text: // To learn how to use this script, refer to the documentation:
  // https://developers.google.com/apps-script/samples/automations/offsite-activity-signup
  
  /*
  Copyright 2022 Google LLC
  
  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  You may obtain a copy of the License at
  
      https://www.apache.org/licenses/LICENSE-2.0
  
  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.
  */
  
  const NUM_ITEMS_TO_RANK = 5;
  const ACTIVITIES_PER_PERSON = 2;
  const NUM_TEST_USERS = 150;
  
  /**
   * Adds custom menu items when opening the sheet.
   */
  function onOpen() {
    let menu = SpreadsheetApp.getUi().createMenu('Activities')
        .addItem('Create form', 'buildForm_')
        .addItem('Generate test data', 'generateTestData_')
        .addItem('Assign activities', 'assignActivities_')
        .addToUi();
  }
  
  /**
   * Builds a form based on the "Activity Schedule" sheet. The form asks attendees to rank their top
   * N choices of activities, where N is defined by NUM_ITEMS_TO_RANK.
   */
  function buildForm_() {
    let ss = SpreadsheetApp.getActiveSpreadsheet();
    if (ss.getFormUrl()) {
      let msg = 'Form already exists. Unlink the form and try again.';
      SpreadsheetApp.getUi().alert(msg);
      return;
    }
    let form = FormApp.create('Activity Signup')
        .setDestination(FormApp.DestinationType.SPREADSHEET, ss.getId())
        .setAllowResponseEdits(true)
        .setLimitOneResponsePerUser(true)
        .setCollectEmail(true);
    let sectionHelpText = Utilities.formatString('Please choose your top %d activities',
        NUM_ITEMS_TO_RANK);
    form.addSectionHeaderItem()
        .setTitle('Activity choices')
        .setHelpText(sectionHelpText);
  
    // Presents activity ranking as a form grid with each activity as a row and rank as a column.
    let rows = loadActivitySchedule_(ss).map(function(activity) {
      return activity.description;
    });
    let columns = range_(1, NUM_ITEMS_TO_RANK).map(function(value) {
      return Utilities.formatString('%s', toOrdinal_(value));
    });
    let gridValidation = FormApp.createGridValidation()
        .setHelpText('Select one item per column.')
        .requireLimitOneResponsePerColumn()
        .build();
    form.addGridItem()
        .setColumns(columns)
        .setRows(rows)
        .setValidation(gridValidation);
  
    form.addListItem()
        .setTitle('Assign other activities if choices are not available?')
        .setChoiceValues(['Yes', 'No']);
  }
  
  /**
   * Assigns activities using a random priority/random serial dictatorship approach. The results
   * are then populated into two new sheets, one listing activities per person, the other listing
   * the rosters for each activity.
   *
   * See https://en.wikipedia.org/wiki/Random_serial_dictatorship for additional information.
   */
  function assignActivities_() {
    let ss = SpreadsheetApp.getActiveSpreadsheet();
    let activities = loadActivitySchedule_(ss);
    let activityIds = activities.map(function(activity) {
      return activity.id;
    });
    let attendees = loadAttendeeResponses_(ss, activityIds);
    assignWithRandomPriority_(attendees, activities, 2);
    writeAttendeeAssignments_(ss, attendees);
    writeActivityRosters_(ss, activities);
  }
  
  /**
   * Selects activities via random priority.
   *
   * @param {object[]} attendees - Array of attendees to assign activities to
   * @param {object[]} activities - Array of all available activities
   * @param {number} numActivitiesPerPerson - Maximum number of activities to assign
   */
  function assignWithRandomPriority_(attendees, activities, numActivitiesPerPerson) {
    let activitiesById = activities.reduce(function(obj, activity) {
      obj[activity.id] = activity;
      return obj;
    }, {});
    for (let i = 0; i < numActivitiesPerPerson; ++i) {
      let randomizedAttendees = shuffleArray_(attendees);
      randomizedAttendees.forEach(function(attendee) {
        makeChoice_(attendee, activitiesById);
      });
    }
  }
  
  /**
   * Attempts to assign an activity for an attendee based on their preferences and current schedule.
   *
   * @param {object} attendee - Attendee looking to join an activity
   * @param {object} activitiesById - Map of all available activities
   */
  function makeChoice_(attendee, activitiesById) {
    for (let i = 0; i < attendee.preferences.length; ++i) {
      let activity = activitiesById[attendee.preferences[i]];
      if (!activity) {
        continue;
      }
      let canJoin = checkAvailability_(attendee, activity);
      if (canJoin) {
        attendee.assigned.push(activity);
        activity.roster.push(attendee);
        break;
      }
    }
  }
  
  /**
   * Checks that an activity has capacity and doesn't conflict with previously assigned
   * activities.
   *
   * @param {object} attendee - Attendee looking to join the activity
   * @param {object} activity - Proposed activity
   * @return {boolean} - True if attendee can join the activity
   */
  function checkAvailability_(attendee, activity) {
    if (activity.capacity <= activity.roster.length) {
      return false;
    }
    let timesConflict = attendee.assigned.some(function(assignedActivity) {
      return !(assignedActivity.startAt.getTime() > activity.endAt.getTime() ||
        activity.startAt.getTime() > assignedActivity.endAt.getTime());
    });
    return !timesConflict;
  };
  
  /**
   * Populates a sheet with the assigned activities for each attendee.
   *
   * @param {Spreadsheet} ss - Spreadsheet to write to.
   * @param {object[]} attendees - Array of attendees with their activity assignments
   */
  function writeAttendeeAssignments_(ss, attendees) {
    let sheet = findOrCreateSheetByName_(ss, 'Activities by person');
    sheet.clear();
    sheet.appendRow(['Email address', 'Activities']);
    sheet.getRange('B1:1').merge();
    let rows = attendees.map(function(attendee) {
      // Prefill row to ensure consistent length otherwise
      // can't bulk update the sheet with range.setValues()
      let row = fillArray_([], ACTIVITIES_PER_PERSON + 1, '');
      row[0] = attendee.email;
      attendee.assigned.forEach(function(activity, index) {
        row[index + 1] = activity.description;
      });
      return row;
    });
    bulkAppendRows_(sheet, rows);
    sheet.setFrozenRows(1);
    sheet.getRange('1:1').setFontWeight('bold');
    sheet.autoResizeColumns(1, sheet.getLastColumn());
  }
  
  /**
   * Populates a sheet with the rosters for each activity.
   *
   * @param {Spreadsheet} ss - Spreadsheet to write to.
   * @param {object[]} activities - Array of activities with their rosters
   */
  function writeActivityRosters_(ss, activities) {
    let sheet = findOrCreateSheetByName_(ss, 'Activity rosters');
    sheet.clear();
    var rows = [];
    var rows = activities.map(function(activity) {
      let roster = activity.roster.map(function(attendee) {
        return attendee.email;
      });
      return [activity.description].concat(roster);
    });
    // Transpose the data so each activity is a column
    rows = transpose_(rows, '');
    bulkAppendRows_(sheet, rows);
    sheet.setFrozenRows(1);
    sheet.getRange('1:1').setFontWeight('bold');
    sheet.autoResizeColumns(1, sheet.getLastColumn());
  }
  
  /**
   * Loads the activity schedule.
   *
   * @param {Spreadsheet} ss - Spreadsheet to load from
   * @return {object[]} Array of available activities.
   */
  function loadActivitySchedule_(ss) {
    let timeZone = ss.getSpreadsheetTimeZone();
    let sheet = ss.getSheetByName('Activity Schedule');
    let rows = sheet.getSheetValues(
        sheet.getFrozenRows() + 1, 1,
        sheet.getLastRow() - 1, sheet.getLastRow());
    let activities = rows.map(function(row, index) {
      let name = row[0];
      let startAt = new Date(row[1]);
      let endAt = new Date(row[2]);
      let capacity = parseInt(row[3]);
      let formattedStartAt= Utilities.formatDate(startAt, timeZone, 'EEE hh:mm a');
      let formattedEndAt = Utilities.formatDate(endAt, timeZone, 'hh:mm a');
      let description = Utilities.formatString('%s (%s-%s)', name, formattedStartAt, formattedEndAt);
      return {
        id: index,
        name: name,
        description: description,
        capacity: capacity,
        startAt: startAt,
        endAt: endAt,
        roster: [],
      };
    });
    return activities;
  }
  
  /**
   * Loads the attendeee response data.
   *
   * @param {Spreadsheet} ss - Spreadsheet to load from
   * @param {number[]} allActivityIds - Full set of available activity IDs
   * @return {object[]} Array of parsed attendee respones.
   */
  function loadAttendeeResponses_(ss, allActivityIds) {
    let sheet = findResponseSheetForForm_(ss);
  
    if (!sheet || sheet.getLastRow() == 1) {
      return undefined;
    }
  
    let rows = sheet.getSheetValues(
        sheet.getFrozenRows() + 1, 1,
        sheet.getLastRow() - 1, sheet.getLastRow());
    let attendees = rows.map(function(row) {
      let _ = row.shift(); // Ignore timestamp
      let email = row.shift();
      let autoAssign = row.pop();
      // Find ranked items in the response data.
      let preferences = row.reduce(function(prefs, value, index) {
        let match = value.match(/(\d+).*/);
        if (!match) {
          return prefs;
        }
        let rank = parseInt(match[1]) - 1; // Convert ordinal to array index
        prefs[rank] = index;
        return prefs;
      }, []);
      if (autoAssign == 'Yes') {
        // If auto assigning additional activites, append a randomized list of all the activities.
        // These will then be considered as if the attendee ranked them.
        let additionalChoices = shuffleArray_(allActivityIds);
        preferences = preferences.concat(additionalChoices);
      }
      return {
        email: email,
        preferences: preferences,
        assigned: [],
      };
    });
    return attendees;
  }
  
  /**
   * Simulates a large number of users responding to the form. This enables users to quickly
   * experience the full solution without having to collect sufficient form responses
   * through other means.
   */
  function generateTestData_() {
    let ss = SpreadsheetApp.getActiveSpreadsheet();
    let sheet = findResponseSheetForForm_(ss);
    if (!sheet) {
      let msg = 'No response sheet found. Create the form and try again.';
      SpreadsheetApp.getUi().alert(msg);
    }
    if (sheet.getLastRow() > 1) {
      let msg = 'Response sheet is not empty, can not generate test data. ' +
        'Remove responses and try again.';
      SpreadsheetApp.getUi().alert(msg);
      return;
    }
  
    let activities = loadActivitySchedule_(ss);
    let choices = fillArray_([], activities.length, '');
    range_(1, 5).forEach(function(value) {
      choices[value] = toOrdinal_(value);
    });
  
    let rows = range_(1, NUM_TEST_USERS).map(function(value) {
      let randomizedChoices = shuffleArray_(choices);
      let email = Utilities.formatString('person%d@example.com', value);
      return [new Date(), email].concat(randomizedChoices).concat(['Yes']);
    });
    bulkAppendRows_(sheet, rows);
  }
  
  /**
   * Retrieves a sheet by name, creating it if it doesn't yet exist.
   *
   * @param {Spreadsheet} ss - Containing spreadsheet
   * @Param {string} name - Name of sheet to return
   * @return {Sheet} Sheet instance
   */
  function findOrCreateSheetByName_(ss, name) {
    let sheet = ss.getSheetByName(name);
    if (sheet) {
      return sheet;
    }
    return ss.insertSheet(name);
  }
  
  /**
   * Faster version of appending multiple rows via ranges. Requires all rows are equal length.
   *
   * @param {Sheet} sheet - Sheet to append to
   * @param {Array<Array<object>>} rows - Rows to append
   */
  function bulkAppendRows_(sheet, rows) {
    let startRow = sheet.getLastRow() + 1;
    let startColumn = 1;
    let numRows = rows.length;
    let numColumns = rows[0].length;
    sheet.getRange(startRow, startColumn, numRows, numColumns).setValues(rows);
  }
  
  /**
   * Copies and randomizes an array.
   *
   * @param {object[]} array - Array to shuffle
   * @return {object[]} randomized copy of the array
   */
  function shuffleArray_(array) {
    let clone = array.slice(0);
    for (let i = clone.length - 1; i > 0; i--) {
      let j = Math.floor(Math.random() * (i + 1));
      let temp = clone[i];
      clone[i] = clone[j];
      clone[j] = temp;
    }
    return clone;
  }
  
  /**
   * Formats an number as an ordinal.
   *
   * See: https://stackoverflow.com/questions/13627308/add-st-nd-rd-and-th-ordinal-suffix-to-a-number/13627586
   *
   * @param {number} i - Number to format
   * @return {string} Formatted string
   */
  function toOrdinal_(i) {
    let j = i % 10;
    let k = i % 100;
    if (j == 1 && k != 11) {
      return i + 'st';
    }
    if (j == 2 && k != 12) {
      return i + 'nd';
    }
    if (j == 3 && k != 13) {
      return i + 'rd';
    }
    return i + 'th';
  }
  
  /**
   * Locates the sheet containing the form responses.
   *
   * @param {Spreadsheet} ss - Spreadsheet instance to search
   * @return {Sheet} Sheet with form responses, undefined if not found.
   */
  function findResponseSheetForForm_(ss) {
    let formUrl = ss.getFormUrl();
    if (!ss || !formUrl) {
      return undefined;
    }
    let sheets = ss.getSheets();
    for (let i in sheets) {
      if (sheets[i].getFormUrl() === formUrl) {
        return sheets[i];
      }
    }
    return undefined;
  }
  
  /**
   * Fills an array with a value ([].fill() not supported in Apps Script).
   *
   * @param {object[]} arr - Array to fill
   * @param {number} length - Number of items to fill.
   * @param {object} value - Value to place at each index.
   * @return {object[]} the array, for chaining purposes
   */
  function fillArray_(arr, length, value) {
    for (let i = 0; i < length; ++i) {
      arr[i] = value;
    }
    return arr;
  }
  
  /**
   * Creates and fills an array with numbers in the range [start, end].
   *
   * @param {number} start - First value in the range, inclusive
   * @param {number} end - Last value in the range, inclusive
   * @return {number[]} Array of values representing the range
   */
  function range_(start, end) {
    let arr = [start];
    let i = start;
    while (i < end) {
      arr.push(i += 1);
    }
    return arr;
  }
  
  /**
   * Transposes a matrix/2d array. For cases where the rows are not the same length,
   * `fillValue` is used where no other value would otherwise be present.
   *
   * @param {Array<Array<object>>} arr - 2D array to transpose
   * @param {object} fillValue - Placeholder for undefined values created as a result
   *     of the transpose. Only required if rows aren't all of equal length.
   * @return {Array<Array<object>>} New transposed array
   */
  function transpose_(arr, fillValue) {
    let transposed = [];
    arr.forEach(function(row, rowIndex) {
      row.forEach(function(col, colIndex) {
        transposed[colIndex] = transposed[colIndex] || fillArray_([], arr.length, fillValue);
        transposed[colIndex][rowIndex] = row[colIndex];
      });
    });
    return transposed;
  }
  