(DIO-2675) Undo pool size template overrides

This implements a delete method for pooltemplate and poolsize. The API
removes the override from Redis and then adds an entry in Redis that
causes the pool manager to wake up and process the removal of the
override.

To facilitate this, a new variable has been created in lib/vmpooler.rb
to hold a copy of the original / pre-override config. This supplemental
copy of the pools is then indexed for use as a reference.

When pool manager wakes up to process an override removal, it looks up
the pre-override value from the config via the new variables mentioned
above.

Just as with entering overrides, no restart is needed. Template and pool
size changes are logged so that anyone watching or reviewing the logs
can see what happened when. The new API endpoints also return values for
both the pre-revert and post-revert value.

lib/vmpooler/api/v1.rb

@@ -28,6 +28,10 @@ module Vmpooler
       Vmpooler::API.settings.config[:pools]
     end
 
+    def pools_at_startup
+      Vmpooler::API.settings.config[:pools_at_startup]
+    end
+
     def pool_exists?(template)
       Vmpooler::API.settings.config[:pool_names].include?(template)
     end
@@ -289,6 +293,32 @@ module Vmpooler
       puts 'd', "[!] [#{poolname}] failed while evaluating usage labels on '#{vmname}' with an error: #{e}"
     end
 
+    def reset_pool_size(poolname)
+      result = { 'ok' => false }
+
+      pool_index = pool_index(pools)
+
+      pools_updated = 0
+      sync_pool_sizes
+
+      pool_size_now = pools[pool_index[poolname]]['size'].to_i
+      pool_size_original = pools_at_startup[pool_index[poolname]]['size'].to_i
+      result['pool_size_before_reset'] = pool_size_now
+      result['pool_size_before_overrides'] = pool_size_original
+
+      unless pool_size_now == pool_size_original
+        pools[pool_index[poolname]]['size'] = pool_size_original
+        backend.hdel('vmpooler__config__poolsize', poolname)
+        backend.sadd('vmpooler__pool__undo_size_override', poolname)
+        pools_updated += 1
+        status 201
+      end
+
+      status 200 unless pools_updated > 0
+      result['ok'] = true
+      result
+    end
+
     def update_pool_size(payload)
       result = { 'ok' => false }
 
@@ -309,6 +339,33 @@ module Vmpooler
       result
     end
 
+    def reset_pool_template(poolname)
+      result = { 'ok' => false }
+
+      pool_index_live = pool_index(pools)
+      pool_index_original = pool_index(pools_at_startup)
+
+      pools_updated = 0
+      sync_pool_templates
+
+      template_now = pools[pool_index_live[poolname]]['template']
+      template_original = pools_at_startup[pool_index_original[poolname]]['template']
+      result['template_before_reset'] = template_now
+      result['template_before_overrides'] = template_original
+
+      unless template_now == template_original
+        pools[pool_index_live[poolname]]['template'] = template_original
+        backend.hdel('vmpooler__config__template', poolname)
+        backend.sadd('vmpooler__pool__undo_template_override', poolname)
+        pools_updated += 1
+        status 201
+      end
+
+      status 200 unless pools_updated > 0
+      result['ok'] = true
+      result
+    end
+
     def update_pool_template(payload)
       result = { 'ok' => false }
 
@@ -1375,6 +1432,26 @@ module Vmpooler
       JSON.pretty_generate(result)
     end
 
+    delete "#{api_prefix}/config/poolsize/:pool/?" do
+      content_type :json
+      result = { 'ok' => false }
+
+      if config['experimental_features']
+        need_token! if Vmpooler::API.settings.config[:auth]
+
+        if pool_exists?(params[:pool])
+          result = reset_pool_size(params[:pool])
+        else
+          metrics.increment('config.invalid.unknown')
+          status 404
+        end
+      else
+        status 405
+      end
+
+      JSON.pretty_generate(result)
+    end
+
     post "#{api_prefix}/config/poolsize/?" do
       content_type :json
       result = { 'ok' => false }
@@ -1406,6 +1483,26 @@ module Vmpooler
       JSON.pretty_generate(result)
     end
 
+    delete "#{api_prefix}/config/pooltemplate/:pool/?" do
+      content_type :json
+      result = { 'ok' => false }
+
+      if config['experimental_features']
+        need_token! if Vmpooler::API.settings.config[:auth]
+
+        if pool_exists?(params[:pool])
+          result = reset_pool_template(params[:pool])
+        else
+          metrics.increment('config.invalid.unknown')
+          status 404
+        end
+      else
+        status 405
+      end
+
+      JSON.pretty_generate(result)
+    end
+
     post "#{api_prefix}/config/pooltemplate/?" do
       content_type :json
       result = { 'ok' => false }