# frozen_string_literal: true

require "active_record/connection_adapters/abstract_adapter"
require "active_record/connection_adapters/statement_pool"
require "active_record/connection_adapters/mysql/column"
require "active_record/connection_adapters/mysql/database_statements"
require "active_record/connection_adapters/mysql/explain_pretty_printer"
require "active_record/connection_adapters/mysql/quoting"
require "active_record/connection_adapters/mysql/schema_creation"
require "active_record/connection_adapters/mysql/schema_definitions"
require "active_record/connection_adapters/mysql/schema_dumper"
require "active_record/connection_adapters/mysql/schema_statements"
require "active_record/connection_adapters/mysql/type_metadata"

module ActiveRecord
  module ConnectionAdapters
    class AbstractMysqlAdapter < AbstractAdapter
      include MySQL::DatabaseStatements
      include MySQL::Quoting
      include MySQL::SchemaStatements

      ##
      # :singleton-method:
      # By default, the Mysql2Adapter will consider all columns of type <tt>tinyint(1)</tt>
      # as boolean. If you wish to disable this emulation you can add the following line
      # to your application.rb file:
      #
      #   ActiveRecord::ConnectionAdapters::Mysql2Adapter.emulate_booleans = false
      class_attribute :emulate_booleans, default: true

      NATIVE_DATABASE_TYPES = {
        primary_key: "bigint auto_increment PRIMARY KEY",
        string:      { name: "varchar", limit: 255 },
        text:        { name: "text" },
        integer:     { name: "int", limit: 4 },
        bigint:      { name: "bigint" },
        float:       { name: "float", limit: 24 },
        decimal:     { name: "decimal" },
        datetime:    { name: "datetime" },
        timestamp:   { name: "timestamp" },
        time:        { name: "time" },
        date:        { name: "date" },
        binary:      { name: "blob" },
        blob:        { name: "blob" },
        boolean:     { name: "tinyint", limit: 1 },
        json:        { name: "json" },
      }

      class StatementPool < ConnectionAdapters::StatementPool # :nodoc:
        private
          def dealloc(stmt)
            stmt.close
          end
      end

      class << self
        def dbconsole(config, options = {})
          mysql_config = config.configuration_hash

          args = {
            host: "--host",
            port: "--port",
            socket: "--socket",
            username: "--user",
            encoding: "--default-character-set",
            sslca: "--ssl-ca",
            sslcert: "--ssl-cert",
            sslcapath: "--ssl-capath",
            sslcipher: "--ssl-cipher",
            sslkey: "--ssl-key",
            ssl_mode: "--ssl-mode"
          }.filter_map { |opt, arg| "#{arg}=#{mysql_config[opt]}" if mysql_config[opt] }

          if mysql_config[:password] && options[:include_password]
            args << "--password=#{mysql_config[:password]}"
          elsif mysql_config[:password] && !mysql_config[:password].to_s.empty?
            args << "-p"
          end

          args << config.database

          find_cmd_and_exec(ActiveRecord.database_cli[:mysql], *args)
        end
      end

      def get_database_version # :nodoc:
        full_version_string = get_full_version
        version_string = version_string(full_version_string)
        Version.new(version_string, full_version_string)
      end

      def mariadb? # :nodoc:
        /mariadb/i.match?(full_version)
      end

      def supports_bulk_alter?
        true
      end

      def supports_index_sort_order?
        !mariadb? && database_version >= "8.0.1"
      end

      def supports_expression_index?
        !mariadb? && database_version >= "8.0.13"
      end

      def supports_transaction_isolation?
        true
      end

      def supports_restart_db_transaction?
        true
      end

      def supports_explain?
        true
      end

      def supports_indexes_in_create?
        true
      end

      def supports_foreign_keys?
        true
      end

      def supports_check_constraints?
        if mariadb?
          database_version >= "10.3.10" || (database_version < "10.3" && database_version >= "10.2.22")
        else
          database_version >= "8.0.16"
        end
      end

      def supports_views?
        true
      end

      def supports_datetime_with_precision?
        true
      end

      def supports_virtual_columns?
        mariadb? || database_version >= "5.7.5"
      end

      # See https://dev.mysql.com/doc/refman/en/optimizer-hints.html for more details.
      def supports_optimizer_hints?
        !mariadb? && database_version >= "5.7.7"
      end

      def supports_common_table_expressions?
        if mariadb?
          database_version >= "10.2.1"
        else
          database_version >= "8.0.1"
        end
      end

      def supports_advisory_locks?
        true
      end

      def supports_insert_on_duplicate_skip?
        true
      end

      def supports_insert_on_duplicate_update?
        true
      end

      def supports_insert_returning?
        mariadb? && database_version >= "10.5.0"
      end

      def get_advisory_lock(lock_name, timeout = 0) # :nodoc:
        query_value("SELECT GET_LOCK(#{quote(lock_name.to_s)}, #{timeout})") == 1
      end

      def release_advisory_lock(lock_name) # :nodoc:
        query_value("SELECT RELEASE_LOCK(#{quote(lock_name.to_s)})") == 1
      end

      def native_database_types
        NATIVE_DATABASE_TYPES
      end

      def index_algorithms
        {
          default: "ALGORITHM = DEFAULT",
          copy:    "ALGORITHM = COPY",
          inplace: "ALGORITHM = INPLACE",
          instant: "ALGORITHM = INSTANT",
        }
      end

      # HELPER METHODS ===========================================

      # Must return the MySQL error number from the exception, if the exception has an
      # error number.
      def error_number(exception) # :nodoc:
        raise NotImplementedError
      end

      # REFERENTIAL INTEGRITY ====================================

      def disable_referential_integrity # :nodoc:
        old = query_value("SELECT @@FOREIGN_KEY_CHECKS")

        begin
          update("SET FOREIGN_KEY_CHECKS = 0")
          yield
        ensure
          update("SET FOREIGN_KEY_CHECKS = #{old}") if active?
        end
      end

      #--
      # DATABASE STATEMENTS ======================================
      #++

      def begin_db_transaction # :nodoc:
        internal_execute("BEGIN", "TRANSACTION", allow_retry: true, materialize_transactions: false)
      end

      def begin_isolated_db_transaction(isolation) # :nodoc:
        # From MySQL manual: The [SET TRANSACTION] statement applies only to the next single transaction performed within the session.
        # So we don't need to implement #reset_isolation_level
        execute_batch(
          ["SET TRANSACTION ISOLATION LEVEL #{transaction_isolation_levels.fetch(isolation)}", "BEGIN"],
          "TRANSACTION",
          allow_retry: true,
          materialize_transactions: false,
        )
      end

      def commit_db_transaction # :nodoc:
        internal_execute("COMMIT", "TRANSACTION", allow_retry: false, materialize_transactions: true)
      end

      def exec_rollback_db_transaction # :nodoc:
        internal_execute("ROLLBACK", "TRANSACTION", allow_retry: false, materialize_transactions: true)
      end

      def exec_restart_db_transaction # :nodoc:
        internal_execute("ROLLBACK AND CHAIN", "TRANSACTION", allow_retry: false, materialize_transactions: true)
      end

      def empty_insert_statement_value(primary_key = nil) # :nodoc:
        "VALUES ()"
      end

      # SCHEMA STATEMENTS ========================================

      # Drops the database specified on the +name+ attribute
      # and creates it again using the provided +options+.
      def recreate_database(name, options = {})
        drop_database(name)
        sql = create_database(name, options)
        reconnect!
        sql
      end

      # Create a new MySQL database with optional <tt>:charset</tt> and <tt>:collation</tt>.
      # Charset defaults to utf8mb4.
      #
      # Example:
      #   create_database 'charset_test', charset: 'latin1', collation: 'latin1_bin'
      #   create_database 'matt_development'
      #   create_database 'matt_development', charset: :big5
      def create_database(name, options = {})
        if options[:collation]
          execute "CREATE DATABASE #{quote_table_name(name)} DEFAULT COLLATE #{quote_table_name(options[:collation])}"
        elsif options[:charset]
          execute "CREATE DATABASE #{quote_table_name(name)} DEFAULT CHARACTER SET #{quote_table_name(options[:charset])}"
        elsif row_format_dynamic_by_default?
          execute "CREATE DATABASE #{quote_table_name(name)} DEFAULT CHARACTER SET `utf8mb4`"
        else
          raise "Configure a supported :charset and ensure innodb_large_prefix is enabled to support indexes on varchar(255) string columns."
        end
      end

      # Drops a MySQL database.
      #
      # Example:
      #   drop_database('sebastian_development')
      def drop_database(name) # :nodoc:
        execute "DROP DATABASE IF EXISTS #{quote_table_name(name)}"
      end

      def current_database
        query_value("SELECT database()", "SCHEMA")
      end

      # Returns the database character set.
      def charset
        show_variable "character_set_database"
      end

      # Returns the database collation strategy.
      def collation
        show_variable "collation_database"
      end

      def table_comment(table_name) # :nodoc:
        scope = quoted_scope(table_name)

        query_value(<<~SQL, "SCHEMA").presence
          SELECT table_comment
          FROM information_schema.tables
          WHERE table_schema = #{scope[:schema]}
            AND table_name = #{scope[:name]}
        SQL
      end

      def change_table_comment(table_name, comment_or_changes) # :nodoc:
        comment = extract_new_comment_value(comment_or_changes)
        comment = "" if comment.nil?
        execute("ALTER TABLE #{quote_table_name(table_name)} COMMENT #{quote(comment)}")
      end

      # Renames a table.
      #
      # Example:
      #   rename_table('octopuses', 'octopi')
      def rename_table(table_name, new_name, **options)
        validate_table_length!(new_name) unless options[:_uses_legacy_table_name]
        schema_cache.clear_data_source_cache!(table_name.to_s)
        schema_cache.clear_data_source_cache!(new_name.to_s)
        execute "RENAME TABLE #{quote_table_name(table_name)} TO #{quote_table_name(new_name)}"
        rename_table_indexes(table_name, new_name, **options)
      end

      # Drops a table or tables from the database.
      #
      # [<tt>:force</tt>]
      #   Set to +:cascade+ to drop dependent objects as well.
      #   Defaults to false.
      # [<tt>:if_exists</tt>]
      #   Set to +true+ to only drop the table if it exists.
      #   Defaults to false.
      # [<tt>:temporary</tt>]
      #   Set to +true+ to drop temporary table.
      #   Defaults to false.
      #
      # Although this command ignores most +options+ and the block if one is given,
      # it can be helpful to provide these in a migration's +change+ method so it can be reverted.
      # In that case, +options+ and the block will be used by #create_table except if you provide more than one table which is not supported.
      def drop_table(*table_names, **options)
        table_names.each { |table_name| schema_cache.clear_data_source_cache!(table_name.to_s) }
        execute "DROP#{' TEMPORARY' if options[:temporary]} TABLE#{' IF EXISTS' if options[:if_exists]} #{table_names.map { |table_name| quote_table_name(table_name) }.join(', ')}#{' CASCADE' if options[:force] == :cascade}"
      end

      def rename_index(table_name, old_name, new_name)
        if supports_rename_index?
          validate_index_length!(table_name, new_name)

          execute "ALTER TABLE #{quote_table_name(table_name)} RENAME INDEX #{quote_table_name(old_name)} TO #{quote_table_name(new_name)}"
        else
          super
        end
      end

      def change_column_default(table_name, column_name, default_or_changes) # :nodoc:
        execute "ALTER TABLE #{quote_table_name(table_name)} #{change_column_default_for_alter(table_name, column_name, default_or_changes)}"
      end

      def build_change_column_default_definition(table_name, column_name, default_or_changes) # :nodoc:
        column = column_for(table_name, column_name)
        return unless column

        default = extract_new_default_value(default_or_changes)
        ChangeColumnDefaultDefinition.new(column, default)
      end

      def change_column_null(table_name, column_name, null, default = nil) # :nodoc:
        validate_change_column_null_argument!(null)

        unless null || default.nil?
          execute("UPDATE #{quote_table_name(table_name)} SET #{quote_column_name(column_name)}=#{quote(default)} WHERE #{quote_column_name(column_name)} IS NULL")
        end

        change_column table_name, column_name, nil, null: null
      end

      def change_column_comment(table_name, column_name, comment_or_changes) # :nodoc:
        comment = extract_new_comment_value(comment_or_changes)
        change_column table_name, column_name, nil, comment: comment
      end

      def change_column(table_name, column_name, type, **options) # :nodoc:
        execute("ALTER TABLE #{quote_table_name(table_name)} #{change_column_for_alter(table_name, column_name, type, **options)}")
      end

      # Builds a ChangeColumnDefinition object.
      #
      # This definition object contains information about the column change that would occur
      # if the same arguments were passed to #change_column. See #change_column for information about
      # passing a +table_name+, +column_name+, +type+ and other options that can be passed.
      def build_change_column_definition(table_name, column_name, type, **options) # :nodoc:
        column = column_for(table_name, column_name)
        type ||= column.sql_type

        unless options.key?(:default)
          options[:default] = column.default
        end

        unless options.key?(:null)
          options[:null] = column.null
        end

        unless options.key?(:comment)
          options[:comment] = column.comment
        end

        if options[:collation] == :no_collation
          options.delete(:collation)
        else
          options[:collation] ||= column.collation if text_type?(type)
        end

        unless options.key?(:auto_increment)
          options[:auto_increment] = column.auto_increment?
        end

        td = create_table_definition(table_name)
        cd = td.new_column_definition(column.name, type, **options)
        ChangeColumnDefinition.new(cd, column.name)
      end

      def rename_column(table_name, column_name, new_column_name) # :nodoc:
        execute("ALTER TABLE #{quote_table_name(table_name)} #{rename_column_for_alter(table_name, column_name, new_column_name)}")
        rename_column_indexes(table_name, column_name, new_column_name)
      end

      def add_index(table_name, column_name, **options) # :nodoc:
        create_index = build_create_index_definition(table_name, column_name, **options)
        return unless create_index

        execute schema_creation.accept(create_index)
      end

      def build_create_index_definition(table_name, column_name, **options) # :nodoc:
        index, algorithm, if_not_exists = add_index_options(table_name, column_name, **options)

        return if if_not_exists && index_exists?(table_name, column_name, name: index.name)

        CreateIndexDefinition.new(index, algorithm)
      end

      def add_sql_comment!(sql, comment) # :nodoc:
        sql << " COMMENT #{quote(comment)}" if comment.present?
        sql
      end

      def foreign_keys(table_name)
        raise ArgumentError unless table_name.present?

        scope = quoted_scope(table_name)

        # MySQL returns 1 row for each column of composite foreign keys.
        fk_info = internal_exec_query(<<~SQL, "SCHEMA")
          SELECT fk.referenced_table_name AS 'to_table',
                 fk.referenced_column_name AS 'primary_key',
                 fk.column_name AS 'column',
                 fk.constraint_name AS 'name',
                 fk.ordinal_position AS 'position',
                 rc.update_rule AS 'on_update',
                 rc.delete_rule AS 'on_delete'
          FROM information_schema.referential_constraints rc
          JOIN information_schema.key_column_usage fk
          USING (constraint_schema, constraint_name)
          WHERE fk.referenced_column_name IS NOT NULL
            AND fk.table_schema = #{scope[:schema]}
            AND fk.table_name = #{scope[:name]}
            AND rc.constraint_schema = #{scope[:schema]}
            AND rc.table_name = #{scope[:name]}
        SQL

        grouped_fk = fk_info.group_by { |row| row["name"] }.values.each { |group| group.sort_by! { |row| row["position"] } }
        grouped_fk.map do |group|
          row = group.first
          options = {
            name: row["name"],
            on_update: extract_foreign_key_action(row["on_update"]),
            on_delete: extract_foreign_key_action(row["on_delete"])
          }

          if group.one?
            options[:column] = unquote_identifier(row["column"])
            options[:primary_key] = row["primary_key"]
          else
            options[:column] = group.map { |row| unquote_identifier(row["column"]) }
            options[:primary_key] = group.map { |row| row["primary_key"] }
          end

          ForeignKeyDefinition.new(table_name, unquote_identifier(row["to_table"]), options)
        end
      end

      def check_constraints(table_name)
        if supports_check_constraints?
          scope = quoted_scope(table_name)

          sql = <<~SQL
            SELECT cc.constraint_name AS 'name',
                  cc.check_clause AS 'expression'
            FROM information_schema.check_constraints cc
            JOIN information_schema.table_constraints tc
            USING (constraint_schema, constraint_name)
            WHERE tc.table_schema = #{scope[:schema]}
              AND tc.table_name = #{scope[:name]}
              AND cc.constraint_schema = #{scope[:schema]}
          SQL
          sql += " AND cc.table_name = #{scope[:name]}" if mariadb?

          chk_info = internal_exec_query(sql, "SCHEMA")

          chk_info.map do |row|
            options = {
              name: row["name"]
            }
            expression = row["expression"]
            expression = expression[1..-2] if expression.start_with?("(") && expression.end_with?(")")
            expression = strip_whitespace_characters(expression)

            unless mariadb?
              # MySQL returns check constraints expression in an already escaped form.
              # This leads to duplicate escaping later (e.g. when the expression is used in the SchemaDumper).
              expression = expression.gsub("\\'", "'")
            end

            CheckConstraintDefinition.new(table_name, expression, options)
          end
        else
          raise NotImplementedError
        end
      end

      def table_options(table_name) # :nodoc:
        create_table_info = create_table_info(table_name)

        # strip create_definitions and partition_options
        # Be aware that `create_table_info` might not include any table options due to `NO_TABLE_OPTIONS` sql mode.
        raw_table_options = create_table_info.sub(/\A.*\n\) ?/m, "").sub(/\n\/\*!.*\*\/\n\z/m, "").strip

        return if raw_table_options.empty?

        table_options = {}

        if / DEFAULT CHARSET=(?<charset>\w+)(?: COLLATE=(?<collation>\w+))?/ =~ raw_table_options
          raw_table_options = $` + $' # before part + after part
          table_options[:charset] = charset
          table_options[:collation] = collation if collation
        end

        # strip AUTO_INCREMENT
        raw_table_options.sub!(/(ENGINE=\w+)(?: AUTO_INCREMENT=\d+)/, '\1')

        # strip COMMENT
        if raw_table_options.sub!(/ COMMENT='.+'/, "")
          table_options[:comment] = table_comment(table_name)
        end

        table_options[:options] = raw_table_options unless raw_table_options == "ENGINE=InnoDB"
        table_options
      end

      # SHOW VARIABLES LIKE 'name'
      def show_variable(name)
        query_value("SELECT @@#{name}", "SCHEMA", materialize_transactions: false, allow_retry: true)
      rescue ActiveRecord::StatementInvalid
        nil
      end

      def primary_keys(table_name) # :nodoc:
        raise ArgumentError unless table_name.present?

        scope = quoted_scope(table_name)

        query_values(<<~SQL, "SCHEMA")
          SELECT column_name
          FROM information_schema.statistics
          WHERE index_name = 'PRIMARY'
            AND table_schema = #{scope[:schema]}
            AND table_name = #{scope[:name]}
          ORDER BY seq_in_index
        SQL
      end

      def case_sensitive_comparison(attribute, value) # :nodoc:
        column = column_for_attribute(attribute)

        if column.collation && !column.case_sensitive?
          attribute.eq(Arel::Nodes::Bin.new(value))
        else
          super
        end
      end

      def can_perform_case_insensitive_comparison_for?(column)
        column.case_sensitive?
      end
      private :can_perform_case_insensitive_comparison_for?

      # In MySQL 5.7.5 and up, ONLY_FULL_GROUP_BY affects handling of queries that use
      # DISTINCT and ORDER BY. It requires the ORDER BY columns in the select list for
      # distinct queries, and requires that the ORDER BY include the distinct column.
      # See https://dev.mysql.com/doc/refman/en/group-by-handling.html
      def columns_for_distinct(columns, orders) # :nodoc:
        order_columns = orders.compact_blank.map { |s|
          # Convert Arel node to string
          s = visitor.compile(s) unless s.is_a?(String)
          # Remove any ASC/DESC modifiers
          s.gsub(/\s+(?:ASC|DESC)\b/i, "")
        }.compact_blank.map.with_index { |column, i| "#{column} AS alias_#{i}" }

        (order_columns << super).join(", ")
      end

      def strict_mode?
        self.class.type_cast_config_to_boolean(@config.fetch(:strict, true))
      end

      def default_index_type?(index) # :nodoc:
        index.using == :btree || super
      end

      def build_insert_sql(insert) # :nodoc:
        no_op_column = quote_column_name(insert.keys.first)

        # MySQL 8.0.19 replaces `VALUES(<expression>)` clauses with row and column alias names, see https://dev.mysql.com/worklog/task/?id=6312 .
        # then MySQL 8.0.20 deprecates the `VALUES(<expression>)` see https://dev.mysql.com/worklog/task/?id=13325 .
        if supports_insert_raw_alias_syntax?
          values_alias = quote_table_name("#{insert.model.table_name.parameterize}_values")
          sql = +"INSERT #{insert.into} #{insert.values_list} AS #{values_alias}"

          if insert.skip_duplicates?
            sql << " ON DUPLICATE KEY UPDATE #{no_op_column}=#{values_alias}.#{no_op_column}"
          elsif insert.update_duplicates?
            if insert.raw_update_sql?
              sql = +"INSERT #{insert.into} #{insert.values_list} ON DUPLICATE KEY UPDATE #{insert.raw_update_sql}"
            else
              sql << " ON DUPLICATE KEY UPDATE "
              sql << insert.touch_model_timestamps_unless { |column| "#{insert.model.quoted_table_name}.#{column}<=>#{values_alias}.#{column}" }
              sql << insert.updatable_columns.map { |column| "#{column}=#{values_alias}.#{column}" }.join(",")
            end
          end
        else
          sql = +"INSERT #{insert.into} #{insert.values_list}"

          if insert.skip_duplicates?
            sql << " ON DUPLICATE KEY UPDATE #{no_op_column}=#{no_op_column}"
          elsif insert.update_duplicates?
            sql << " ON DUPLICATE KEY UPDATE "
            if insert.raw_update_sql?
              sql << insert.raw_update_sql
            else
              sql << insert.touch_model_timestamps_unless { |column| "#{column}<=>VALUES(#{column})" }
              sql << insert.updatable_columns.map { |column| "#{column}=VALUES(#{column})" }.join(",")
            end
          end
        end

        sql << " RETURNING #{insert.returning}" if insert.returning
        sql
      end

      def check_version # :nodoc:
        if database_version < "5.6.4"
          raise DatabaseVersionError, "Your version of MySQL (#{database_version}) is too old. Active Record supports MySQL >= 5.6.4."
        end
      end

      #--
      # QUOTING ==================================================
      #++

      # Quotes strings for use in SQL input.
      def quote_string(string)
        with_raw_connection(allow_retry: true, materialize_transactions: false) do |connection|
          connection.escape(string)
        end
      end

      class << self
        def extended_type_map(default_timezone: nil, emulate_booleans:) # :nodoc:
          super(default_timezone: default_timezone).tap do |m|
            if emulate_booleans
              m.register_type %r(^tinyint\(1\))i, Type::Boolean.new
            end
          end
        end

        private
          def initialize_type_map(m)
            super

            m.register_type %r(tinytext)i,   Type::Text.new(limit: 2**8 - 1)
            m.register_type %r(tinyblob)i,   Type::Binary.new(limit: 2**8 - 1)
            m.register_type %r(text)i,       Type::Text.new(limit: 2**16 - 1)
            m.register_type %r(blob)i,       Type::Binary.new(limit: 2**16 - 1)
            m.register_type %r(mediumtext)i, Type::Text.new(limit: 2**24 - 1)
            m.register_type %r(mediumblob)i, Type::Binary.new(limit: 2**24 - 1)
            m.register_type %r(longtext)i,   Type::Text.new(limit: 2**32 - 1)
            m.register_type %r(longblob)i,   Type::Binary.new(limit: 2**32 - 1)
            m.register_type %r(^float)i,     Type::Float.new(limit: 24)
            m.register_type %r(^double)i,    Type::Float.new(limit: 53)

            register_integer_type m, %r(^bigint)i,    limit: 8
            register_integer_type m, %r(^int)i,       limit: 4
            register_integer_type m, %r(^mediumint)i, limit: 3
            register_integer_type m, %r(^smallint)i,  limit: 2
            register_integer_type m, %r(^tinyint)i,   limit: 1

            m.alias_type %r(year)i, "integer"
            m.alias_type %r(bit)i,  "binary"
          end

          def register_integer_type(mapping, key, **options)
            mapping.register_type(key) do |sql_type|
              if /\bunsigned\b/.match?(sql_type)
                Type::UnsignedInteger.new(**options)
              else
                Type::Integer.new(**options)
              end
            end
          end

          def extract_precision(sql_type)
            if /\A(?:date)?time(?:stamp)?\b/.match?(sql_type)
              super || 0
            else
              super
            end
          end
      end

      EXTENDED_TYPE_MAPS = Concurrent::Map.new
      EMULATE_BOOLEANS_TRUE = { emulate_booleans: true }.freeze

      private
        def strip_whitespace_characters(expression)
          expression = expression.gsub(/\\n|\\\\/, "")
          expression = expression.gsub(/\s{2,}/, " ")
          expression
        end

        def extended_type_map_key
          if @default_timezone
            { default_timezone: @default_timezone, emulate_booleans: emulate_booleans }
          elsif emulate_booleans
            EMULATE_BOOLEANS_TRUE
          end
        end

        def handle_warnings(sql)
          return if ActiveRecord.db_warnings_action.nil? || @raw_connection.warning_count == 0

          @affected_rows_before_warnings = @raw_connection.affected_rows
          warning_count = @raw_connection.warning_count
          result = @raw_connection.query("SHOW WARNINGS")
          result = [
            ["Warning", nil, "Query had warning_count=#{warning_count} but ‘SHOW WARNINGS’ did not return the warnings. Check MySQL logs or database configuration."],
          ] if result.count == 0
          result.each do |level, code, message|
            warning = SQLWarning.new(message, code, level, sql, @pool)
            next if warning_ignored?(warning)

            ActiveRecord.db_warnings_action.call(warning)
          end
        end

        def warning_ignored?(warning)
          warning.level == "Note" || super
        end

        # See https://dev.mysql.com/doc/mysql-errors/en/server-error-reference.html
        ER_DB_CREATE_EXISTS     = 1007
        ER_FILSORT_ABORT        = 1028
        ER_DUP_ENTRY            = 1062
        ER_SERVER_SHUTDOWN      = 1053
        ER_NOT_NULL_VIOLATION   = 1048
        ER_NO_REFERENCED_ROW    = 1216
        ER_ROW_IS_REFERENCED    = 1217
        ER_DO_NOT_HAVE_DEFAULT  = 1364
        ER_ROW_IS_REFERENCED_2  = 1451
        ER_NO_REFERENCED_ROW_2  = 1452
        ER_DATA_TOO_LONG        = 1406
        ER_OUT_OF_RANGE         = 1264
        ER_LOCK_DEADLOCK        = 1213
        ER_CANNOT_ADD_FOREIGN   = 1215
        ER_CANNOT_CREATE_TABLE  = 1005
        ER_LOCK_WAIT_TIMEOUT    = 1205
        ER_QUERY_INTERRUPTED    = 1317
        ER_CONNECTION_KILLED    = 1927
        CR_SERVER_GONE_ERROR    = 2006
        CR_SERVER_LOST          = 2013
        ER_QUERY_TIMEOUT        = 3024
        ER_FK_INCOMPATIBLE_COLUMNS = 3780
        ER_CLIENT_INTERACTION_TIMEOUT = 4031

        def translate_exception(exception, message:, sql:, binds:)
          case error_number(exception)
          when nil
            if exception.message.match?(/MySQL client is not connected/i)
              ConnectionNotEstablished.new(exception, connection_pool: @pool)
            else
              super
            end
          when ER_CONNECTION_KILLED, ER_SERVER_SHUTDOWN, CR_SERVER_GONE_ERROR, CR_SERVER_LOST, ER_CLIENT_INTERACTION_TIMEOUT
            ConnectionFailed.new(message, sql: sql, binds: binds, connection_pool: @pool)
          when ER_DB_CREATE_EXISTS
            DatabaseAlreadyExists.new(message, sql: sql, binds: binds, connection_pool: @pool)
          when ER_DUP_ENTRY
            RecordNotUnique.new(message, sql: sql, binds: binds, connection_pool: @pool)
          when ER_NO_REFERENCED_ROW, ER_ROW_IS_REFERENCED, ER_ROW_IS_REFERENCED_2, ER_NO_REFERENCED_ROW_2
            InvalidForeignKey.new(message, sql: sql, binds: binds, connection_pool: @pool)
          when ER_CANNOT_ADD_FOREIGN, ER_FK_INCOMPATIBLE_COLUMNS
            mismatched_foreign_key(message, sql: sql, binds: binds, connection_pool: @pool)
          when ER_CANNOT_CREATE_TABLE
            if message.include?("errno: 150")
              mismatched_foreign_key(message, sql: sql, binds: binds, connection_pool: @pool)
            else
              super
            end
          when ER_DATA_TOO_LONG
            ValueTooLong.new(message, sql: sql, binds: binds, connection_pool: @pool)
          when ER_OUT_OF_RANGE
            RangeError.new(message, sql: sql, binds: binds, connection_pool: @pool)
          when ER_NOT_NULL_VIOLATION, ER_DO_NOT_HAVE_DEFAULT
            NotNullViolation.new(message, sql: sql, binds: binds, connection_pool: @pool)
          when ER_LOCK_DEADLOCK
            Deadlocked.new(message, sql: sql, binds: binds, connection_pool: @pool)
          when ER_LOCK_WAIT_TIMEOUT
            LockWaitTimeout.new(message, sql: sql, binds: binds, connection_pool: @pool)
          when ER_QUERY_TIMEOUT, ER_FILSORT_ABORT
            StatementTimeout.new(message, sql: sql, binds: binds, connection_pool: @pool)
          when ER_QUERY_INTERRUPTED
            QueryCanceled.new(message, sql: sql, binds: binds, connection_pool: @pool)
          else
            super
          end
        end

        def change_column_for_alter(table_name, column_name, type, **options)
          cd = build_change_column_definition(table_name, column_name, type, **options)
          schema_creation.accept(cd)
        end

        def rename_column_for_alter(table_name, column_name, new_column_name)
          return rename_column_sql(table_name, column_name, new_column_name) if supports_rename_column?

          column  = column_for(table_name, column_name)
          options = {
            default: column.default,
            null: column.null,
            auto_increment: column.auto_increment?,
            comment: column.comment
          }

          current_type = internal_exec_query("SHOW COLUMNS FROM #{quote_table_name(table_name)} LIKE #{quote(column_name)}", "SCHEMA").first["Type"]
          td = create_table_definition(table_name)
          cd = td.new_column_definition(new_column_name, current_type, **options)
          schema_creation.accept(ChangeColumnDefinition.new(cd, column.name))
        end

        def add_index_for_alter(table_name, column_name, **options)
          index, algorithm, _ = add_index_options(table_name, column_name, **options)
          algorithm = ", #{algorithm}" if algorithm

          "ADD #{schema_creation.accept(index)}#{algorithm}"
        end

        def remove_index_for_alter(table_name, column_name = nil, **options)
          index_name = index_name_for_remove(table_name, column_name, options)
          "DROP INDEX #{quote_column_name(index_name)}"
        end

        def supports_insert_raw_alias_syntax?
          !mariadb? && database_version >= "8.0.19"
        end

        def supports_rename_index?
          if mariadb?
            database_version >= "10.5.2"
          else
            database_version >= "5.7.6"
          end
        end

        def supports_rename_column?
          if mariadb?
            database_version >= "10.5.2"
          else
            database_version >= "8.0.3"
          end
        end

        def configure_connection
          super
          variables = @config.fetch(:variables, {}).stringify_keys

          # Increase timeout so the server doesn't disconnect us.
          wait_timeout = self.class.type_cast_config_to_integer(@config[:wait_timeout])
          wait_timeout = 2147483 unless wait_timeout.is_a?(Integer)
          variables["wait_timeout"] = wait_timeout

          defaults = [":default", :default].to_set

          # Make MySQL reject illegal values rather than truncating or blanking them, see
          # https://dev.mysql.com/doc/refman/en/sql-mode.html#sqlmode_strict_all_tables
          # If the user has provided another value for sql_mode, don't replace it.
          if sql_mode = variables.delete("sql_mode")
            sql_mode = quote(sql_mode)
          elsif !defaults.include?(strict_mode?)
            if strict_mode?
              sql_mode = "CONCAT(@@sql_mode, ',STRICT_ALL_TABLES')"
            else
              sql_mode = "REPLACE(@@sql_mode, 'STRICT_TRANS_TABLES', '')"
              sql_mode = "REPLACE(#{sql_mode}, 'STRICT_ALL_TABLES', '')"
              sql_mode = "REPLACE(#{sql_mode}, 'TRADITIONAL', '')"
            end
            sql_mode = "CONCAT(#{sql_mode}, ',NO_AUTO_VALUE_ON_ZERO')"
          end
          sql_mode_assignment = "@@SESSION.sql_mode = #{sql_mode}, " if sql_mode

          # NAMES does not have an equals sign, see
          # https://dev.mysql.com/doc/refman/en/set-names.html
          # (trailing comma because variable_assignments will always have content)
          if @config[:encoding]
            encoding = +"NAMES #{@config[:encoding]}"
            encoding << " COLLATE #{@config[:collation]}" if @config[:collation]
            encoding << ", "
          end

          # Gather up all of the SET variables...
          variable_assignments = variables.filter_map do |k, v|
            if defaults.include?(v)
              "@@SESSION.#{k} = DEFAULT" # Sets the value to the global or compile default
            elsif !v.nil?
              "@@SESSION.#{k} = #{quote(v)}"
            end
          end.join(", ")

          # ...and send them all in one query
          raw_execute("SET #{encoding} #{sql_mode_assignment} #{variable_assignments}", "SCHEMA")
        end

        def column_definitions(table_name) # :nodoc:
          internal_exec_query("SHOW FULL FIELDS FROM #{quote_table_name(table_name)}", "SCHEMA")
        end

        def create_table_info(table_name) # :nodoc:
          internal_exec_query("SHOW CREATE TABLE #{quote_table_name(table_name)}", "SCHEMA").first["Create Table"]
        end

        def arel_visitor
          Arel::Visitors::MySQL.new(self)
        end

        def build_statement_pool
          StatementPool.new(self.class.type_cast_config_to_integer(@config[:statement_limit]))
        end

        def mismatched_foreign_key_details(message:, sql:)
          foreign_key_pat =
            /Referencing column '(\w+)' and referenced/i =~ message ? $1 : '\w+'

          match = %r/
            (?:CREATE|ALTER)\s+TABLE\s*(?:`?\w+`?\.)?`?(?<table>\w+)`?.+?
            FOREIGN\s+KEY\s*\(`?(?<foreign_key>#{foreign_key_pat})`?\)\s*
            REFERENCES\s*(`?(?<target_table>\w+)`?)\s*\(`?(?<primary_key>\w+)`?\)
          /xmi.match(sql)

          options = {}

          if match
            options[:table] = match[:table]
            options[:foreign_key] = match[:foreign_key]
            options[:target_table] = match[:target_table]
            options[:primary_key] = match[:primary_key]
            options[:primary_key_column] = column_for(match[:target_table], match[:primary_key])
          end

          options
        end

        def mismatched_foreign_key(message, sql:, binds:, connection_pool:)
          options = {
            message: message,
            sql: sql,
            binds: binds,
            connection_pool: connection_pool
          }

          if sql
            options.update mismatched_foreign_key_details(message: message, sql: sql)
          else
            options[:query_parser] = ->(sql) { mismatched_foreign_key_details(message: message, sql: sql) }
          end

          MismatchedForeignKey.new(**options)
        end

        def version_string(full_version_string)
          if full_version_string && matches = full_version_string.match(/^(?:5\.5\.5-)?(\d+\.\d+\.\d+)/)
            matches[1]
          else
            raise DatabaseVersionError, "Unable to parse MySQL version from #{full_version_string.inspect}"
          end
        end
    end
  end
end