require 'sequel_core/database/schema'

module Sequel
  # Array of all databases to which Sequel has connected.  If you are
  # developing an application that can connect to an arbitrary number of 
  # databases, delete the database objects from this or they will not get
  # garbage collected.
  DATABASES = []

  # A Database object represents a virtual connection to a database.
  # The Database class is meant to be subclassed by database adapters in order
  # to provide the functionality needed for executing queries.
  class Database
    include Schema::SQL

    # Array of supported database adapters
    ADAPTERS = %w'ado db2 dbi informix jdbc mysql odbc odbc_mssql openbase oracle postgres sqlite'.collect{|x| x.to_sym}

    SQL_BEGIN = 'BEGIN'.freeze
    SQL_COMMIT = 'COMMIT'.freeze
    SQL_ROLLBACK = 'ROLLBACK'.freeze

    # Hash of adapters that have been used
    @@adapters = Hash.new

    # Whether to use the single threaded connection pool by default
    @@single_threaded = false

    # Whether to quote identifiers (columns and tables) by default
    @@quote_identifiers = true

    # Array of SQL loggers to use for this database
    attr_accessor :loggers

    # The options for this database
    attr_reader :opts
    
    # The connection pool for this database
    attr_reader :pool

    # Whether to quote identifiers (columns and tables) for this database
    attr_writer :quote_identifiers

    # Constructs a new instance of a database connection with the specified
    # options hash.
    #
    # Sequel::Database is an abstract class that is not useful by itself.
    def initialize(opts = {}, &block)
      @opts = opts
      
      @quote_identifiers = opts[:quote_identifiers] || @@quote_identifiers
      @single_threaded = opts[:single_threaded] || @@single_threaded
      @schemas = nil
      @pool = (@single_threaded ? SingleThreadedPool : ConnectionPool).new(connection_pool_default_options.merge(opts), &block)
      @pool.connection_proc = proc {connect} unless block

      @loggers = Array(opts[:logger]) + Array(opts[:loggers])
      ::Sequel::DATABASES.push(self)
    end
    
    ### Class Methods ###

    # The Database subclass for the given adapter scheme.
    # Raises Sequel::Error::AdapterNotFound if the adapter
    # could not be loaded.
    def self.adapter_class(scheme)
      scheme = scheme.to_s.gsub('-', '_').to_sym
      
      if (klass = @@adapters[scheme]).nil?
        # attempt to load the adapter file
        begin
          require "sequel_core/adapters/#{scheme}"
        rescue LoadError => e
          raise Error::AdapterNotFound, "Could not load #{scheme} adapter:\n  #{e.message}"
        end
        
        # make sure we actually loaded the adapter
        if (klass = @@adapters[scheme]).nil?
          raise Error::AdapterNotFound, "Could not load #{scheme} adapter"
        end
      end
      return klass
    end
        
    # Returns the scheme for the Database class.
    def self.adapter_scheme
      @scheme
    end
    
    # Connects to a database.  See Sequel.connect.
    def self.connect(conn_string, opts = nil, &block)
      if conn_string.is_a?(String)
        uri = URI.parse(conn_string)
        scheme = uri.scheme
        scheme = :dbi if scheme =~ /^dbi-(.+)/
        c = adapter_class(scheme)
        opts = c.uri_to_options(uri).merge(opts || {})
      else
        opts = conn_string.merge(opts || {})
        c = adapter_class(opts[:adapter] || opts['adapter'])
      end
      # process opts a bit
      opts = opts.inject({}) do |m, kv| k, v = *kv
        k = :user if k.to_s == 'username'
        m[k.to_sym] = v
        m
      end
      if block
        begin
          yield(db = c.new(opts))
        ensure
          db.disconnect if db
          ::Sequel::DATABASES.delete(db)
        end
        nil
      else
        c.new(opts)
      end
    end

    # Sets the default quote_identifiers mode for new databases.
    # See Sequel.quote_identifiers=.
    def self.quote_identifiers=(value)
      @@quote_identifiers = value
    end

    # Sets the default single_threaded mode for new databases.
    # See Sequel.single_threaded=.
    def self.single_threaded=(value)
      @@single_threaded = value
    end

    # Converts a uri to an options hash. These options are then passed
    # to a newly created database object.
    def self.uri_to_options(uri)
      if uri.is_a?(String)
        uri = URI.parse(uri)
      end
      # special case for sqlite
      if uri.scheme == 'sqlite'
        {
          :user => uri.user,
          :password => uri.password,
          :database => (uri.host.nil? && uri.path == '/') ? nil : "#{uri.host}#{uri.path}"
        }
      else
        {
          :user => uri.user,
          :password => uri.password,
          :host => uri.host,
          :port => uri.port,
          :database => (m = /\/(.*)/.match(uri.path)) && (m[1])
        }
      end
    end
    
    ### Private Class Methods ###

    # Sets the adapter scheme for the Database class. Call this method in
    # descendnants of Database to allow connection using a URL. For example the
    # following:
    #
    #   class Sequel::MyDB::Database < Sequel::Database
    #     set_adapter_scheme :mydb
    #     ...
    #   end
    #
    # would allow connection using:
    #
    #   Sequel.connect('mydb://user:password@dbserver/mydb')
    def self.set_adapter_scheme(scheme) # :nodoc:
      @scheme = scheme
      @@adapters[scheme.to_sym] = self
    end
    metaprivate :set_adapter_scheme
    
    ### Instance Methods ###

    # Executes the supplied SQL statement. The SQL can be supplied as a string
    # or as an array of strings. If an array is given, comments and excessive 
    # white space are removed. See also Array#to_sql.
    def <<(sql)
      execute((Array === sql) ? sql.to_sql : sql)
    end
    
    # Returns a dataset from the database. If the first argument is a string,
    # the method acts as an alias for Database#fetch, returning a dataset for
    # arbitrary SQL:
    #
    #   DB['SELECT * FROM items WHERE name = ?', my_name].print
    #
    # Otherwise, acts as an alias for Database#from, setting the primary
    # table for the dataset:
    #
    #   DB[:items].sql #=> "SELECT * FROM items"
    def [](*args, &block)
      (String === args.first) ? fetch(*args, &block) : from(*args, &block)
    end
    
    # Connects to the database. This method should be overridden by descendants.
    def connect
      raise NotImplementedError, "#connect should be overridden by adapters"
    end
    
    # Returns a blank dataset
    def dataset
      ds = Sequel::Dataset.new(self)
    end
    
    # Disconnects from the database. This method should be overridden by 
    # descendants.
    def disconnect
      raise NotImplementedError, "#disconnect should be overridden by adapters"
    end

    # Executes the given SQL. This method should be overridden in descendants.
    def execute(sql)
      raise NotImplementedError, "#execute should be overridden by adapters"
    end
    
    # Fetches records for an arbitrary SQL statement. If a block is given,
    # it is used to iterate over the records:
    #
    #   DB.fetch('SELECT * FROM items'){|r| p r}
    #
    # The method returns a dataset instance:
    #
    #   DB.fetch('SELECT * FROM items').print
    #
    # Fetch can also perform parameterized queries for protection against SQL
    # injection:
    #
    #   DB.fetch('SELECT * FROM items WHERE name = ?', my_name).print
    def fetch(sql, *args, &block)
      ds = dataset
      sql = sql.gsub('?') {|m|  ds.literal(args.shift)}
      ds.opts[:sql] = sql
      ds.fetch_rows(sql, &block) if block
      ds
    end
    alias_method :>>, :fetch
    
    # Returns a new dataset with the from method invoked. If a block is given,
    # it is used as a filter on the dataset.
    def from(*args, &block)
      ds = dataset.from(*args)
      block ? ds.filter(&block) : ds
    end
    
    # Returns a single value from the database, e.g.:
    #
    #   # SELECT 1
    #   DB.get(1) #=> 1 
    #
    #   # SELECT version()
    #   DB.get(:version[]) #=> ...
    def get(expr)
      dataset.get(expr)
    end
    
    # Returns a string representation of the database object including the
    # class name and the connection URI (or the opts if the URI
    # cannot be constructed).
    def inspect
      "#<#{self.class}: #{(uri rescue opts).inspect}>" 
    end

    # Log a message at level info to all loggers.  All SQL logging
    # goes through this method.
    def log_info(message)
      @loggers.each{|logger| logger.info(message)}
    end

    # Return the first logger or nil if no loggers are being used.
    # Should only be used for backwards compatibility.
    def logger
      @loggers.first
    end

    # Replace the array of loggers with the given logger(s).
    def logger=(logger)
      @loggers = Array(logger)
    end

    # Returns true unless the database is using a single-threaded connection pool.
    def multi_threaded?
      !@single_threaded
    end
    
    # Returns a dataset modified by the given query block.  See Dataset#query.
    def query(&block)
      dataset.query(&block)
    end
    
    # Returns true if the database quotes identifiers.
    def quote_identifiers?
      @quote_identifiers
    end
    
    # Returns a new dataset with the select method invoked.
    def select(*args)
      dataset.select(*args)
    end
    
    # Default serial primary key options.
    def serial_primary_key_options
      {:primary_key => true, :type => :integer, :auto_increment => true}
    end
    
    # Returns true if the database is using a single-threaded connection pool.
    def single_threaded?
      @single_threaded
    end
    
    # Acquires a database connection, yielding it to the passed block.
    def synchronize(&block)
      @pool.hold(&block)
    end

    # Returns true if a table with the given name exists.
    def table_exists?(name)
      begin 
        if respond_to?(:tables)
          tables.include?(name.to_sym)
        else
          from(name).first
          true
        end
      rescue
        false
      end
    end
    
    # Attempts to acquire a database connection.  Returns true if successful.
    # Will probably raise an error if unsuccessful.
    def test_connection
      synchronize{|conn|}
      true
    end
    
    # A simple implementation of SQL transactions. Nested transactions are not 
    # supported - calling #transaction within a transaction will reuse the 
    # current transaction. Should be overridden for databases that support nested 
    # transactions.
    def transaction
      @pool.hold do |conn|
        @transactions ||= []
        if @transactions.include? Thread.current
          return yield(conn)
        end
        log_info(SQL_BEGIN)
        conn.execute(SQL_BEGIN)
        begin
          @transactions << Thread.current
          yield(conn)
        rescue Exception => e
          log_info(SQL_ROLLBACK)
          conn.execute(SQL_ROLLBACK)
          raise e unless Error::Rollback === e
        ensure
          unless e
            log_info(SQL_COMMIT)
            conn.execute(SQL_COMMIT)
          end
          @transactions.delete(Thread.current)
        end
      end
    end
    
    # Typecast the value to the given column_type. Can be overridden in
    # adapters to support database specific column types.
    def typecast_value(column_type, value)
      return nil if value.nil?
      case column_type
      when :integer
        Integer(value)
      when :string
        value.to_s
      when :float
        Float(value)
      when :boolean
        case value
        when false, 0, "0", /\Af(alse)?\z/i
          false
        else
          value.blank? ? nil : true
        end
      when :date
        case value
        when Date
          value
        when DateTime, Time
          Date.new(value.year, value.month, value.day)
        when String
          value.to_date
        else
          raise ArgumentError, "invalid value for Date: #{value.inspect}"
        end
      when :datetime
        case value
        when DateTime
          value
        when Date
          DateTime.new(value.year, value.month, value.day)
        when Time
          DateTime.new(value.year, value.month, value.day, value.hour, value.min, value.sec)
        when String
          value.to_datetime
        else
          raise ArgumentError, "invalid value for DateTime: #{value.inspect}"
        end
      else
        value
      end
    end 

    # Returns the URI identifying the database.
    # This method can raise an error if the database used options
    # instead of a connection string.
    def uri
      uri = URI::Generic.new(
        self.class.adapter_scheme.to_s,
        nil,
        @opts[:host],
        @opts[:port],
        nil,
        "/#{@opts[:database]}",
        nil,
        nil,
        nil
      )
      uri.user = @opts[:user]
      uri.password = @opts[:password] if uri.user
      uri.to_s
    end
    alias_method :url, :uri
    
    private

    # The default options for the connection pool.
    def connection_pool_default_options
      {}
    end
  end
end