(); // read the next 1000 unique policy numbers from the csv
    state.getInProcessing() // => Set<String> policyNumbers

    // Batch QueryLocator to process FROM Policy WHERE PolicyNumber IN state.getInProgress()
    Database.executeBatch(new CSVBatch(state)); 
  }
}