module ThinkingSphinx
  # Attributes - eternally useful when it comes to filtering, sorting or
  # grouping. This class isn't really useful to you unless you're hacking
  # around with the internals of Thinking Sphinx - but hey, don't let that
  # stop you.
  #
  # One key thing to remember - if you're using the attribute manually to
  # generate SQL statements, you'll need to set the base model, and all the
  # associations. Which can get messy. Use Index.link!, it really helps.
  # 
  class Attribute
    attr_accessor :alias, :columns, :associations, :model
    
    # To create a new attribute, you'll need to pass in either a single Column
    # or an array of them, and some (optional) options.
    #
    # Valid options are:
    # - :as   => :alias_name 
    # - :type => :attribute_type
    #
    # Alias is only required in three circumstances: when there's
    # another attribute or field with the same name, when the column name is
    # 'id', or when there's more than one column.
    # 
    # Type is not required, unless you want to force a column to be a certain
    # type (but keep in mind the value will not be CASTed in the SQL
    # statements). The only time you really need to use this is when the type
    # can't be figured out by the column - ie: when not actually using a
    # database column as your source.
    # 
    # Example usage:
    #
    #   Attribute.new(
    #     Column.new(:created_at)
    #   )
    #
    #   Attribute.new(
    #     Column.new(:posts, :id),
    #     :as => :post_ids
    #   )
    #
    #   Attribute.new(
    #     [Column.new(:pages, :id), Column.new(:articles, :id)],
    #     :as => :content_ids
    #   )
    #
    #   Attribute.new(
    #     Column.new("NOW()"),
    #     :as   => :indexed_at,
    #     :type => :datetime
    #   )
    #
    # If you're creating attributes for latitude and longitude, don't forget
    # that Sphinx expects these values to be in radians.
    #  
    def initialize(columns, options = {})
      @columns      = Array(columns)
      @associations = {}
      
      raise "Cannot define a field with no columns. Maybe you are trying to index a field with a reserved name (id, name). You can fix this error by using a symbol rather than a bare name (:id instead of id)." if @columns.empty? || @columns.any? { |column| !column.respond_to?(:__stack) }
      
      @alias        = options[:as]
      @type         = options[:type]
    end
    
    # Get the part of the SELECT clause related to this attribute. Don't forget
    # to set your model and associations first though.
    #
    # This will concatenate strings and arrays of integers, and convert
    # datetimes to timestamps, as needed.
    # 
    def to_select_sql
      clause = @columns.collect { |column|
        column_with_prefix(column)
      }.join(', ')
      
      separator = all_ints? ? ',' : ' '
      
      clause = concatenate(clause, separator)       if concat_ws?
      clause = group_concatenate(clause, separator) if is_many?
      clause = cast_to_datetime(clause)             if type == :datetime
      clause = convert_nulls(clause)                if type == :string
      
      "#{clause} AS #{quote_column(unique_name)}"
    end
    
    # Get the part of the GROUP BY clause related to this attribute - if one is
    # needed. If not, all you'll get back is nil. The latter will happen if
    # there isn't actually a real column to get data from, or if there's
    # multiple data values (read: a has_many or has_and_belongs_to_many
    # association).
    # 
    def to_group_sql
      case
      when is_many?, is_string?, ThinkingSphinx.use_group_by_shortcut?
        nil
      else
        @columns.collect { |column|
          column_with_prefix(column)
        }
      end
    end
    
    # Generates the appropriate attribute statement for a Sphinx configuration
    # file, depending on the attribute's type.
    # 
    def to_sphinx_clause
      case type
      when :multi
        "sql_attr_multi       = uint #{unique_name} from field"
      when :datetime
        "sql_attr_timestamp   = #{unique_name}"
      when :string
        "sql_attr_str2ordinal = #{unique_name}"
      when :float
        "sql_attr_float       = #{unique_name}"
      when :boolean
        "sql_attr_bool        = #{unique_name}"
      else
        "sql_attr_uint        = #{unique_name}"
      end
    end
    
    # Returns the unique name of the attribute - which is either the alias of
    # the attribute, or the name of the only column - if there is only one. If
    # there isn't, there should be an alias. Else things probably won't work.
    # Consider yourself warned.
    # 
    def unique_name
      if @columns.length == 1
        @alias || @columns.first.__name
      else
        @alias
      end
    end
    
    private
    
    def concatenate(clause, separator = ' ')
      case @model.connection.class.name
      when "ActiveRecord::ConnectionAdapters::MysqlAdapter"
        "CONCAT_WS('#{separator}', #{clause})"
      when "ActiveRecord::ConnectionAdapters::PostgreSQLAdapter"
        clause.split(', ').join(" || '#{separator}' || ")
      else
        clause
      end
    end
    
    def group_concatenate(clause, separator = ' ')
      case @model.connection.class.name
      when "ActiveRecord::ConnectionAdapters::MysqlAdapter"
        "GROUP_CONCAT(#{clause} SEPARATOR '#{separator}')"
      when "ActiveRecord::ConnectionAdapters::PostgreSQLAdapter"
        "array_to_string(array_accum(#{clause}), '#{separator}')"
      else
        clause
      end
    end
    
    def cast_to_string(clause)
      case @model.connection.class.name
      when "ActiveRecord::ConnectionAdapters::MysqlAdapter"
        "CAST(#{clause} AS CHAR)"
      when "ActiveRecord::ConnectionAdapters::PostgreSQLAdapter"
        clause
      else
        clause
      end
    end
    
    def cast_to_datetime(clause)
      case @model.connection.class.name
      when "ActiveRecord::ConnectionAdapters::MysqlAdapter"
        "UNIX_TIMESTAMP(#{clause})"
      when "ActiveRecord::ConnectionAdapters::PostgreSQLAdapter"
        clause # Rails' datetimes are timestamps in PostgreSQL
      else
        clause
      end
    end
    
    def convert_nulls(clause)
      case @model.connection.class.name
      when "ActiveRecord::ConnectionAdapters::MysqlAdapter"
        "IFNULL(#{clause}, '')"
      when "ActiveRecord::ConnectionAdapters::PostgreSQLAdapter"
        "COALESCE(#{clause}, '')"
      else
        clause
      end
    end
    
    def quote_column(column)
      @model.connection.quote_column_name(column)
    end
    
    # Indication of whether the columns should be concatenated with a space
    # between each value. True if there's either multiple sources or multiple
    # associations.
    # 
    def concat_ws?
      multiple_associations? || @columns.length > 1
    end
    
    # Checks the association tree for each column - if they're all the same,
    # returns false.
    # 
    def multiple_sources?
      first = associations[@columns.first]
      
      !@columns.all? { |col| associations[col] == first }
    end
    
    # Checks whether any column requires multiple associations (which only
    # happens for polymorphic situations).
    # 
    def multiple_associations?
      associations.any? { |col,assocs| assocs.length > 1 }
    end
    
    # Builds a column reference tied to the appropriate associations. This
    # dives into the associations hash and their corresponding joins to
    # figure out how to correctly reference a column in SQL.
    # 
    def column_with_prefix(column)
      if column.is_string?
        column.__name
      elsif associations[column].empty?
        "#{@model.quoted_table_name}.#{quote_column(column.__name)}"
      else
        associations[column].collect { |assoc|
          "#{@model.connection.quote_table_name(assoc.join.aliased_table_name)}" + 
          ".#{quote_column(column.__name)}"
        }.join(', ')
      end
    end
    
    # Could there be more than one value related to the parent record? If so,
    # then this will return true. If not, false. It's that simple.
    # 
    def is_many?
      associations.values.flatten.any? { |assoc| assoc.is_many? }
    end
    
    # Returns true if any of the columns are string values, instead of database
    # column references.
    def is_string?
      columns.all? { |col| col.is_string? }
    end
    
    # Returns the type of the column. If that's not already set, it returns
    # :multi if there's the possibility of more than one value, :string if
    # there's more than one association, otherwise it figures out what the
    # actual column's datatype is and returns that.
    def type
      @type ||= case
      when is_many?
        :multi
      when @associations.values.flatten.length > 1
        :string
      else
        klass = @associations.values.flatten.first ? 
          @associations.values.flatten.first.reflection.klass : @model
        klass.columns.detect { |col|
          @columns.collect { |c| c.__name.to_s }.include? col.name
        }.type
      end
    end
    
    def all_ints?
      @columns.all? { |col|
        klasses = @associations[col].empty? ? [@model] :
          @associations[col].collect { |assoc| assoc.reflection.klass }
        klasses.all? { |klass|
          column = klass.columns.detect { |column| column.name == col.__name.to_s }
          !column.nil? && column.type == :integer
        }
      }
    end
  end
end