'use strict';

const {Unit} = require('../../../models/units');
const {BadRequest} = require('../../_shared/errors');
// ----------------------------------------------------------------------------
/**
 * @param {*} req
 * @return {promise}
 */
async function getContextFields(req) {
  if (!req.query.displayType) throw new BadRequest('displayType');

  let aggregate = buildAggregateQuery(req);

  const aggregateResult = await Unit.aggregate(aggregate).exec();

  if (aggregateResult[0].measurements.length === 0) throw new BadRequest('displayType');
  if (aggregateResult[0].influxTables.length === 0) throw new BadRequest('displayType');

  let tableSet = new Set(aggregateResult[0].influxTables);
  aggregateResult[0].influxTables = [...tableSet];

  return aggregateResult[0];
}


/**
 * @param {*} req
 * @return {*}
 */
function buildAggregateQuery(req) {
  const match = buildMatch(req);
  const filterProject = buildFilterProject(req);
  const formatProject = buildFormatProject();
  return [match, filterProject, formatProject];
}


/**
 * @param {*} req
 * @return {Object}
 */
function buildMatch(req) {
  return {$match: {'_id': req.unit._id}};
}


/**
 * @param {*} req
 * @return {Object}
 */
function buildFilterProject(req) {
  const displayType = req.query.displayType;
  let filterProject = {
    $project: {
      measurements: {
        $filter: {
          input: '$measurements',
          as: 'measurements',
          cond: {$and: [{$eq: [`$$measurements.displayTypes.${displayType}`, true]}]},
        },
      },
      _id: false,
    },
  };

  // Find a better way to do that (like with array as query parameter)
  let queryFields = [];
  if (req.query.field1) queryFields.push(req.query.field1);
  if (req.query.field2) queryFields.push(req.query.field2);
  if (req.query.field3) queryFields.push(req.query.field3);
  if (req.query.field4) queryFields.push(req.query.field4);

  if (queryFields.length > 0) {
    const condition = {$in: [`$$measurements.name`, queryFields]};
    filterProject.$project.measurements.$filter.cond.$and.push(condition);
  }

  return filterProject;
}

/**
 * @return {Object}
 */
function buildFormatProject() {
  const formatProject = {
    $project: {
      measurements: '$measurements',
      influxTables: '$measurements.influxTable',
    },
  };

  return formatProject;
}

module.exports = {getContextFields};