# frozen_string_literal: true

RSpec.describe Fear::PartialFunction do
  describe "Fear.case()" do
    context "condition is extractor" do
      subject do
        Fear.xcase("[1, [2, second_of_second, *], 3, *rest]") do |second_of_second:, rest:|
          [second_of_second, rest]
        end
      end

      it { is_expected.to be_defined_at([1, [2, 2, 3, 4], 3, 6, 7]) }
      it { is_expected.not_to be_defined_at([1, [1, 3, 3, 4], 3, 6, 7]) }
      it { is_expected.not_to be_defined_at([1, [1, 2, 3, 4], 4, 6, 7]) }
    end

    context "condition as symbol" do
      subject { Fear.case(:even?) { |x| x } }

      it "matches against the same symbol" do
        is_expected.to be_defined_at(:even?)
        is_expected.not_to be_defined_at(3)
      end
    end

    context "condition as Class" do
      subject { Fear.case(Integer) { |x| x } }

      it do
        is_expected.to be_defined_at(4)
        is_expected.not_to be_defined_at("3")
      end
    end

    context "condition as Proc" do
      subject { Fear.case(->(x) { x.even? }) { |x| x } }

      it do
        is_expected.to be_defined_at(4)
        is_expected.not_to be_defined_at(3)
      end
    end

    context "multiple condition" do
      subject { Fear.case(Integer, :even?.to_proc, ->(x) { x % 3 == 0 }) { |x| x } }

      it do
        is_expected.to be_defined_at(12)
        is_expected.not_to be_defined_at(12.0)
        is_expected.not_to be_defined_at("3")
        is_expected.not_to be_defined_at(3)
        is_expected.not_to be_defined_at(4)
      end
    end

    context "multiple condition 2" do
      subject { Fear.case(Integer, 4) { |x| x } }

      it do
        is_expected.to be_defined_at(4)
        is_expected.not_to be_defined_at(3)
      end
    end
  end

  describe "#lift" do
    let(:lifted) { partial_function.lift }

    let(:partial_function) { Fear.case(->(v) { v != 0 }) { |x| 4 / x } }

    context "defined" do
      subject { lifted.(2) }

      it { is_expected.to eq(Fear::Some.new(2)) }
    end

    context "not defined" do
      subject { lifted.(0) }

      it { is_expected.to eq(Fear::None) }
    end
  end

  describe "#defined_at?" do
    let(:partial_function) { Fear.case(->(v) { v == 42 }) {} }

    it "defined at" do
      expect(partial_function.defined_at?(42)).to eq(true)
    end

    it "not defined at" do
      expect(partial_function.defined_at?(24)).to eq(false)
    end
  end

  describe "#call" do
    let(:partial_function) { Fear.case(->(v) { v != 0 }) { |x| 4 / x } }

    context "defined" do
      subject { partial_function.(2) }

      it { is_expected.to eq(2) }
    end

    context "not defined" do
      subject { -> { partial_function.(0) } }

      it { is_expected.to raise_error(Fear::MatchError, "partial function not defined at: 0") }
    end

    context "defined and condition is extractor" do
      subject { partial_function.([1, 2, 3, 4, 5]) }

      let(:partial_function) do
        Fear.xcase("[1, second, 3, *rest]") { |second:, rest:| [second, rest] }
      end

      it { is_expected.to eq([2, [4, 5]]) }
    end
  end

  describe "#to_proc", "#call" do
    let(:partial_function) { Fear.case(->(v) { v != 0 }) { |x| 4 / x }.to_proc }

    context "defined" do
      subject { partial_function.(2) }

      it { is_expected.to eq(2) }
    end

    context "not defined" do
      subject { -> { partial_function.(0) } }

      it { is_expected.to raise_error(Fear::MatchError, "partial function not defined at: 0") }
    end
  end

  describe "#call_or_else" do
    let(:default) { ->(x) { "division by #{x} impossible" } }
    let(:partial_function) { Fear.case(->(x) { x != 0 }) { |x| 4 / x } }

    context "defined" do
      subject { partial_function.call_or_else(2, &default) }

      it { is_expected.to eq(2) }
    end

    context "not defined" do
      subject { partial_function.call_or_else(0, &default) }

      it { is_expected.to eq("division by 0 impossible") }
    end
  end

  describe "#and_then" do
    let(:partial_function) { Fear.case(->(v) { v == 42 }) {} }
    let(:and_then) { ->(x) { x } }

    context "block given, arguments not given" do
      subject { -> { partial_function.and_then(&and_then) } }

      it { is_expected.not_to raise_error }
    end

    context "block given, argument given" do
      subject { -> { partial_function.and_then(and_then, &and_then) } }

      it { is_expected.to raise_error(ArgumentError) }
    end

    context "block given, arguments given" do
      subject { -> { partial_function.and_then(and_then, 42, &and_then) } }

      it { is_expected.to raise_error(ArgumentError) }
    end

    context "block not given, arguments not given" do
      subject { -> { partial_function.and_then } }

      it { is_expected.to raise_error(ArgumentError) }
    end

    context "block net given, arguments given" do
      subject { -> { partial_function.and_then(and_then) } }

      it { is_expected.not_to raise_error }
    end
  end
end