Extracting an array of similar hash objects from a JSON file into a csv, following some very basic assumptions.

jsoncsv.rb

#!/usr/bin/env ruby
# frozen_string_literal: true

require "json"
require "csv"
require "optionparser"

#
# Option Handling
#
@options = {}
options = ARGV.options do |opts|
  opts.banner = "Usage: jsoncsv -i /path/to/input.json -o /path/to/output.csv"

  opts.accept(JSON) do |json|
    JSON.parse(File.read(json))
  rescue JSON::ParserError => e
    raise OptionParser::InvalidArgument, e.message
  end

  opts.on '-i', '--input [JSONFILE]', JSON, 'Input JSON filepath'
  opts.on '-o', '--output [CSVFILE]', String, 'Output CSV filepath'
end.freeze
options.permute! into: @options
raise ArgumentError, "provide an input json file: \n#{options.banner}" unless @options[:input]

#
# Processing & Checking
#

def csvable_array?(candidate_array)
  return false unless candidate_array.is_a?(Array)
  return candidate_array.map { |a| a.keys rescue nil }.tally.values.max > 2
end

# Output to CSV
def output_csv(json_array, dest = @options[:output])
  # Get all potential keys
  keys = json_array.flat_map(&:keys).uniq
  # Write the csv
  out = dest ? File.open(dest, "w+") : $stdout.dup
  CSV(out) do |csv|
    csv << keys
    json_array.each do |json_hash|
      csv << keys.map { |k| json_hash[k] }
    end
  end
  out.close
  exit
end

# Check root
output_csv(@options[:input]) if csvable_array?(@options[:input])

# Check first children
# FEATURE: Make this step through all children to handle more json files.
@options[:input].each_value do |v|
  next unless v.is_a?(Array)
  output_csv(v) if csvable_array?(v)
end