# Adapted from StackOverflow answers:
# http://stackoverflow.com/a/8477067/1319740
# and
# http://stackoverflow.com/a/18113090/1319740
# With help from:
# http://technicalpickles.com/posts/parsing-csv-with-ruby/

# A small rake task that validates that all required headers are present in a csv
# then converts the csv to an array of hashes with column headers as keys mapped 
# to relevant row values. 
#
# The data can then be passed wherever it is needed. 

namespace :csv do
  desc 'take a csv file and transform it into an array of hashes with headers as keys'
  task :to_hash, [:csv_file_path] => :environment do |task, args|
    unless args.csv_file_path.present?
      ($stderr.puts "ERROR: Please include file path -- Usage: rake csv:to_hash[path/to/csv/file]" && return) 
    end
    
    # Check the csv to make sure all required headers are present before reading whole file
    required_headers = %i(id) # Add any required csv headers here
    headers = CSV.open(args.csv_file_path, 'r', :headers => true, :header_converters => :symbol) do |csv| 
      csv.first.headers
    end
    
    if (required_headers - headers).any?
      %stderr.puts "ERROR: Please include #{required_headers} headers in your csv file" && return
    end
    
    # Now we read and transform file
    
    # First set up any custom converters -- This one turns blank row values to nils
    CSV::Converters[:blank_to_nil] = lambda do |field|
      field && field.empty? ? nil : field
    end
    
    # Then we create and populate our array
    attrs = []
    
    CSV.foreach(args.csv_file_path, :headers => true, :header_converters => :symbol, :converters => [:all, :blank_to_nil]) do |row|
      attrs << Hash[row.headers.zip(row.fields)]
    end
    
    # You can now pass the attrs array wherever you need -- for example a background job 
    # that creates/validates/saves model objects
    attrs
  end
end