JSONWildcard: A tiny singleton to generate JSON templates.

json_wildcard.rb

# frozen_string_literal: true

# A tiny singleton to generate JSON templates.
#
# === Example:
#
#   template = JSONWildcard["example" => Array.new(5, "%s")]
#   # => {"example":[%1$s,%2$s,%3$s,%4$s,%5$s]}
#
#   JSONWildcard.format(template, 1, 2, 3, 4, 5)
#   # => {"example":[1,2,3,4,5]}
class JSONWildcard
  PATTERN = %r(\"%(?:(\d+)\$)?([sdf])\").freeze
  private_constant :PATTERN

  # :call-seq:
  #   JSONWildcard.(serializable_hash) → String
  #   JSONWildcard[serializable_hash]  → String
  def self.call(hsh)
    matches, last_n = 0, nil

    hsh.to_json.gsub(PATTERN) do |s|
      match = Regexp.last_match
      matches += 1

      if match[1].present?
        last_n = match[1].to_i
      elsif last_n.nil?
        last_n = matches
      else
        last_n += 1
      end

      "%#{last_n}$#{match[2]}"
    end
  end

  singleton_class.alias_method :[], :call

  # :call-seq:
  #   JSONWildcard.format(template, *values[, serialize: true]) → String
  def self.format(json, *sources, serialize: true)
    sources.map!(&:to_json) if serialize
    sprintf(json, *sources)
  end
end