const { isNumber, chunk, flatten } = require('lodash');
const Bluebird = require('bluebird');

module.exports = function batchInsert(
  client,
  tableName,
  batch,
  chunkSize = 1000
) {
  let returning = void 0;
  let autoTransaction = true;
  let transaction = null;

  const getTransaction = () =>
    new Bluebird((resolve, reject) => {
      if (transaction) {
        autoTransaction = false;
        return resolve(transaction);
      }

      autoTransaction = true;
      client.transaction(resolve).catch(reject);
    });

  const wrapper = Object.assign(
    new Bluebird((resolve, reject) => {
      const chunks = chunk(batch, chunkSize);

      if (!isNumber(chunkSize) || chunkSize < 1) {
        return reject(new TypeError(`Invalid chunkSize: ${chunkSize}`));
      }

      if (!Array.isArray(batch)) {
        return reject(
          new TypeError(`Invalid batch: Expected array, got ${typeof batch}`)
        );
      }

      //Next tick to ensure wrapper functions are called if needed
      return Bluebird.delay(1)
        .then(getTransaction)
        .then((tr) => {
          return Bluebird.mapSeries(chunks, (items) =>
            tr(tableName).insert(items, returning)
          )
            .then((result) => {
              result = flatten(result || []);

              if (autoTransaction) {
                //TODO: -- Oracle tr.commit() does not return a 'thenable' !? Ugly hack for now.
                return (tr.commit(result) || Bluebird.resolve()).then(
                  () => result
                );
              }

              return result;
            })
            .catch((error) => {
              if (autoTransaction) {
                return tr.rollback(error).then(() => Bluebird.reject(error));
              }

              return Bluebird.reject(error);
            });
        })
        .then(resolve)
        .catch(reject);
    }),
    {
      returning(columns) {
        returning = columns;

        return this;
      },
      transacting(tr) {
        transaction = tr;

        return this;
      },
    }
  );

  return wrapper;
};