const chunk = require('lodash/chunk');
const flatten = require('lodash/flatten');
const delay = require('./internal/delay');
const { isNumber } = require('../util/is');

function batchInsert(client, tableName, batch, chunkSize = 1000) {
  let returning = undefined;
  let transaction = null;
  if (!isNumber(chunkSize) || chunkSize < 1) {
    throw new TypeError(`Invalid chunkSize: ${chunkSize}`);
  }
  if (!Array.isArray(batch)) {
    throw new TypeError(`Invalid batch: Expected array, got ${typeof batch}`);
  }
  const chunks = chunk(batch, chunkSize);

  const runInTransaction = (cb) => {
    if (transaction) {
      return cb(transaction);
    }
    return client.transaction(cb);
  };

  return Object.assign(
    Promise.resolve().then(async () => {
      //Next tick to ensure wrapper functions are called if needed
      await delay(1);
      return runInTransaction(async (tr) => {
        const chunksResults = [];
        for (const items of chunks) {
          chunksResults.push(await tr(tableName).insert(items, returning));
        }
        return flatten(chunksResults);
      });
    }),
    {
      returning(columns) {
        returning = columns;

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

        return this;
      },
    }
  );
}

module.exports = batchInsert;