module SQLite3

  # The Translator class encapsulates the logic and callbacks necessary for
  # converting string data to a value of some specified type. Every Database
  # instance may have a Translator instance, in order to assist in type
  # translation (Database#type_translation).
  #
  # Further, applications may define their own custom type translation logic
  # by registering translator blocks with the corresponding database's
  # translator instance (Database#translator).
  class Translator

    # Create a new Translator instance. It will be preinitialized with default
    # translators for most SQL data types.
    def initialize
      @translators = Hash.new(proc { |type, value| value })
      @type_name_cache = {}
      register_default_translators
    end

    # Add a new translator block, which will be invoked to process type
    # translations to the given type. The type should be an SQL datatype, and
    # may include parentheses (i.e., "VARCHAR(30)"). However, any parenthetical
    # information is stripped off and discarded, so type translation decisions
    # are made solely on the "base" type name.
    #
    # The translator block itself should accept two parameters, "type" and
    # "value". In this case, the "type" is the full type name (including
    # parentheses), so the block itself may include logic for changing how a
    # type is translated based on the additional data. The "value" parameter
    # is the (string) data to convert.
    #
    # The block should return the translated value.
    def add_translator(type, &block) # :yields: type, value
      @translators[ type_name(type) ] = block
    end

    # Translate the given string value to a value of the given type. In the
    # absense of an installed translator block for the given type, the value
    # itself is always returned. Further, +nil+ values are never translated,
    # and are always passed straight through regardless of the type parameter.
    def translate(type, value)
      unless value.nil?
        @translators[ type_name(type) ].call(type, value)
      end
    end

    # A convenience method for working with type names. This returns the "base"
    # type name, without any parenthetical data.
    def type_name(type)
      @type_name_cache[type] ||= begin
                                   type = "" if type.nil?
                                   type = $1 if type =~ /^(.*?)\(/
                                   type.upcase
                                 end
    end
    private :type_name

    # Register the default translators for the current Translator instance.
    # This includes translators for most major SQL data types.
    def register_default_translators
      [ "time",
        "timestamp" ].each { |type| add_translator(type) { |t, v| Time.parse(v) } }

      add_translator("date") { |t,v| Date.parse(v) }
      add_translator("datetime") { |t,v| DateTime.parse(v) }

      [ "decimal",
        "float",
        "numeric",
        "double",
        "real",
        "dec",
        "fixed" ].each { |type| add_translator(type) { |t,v| v.to_f } }

      [ "integer",
        "smallint",
        "mediumint",
        "int",
        "bigint" ].each { |type| add_translator(type) { |t,v| v.to_i } }

      [ "bit",
        "bool",
        "boolean" ].each do |type|
        add_translator(type) do |t,v|
          !(v.strip.gsub(/00+/,"0") == "0" ||
            v.downcase == "false" ||
            v.downcase == "f" ||
            v.downcase == "no" ||
            v.downcase == "n")
        end
      end

      add_translator("tinyint") do |type, value|
        if type =~ /\(\s*1\s*\)/
          value.to_i == 1
        else
          value.to_i
        end
      end
    end
    private :register_default_translators

  end

end