require 'spec_helper'

describe Immutable::Vector do
  describe '#bsearch' do
    let(:vector) { V[5,10,20,30] }

    context 'with a block which returns false for elements below desired position, and true for those at/above' do
      it 'returns the first element for which the predicate is true' do
        vector.bsearch { |x| x > 10 }.should be(20)
        vector.bsearch { |x| x > 1 }.should be(5)
        vector.bsearch { |x| x > 25 }.should be(30)
      end

      context 'if the block always returns false' do
        it 'returns nil' do
          vector.bsearch { false }.should be_nil
        end
      end

      context 'if the block always returns true' do
        it 'returns the first element' do
          vector.bsearch { true }.should be(5)
        end
      end
    end

    context 'with a block which returns a negative number for elements below desired position, zero for the right element, and positive for those above' do
      it 'returns the element for which the block returns zero' do
        vector.bsearch { |x| x <=> 10 }.should be(10)
      end

      context 'if the block always returns positive' do
        it 'returns nil' do
          vector.bsearch { 1 }.should be_nil
        end
      end

      context 'if the block always returns negative' do
        it 'returns nil' do
          vector.bsearch { -1 }.should be_nil
        end
      end

      context 'if the block returns sometimes positive, sometimes negative, but never zero' do
        it 'returns nil' do
          vector.bsearch { |x| x <=> 11 }.should be_nil
        end
      end

      context 'if not passed a block' do
        it 'returns an Enumerator' do
          enum = vector.bsearch
          enum.should be_a(Enumerator)
          enum.each { |x| x <=> 10 }.should == 10
        end
      end
    end

    context 'on an empty vector' do
      it 'returns nil' do
        V.empty.bsearch { |x| x > 5 }.should be_nil
      end
    end
  end
end