Add /summary endpoint

Add an endpoint that returns clone totals and average clone time for
the given time spans. The time spans are determined by the query
parameters "from" and "to", with the resulting range being inclusive of
both. If you want a single day, it should be both the "from" and the
"to" value.

lib/vmpooler/api.rb

@@ -31,6 +31,10 @@ module Vmpooler
 
             hostname
           end
+
+          def validate_date_str(date_str)
+            /^\d{4}-\d{2}-\d{2}$/ === date_str
+          end
         end
 
         get '/' do
@@ -207,6 +211,74 @@ module Vmpooler
           JSON.pretty_generate(Hash[result.sort_by { |k, _v| k }])
         end
 
+        get '/summary/?' do
+          result = {
+              clone_total: 0,
+              clone_average: 0,
+              daily: []   # used for daily info
+          }
+
+          from_param, to_param = params[:from], params[:to]
+
+          # Check date formats.
+          # It is ok if to_param is nil, we will assume this means 'today'
+          if to_param.nil?
+            to_param = Date.today.to_s
+          elsif !validate_date_str(to_param.to_s)
+            halt 400, 'Invalid "to" date format, must match YYYY-MM-DD'
+          end
+
+          # We do need a from date, however.
+          if from_param.nil? or !validate_date_str(from_param.to_s)
+          halt 400, 'Invalid "from" date format, must match YYYY-MM-DD'
+          end
+
+          from_date, to_date = Date.parse(from_param), Date.parse(to_param)
+
+          if to_date < from_date
+            halt 400, 'Date range is invalid, "to" cannot come before "from".'
+          elsif from_date > Date.today
+            halt 400, 'Date range is invalid, "from" must be in the past.'
+          end
+
+          # total clone time for entire duration requested.
+          total_clone_time = 0
+
+          # generate sequence/range for from_date to to_date (inclusive).
+          # for each date, calculate the day's clone total & average, as well
+          # as add to total/overall values.
+          (from_date..to_date).each do |date|
+            me = {
+                day: date.to_s,
+                clone_total: $redis.hlen('vmpooler__clone__' + date.to_s),
+                clone_average: 0
+            }
+            result[:clone_total] += me[:clone_total]
+
+            clone_time = $redis.hvals('vmpooler__clone__' + date.to_s).map(&:to_f).reduce(:+)
+            total_clone_time += clone_time.to_f
+
+            # if clone_total > 0, calculate clone_average.
+            # this prevents divide by 0 problems.
+            if me[:clone_total] > 0
+              me[:clone_average] = clone_time / me[:clone_total]
+            else
+              me[:clone_average] = 0
+            end
+
+            # add to daily array
+            result[:daily].push(me)
+          end
+
+          # again, calc clone_average if we had clones.
+          if result[:clone_total] > 0
+            result[:clone_average] = total_clone_time / result[:clone_total]
+          end
+
+          content_type :json
+          JSON.pretty_generate(result)
+        end
+
         get '/vm/?' do
           content_type :json