1 files changed, 54 insertions, 0 deletions
diff --git a/activesupport/lib/active_support/duration/iso8601_serializer.rb b/activesupport/lib/active_support/duration/iso8601_serializer.rb
new file mode 100644
index 0000000000..1125454919
--- /dev/null
+++ b/activesupport/lib/active_support/duration/iso8601_serializer.rb
@@ -0,0 +1,54 @@
+# frozen_string_literal: true
+
+require "active_support/core_ext/object/blank"
+
+module ActiveSupport
+  class Duration
+    # Serializes duration to string according to ISO 8601 Duration format.
+    class ISO8601Serializer # :nodoc:
+      def initialize(duration, precision: nil)
+        @duration = duration
+        @precision = precision
+      end
+
+      # Builds and returns output string.
+      def serialize
+        parts, sign = normalize
+        return "PT0S" if parts.empty?
+
+        output = +"P"
+        output << "#{parts[:years]}Y"   if parts.key?(:years)
+        output << "#{parts[:months]}M"  if parts.key?(:months)
+        output << "#{parts[:weeks]}W"   if parts.key?(:weeks)
+        output << "#{parts[:days]}D"    if parts.key?(:days)
+        time = +""
+        time << "#{parts[:hours]}H"     if parts.key?(:hours)
+        time << "#{parts[:minutes]}M"   if parts.key?(:minutes)
+        if parts.key?(:seconds)
+          time << "#{sprintf(@precision ? "%0.0#{@precision}f" : '%g', parts[:seconds])}S"
+        end
+        output << "T#{time}" unless time.empty?
+        "#{sign}#{output}"
+      end
+
+      private
+
+        # Return pair of duration's parts and whole duration sign.
+        # Parts are summarized (as they can become repetitive due to addition, etc).
+        # Zero parts are removed as not significant.
+        # If all parts are negative it will negate all of them and return minus as a sign.
+        def normalize
+          parts = @duration.parts.each_with_object(Hash.new(0)) do |(k, v), p|
+            p[k] += v  unless v.zero?
+          end
+          # If all parts are negative - let's make a negative duration
+          sign = ""
+          if parts.values.all? { |v| v < 0 }
+            sign = "-"
+            parts.transform_values!(&:-@)
+          end
+          [parts, sign]
+        end
+    end
+  end
+end