# A Metric is used to collect data about things
#
# The concept is reified here for a better organization and documentation
interface Metric

	# Type of elements measured by this metric.
	type ELM: Object

	# Type of values used to measure elements.
	type VAL: Object

	# Type of data representation used to associate elements and values.
	type RES: Map[ELM, VAL]

	# The name of this metric (generally an acronym about the metric).
	fun name: String is abstract

	# A long and understandable description about what is measured by this metric.
	fun desc: String is abstract

	# Clear all results for this metric
	fun clear is abstract

	# Values for each element
	fun values: RES is abstract

	# Collect metric values on elements
	fun collect(elements: Collection[ELM]) is abstract

	# The value calculated for the element
	fun [](element: ELM): VAL do return values[element]

	# Does the element have a value for this metric?
	fun has_element(element: ELM): Bool do return values.has_key(element)

	# The values average
	fun avg: Float is abstract

	# Pretty print the metric results in console
	fun to_console(indent: Int, colors: Bool) do
		if values.is_empty then
			if colors then
				print "{"\t" * indent}{name}: {desc} -- nothing".green
			else
				print "{"\t" * indent}{name}: {desc} -- nothing"
			end
			return
		end

		var max = self.max
		var min = self.min
		if colors then
			print "{"\t" * indent}{name}: {desc}".green
			print "{"\t" * indent}  avg: {avg}".light_gray
			print "{"\t" * indent}  max: {max} ({self[max]})".light_gray
			print "{"\t" * indent}  min: {min} ({self[min]})".light_gray
			print "{"\t" * indent}  std: {std_dev}".light_gray
		else
			print "{"\t" * indent}{name}: {desc}"
			print "{"\t" * indent}  avg: {avg}"
			print "{"\t" * indent}  max: {max} ({self[max]})"
			print "{"\t" * indent}  min: {min} ({self[min]})"
			print "{"\t" * indent}  std: {std_dev}"
		end
	end

	# The sum of all the values.
	fun sum: VAL is abstract

	# The values standard derivation
	fun std_dev: Float is abstract

	# The element with the highest value
	fun max: ELM is abstract

	# The element with the lowest value
	fun min: ELM is abstract

	# The value threshold above what elements are considered as 'interesting'
	fun threshold: Float do return avg + std_dev

	# The set of element above the threshold
	fun above_threshold: Set[ELM] is abstract

	# Sort the metric keys by values
	fun sort: Array[ELM] do
		return values.keys_sorted_by_values(default_reverse_comparator)
	end
end