Flatten JSON to a two column CSV with defined separator and convert it back from CSV to JSON again. Useful for JSON I18n files amongst other things.

json_csv_converter.rb

#!/usr/bin/env ruby

USAGE = <<~DOC
USAGE:
    ruby json_csv_converter.rb <in_file> <separator(optional)>

EXAMPLES:
    Convert JSON to CSV
    $ ruby json_csv_converter.rb file.json

    Convert CSV to JSON with / as level separator
    $ ruby json_csv_converter.rb file.csv /
DOC

module Enumerable
  def flatten_with_path(separator, parent_prefix = nil)
    res = {}

    self.each_with_index do |elem, i|
      if elem.is_a?(Array)
        k, v = elem
      else
        k, v = i, elem
      end

      key = parent_prefix ? "#{parent_prefix}#{separator}#{k}" : k # assign key name for result hash

      if v.is_a? Enumerable
        res.merge!(v.flatten_with_path(separator, key)) # recursive call to flatten child elements
      else
        res[key] = v
      end
    end

    res
  end
end

# set nested hash values
def dig_set(hash, keys, value)
  key = keys.first
  if keys.length == 1
    hash[key] = value
  else
    hash[key] = {} unless hash[key]
    dig_set(hash[key], keys.slice(1..-1), value)
  end
end

def die(*args)
  puts USAGE
  puts
  raise *args
end

def json_to_csv(path, separator)
  json = JSON.parse(File.read(path))
  csv_string = CSV.generate do |csv|
    json.flatten_with_path(separator).each { |k, v| csv << [k, v] }
  end

  puts csv_string
end

def csv_to_json(path, separator)
  csv = CSV.read(path)
  hash = {}

  csv.each do |key, value|
    next if key.nil?
    dig_set(hash, key.split(separator), value)
  end

  JSON.pretty_generate(hash)
end

# main
require 'json'
require 'csv'

path = ARGV[0] or die 'missing file argument'
separator = ARGV[1] || '.'
filetype = path.split('.').last

if filetype == 'csv'
  puts csv_to_json(path, separator)
elsif filetype == 'json'
  puts json_to_csv(path, separator)
else
  die "unknown format #{filetype}, must be .csv or .json!"
end