require 'smilodon/errors'
require 'smilodon/logger'

# Smilodon includes helper methods to ease parsing data files.
# Assigning a header and iterating over rows is handled by the
# module via a simple configuration.
# 
# @example
#   Define a module and extend it with the populator module.
#
# @example A Custom Populator.
#   module CustomPopulator
#     extend Populator
#     populates 'CustomFile'
#
#     def process(row)
#       ...
#     end
#   end
#
# @note As noted in the example the extended module defines the
#   logic to process a single row.

module Smilodon
  module Populator

    # Default directory location for data files.
    DIRECTORY = 'files'

    # Default data file type is CSV.
    TYPE = 'csv'

    # Attribute accessors for the directory, file name, header, count, rows and before hook.
    attr_accessor :logger, :directory, :file, :type, :header, :count, :rows, :before

    # Configuration helper.
    #
    # @param [String] file The data file name.
    # @option options [String] :directory ('db/populate/data_files') The location of the data file.
    # @option options [String] :type ('csv') The data file type.
    # @option options [Boolean] :header Set true if the file has a header.
    # @option options [String] :before The method to call before the run.
    def populates(file, options = {})
      # Setup the logger to log populator warnings and messages.
      self.logger = PopulateLogger.setup

      self.directory = options[:directory] || DIRECTORY
      self.file = file
      self.type = options[:type] || TYPE
      self.header = options[:header]
      self.before = options[:before]
    end

    # Parses the data file content and processes each row.
    #
    # @return [Boolean] Returns true if all rows are processed successfully.
    def run

      # Call the before hook if defined.
      #
      # @usage
      #   populates 'TestFile', :before => :inactivate
      send(before) if before

      rows = parser.parse(read)
      self.count = header ? rows.count - 1 : rows.count
      self.header = rows.shift if header
      count.times { process(rows.shift) }

      # Return true when all rows are processed.
      return true
    end

    # Stub method to be defined in the extended module.
    # 
    # @raise [Exception] Raises an exception if the extended module does not override the method.
    def process(row = nil)
      raise MethodNotOverridden
    end

    private
    
    # The parser to use based on the type of data file.
    #
    # @return [Parser, #parse] Returns the parser class to use.
    def parser
      if type == 'csv'
        require 'csv'
        return CSV::Reader
      end
    end

    # Absolute path for the data file.
    # 
    # @return [String] The absolute path.
    def path
      "#{Rails.root}/#{directory}/#{file}.#{type}"
    end

    # Reads the data file.
    #
    # @return [File] The data file contents.
    # @raise [DataFileNotConfigured] Raises an exception when the file is not configured.
    # @raise [MissingDataFile] Raises an exception when the configured file is missing.
    def read
      raise DataFileNotConfigured unless file
      raise MissingDataFile unless File.exist?(path)
      File.read path
    end
  end
end