range_set.rb

require 'active_support/core_ext/range/overlaps'

class RangeSet
  include Enumerable

  def initialize(ranges = [])
    @ranges = Set.new(self.class.merge_all(ranges.to_a))
  end

  def <<(range)
    raise ArgumentError, 'RangeSet only accepts Range objects' unless range.is_a?(Range)

    @ranges = Set.new(self.class.merge_all(@ranges.to_a + [range]))
  end

  def +(other)
    self.class.new([*@ranges, *other.to_a])
  end

  def each(&block)
    @ranges.each(&block)
  end

  def include?(value)
    @ranges.any? { |r| r.include?(value) }
  end

  def self.merge_all(ranges)
    set = Set.new
    queue = ranges.dup

    while queue.any?
      range = queue.shift
      overlapping, not_overlapping = set.partition { |r| r.overlaps?(range) }
      if overlapping.empty?
        set << range
      else
        new_range = (overlapping + [range]).reduce { |a, b| merge2(a, b) }
        queue << new_range
        set = not_overlapping
      end
    end

    set
  end

  def self.merge2(a, b)
    low = [a.begin, b.begin].min
    high, exclude_end =
      if a.end == b.end
        [a.end, a.exclude_end? && b.exclude_end?]
      elsif a.end > b.end
        [a.end, a.exclude_end?]
      else
        [b.end, b.exclude_end?]
      end
    Range.new(low, high, exclude_end)
  end
end

range_set_spec.rb

require 'date'

RSpec.describe RangeSet do
  subject(:range_set) { described_class.new(initializer) }

  it 'merges two overlapping ranges' do
    expect(described_class.new([1..5, 3..7]).to_a).to eq([1..7])
  end

  it 'does not merge two non-overlapping ranges' do
    expect(described_class.new([1..5, 6..10]).to_a).to eq([1..5, 6..10])
  end

  it 'does not merge excluded ends' do
    expect(described_class.new([1...5, 5..10]).to_a).to eq([1...5, 5..10])
  end

  it 'correctly merges ranges with identical ends but mismatched exclude_ends' do
    expect(described_class.new([1...5, 3..5]).to_a).to eq([1..5])
  end

  it 'works with dates' do
    expect(described_class.new([
      Date.new(2023, 4, 1)..Date.new(2023, 7, 27),
      Date.new(2023, 7, 2)..Date.new(2023, 9, 8)
    ]).to_a)
      .to eq([Date.new(2023, 4, 1)..Date.new(2023, 9, 8)])
  end
end