Add ability to listen for events on multi bar

lib/tty/progressbar/multi.rb

@@ -51,6 +51,12 @@ def initialize(*args)
         @rows = 0
         @top_bar = nil
         @top_bar = register(format) if format
+
+        @callbacks = {
+          progress: [],
+          stopped:  [],
+          done:     []
+        }
       end
 
       # Register a new progress bar
@@ -91,7 +97,9 @@ def next_row
       #
       # @api public
       def observe(bar)
-        bar.on(:progress) { top_bar.current = current }
+        bar.on(:progress) { top_bar.current = current; emit(:progress) }
+           .on(:done)     { top_bar.finish; emit(:done) if complete?  }
+           .on(:stopped)  { top_bar.stop; emit(:stopped) if stopped? }
       end
 
       # Get the top level bar if it exists
@@ -136,6 +144,15 @@ def complete?
         (@bars - [@top_bar]).dup.all?(&:complete?)
       end
 
+      # Check if any of the registered progress bars is stopped
+      #
+      # @return [Boolean]
+      #
+      # @api public
+      def stopped?
+        (@bars - [@top_bar]).dup.any?(&:stopped?)
+      end
+
       # Stop all progress bars
       #
       # @api public
@@ -147,6 +164,7 @@ def stop
       #
       # @api public
       def finish
+        @top_bar.finish if @top_bar
         @bars.dup.each(&:finish)
       end
 
@@ -172,6 +190,32 @@ def line_inset(bar)
           @inset_opts[:middle]
         end
       end
+
+      # Listen on event
+      #
+      # @param [Symbol] name
+      #   the event name to listen on
+      #
+      # @api public
+      def on(name, &callback)
+        unless @callbacks.key?(name)
+          raise ArgumentError, "The event #{name} does not exist. "\
+                               " Use :progress, :stopped, or :done instead"
+        end
+        @callbacks[name] << callback
+        self
+      end
+
+      private
+
+      # Fire an event by name
+      #
+      # @api private
+      def emit(name, *args)
+        @callbacks[name].each do |callback|
+          callback.(*args)
+        end
+      end
     end # Multi
   end # ProgressBar
 end # TTY

spec/unit/multi/events_spec.rb

@@ -0,0 +1,64 @@
+# encoding: utf-8
+
+RSpec.describe TTY::ProgressBar::Multi, 'events' do
+  let(:output) { StringIO.new('', 'w+') }
+
+  it "emits :progress eent when any of the registerd bars advances" do
+    events = []
+    bars = TTY::ProgressBar::Multi.new("[:bar]", output: output, total: 5)
+    bars.on(:progress) { events << :progress }
+
+    bar = bars.register "one [:bar]"
+    bar.advance
+
+    expect(events).to eq([:progress])
+  end
+
+  it "emits :done event when all progress bars finished" do
+    events = []
+    bars = TTY::ProgressBar::Multi.new("[:bar]", output: output, total: 5)
+    bars.on(:done) { events << :done }
+
+    bar = bars.register "one [:bar]"
+
+    bar.finish
+
+    expect(events).to eq([:done])
+  end
+
+  it "emits :done event when top level bar finished" do
+    events = []
+    bars = TTY::ProgressBar::Multi.new("[:bar]", output: output, total: 5)
+    bars.on(:done) { events << :done }
+
+    bars.register "one [:bar]"
+
+    bars.finish
+
+    expect(events).to eq([:done])
+  end
+
+  it "emits :stopped event when all registerd bars are stopped" do
+    events = []
+    bars = TTY::ProgressBar::Multi.new("[:bar]", output: output, total: 5)
+    bars.on(:stopped) { events << :stopped }
+
+    bar = bars.register "one [:bar]"
+
+    bar.stop
+
+    expect(events).to eq([:stopped])
+  end
+
+  it "emits :stopped event when top level bar finished" do
+    events = []
+    bars = TTY::ProgressBar::Multi.new("[:bar]", output: output, total: 5)
+    bars.on(:stopped) { events << :stopped }
+
+    bars.register "one [:bar]"
+
+    bars.stop
+
+    expect(events).to eq([:stopped])
+  end
+end