# Serializer of Nit objects to Json string.
class JsonSerializer
	super CachingSerializer

	# Target writing stream
	var stream: Writer

	# Write plain JSON? Standard JSON without metadata for deserialization
	#
	# If `false`, the default, serialize to support deserialization:
	#
	# * Write metadata, including the types of the serialized objects so they can
	#   be deserialized to their original form using `JsonDeserializer`.
	# * Use references when an object has already been serialized so to not duplicate it.
	# * Support cycles in references.
	# * Preserve the Nit `Char` and `Byte` types as special objects.
	# * The generated JSON is standard and can be read by non-Nit programs.
	#   However, some Nit types are not represented by the simplest possible JSON representation.
	#   With the added metadata, it can be complex to read.
	#
	# If `true`, serialize for other programs:
	#
	# * Nit objects are serialized to pure and standard JSON so they can
	#   be easily read by non-Nit programs and humans.
	# * Nit objects are serialized for every references, so they can be duplicated.
	#   It is easier to read but it creates a larger output.
	# * Does not support cycles, will replace the problematic references by `null`.
	# * Does not serialize the metadata needed to deserialize the objects
	#   back to regular Nit objects.
	# * Keys of Nit `HashMap` are converted to their string representation using `to_s`.
	var plain_json = false is writable

	# Write pretty JSON for human eyes?
	#
	# Toggles skipping lines between attributes of an object and
	# properly indent the written JSON.
	var pretty_json = false is writable

	# Current indentation level used for writing `pretty_json`
	private var indent_level = 0

	# List of the current open objects, the first is the main target of the serialization
	#
	# Used only when `plain_json == true` to detect cycles in serialization.
	private var open_objects = new Array[Object]

	# Has the first attribute of the current object already been serialized?
	#
	# Used only when `plain_json == true`.
	private var first_attribute = false

	redef var current_object = null

	redef fun serialize(object)
	do
		if object == null then
			stream.write "null"
		else
			if plain_json then
				for o in open_objects do
					if object.is_same_serialized(o) then
						# Cycle, can't be managed in plain json
						warn "Cycle detected in serialized object, replacing reference with 'null'."
						stream.write "null"
						return
					end
				end

				open_objects.add object
			end

			first_attribute = true
			var last_object = current_object
			current_object = object
			object.accept_json_serializer self
			first_attribute = false
			current_object = last_object

			if plain_json then open_objects.pop
		end
	end

	redef fun serialize_attribute(name, value)
	do
		if not plain_json or not first_attribute then
			stream.write ","
		end
		first_attribute = false

		new_line_and_indent
		stream.write "\""
		stream.write name
		stream.write "\":"
		if pretty_json then stream.write " "
		super
	end

	redef fun serialize_reference(object)
	do
		if not plain_json and cache.has_object(object) then
			# if already serialized, add local reference
			var id = cache.id_for(object)
			stream.write "\{"
			indent_level += 1
			new_line_and_indent
			stream.write "\"__kind\": \"ref\", \"__id\": "
			stream.write id.to_s
			indent_level -= 1
			new_line_and_indent
			stream.write "\}"
		else
			# serialize here
			serialize object
		end
	end

	# Write a new line and indent it, only if `pretty_json`
	private fun new_line_and_indent
	do
		if pretty_json then
			stream.write "\n"
			for i in indent_level.times do stream.write "\t"
		end
	end
end