# frozen_string_literal: true

require 'spec_helper'

RSpec.describe Gitlab::Database::LoadBalancing::HostList do
  def expect_metrics(hosts)
    expect(Gitlab::Metrics.registry.get(:db_load_balancing_hosts).get({})).to eq(hosts)
  end

  before do
    allow(Gitlab::Database)
      .to receive(:create_connection_pool)
      .and_return(ActiveRecord::Base.connection_pool)
  end

  let(:load_balancer) { double(:load_balancer) }
  let(:host_count) { 2 }

  let(:host_list) do
    hosts = Array.new(host_count) do
      Gitlab::Database::LoadBalancing::Host.new('localhost', load_balancer, port: 5432)
    end

    described_class.new(hosts)
  end

  describe '#initialize' do
    it 'sets metrics for current number of hosts and current index' do
      host_list

      expect_metrics(2)
    end
  end

  describe '#length' do
    it 'returns the number of hosts in the list' do
      expect(host_list.length).to eq(2)
    end
  end

  describe '#host_names_and_ports' do
    context 'with ports' do
      it 'returns the host names of all hosts' do
        hosts = [
          ['localhost', 5432],
          ['localhost', 5432]
        ]

        expect(host_list.host_names_and_ports).to eq(hosts)
      end
    end

    context 'without ports' do
      let(:host_list) do
        hosts = Array.new(2) do
          Gitlab::Database::LoadBalancing::Host.new('localhost', load_balancer)
        end

        described_class.new(hosts)
      end

      it 'returns the host names of all hosts' do
        hosts = [
          ['localhost', nil],
          ['localhost', nil]
        ]

        expect(host_list.host_names_and_ports).to eq(hosts)
      end
    end
  end

  describe '#manage_pool?' do
    before do
      allow(Gitlab::Database).to receive(:create_connection_pool) { double(:connection) }
    end

    context 'when the testing pool belongs to one host of the host list' do
      it 'returns true' do
        pool = host_list.hosts.first.pool

        expect(host_list.manage_pool?(pool)).to be(true)
      end
    end

    context 'when the testing pool belongs to a former host of the host list' do
      it 'returns false' do
        pool = host_list.hosts.first.pool
        host_list.hosts = [
          Gitlab::Database::LoadBalancing::Host.new('foo', load_balancer)
        ]

        expect(host_list.manage_pool?(pool)).to be(false)
      end
    end

    context 'when the testing pool belongs to a new host of the host list' do
      it 'returns true' do
        host = Gitlab::Database::LoadBalancing::Host.new('foo', load_balancer)
        host_list.hosts = [host]

        expect(host_list.manage_pool?(host.pool)).to be(true)
      end
    end

    context 'when the testing pool does not have any relation with the host list' do
      it 'returns false' do
        host = Gitlab::Database::LoadBalancing::Host.new('foo', load_balancer)

        expect(host_list.manage_pool?(host.pool)).to be(false)
      end
    end
  end

  describe '#hosts' do
    it 'returns a copy of the host' do
      first = host_list.hosts

      expect(host_list.hosts).to eq(first)
      expect(host_list.hosts.object_id).not_to eq(first.object_id)
    end
  end

  describe '#hosts=' do
    it 'updates the list of hosts to use' do
      host_list.hosts = [
        Gitlab::Database::LoadBalancing::Host.new('foo', load_balancer)
      ]

      expect(host_list.length).to eq(1)
      expect(host_list.hosts[0].host).to eq('foo')
      expect_metrics(1)
    end
  end

  describe '#next' do
    it 'returns a host' do
      expect(host_list.next)
        .to be_an_instance_of(Gitlab::Database::LoadBalancing::Host)
    end

    it 'cycles through all available hosts' do
      expect(host_list.next).to eq(host_list.hosts[0])
      expect_metrics(2)

      expect(host_list.next).to eq(host_list.hosts[1])
      expect_metrics(2)

      expect(host_list.next).to eq(host_list.hosts[0])
      expect_metrics(2)
    end

    it 'skips hosts that are offline' do
      allow(host_list.hosts[0]).to receive(:online?).and_return(false)

      expect(host_list.next).to eq(host_list.hosts[1])
      expect_metrics(2)
    end

    it 'returns nil if no hosts are online' do
      host_list.hosts.each do |host|
        allow(host).to receive(:online?).and_return(false)
      end

      expect(host_list.next).to be_nil
      expect_metrics(2)
    end

    it 'returns nil if no hosts are available' do
      expect(described_class.new.next).to be_nil
    end
  end

  describe '#shuffle' do
    let(:host_count) { 3 }

    it 'randomizes the list' do
      2.times do
        all_hosts = host_list.hosts

        host_list.shuffle

        expect(host_list.length).to eq(host_count)
        expect(host_list.hosts).to contain_exactly(*all_hosts)
      end
    end
  end
end