DataLoader.js

import $ from 'jquery'
import cheaterDepaginate from 'jsx/shared/CheatDepaginator'
import _ from 'underscore'
  // loaders
  const getAssignmentGroups = (url, params) => {
    return cheaterDepaginate(url, params);
  };
  const getCustomColumns = (url) => {
    return $.ajaxJSON(url, "GET", {});
  };
  const getSections = (url) => {
    return $.ajaxJSON(url, "GET", {});
  };
  const getEffectiveDueDates = (url) => {
    return $.ajaxJSON(url, "GET", {});
  };

  // submission loading is tricky
  let pendingStudentsForSubmissions;
  let submissionsLoaded;
  let studentsLoaded;
  let submissionChunkCount;
  let gotSubmissionChunkCount;
  let submissionsLoading = false;
  let submissionURL;
  let submissionParams;
  let submissionChunkSize;
  let submissionChunkCb;

  const gotSubmissionsChunk = (data) => {
    gotSubmissionChunkCount++;
    submissionChunkCb(data);

    if (gotSubmissionChunkCount === submissionChunkCount &&
        studentsLoaded.isResolved()) {
      submissionsLoaded.resolve();
    }
  };

  const getPendingSubmissions = () => {
    while (pendingStudentsForSubmissions.length) {
      const studentIds = pendingStudentsForSubmissions.splice(0, submissionChunkSize);
      submissionChunkCount++;
      $.ajaxJSON(submissionURL, "GET",
                 {student_ids: studentIds, ...submissionParams},
                 gotSubmissionsChunk);
    }
  };

  const getSubmissions = (url, params, cb, chunkSize) => {
    submissionURL = url;
    submissionParams = params;
    submissionChunkCb = cb;
    submissionChunkSize = chunkSize;

    submissionsLoaded = $.Deferred();
    submissionChunkCount = 0;
    gotSubmissionChunkCount = 0;

    submissionsLoading = true;
    getPendingSubmissions();
    return submissionsLoaded;
  };

  const getStudents = (url, params, studentChunkCb) => {
    pendingStudentsForSubmissions = [];

    const gotStudentPage = (students) => {
      studentChunkCb(students);

      const studentIds = _.pluck(students, 'id');
      [].push.apply(pendingStudentsForSubmissions, studentIds);

      if (submissionsLoading) {
        getPendingSubmissions();
      }
    };

    studentsLoaded = cheaterDepaginate(url, params, gotStudentPage);
    return studentsLoaded;
  };

  const getDataForColumn = (column, url, params, cb) => {
    url = url.replace(/:id/, column.id);
    const augmentedCallback = (data) => cb(column, data);
    return cheaterDepaginate(url, params, augmentedCallback);
  };

  const getCustomColumnData = (url, params, cb, customColumnsDfd, waitForDfds) => {
    const customColumnDataLoaded = $.Deferred();
    let customColumnDataDfds;

    // waitForDfds ensures that custom column data is loaded *last*
    $.when.apply($, waitForDfds).then(() => {
      customColumnsDfd.then(customColumns => {
        customColumnDataDfds = customColumns.map(col => getDataForColumn(col, url, params, cb));
      });
    });

    $.when.apply($, customColumnDataDfds)
      .then(() => customColumnDataLoaded.resolve());

    return customColumnDataLoaded;
  };

  const loadGradebookData = (opts) => {
    const gotAssignmentGroups = getAssignmentGroups(opts.assignmentGroupsURL, opts.assignmentGroupsParams);
    if (opts.onlyLoadAssignmentGroups) {
      return { gotAssignmentGroups };
    }

    const gotEffectiveDueDates = getEffectiveDueDates(opts.effectiveDueDatesURL);
    const gotCustomColumns = getCustomColumns(opts.customColumnsURL);
    const gotStudents = getStudents(opts.studentsURL, opts.studentsParams, opts.studentsPageCb);
    const gotSubmissions = getSubmissions(opts.submissionsURL, opts.submissionsParams, opts.submissionsChunkCb, opts.submissionsChunkSize);
    const gotCustomColumnData = getCustomColumnData(opts.customColumnDataURL,
        opts.customColumnDataParams,
        opts.customColumnDataPageCb,
        gotCustomColumns,
        [gotSubmissions]);

    return {
      gotAssignmentGroups: gotAssignmentGroups,
      gotCustomColumns: gotCustomColumns ,
      gotStudents: gotStudents,
      gotSubmissions: gotSubmissions,
      gotCustomColumnData: gotCustomColumnData,
      gotEffectiveDueDates: gotEffectiveDueDates,
    };
  };

export default { loadGradebookData: loadGradebookData, getDataForColumn: getDataForColumn }