# frozen_string_literal: true

RSpec.describe Fear::PartialFunction, "#and_then" do
  context "proc" do
    subject(:pf_and_f) { partial_function.and_then(&function) }

    let(:partial_function) { Fear.case(->(x) { x.even? }) { |x| "pf: #{x}" } }
    let(:function) { ->(x) { "f: #{x}" } }

    describe "#defined_at?" do
      context "defined" do
        subject { pf_and_f.defined_at?(4) }

        it { is_expected.to eq(true) }
      end

      context "not defined" do
        subject { pf_and_f.defined_at?(3) }

        it { is_expected.to eq(false) }
      end
    end

    describe "#call" do
      context "defined" do
        subject { pf_and_f.(4) }

        it { is_expected.to eq("f: pf: 4") }
      end

      context "not defined" do
        subject { -> { pf_and_f.(3) } }

        it { is_expected.to raise_error(Fear::MatchError, "partial function not defined at: 3") }
      end
    end

    describe "#call_or_else" do
      let(:fallback) { ->(x) { "fallback: #{x}" } }

      context "defined" do
        subject { pf_and_f.call_or_else(4, &fallback) }

        it { is_expected.to eq("f: pf: 4") }
      end

      context "not defined" do
        subject { pf_and_f.call_or_else(3, &fallback) }

        it { is_expected.to eq("fallback: 3") }
      end
    end
  end

  context "partial function" do
    subject(:first_and_then_second) { first.and_then(second) }

    describe "#defined_at?" do
      context "first defined, second defined on result of first" do
        subject { first_and_then_second.defined_at?(6) }

        let(:first) { Fear.case(->(x) { x.even? }) { |x| x / 2 } }
        let(:second) { Fear.case(->(x) { x % 3 == 0 }) { |x| x / 3 } }

        it { is_expected.to eq(true) }
      end

      context "first defined, second not defined on result of first" do
        subject { first_and_then_second.defined_at?(4) }

        let(:first) { Fear.case(->(x) { x.even? }) { |x| x / 2 } }
        let(:second) { Fear.case(->(x) { x % 3 == 0 }) { |x| x / 3 } }

        it { is_expected.to eq(false) }
      end

      context "first not defined" do
        subject { first_and_then_second.defined_at?(3) }

        let(:first) { Fear.case(->(x) { x.even? }) { |x| "first: #{x}" } }
        let(:second) { Fear.case(->(x) { x % 3 == 0 }) { |x| "second: #{x}" } }

        it { is_expected.to eq(false) }
      end
    end

    describe "#call" do
      context "first defined, second defined on result of first" do
        subject { first_and_then_second.(6) }

        let(:first) { Fear.case(->(x) { x.even? }) { |x| x / 2 } }
        let(:second) { Fear.case(->(x) { x % 3 == 0 }) { |x| x / 3 } }

        it { is_expected.to eq(1) }
      end

      context "first defined, second not defined on result of first" do
        subject { -> { first_and_then_second.(4) } }

        let(:first) { Fear.case(->(x) { x.even? }) { |x| x / 2 } }
        let(:second) { Fear.case(->(x) { x % 3 == 0 }) { |x| x / 3 } }

        it { is_expected.to raise_error(Fear::MatchError, "partial function not defined at: 2") }
      end

      context "first not defined" do
        subject { -> { first_and_then_second.(3) } }

        let(:first) { Fear.case(->(x) { x.even? }) { |x| "first: #{x}" } }
        let(:second) { Fear.case(->(x) { x % 3 == 0 }) { |x| "second: #{x}" } }

        it { is_expected.to raise_error(Fear::MatchError, "partial function not defined at: 3") }
      end
    end

    describe "#call_or_else" do
      let(:fallback) { ->(x) { "fallback: #{x}" } }

      context "first defined, second defined on result of first" do
        subject { first_and_then_second.call_or_else(6, &fallback) }

        let(:first) { Fear.case(->(x) { x.even? }) { |x| x / 2 } }
        let(:second) { Fear.case(->(x) { x % 3 == 0 }) { |x| x / 3 } }

        it { is_expected.to eq(1) }
      end

      context "first defined, second not defined on result of first" do
        subject { first_and_then_second.call_or_else(4, &fallback) }

        let(:first) { Fear.case(->(x) { x.even? }) { |x| x / 2 } }
        let(:second) { Fear.case(->(x) { x % 3 == 0 }) { |x| x / 3 } }

        it { is_expected.to eq("fallback: 4") }
      end

      context "first not defined" do
        subject { first_and_then_second.call_or_else(3, &fallback) }

        let(:first) { Fear.case(->(x) { x.even? }) { |x| "first: #{x}" } }
        let(:second) { Fear.case { |x| "second: #{x}" } }

        it { is_expected.to eq("fallback: 3") }
      end
    end
  end
end