# frozen_string_literal: true

require 'spec_helper'

RSpec.describe Gitlab::Database::Reindexing::ConcurrentReindex, '#perform' do
  subject { described_class.new(index, logger: logger) }

  let(:table_name) { '_test_reindex_table' }
  let(:column_name) { '_test_column' }
  let(:index_name) { '_test_reindex_index' }
  let(:index) { instance_double(Gitlab::Database::PostgresIndex, indexrelid: 42, name: index_name, schema: 'public', partitioned?: false, unique?: false, exclusion?: false, definition: 'CREATE INDEX _test_reindex_index ON public._test_reindex_table USING btree (_test_column)') }
  let(:logger) { double('logger', debug: nil, info: nil, error: nil ) }
  let(:connection) { ActiveRecord::Base.connection }

  before do
    connection.execute(<<~SQL)
      CREATE TABLE #{table_name} (
        id serial NOT NULL PRIMARY KEY,
        #{column_name} integer NOT NULL);

      CREATE INDEX #{index.name} ON #{table_name} (#{column_name});
    SQL
  end

  context 'when the index is unique' do
    before do
      allow(index).to receive(:unique?).and_return(true)
    end

    it 'raises an error' do
      expect do
        subject.perform
      end.to raise_error(described_class::ReindexError, /UNIQUE indexes are currently not supported/)
    end
  end

  context 'when the index is partitioned' do
    before do
      allow(index).to receive(:partitioned?).and_return(true)
    end

    it 'raises an error' do
      expect do
        subject.perform
      end.to raise_error(described_class::ReindexError, /partitioned indexes are currently not supported/)
    end
  end

  context 'when the index serves an exclusion constraint' do
    before do
      allow(index).to receive(:exclusion?).and_return(true)
    end

    it 'raises an error' do
      expect do
        subject.perform
      end.to raise_error(described_class::ReindexError, /indexes serving an exclusion constraint are currently not supported/)
    end
  end

  context 'when the index is a lingering temporary index from a previous reindexing run' do
    context 'with the temporary index prefix' do
      let(:index_name) { 'tmp_reindex_something' }

      it 'raises an error' do
        expect do
          subject.perform
        end.to raise_error(described_class::ReindexError, /left-over temporary index/)
      end
    end

    context 'with the replaced index prefix' do
      let(:index_name) { 'old_reindex_something' }

      it 'raises an error' do
        expect do
          subject.perform
        end.to raise_error(described_class::ReindexError, /left-over temporary index/)
      end
    end
  end

  context 'replacing the original index with a rebuilt copy' do
    let(:replacement_name) { 'tmp_reindex_42' }
    let(:replaced_name) { 'old_reindex_42' }

    let(:create_index) { "CREATE INDEX CONCURRENTLY #{replacement_name} ON public.#{table_name} USING btree (#{column_name})" }
    let(:drop_index) do
      <<~SQL
        DROP INDEX CONCURRENTLY
        IF EXISTS "public"."#{replacement_name}"
      SQL
    end

    let!(:original_index) { find_index_create_statement }

    it 'integration test: executing full index replacement without mocks' do
      allow(connection).to receive(:execute).and_wrap_original do |method, sql|
        method.call(sql.sub(/CONCURRENTLY/, ''))
      end

      subject.perform

      check_index_exists
    end

    context 'mocked specs' do
      before do
        allow(subject).to receive(:connection).and_return(connection)
        allow(connection).to receive(:execute).and_call_original
      end

      it 'replaces the existing index with an identical index' do
        expect(connection).to receive(:execute).with('SET statement_timeout TO \'21600s\'').twice

        expect_to_execute_concurrently_in_order(create_index)

        expect_next_instance_of(::Gitlab::Database::WithLockRetries) do |instance|
          expect(instance).to receive(:run).with(raise_on_exhaustion: true).and_yield
        end

        expect_index_rename(index.name, replaced_name)
        expect_index_rename(replacement_name, index.name)
        expect_index_rename(replaced_name, replacement_name)

        expect_to_execute_concurrently_in_order(drop_index)

        subject.perform

        check_index_exists
      end

      context 'when a dangling index is left from a previous run' do
        before do
          connection.execute("CREATE INDEX #{replacement_name} ON #{table_name} (#{column_name})")
        end

        it 'replaces the existing index with an identical index' do
          expect(connection).to receive(:execute).with('SET statement_timeout TO \'21600s\'').exactly(3).times

          expect_to_execute_concurrently_in_order(drop_index)
          expect_to_execute_concurrently_in_order(create_index)

          expect_next_instance_of(::Gitlab::Database::WithLockRetries) do |instance|
            expect(instance).to receive(:run).with(raise_on_exhaustion: true).and_yield
          end

          expect_index_rename(index.name, replaced_name)
          expect_index_rename(replacement_name, index.name)
          expect_index_rename(replaced_name, replacement_name)

          expect_to_execute_concurrently_in_order(drop_index)

          subject.perform

          check_index_exists
        end
      end

      context 'when it fails to create the replacement index' do
        it 'safely cleans up and signals the error' do
          expect(connection).to receive(:execute).with(create_index).ordered
            .and_raise(ActiveRecord::ConnectionTimeoutError, 'connect timeout')

          expect_to_execute_concurrently_in_order(drop_index)

          expect { subject.perform }.to raise_error(ActiveRecord::ConnectionTimeoutError, /connect timeout/)

          check_index_exists
        end
      end

      context 'when the replacement index is not valid' do
        it 'safely cleans up and signals the error' do
          replacement_index = double('replacement index', valid_index?: false)
          allow(Gitlab::Database::PostgresIndex).to receive(:find_by).with(schema: 'public', name: replacement_name).and_return(nil, replacement_index)

          expect_to_execute_concurrently_in_order(create_index)

          expect_to_execute_concurrently_in_order(drop_index)

          expect { subject.perform }.to raise_error(described_class::ReindexError, /replacement index was created as INVALID/)

          check_index_exists
        end
      end

      context 'when a database error occurs while swapping the indexes' do
        it 'safely cleans up and signals the error' do
          replacement_index = double('replacement index', valid_index?: true)
          allow(Gitlab::Database::PostgresIndex).to receive(:find_by).with(schema: 'public', name: replacement_name).and_return(nil, replacement_index)

          expect_to_execute_concurrently_in_order(create_index)

          expect_next_instance_of(::Gitlab::Database::WithLockRetries) do |instance|
            expect(instance).to receive(:run).with(raise_on_exhaustion: true).and_yield
          end

          expect_index_rename(index.name, replaced_name).and_raise(ActiveRecord::ConnectionTimeoutError, 'connect timeout')

          expect_to_execute_concurrently_in_order(drop_index)

          expect { subject.perform }.to raise_error(ActiveRecord::ConnectionTimeoutError, /connect timeout/)

          check_index_exists
        end
      end

      context 'when with_lock_retries fails to acquire the lock' do
        it 'safely cleans up and signals the error' do
          expect_to_execute_concurrently_in_order(create_index)

          expect_next_instance_of(::Gitlab::Database::WithLockRetries) do |instance|
            expect(instance).to receive(:run).with(raise_on_exhaustion: true)
              .and_raise(::Gitlab::Database::WithLockRetries::AttemptsExhaustedError, 'exhausted')
          end

          expect_to_execute_concurrently_in_order(drop_index)

          expect { subject.perform }.to raise_error(::Gitlab::Database::WithLockRetries::AttemptsExhaustedError, /exhausted/)

          check_index_exists
        end
      end
    end
  end

  def expect_to_execute_concurrently_in_order(sql)
    # Indexes cannot be created CONCURRENTLY in a transaction. Since the tests are wrapped in transactions,
    # verify the original call but pass through the non-concurrent form.
    expect(connection).to receive(:execute).with(sql).ordered.and_wrap_original do |method, sql|
      method.call(sql.sub(/CONCURRENTLY/, ''))
    end
  end

  def expect_index_rename(from, to)
    expect(connection).to receive(:execute).with(<<~SQL).ordered
      ALTER INDEX "public"."#{from}"
      RENAME TO "#{to}"
    SQL
  end

  def find_index_create_statement
    ActiveRecord::Base.connection.select_value(<<~SQL)
      SELECT indexdef
      FROM pg_indexes
      WHERE schemaname = 'public'
      AND indexname = #{ActiveRecord::Base.connection.quote(index.name)}
    SQL
  end

  def check_index_exists
    expect(find_index_create_statement).to eq(original_index)
  end
end