Metacat

# Copyright: 2006 Regents of the University of California,

# Santa Barbara Coastal LTER

# http://sbcdata.lternet.edu/

#

# This program is free software; you can redistribute it and/or modify

# it under the terms of the GNU General Public License as published by

# the Free Software Foundation; either version 2 of the License, or

# (at your option) any later version.

# 

# This program is distributed in the hope that it will be useful,

# but WITHOUT ANY WARRANTY; without even the implied warranty of

# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

# GNU General Public License for more details.

# 

# You should have received a copy of the GNU General Public License

# along with this program; if not, write to the Free Software

# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA

# 02111-1307  USA

$:.unshift File.join(File.dirname(__FILE__), "..", "lib")

require "eml.rb"

# ==  What is it

# Each EML document can contain DataTable elements representing(in most cases) plain

# text data. The attributes of this data, such as column names, types, domain info,

# are documented in the eml metadata. DataTable encapsulates data table elements from

# eml documents in the instance variable @metadata.

# 

# The purpose of this class is to provide methods to easily access metadata attributes

# pertaining to the data table. It can also be extended for specific

# applications to process the data based on the metadata description.

# == Examples

# === Get the location where this data file is stored

#   eml = metacat.find(:docid => 'somedoc.1.1')

#   data_table = eml.data_tables[0]

#   data_table.location

#   => ecogrid://knb/pisco_cbs.30.3

# === Write the data file to disk

#   # note we are using a block so the whole file isn't loaded to RAM

#   file = File.new("./tmp/#{data_table.id}")

#   data_table.read do |buffer|

#     file.write(buffer)

#   end

#   file.close 

class DataTable

  attr_reader :metadata, :eml

  def initialize(data_table_element, eml)

    @metadata = data_table_element

    @eml = eml

  end

  # Methods for accessing eml metadata

  # ----------------------------------

  # pulls the docid from distribution element

  def docid

    @docid ||= location.reverse.match('[^/]+')[0].reverse

  end

  # refers to the docid function

  def id

    docid

  end

  # attribute reader for online distribution

  def location

    @location ||= @metadata.elements['physical/distribution/online/url'].text

  end

  def physical

    @metadata.elements['physical']

  end

  # only supports unit bytes

  def size

    physical.elements['size'].text.to_i

  end

  def data_format

    physical.elements['dataFormat'].elements[1].name

  end

  def field_delimiter

    text_format.elements[]

  end

  def text_format

    physical.elements['dataFormat/textFormat']

  end

  def simple_delimited

    if text_format

      text_format.elements['simpleDelimited']

    else

      raise "data table is not in textFormat"

    end

  end

  def num_headers

    if text_format

      text_format.elements['numHeaderLines'].text.to_i      

    else

      raise "data table is not in textFormat"

    end

  end

  def record_delimiter

    if text_format

      text_format.elements['recordDelimiter'].text      

    else

      raise "data table is not in textFormat"

    end

  end

  def field_delimiter

    if simple_delimited

      simple_delimited.elements['fieldDelimiter'].text      

    else

      raise "data table is not in simpleDelimited format"

    end

  end

  def columns

    cols = Array.new

    @metadata.elements.each('attributeList/attribute') do |col|

      cols.push col

    end

    return cols

  end

  def entity_name

    @metadata.elements['entityName'].text

  end

  # ---------------------------

  # End Metadata Access Methods

  # reads the dataTable text from the url or docid specified

  # by the physical/distribution/online/url entity

  def read

    if(location =~ /ecogrid/)

      #we need to pull out the docid and do a read on metacat

      #get self.location, and pull out the string after the last "/"

      uri = URI.parse(PATH_TO_METACAT)

      uri.query = "action=read&qformat=xml&docid=#{docid}"

      # Use Net:HTTP first to get the content_type

      http = Net::HTTP.start(uri.host, uri.port)

      http.request_get(uri.to_s) do |response|

        if(response.content_type == 'text/xml')

          # error message

          doc = REXML::Document.new(response.read_body)

          if(doc.root.name == 'error')

            raise doc.root.text

          else

            raise "Unrecognized response from metacat at #{PATH_TO_METACAT}"

          end

        elsif(response.content_type == 'text/plain')

          response.read_body do |f|

            yield f

          end

        else

          raise "Unrecognized content type \"#{response.content_type}\" " +

                "from metacat at #{PATH_TO_METACAT}"

        end

      end

    elsif(location =~ /http/)

      uri = URI.parse(location)

      http = Net::HTTP.start(uri.host, uri.port)

      http.request_get(uri.to_s) do |response|

        response.read_body do |f|

          yield f

        end

      end

    else

      raise 'Unknown location for dataTable'

    end

  end 

end