const AWS = require('aws-sdk');
const docClient = new AWS.DynamoDB.DocumentClient();

/**
 * Given a parameters object, queries a table and returns the items in an array.
 * If no valid matching items are found, returns an empty array.
 * @param {object} params - DynamoDB query params
 * @param {boolean} recursiveEvaluate - boolean whether operation should continue
 * until all results are retrieved. Default value is true.
 */
exports.queryTable = async (params, recursiveEvaluate = true) => {
  let _data = [], _errors = [];
  let queryParams = params;
  
  const ERROR_THRESHOLD = 3;
  
  do {
    try {
      let query = await docClient.query(queryParams).promise();
      queryParams.ExclusiveStartKey = null; // reset start key
      
      if (query.LastEvaluatedKey && recursiveEvaluate) {
        queryParams.ExclusiveStartKey = query.LastEvaluatedKey;
      }
      
      _data = [..._data, ...query.Items];
      
    } catch(e) {
      _errors.push({ message: 'unable to query table', error: e });
    }
  } while (queryParams.ExclusiveStartKey && _errors.length < ERROR_THRESHOLD);

  return {
    message: `Table ${params.TableName} queried.`,
    data: _data,
    errors: _errors,
  };
}