to_json.cr

class Object
  def to_json
    String.build do |str|
      to_json str
    end
  end

  def to_json(io : IO)
    JSON.build(io) do |json|
      to_json(json)
    end
  end

  def to_pretty_json(indent : String = "  ")
    String.build do |str|
      to_pretty_json str, indent: indent
    end
  end

  def to_pretty_json(io : IO, indent : String = "  ")
    JSON.build(io, indent: indent) do |json|
      to_json(json)
    end
  end
end

struct Nil
  def to_json(json : JSON::Builder)
    json.null
  end
end

struct Bool
  def to_json(json : JSON::Builder)
    json.bool(self)
  end
end

struct Int
  def to_json(json : JSON::Builder)
    json.number(self)
  end
end

struct Float
  def to_json(json : JSON::Builder)
    json.number(self)
  end
end

class String
  def to_json(json : JSON::Builder)
    json.string(self)
  end
end

struct Symbol
  def to_json(json : JSON::Builder)
    json.string(to_s)
  end
end

class Array
  def to_json(json : JSON::Builder)
    json.array do
      each &.to_json(json)
    end
  end
end

struct Set
  def to_json(json : JSON::Builder)
    json.array do
      each &.to_json(json)
    end
  end
end

class Hash
  def to_json(json : JSON::Builder)
    json.object do
      each do |key, value|
        json.field key do
          value.to_json(json)
        end
      end
    end
  end
end

struct Tuple
  def to_json(json : JSON::Builder)
    json.array do
      {% for i in 0...T.size %}
        self[{{i}}].to_json(json)
      {% end %}
    end
  end
end

struct NamedTuple
  def to_json(json : JSON::Builder)
    json.object do
      {% for key in T.keys %}
        json.field {{key.stringify}} do
          self[{{key.symbolize}}].to_json(json)
        end
      {% end %}
    end
  end
end

struct Time::Format
  def to_json(value : Time, json : JSON::Builder)
    format(value).to_json(json)
  end
end

struct Enum
  def to_json(json : JSON::Builder)
    json.number(value)
  end
end

struct Time
  # Emits a string formated according to [RFC 3339](https://tools.ietf.org/html/rfc3339)
  # ([ISO 8601](http://xml.coverpages.org/ISO-FDIS-8601.pdf) profile).
  #
  # The JSON format itself does not specify a time data type, this method just
  # assumes that a string holding a RFC 3339 time format will be interpreted as
  # a time value.
  #
  # See `#from_json` for reference.
  def to_json(json : JSON::Builder)
    json.string(Time::Format::RFC_3339.format(self, fraction_digits: 0))
  end
end

# Converter to be used with `JSON.mapping` and `YAML.mapping`
# to serialize a `Time` instance as the number of seconds
# since the unix epoch. See `Time#to_unix`.
#
# ```
# require "json"
#
# class Person
#   JSON.mapping({
#     birth_date: {type: Time, converter: Time::EpochConverter},
#   })
# end
#
# person = Person.from_json(%({"birth_date": 1459859781}))
# person.birth_date # => 2016-04-05 12:36:21 UTC
# person.to_json    # => %({"birth_date":1459859781})
# ```
module Time::EpochConverter
  def self.to_json(value : Time, json : JSON::Builder)
    json.number(value.to_unix)
  end
end

# Converter to be used with `JSON.mapping` and `YAML.mapping`
# to serialize a `Time` instance as the number of milliseconds
# since the unix epoch. See `Time#to_unix_ms`.
#
# ```
# require "json"
#
# class Timestamp
#   JSON.mapping({
#     value: {type: Time, converter: Time::EpochMillisConverter},
#   })
# end
#
# timestamp = Timestamp.from_json(%({"value": 1459860483856}))
# timestamp.value   # => 2016-04-05 12:48:03.856 UTC
# timestamp.to_json # => %({"value":1459860483856})
# ```
module Time::EpochMillisConverter
  def self.to_json(value : Time, json : JSON::Builder)
    json.number(value.to_unix_ms)
  end
end

# Converter to be used with `JSON.mapping` to read the raw
# value of a JSON object property as a `String`.
#
# It can be useful to read ints and floats without losing precision,
# or to read an object and deserialize it later based on some
# condition.
#
# ```
# require "json"
#
# class Raw
#   JSON.mapping({
#     value: {type: String, converter: String::RawConverter},
#   })
# end
#
# raw = Raw.from_json(%({"value": 123456789876543212345678987654321}))
# raw.value   # => "123456789876543212345678987654321"
# raw.to_json # => %({"value":123456789876543212345678987654321})
# ```
module String::RawConverter
  def self.to_json(value : String, json : JSON::Builder)
    json.raw(value)
  end
end