#ruby-201909301511.rb

require 'yaml'

prefixes = { 'tel' => 'Tel.: ', 'fax' => 'Fax: ', 'email' => 'E-Mail: ', 'website' => 'Website: ' }
regexes = prefixes.transform_values { |prefix| /\A#{Regexp.escape(prefix)}/ }
contacts = []

File.open('/path/to/data.txt') do |data| 
  # If a zero-length record separator is supplied, the string is split
  # into paragraphs delimited by multiple successive newlines.
  # https://ruby-doc.org/core-2.6.4/String.html#method-i-each_line
  data.each_line('') do |contact_text|
    # split the paragraph into lines, chomp the newline character at the end and remove empty values
    contact_lines = contact_text.each_line("\n", chomp: true).reject(&:empty?)
    contact = { 'name' => contact_lines.shift, 'address' => contact_lines.shift }
    
    regexes.each do |key, regex|
      index = contact_lines.find_index(&regex.method(:match?))
      contact[key] = (contact_lines.delete_at(index).sub(regex, '') if index)
    end
    
    contacts << contact
  end
end

File.open('/path/to/data.yaml', 'w+') { |file| file.write(contacts.to_yaml) }