require 'mysql2'
require 'logger'

require 'active_record'
require 'active_record/base'
require 'active_record/connection_adapters/abstract_adapter'
require 'active_record/connection_adapters/abstract_mysql_adapter'
require 'active_record/connection_adapters/mysql2_adapter'
require 'active_record/connection_adapters/abstract/connection_pool'
require 'active_support'

require 'activerecord/mysql/reconnect/version'
require 'activerecord/mysql/reconnect/base_ext'
# XXX:
#require 'activerecord/mysql/reconnect/abstract_adapter_ext'
require 'activerecord/mysql/reconnect/abstract_mysql_adapter_ext'
require 'activerecord/mysql/reconnect/mysql2_adapter_ext'
require 'activerecord/mysql/reconnect/connection_pool_ext'

module Activerecord::Mysql::Reconnect
  DEFAULT_EXECUTION_TRIES = 3
  DEFAULT_EXECUTION_RETRY_WAIT = 0.5

  WITHOUT_RETRY_KEY = 'activerecord-mysql-reconnect-without-retry'
  RETRYABLE_TRANSACTION_KEY = 'activerecord-mysql-reconnect-transaction-retry'

  HANDLE_ERROR = [
    ActiveRecord::StatementInvalid,
    Mysql2::Error,
  ]

  HANDLE_R_ERROR_MESSAGES = [
    'Lost connection to MySQL server during query',
  ]

  HANDLE_RW_ERROR_MESSAGES = [
    'MySQL server has gone away',
    'Server shutdown in progress',
    'closed MySQL connection',
    "Can't connect to MySQL server",
    'Query execution was interrupted',
    'Access denied for user',
  ]

  HANDLE_ERROR_MESSAGES = HANDLE_R_ERROR_MESSAGES + HANDLE_RW_ERROR_MESSAGES

  READ_SQL_REGEXP = /\A\s*(?:SELECT|SHOW|SET)\b/i

  class << self
    def execution_tries
      ActiveRecord::Base.execution_tries || DEFAULT_EXECUTION_TRIES
    end

    def execution_retry_wait
      ActiveRecord::Base.execution_retry_wait || DEFAULT_EXECUTION_RETRY_WAIT
    end

    def enable_retry
      !!ActiveRecord::Base.enable_retry
    end

    def retry_read_only
      !!ActiveRecord::Base.retry_read_only
    end

    def retryable(opts)
      block     = opts.fetch(:proc)
      on_error  = opts[:on_error]
      conn      = opts[:connection]
      tries     = self.execution_tries
      retval    = nil

      retryable_loop(tries) do |n|
        begin
          retval = block.call
          break
        rescue => e
          if enable_retry and (tries.zero? or n < tries) and should_handle?(e, opts)
            on_error.call if on_error
            wait = self.execution_retry_wait * n

            opt_msgs = ["cause: #{e} [#{e.class}]"]

            if conn and conn.kind_of?(Mysql2::Client)
              opt_msgs << 'connection: ' + [:host, :database, :username].map {|k| "#{k}=#{conn.query_options[k]}" }.join(";")
            end

            logger.warn("MySQL server has gone away. Trying to reconnect in #{wait} seconds. (#{opt_msgs.join(', ')})")
            sleep(wait)
            next
          else
            raise e
          end
        end
      end

      return retval
    end

    def logger
      if defined?(Rails)
        Rails.logger || ActiveRecord::Base.logger || Logger.new($stderr)
      else
        ActiveRecord::Base.logger || Logger.new($stderr)
      end
    end

    def without_retry
      begin
        Thread.current[WITHOUT_RETRY_KEY] = true
        yield
      ensure
        Thread.current[WITHOUT_RETRY_KEY] = nil
      end
    end

    def without_retry?
      !!Thread.current[WITHOUT_RETRY_KEY]
    end

    def retryable_transaction
      begin
        Thread.current[RETRYABLE_TRANSACTION_KEY] = []

        ActiveRecord::Base.transaction do
          yield
        end
      ensure
        Thread.current[RETRYABLE_TRANSACTION_KEY] = nil
      end
    end

    def retryable_transaction_buffer
      Thread.current[RETRYABLE_TRANSACTION_KEY]
    end

    private

    def retryable_loop(n)
      if n.zero?
        loop { n += 1 ; yield(n) }
      else
        n.times {|i| yield(i + 1) }
      end
    end

    def should_handle?(e, opts = {})
      sql       = opts[:sql]
      read_only = opts[:read_only]

      if without_retry?
        return false
      end

      unless HANDLE_ERROR.any? {|i| e.kind_of?(i) }
        return false
      end

      unless Regexp.union(HANDLE_ERROR_MESSAGES) =~ e.message
        return false
      end

      if sql and READ_SQL_REGEXP !~ sql
        if read_only or Regexp.union(HANDLE_R_ERROR_MESSAGES) =~ e.message
          return false
        end
      end

      return true
    end
  end # end of class methods
end