gradebook_importer.rb

# frozen_string_literal: true

#
# Copyright (C) 2011 - present Instructure, Inc.
#
# This file is part of Canvas.
#
# Canvas is free software: you can redistribute it and/or modify it under
# the terms of the GNU Affero General Public License as published by the Free
# Software Foundation, version 3 of the License.
#
# Canvas is distributed in the hope that it will be useful, but WITHOUT ANY
# WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
# A PARTICULAR PURPOSE. See the GNU Affero General Public License for more
# details.
#
# You should have received a copy of the GNU Affero General Public License along
# with this program. If not, see <http://www.gnu.org/licenses/>.
#

require 'csv'

class GradebookImporter
  ASSIGNMENT_PRELOADED_FIELDS = %i/
    id title points_possible grading_type updated_at context_id context_type group_category_id
    created_at due_at only_visible_to_overrides moderated_grading grades_published_at final_grader_id
  /.freeze

  class NegativeId
    class << self
      def generate
        instance.next
      end

      def instance
        @@inst ||= new
      end
    end
    def next
      @i ||= 0
      @i -= 1
    end
  end

  class InvalidHeaderRow < StandardError; end

  OverrideColumnInfo = Struct.new(:grading_period_id, :index, keyword_init: true)
  OverrideScoreChange = Struct.new(:grading_period_id, :student_id, :current_score, :new_score, keyword_init: true) do
    def course_score?
      grading_period_id.nil?
    end
  end

  attr_reader :context, :contents, :attachment, :assignments, :students,
              :submissions, :missing_assignments, :missing_students, :upload

  def self.create_from(progress, gradebook_upload, user, attachment)
    self.new(gradebook_upload, attachment, user, progress).parse!
  rescue CSV::MalformedCSVError => e
    Canvas::Errors.capture_exception(:gradebook_import, e, :info)
    # this isn't actually "retryable", but this error will make sure
    # the job is marked "failed" without generating alarm noise.
    raise Delayed::RetriableError, "Gradebook import did not parse cleanly"
  end

  def initialize(upload=nil, attachment=nil, user=nil, progress=nil)
    @upload = upload
    @context = upload.course

    raise ArgumentError, "Must provide a valid context for this gradebook." unless valid_context?(@context)
    raise ArgumentError, "Must provide attachment." unless attachment

    @user = user
    @attachment = attachment
    @progress = progress

    GuardRail.activate(:secondary) do
      @visible_assignments = AssignmentStudentVisibility.visible_assignment_ids_in_course_by_user(
        course_id: @context.id, user_id: @context.all_students.pluck(:id)
      )
    end
  end

  CSV::Converters[:nil] = lambda do |e|
    begin
      e.nil? ? e : raise
    rescue
      e
    end
  end

  CSV::Converters[:decimal_comma_to_period] = -> (field) do
    if field =~ /^-?[0-9.,]+%?$/
      # This field is a pure number or percentage => let's normalize it
      number_parts = field.split(/[,.]/)
      last_number_part = number_parts.pop

      if number_parts.empty?
        last_number_part
      else
        [number_parts.join(), last_number_part].join('.')
      end
    else
      field
    end
  end

  def parse!
    # preload a ton of data that presumably we'll be querying
    @context.preload_user_roles!
    @all_assignments = @context.assignments.
      preload({ context: :account }).
      published.
      gradeable.
      select(ASSIGNMENT_PRELOADED_FIELDS).
      to_a

    Assignment.preload_unposted_anonymous_submissions(@all_assignments)
    @all_assignments = @all_assignments.index_by(&:id)
    @all_students = @context.all_students
      .select(['users.id', :name, :sortable_name, 'users.updated_at'])
      .index_by(&:id)

    @assignments = nil
    @root_accounts = {}
    @pseudonyms_by_sis_id = {}
    @pseudonyms_by_login_id = {}
    @students = []
    @pp_row = []
    @warning_messages = {
      prevented_new_assignment_creation_in_closed_period: false,
      prevented_grading_ungradeable_submission: false,
      prevented_changing_read_only_column: false
    }
    @parsed_custom_column_data = {}
    @override_column_indices = {}
    @gradebook_importer_assignments = {}
    @gradebook_importer_custom_columns = {}
    @gradebook_importer_override_scores = {}

    begin
      csv_stream do |row|
        already_processed = check_for_non_student_row(row)
        unless already_processed
          @students << process_student(row)
          process_submissions(row, @students.last)
        end
      end
    rescue InvalidHeaderRow
      @progress.message = "Invalid header row"
      @progress.workflow_state = "failed"
      @progress.save
      return
    end

    @missing_assignments = []
    @missing_assignments = @all_assignments.values - @assignments if @missing_assignment
    @missing_students = []
    @missing_students = @all_students.values - @students if @missing_student

    # look up existing score for everything that was provided
    assignment_ids = @missing_assignment ? @all_assignments.values : @assignments
    user_ids = @missing_student ? @all_students.values : @students
    # preload periods to avoid N+1s
    periods = GradingPeriod.for(@context)
    # preload is_admin to avoid N+1
    is_admin = @context.account_membership_allows(@user)
    # Preload effective due dates to avoid N+1s
    effective_due_dates = EffectiveDueDates.for_course(@context, @all_assignments.values)

    @original_submissions = @context.submissions
      .preload(:grading_period, assignment: { context: :account })
      .select(['submissions.id', :assignment_id, :user_id, :grading_period_id, :score, :excused, :cached_due_date, :course_id, 'submissions.updated_at'])
      .where(assignment_id: assignment_ids, user_id: user_ids)
      .map do |submission|
        is_gradeable = gradeable?(submission: submission, is_admin: is_admin)
        score = submission.excused? ? "EX" : submission.score.to_s
        {
          user_id: submission.user_id,
          assignment_id: submission.assignment_id,
          score: score,
          gradeable: is_gradeable
        }
      end

    # cache the score on the existing object
    original_submissions_by_student = @original_submissions.inject({}) do |r, s|
      r[s[:user_id]] ||= {}
      r[s[:user_id]][s[:assignment_id]] ||= {}
      r[s[:user_id]][s[:assignment_id]][:score] = s[:score]
      r[s[:user_id]][s[:assignment_id]][:gradeable] = s[:gradeable]
      r
    end

    @students.each do |student|
      @gradebook_importer_assignments[student.id].each do |submission|
        submission_assignment_id = submission.fetch('assignment_id').to_i
        assignment = original_submissions_by_student.
          fetch(student.id, {}).
          fetch(submission_assignment_id, {})
        submission['original_grade'] = assignment.fetch(:score, nil)
        submission['gradeable'] = assignment.fetch(:gradable, nil)

        if submission.fetch('gradeable').nil?
          assignment = @all_assignments[submission['assignment_id']] || @context.assignments.build
          new_submission = Submission.new
          new_submission.user = student
          new_submission.assignment = assignment
          edd = effective_due_dates.find_effective_due_date(student.id, assignment.id)
          new_submission.cached_due_date = edd.fetch(:due_at, nil)
          new_submission.grading_period_id = edd.fetch(:grading_period_id, nil)
          submission['gradeable'] = !edd.fetch(:in_closed_grading_period, false) && gradeable?(
            submission: new_submission,
            is_admin: is_admin
          )
        end
      end
      @gradebook_importer_custom_columns[student.id].each do |column_id, student_custom_column_cell|
        custom_column = custom_gradebook_columns.detect {|custom_col| custom_col.id == column_id}
        datum = custom_column.custom_gradebook_column_data.detect {|custom_column_datum| custom_column_datum.user_id == student.id}
        student_custom_column_cell['current_content'] = datum&.content
      end
    end

    set_current_override_scores if allow_override_scores?

    translate_pass_fail(@assignments, @students, @gradebook_importer_assignments)
    unless @missing_student
      # weed out assignments with no changes
      indexes_to_delete = []
      @assignments.each_with_index do |assignment, idx|
        next if assignment.changed? && !readonly_assignment?(idx)
        indexes_to_delete << idx if readonly_assignment?(idx) || @students.all? do |student|
          submission = @gradebook_importer_assignments[student.id][idx]

          # Have potentially mixed case excused in grade match case
          # expectations for the compare so it doesn't look changed
          submission['grade'] = 'EX' if submission['grade'].to_s.casecmp('EX') == 0
          no_change = no_change_to_submission?(submission)

          @warning_messages[:prevented_grading_ungradeable_submission] = true if !submission['gradeable'] && !no_change

          no_change || !submission['gradeable']
        end
      end

      custom_column_ids_to_skip_on_import = []
      custom_gradebook_columns.each do |custom_column|
        no_change = true
        if @parsed_custom_column_data.include?(custom_column.id) && !custom_column.deleted?
          no_change = no_change_to_column_values?(column_id: custom_column.id)

          @warning_messages[:prevented_changing_read_only_column] = true if !no_change && custom_column.read_only
        end

        if no_change || exclude_custom_column_on_import(column: custom_column)
          custom_column_ids_to_skip_on_import << custom_column.id
        end
      end

      indexes_to_delete.reverse_each do |index|
        @assignments.delete_at(index)
        @students.each do |student|
          @gradebook_importer_assignments[student.id].delete_at(index)
        end
      end

      @custom_gradebook_columns = @custom_gradebook_columns.reject { |custom_col| custom_column_ids_to_skip_on_import.include?(custom_col.id) }
      @students.each do |student|
        @gradebook_importer_custom_columns[student.id].reject! do |column_id, _custom_col|
          custom_column_ids_to_skip_on_import.include?(column_id)
        end
      end

      @students.each do |student|
        @gradebook_importer_assignments[student.id].select! { |sub| sub['gradeable'] }
      end

      @unchanged_assignments = !indexes_to_delete.empty?

      grading_period_ids_with_updated_overrides = remove_override_scores_for_unchanged_grading_periods!

      @students = [] if @assignments.empty? && @custom_gradebook_columns.empty? && grading_period_ids_with_updated_overrides.empty?
    end

    # remove concluded enrollments
    prior_enrollment_ids = (
      @all_students.keys - @context.gradable_students.pluck(:user_id).map(&:to_i)
    ).to_set
    @students.delete_if { |s| prior_enrollment_ids.include? s.id }

    @original_submissions = [] unless @missing_student || @missing_assignment

    if prevent_new_assignment_creation?(periods, is_admin)
      @assignments.delete_if do |assignment|
        new_assignment = assignment.new_record?
        if new_assignment
          @warning_messages[:prevented_new_assignment_creation_in_closed_period] = true
        end
        new_assignment
      end
    end

    @upload.gradebook = self.as_json
    @upload.save!
  end

  def translate_pass_fail(assignments, students, gradebook_importer_assignments)
    assignments.each_with_index do |assignment, idx|
      next unless assignment.grading_type == "pass_fail"
      students.each do |student|
        submission = gradebook_importer_assignments.fetch(student.id)[idx]
        if submission['grade'].present? && (submission['grade'].to_s.casecmp('EX') != 0)
          gradebook_importer_assignments.fetch(student.id)[idx]['grade'] = assignment.score_to_grade(submission['grade'], \
            submission['grade'])
        end
        if submission['original_grade'].present? && (submission['original_grade'] != 'EX')
          gradebook_importer_assignments.fetch(student.id)[idx]['original_grade'] = assignment.score_to_grade(submission['original_grade'],\
            submission['original_grade'])
        end
        if submission['grade'].to_s.casecmp('EX') == 0
          submission['grade'] = 'EX'
        end
      end
    end
  end

  def process_custom_column_headers(row)
    row.each_with_index do |header_column, index|
      next if GRADEBOOK_IMPORTER_RESERVED_NAMES.include?(header_column)
      gradebook_column = custom_gradebook_columns.detect { |column| column.title == header_column }
      next if gradebook_column.blank?

      @parsed_custom_column_data[gradebook_column.id] = {
        title: header_column,
        index: index,
        read_only: gradebook_column.read_only
      }
    end
  end

  def strip_custom_columns(stripped_row)
    @parsed_custom_column_data.each_value do |column|
      stripped_row.delete(column[:title])
    end
    stripped_row
  end

  def process_header(row)
    raise InvalidHeaderRow unless header?(row)

    # Handle override columns before we strip out the "non-assignment" columns
    @override_column_indices = detect_override_columns(row)
    row = strip_non_assignment_columns(row)
    row = strip_custom_columns(row)
    parse_assignments(row) # requires non-assignment columns to be stripped
  end

  def header?(row)
    return false unless row_has_student_headers? row

    # this is here instead of in process_header() because @parsed_custom_column_data needs to be updated before update_column_count()
    process_custom_column_headers(row)

    update_column_count row

    return false if last_student_info_column(row) !~ /Section/

    true
  end

  def last_student_info_column(row)
    # Custom Columns are between section and assignments
    row[@student_columns - (1 + @parsed_custom_column_data.length)]
  end

  def row_has_student_headers?(row)
    row.length > 3 && row[0] =~ /Student/ && row[1] =~ /ID/
  end

  def update_column_count(row)
    # A side effect that's necessary to finish validation, but needs to come
    # after the row.length check above.
    @student_columns = 3 # name, user id, section
    if row[2] =~ /SIS\s+Login\s+ID/
      @sis_login_id_column = 2
      @student_columns += 1
    elsif row[2] =~ /SIS\s+User\s+ID/ && row[3] =~ /SIS\s+Login\s+ID/
      # Integration id might be after sis id and login id, ignore it.
      i = row[4] =~ /Integration\s+ID/ ? 1 : 0
      @sis_user_id_column = 2
      @sis_login_id_column = 3
      @student_columns += 2 + i
      if row[4 + i] =~ /Root\s+Account/
        @student_columns += 1
        @root_account_column = 4 + i
      end
    end

    # For Custom Columns
    @student_columns += @parsed_custom_column_data.length
  end

  GRADEBOOK_IMPORTER_RESERVED_NAMES = [
    "Student",
    "ID",
    "SIS User ID",
    "SIS Login ID",
    "Section",
    "Integration ID",
    "Root Account"
  ].freeze

  NON_ASSIGNMENT_COLUMN_HEADERS = [
    "Current Score",
    "Current Points",
    "Current Grade",
    "Final Score",
    "Final Points",
    "Final Grade",
    "Override Score",
    "Override Grade"
  ].freeze

  def strip_non_assignment_columns(stripped_row)
    drop_student_information_columns(stripped_row)

    # This regexp will also include columns for unposted scores, which
    # will be one of these values with "Unposted" prepended.
    while stripped_row.last =~ Regexp.new(NON_ASSIGNMENT_COLUMN_HEADERS.join('|'))
      stripped_row.pop
    end
    stripped_row
  end

  def drop_student_information_columns(row)
    row.shift(@student_columns)
  end

  # this method requires non-assignment columns to be stripped from the row
  def parse_assignments(stripped_row)
    stripped_row.map do |name_and_id|
      title, id = Assignment.title_and_id(name_and_id)
      assignment = @all_assignments[id.to_i] if id.present?
      # backward compat
      assignment ||= @all_assignments.find { |_id, a| a.title == name_and_id }
        .try(:last)
      assignment ||= Assignment.new(:title => title || name_and_id)
      assignment.previous_id = assignment.id
      assignment.id ||= NegativeId.generate

      @missing_assignment ||= assignment.new_record?
      assignment
    end.compact
  end

  def detect_override_columns(row)
    row.map.with_index { |header, index| parse_override_column(header, index) }.compact
  end

  def parse_override_column(title, index)
    # Match "Override Score" either on its own or followed by the title of a
    # grading period (e.g., "Override Score (Fall 2020)")
    @override_column_re ||= /^Override Score(?:\s*\((.*)\))?$/
    @grading_periods ||= GradingPeriod.for(@context)

    return unless (match = @override_column_re.match(title))

    grading_period_title = match.captures.first
    # A match with no grading period is okay, but if a grading period title was
    # given, make sure it's valid
    if grading_period_title.present?
      grading_period = @grading_periods.find_by(title: grading_period_title)
      return if grading_period.blank?
    end

    OverrideColumnInfo.new(grading_period_id: grading_period&.id, index: index)
  end

  def prevent_new_assignment_creation?(periods, is_admin)
    return false unless @context.grading_periods?
    return false if is_admin

    GradingPeriod.date_in_closed_grading_period?(
      course: @context,
      date: nil,
      periods: periods
    )
  end

  def process_pp(row)
    @pp_row = row
    @assignments.each_with_index do |assignment, idx|
      assignment.points_possible = row[idx] if row[idx]
    end
  end

  def process_student(row)
    student_id = row[1] # the second column in the csv should have the student_id for each row
    student = @all_students[student_id.to_i] if student_id.present?
    unless student
      ra_sis_id = row[@root_account_column].presence if @root_account_column
      unless @root_accounts.key?(ra_sis_id)
        ra = ra_sis_id.nil? ? @context.root_account : Account.find_by_domain(ra_sis_id)
        add_root_account_to_pseudonym_cache(ra) if ra
        @root_accounts[ra_sis_id] = ra
      end
      ra = @root_accounts[ra_sis_id]
      if ra && @sis_user_id_column && row[@sis_user_id_column].present?
        sis_user_id = [ra.id, row[@sis_user_id_column]]
      end
      if ra && @sis_login_id_column && row[@sis_login_id_column].present?
        sis_login_id = [ra.id, row[@sis_login_id_column]]
      end
      pseudonym = @pseudonyms_by_sis_id[sis_user_id] if sis_user_id
      pseudonym ||= @pseudonyms_by_login_id[sis_login_id] if sis_login_id
      student = @all_students[pseudonym.user_id] if pseudonym
    end
    if row[0].present?
      student ||= @all_students.find do |_id, s|
        s.name == row[0] || s.sortable_name == row[0]
      end.try(:last)
    end
    student ||= User.new(:name => row[0])
    student.previous_id = student.id
    student.id ||= NegativeId.generate
    @missing_student ||= student.new_record?
    student
  end

  def process_submissions(row, student)
    importer_submissions = []
    @assignments.each_with_index do |assignment, idx|
      assignment_id = assignment.new_record? ? assignment.id : assignment.previous_id
      grade = row[idx + @student_columns]&.strip
      if !assignment_visible_to_student(student, assignment, assignment_id, @visible_assignments)
        grade = ''
      end
      new_submission = {
        'grade' => grade,
        'assignment_id' => assignment_id,
      }
      importer_submissions << new_submission
    end

    # custom columns
    importer_custom_columns = {}

    @parsed_custom_column_data.each do |id, custom_column|
      column_index = custom_column[:index]
      new_custom_column_data = {
        'new_content' => row[column_index],
        'column_id' => id
      }
      importer_custom_columns[id] = new_custom_column_data
    end

    @gradebook_importer_custom_columns[student.id] = importer_custom_columns
    @gradebook_importer_assignments[student.id] = importer_submissions

    if allow_override_scores?
      @gradebook_importer_override_scores[student.id] = @override_column_indices.map do |column|
        OverrideScoreChange.new(
          grading_period_id: column.grading_period_id,
          new_score: row[column.index],
          student_id: student.id
        )
      end
    end
  end

  def assignment_visible_to_student(student, assignment, assignment_id, visible_assignments)
    return true unless visible_assignments # wont be set if DA is off
    return true if assignment.new_record? || student.new_record?

    assignments_visible_to_student = visible_assignments[student.id].to_set
    assignments_visible_to_student.try(:include?, assignment_id)
  end

  def as_json(_options={})
    {
      :students => @students.map { |s| student_to_hash(s) },
      :assignments => @assignments.map { |a| assignment_to_hash(a) },
      :missing_objects => {
        :assignments => @missing_assignments.map { |a| assignment_to_hash(a) },
        :students => @missing_students.map { |s| student_to_hash(s) }
      },
      :original_submissions => @original_submissions,
      :unchanged_assignments => @unchanged_assignments,
      :warning_messages => @warning_messages,
      :custom_columns => custom_gradebook_columns.map { |cc| custom_columns_to_hash(cc) },
    }.tap do |hash|
      hash[:override_scores] = override_score_json if allow_override_scores?
    end
  end

  protected

  def override_score_json
    includes_course_scores = false
    grading_period_ids = Set.new

    @gradebook_importer_override_scores.each_value do |changes_for_student|
      includes_course_scores ||= changes_for_student.any?(&:course_score?)
      grading_period_ids = grading_period_ids.merge(changes_for_student.map(&:grading_period_id).compact)
    end

    {
      grading_periods: GradingPeriod.periods_json(@grading_periods.where(id: grading_period_ids), @user),
      includes_course_scores: includes_course_scores
    }
  end

  def custom_gradebook_columns
    @custom_gradebook_columns ||= @context.custom_gradebook_columns.active.to_a
  end

  def identify_delimiter(rows)
    field_counts = {}
    %w[; ,].each do |separator|
      begin
        field_counts[separator] = 0
        field_count_by_row = rows.map { |line| CSV.parse_line(line, col_sep: separator).size }

        # If the number of fields generated by this separator is consistent for all lines,
        # we should be able to assume it's a valid delimiter for this file
        field_counts[separator] = field_count_by_row.first if field_count_by_row.uniq.size == 1
      rescue CSV::MalformedCSVError => e
      end
    end

    field_counts[';'] > field_counts[','] ? :semicolon : :comma
  end

  def semicolon_delimited?(csv_file)
    first_lines = []
    File.open(csv_file.path) do |csv|
      while !csv.eof? && first_lines.size < 3
        first_lines << csv.readline
      end
    end

    return false if first_lines.blank?

    identify_delimiter(first_lines) == :semicolon
  end

  def check_for_non_student_row(row)
    # check if this is the first row, a header row
    if @assignments.nil?
      @assignments = process_header(row)
      return true
    end


    if row[0] =~ /Points Possible/
      # this row is describing the assignment, has no student data
      row.shift(@student_columns)
      process_pp(row)
      return true
    end

    if row.compact.all? { |column| column =~ /^\s*(Muted|Manual Posting.*)?\s*$/i }
      # This row indicates muted assignments (or manually posted assignments if
      # post policies is enabled) and should not be processed at all
      return true
    end

    false # nothing unusual, signal to process as a student row
  end

  def csv_stream
    csv_file = attachment.open(need_local_file: true)
    is_semicolon_delimited = semicolon_delimited?(csv_file)
    csv_parse_options = {
      converters: %i(nil decimal_comma_to_period),
      skip_lines: /^[;, ]+$/,
      col_sep: is_semicolon_delimited ? ";" : ","
    }

    # using "foreach" rather than "parse" processes a chunk of the
    # file at a time rather than loading the whole file into memory
    # at once, a boon for memory consumption
    CSV.foreach(csv_file.path, **csv_parse_options) do |row|
      yield row
    end
  end

  def add_root_account_to_pseudonym_cache(root_account)
    pseudonyms = root_account.shard.activate do
      root_account.pseudonyms
        .active
        .select([:id, :unique_id, :sis_user_id, :user_id])
        .where(:user_id => @all_students.values).to_a
    end
    pseudonyms.each do |pseudonym|
      @pseudonyms_by_sis_id[[root_account.id, pseudonym.sis_user_id]] = pseudonym
      @pseudonyms_by_login_id[[root_account.id, pseudonym.unique_id]] = pseudonym
    end
  end

  def custom_columns_to_hash(cc)
    {
      id: cc.id,
      title: cc.title,
      read_only: cc.read_only,
    }
  end

  def student_to_hash(student)
    {
      :last_name_first => student.last_name_first,
      :name => student.name,
      :previous_id => student.previous_id,
      :id => student.id,
      :submissions => @gradebook_importer_assignments[student.id],
      :custom_column_data => @gradebook_importer_custom_columns[student.id]&.values
    }.tap do |hash|
      hash[:override_scores] = @gradebook_importer_override_scores[student.id]&.map(&:to_h) if allow_override_scores?
    end
  end

  def assignment_to_hash(assignment)
    {
      :id => assignment.id,
      :previous_id => assignment.previous_id,
      :title => assignment.title,
      :points_possible => assignment.points_possible,
      :grading_type => assignment.grading_type
    }
  end

  def valid_context?(context=nil)
    context && [
      :students,
      :assignments,
      :submissions,
      :students=,
      :assignments=,
      :submissions=
    ].all?{ |m| context.respond_to?(m) }
  end

  def readonly_assignment?(index)
    @pp_row[index] =~ /read\s+only/
  end

  private

  def gradeable?(submission:, is_admin: false)
    # `submission#grants_right?` will check if the user
    # is an admin, but if we've pre-loaded that value already
    # to avoid an N+1, check that first.
    assignment = @all_assignments[submission.assignment_id]
    return false if assignment&.unposted_anonymous_submissions?

    is_admin || submission.grants_right?(@user, :grade)
  end

  def no_change_to_column_values?(column_id:)
    @students.all? do |student|
      custom_column_datum = @gradebook_importer_custom_columns[student.id][column_id]

      return true if custom_column_datum['current_content'].blank? && custom_column_datum['new_content'].blank?
      custom_column_datum['current_content'] == custom_column_datum['new_content']
    end
  end

  def exclude_custom_column_on_import(column:)
    column.deleted? || column.read_only
  end

  def no_change_to_value?(new_value:, current_value:, consider_excused: false)
    return true if new_value == current_value
    return true if current_value.blank? && new_value.blank?

    return false unless current_value.present? && new_value.present?

    if consider_excused
      return false if new_value.to_s.casecmp('EX') == 0 || current_value.casecmp('EX') == 0
    end

    # The exporter exports scores rounded to two decimal places (which is also
    # the maximum level of precision shown in the gradebook), so 123.456 will
    # be exported as 123.46. To avoid false reports that scores have changed,
    # compare existing values and new values at that same level of precision,
    # and compare them as strings to match how the exporter outputs them.
    I18n.n(current_value, precision: 2) == I18n.n(new_value, precision: 2)
  end

  def no_change_to_submission?(submission)
    no_change_to_value?(new_value: submission['grade'], current_value: submission['original_grade'], consider_excused: true)
  end

  def set_current_override_scores
    current_override_scores_query.find_each do |existing_score|
      student_id = existing_score.enrollment.user_id
      matching_score_change = @gradebook_importer_override_scores[student_id].detect do |score_change|
        score_change.grading_period_id == existing_score.grading_period_id
      end
      matching_score_change&.current_score = existing_score.override_score&.to_s
    end
  end

  def current_override_scores_query
    override_scores_by_grading_period_id = @gradebook_importer_override_scores.values.flatten.
      group_by { |score| score[:grading_period_id] }
    return Score.none if override_scores_by_grading_period_id.blank?

    base_scope = Score.active.joins(:enrollment).
      preload(:enrollment).
      merge(Enrollment.active).
      where(enrollments: {course: @context})

    scopes = override_scores_by_grading_period_id.map do |grading_period_id, scores|
      scope_for_period = base_scope.where(enrollments: {user_id: scores.map(&:student_id)})

      if grading_period_id.nil?
        scope_for_period.where(course_score: true)
      else
        scope_for_period.where(grading_period_id: grading_period_id)
      end
    end

    scopes.reduce { |result, scope| result.union(scope) }
  end

  # Returns a set of grading period IDs with at least one changed override
  # grade, which will include nil if course override grades were changed
  def remove_override_scores_for_unchanged_grading_periods!
    return Set.new unless allow_override_scores?

    grading_period_ids_with_changes = Set.new
    @gradebook_importer_override_scores.each_value do |scores|
      changed_scores = scores.reject do |score|
        no_change_to_value?(new_value: score.new_score, current_value: score.current_score)
      end

      grading_period_ids_with_changes.merge(changed_scores.map(&:grading_period_id))
    end

    @gradebook_importer_override_scores.each_value do |scores|
      scores.select! { |score| grading_period_ids_with_changes.include?(score.grading_period_id) }
    end

    grading_period_ids_with_changes
  end

  def allow_override_scores?
    @context.allow_final_grade_override? && Account.site_admin.feature_enabled?(:import_override_scores_in_gradebook)
  end
end