datetime_range_examples.exs

def intervals_overlap?({%DateTime{}, _} = i1, {%DateTime{}, _} = i2) do
  case {i1, i2} do
    {{_left1, nil}, {_left2, nil}} ->
      true

    {{left1, nil}, {_left2, right2}} ->
      before_inclusive?(left1, right2)

    {{_left1, right1}, {left2, nil}} ->
      before_inclusive?(left2, right1)

    {{left1, right1}, {left2, right2}} ->
      between_inclusive?(left2, left1, right1) or between_inclusive?(left1, left2, right2)
  end
end

def disjoint?({%DateTime{} = left1, right1}, {%DateTime{} = left2, right2}) do

  case {right1, right2} do
    {nil, nil} ->
      false

    {%DateTime{}, nil} ->
      DateTime.compare(right1, left2) == :lt

    {nil, %DateTime{}} ->
      DateTime.compare(right2, left1) == :lt

    {%DateTime{}, %DateTime{}} ->
      DateTime.compare(right1, left2) == :lt or
        DateTime.compare(right2, left1) == :lt
  end
end

def within_inclusive?(
        {%DateTime{} = inside_left, inside_right},
        {%DateTime{} = outside_left, outside_right}
      ) do
  cond do
    is_nil(inside_right) and is_nil(outside_right) ->
      true

    is_nil(inside_right) or is_nil(outside_right) ->
      before_inclusive?(outside_left, inside_left)

    true ->
      between_inclusive?(inside_left, outside_left, outside_right) &&
        between_inclusive?(inside_right, outside_left, outside_right)
  end
end

def between_inclusive?(%DateTime{} = dt, %DateTime{} = left, %DateTime{} = right) do
  before_inclusive?(left, dt) && before_inclusive?(dt, right)
end

def before_inclusive?(%DateTime{} = left, %DateTime{} = right) do
  DateTime.compare(left, right) != :gt
end