Generate thumbnail generation tails after a bulk transaction

services/api/handlers/bulk.js

@@ -9,13 +9,13 @@ exports.post = function(request, reply) {
         return reply(Boom.wrap(err));
       }
 
-      request.server.methods.newrelic.createTracer(
-        'process cache invalidations',
-        request.server.methods.bulk.invalidateCaches
-      );
-      request.server.methods.bulk.invalidateCaches(request, results.map(function(result) {
+      var rawResults = results.map(function(result) {
         return result.raw;
-      }));
+      });
+
+      request.server.methods.bulk.invalidateCaches(request, rawResults);
+
+      request.server.methods.projects.processBulkThumbnailRequests(request, rawResults);
 
       reply({
         status: 'success',

services/api/handlers/elements.js

@@ -98,9 +98,8 @@ exports.patch = {
         }
 
         var thumbTail = request.tail('updating project thumbnail');
-        process.nextTick(function() {
-          request.server.methods.projects.checkPageId(request.pre.page, thumbTail);
-        });
+
+        request.server.methods.projects.checkPageId(request.pre.page, thumbTail);
 
         request.server.methods.cache.invalidateKey(
           'elements',

services/api/handlers/pages.js

@@ -118,9 +118,8 @@ exports.patch = {
 
         var page = request.server.methods.utils.formatPage(result.rows);
         var thumbTail = request.tail('updating project thumbnail');
-        process.nextTick(function() {
-          request.server.methods.projects.checkPageId(page, thumbTail);
-        });
+
+        request.server.methods.projects.checkPageId(page, thumbTail);
 
         request.server.methods.cache.invalidateKey(
           'pages',

services/api/lib/thumbnails.js

@@ -4,7 +4,18 @@ exports.register = function(server, options, done) {
   var qs = require('querystring');
   var request = require('request');
   var pageRenderUrl = process.env.PAGE_RENDER_URL;
-  var req;
+
+  var req = request.defaults({
+    baseUrl: process.env.THUMBNAIL_SERVICE_URL,
+    method: 'post',
+    json: true,
+    headers: {
+      accept: 'application/json'
+    },
+    body: {
+      wait: true
+    }
+  });
 
   function buildPageRenderUrl(user, project, page) {
     var urlObj = url.parse(pageRenderUrl);
@@ -69,48 +80,94 @@ exports.register = function(server, options, done) {
     });
   }
 
-  // Check if the given page has the lowest id in its parent project
-  // If it is, then request a new thumbnail
+  // Check if the given page has the lowest id of all pages in its parent project
+  // In most cases, this means the first page created when a project is created (situated at 0,0)
   function checkPageId(page, tail) {
-    if ( !process.env.THUMBNAIL_SERVICE_URL ) {
-      return tail();
-    }
-
-    server.methods.pages.min([
-      page.project_id
-    ], function(err, result) {
-      if ( err ) {
-        server.log('error', {
-          details: 'Error querying DB for lowest page ID in project: ' + page.project_id,
-          error: err
-        });
-        return tail(err);
-      }
-      var row = result.rows[0];
-
-      if ( row.page_id !== page.id ) {
-        server.debug('Thumbnail update not required');
+    process.nextTick(function() {
+      if ( !process.env.THUMBNAIL_SERVICE_URL ) {
         return tail();
       }
+      server.methods.pages.min([
+        page.project_id
+      ], function(err, result) {
+        if ( err ) {
+          server.log('error', {
+            details: 'Error querying DB for lowest page ID in project: ' + page.project_id,
+            error: err
+          });
+          return tail(err);
+        }
+
+        var row = result.rows[0];
+
+        if ( !row || row.page_id !== page.id ) {
+          server.debug('Thumbnail update not required');
+          return tail();
+        }
 
-      server.debug('Updating thumbnail for project');
-      generateThumbnail(row, tail);
+        server.debug('Updating thumbnail for project');
+        generateThumbnail(row, tail);
+      });
     });
   }
 
-  req = request.defaults({
-    baseUrl: process.env.THUMBNAIL_SERVICE_URL,
-    method: 'post',
-    json: true,
-    headers: {
-      accept: 'application/json'
-    },
-    body: {
-      wait: true
+  // project updates, and any kind of delete don't trigger thumbnail changes.
+  function filterRawResult(result) {
+    return result.type !== 'projects' && result.method !== 'remove';
+  }
+
+  // extract just the page_id and project_id from the result data
+  function transformResult(result) {
+    var rowData = result.rows[0];
+    var projectId = rowData.project_id;
+    var pageId = rowData.page_id || rowData.id;
+
+    return {
+      project_id: +projectId,
+      page_id: +pageId
+    };
+  }
+
+  // reduce the array of actions into an array of checks to perform, to determine if a thumbnail update is required
+  function reduceIntoUpdates(pendingChecks, result) {
+    var resultData;
+
+    // iterate over existing thumbnail updates for comparisons with current action
+    for (var i = 0; i < pendingChecks.length; i++) {
+      resultData = pendingChecks[i];
+      if (resultData.project_id !== result.project_id) {
+        continue;
+      }
+      if (result.page_id < resultData.page_id) {
+        break;
+      }
+      return pendingChecks;
     }
-  });
 
-  server.method('projects.checkPageId', checkPageId);
+    pendingChecks.push(result);
+    return pendingChecks;
+  }
+
+  // pass each resulting action into checkPageId, generating a request tail
+  // for each check (we don't want to block the request on these checks)
+  function checkAction(request, action) {
+    checkPageId(action, request.tail('updating project thumbnail'));
+  }
+
+  // We need only check if a thumbnail update is necessary for the lowest pageId in a given set of actions
+  function processBulkThumbnailRequests(request, rawResults) {
+    rawResults.filter(filterRawResult)
+    .map(transformResult)
+    .reduce(reduceIntoUpdates, [])
+    .forEach(checkAction.bind(this, request));
+  }
+
+  server.method('projects.checkPageId', checkPageId, {
+    callback: false
+  });
+  server.method('projects.processBulkThumbnailRequests', processBulkThumbnailRequests, {
+    callback: false
+  });
   done();
 };