fixing Issue19

package.json

@@ -29,6 +29,7 @@
     "canonical-json": "0.0.4",
     "chai": "^3.4.0",
     "coffeeify": "^1.1.0",
+    "coffee-script": "^1.7.1",
     "gulp": "git://github.com/gulpjs/gulp.git#4.0",
     "gulp-coffee": "^2.3.1",
     "gulp-concat": "^2.6.0",

src/DataSource.coffee

@@ -3,20 +3,6 @@ async = require 'async'
 
 # Fetches data for queries
 module.exports = class DataSource
-  # Gets the data for a lookup of queries
-  # e.g. { a: <some jsonql>, b: <some jsonql> }
-  # Calls cb with (null, { a: <rows for a query>, b: <rows for b query> }
-  # or (error) if there was an error
-  performQueries: (queries, cb) ->
-    async.map _.pairs(queries), (item, callback) =>
-      @performQuery(item[1], (err, rows) =>
-        callback(err, [item[0], rows])
-        )
-    , (err, items) =>
-      if err
-        return cb(err)
-      else
-        cb(null, _.object(items))
 
   # Performs a single query. Calls cb with rows
   performQuery: (query, cb) ->

src/PriorityDataQueue.coffee

@@ -0,0 +1,30 @@
+async = require 'async'
+
+PriorityDataSource = require './PriorityDataSource'
+
+# Creates PriorityDataSource from DataSource
+module.exports = class PriorityDataQueue
+
+  constructor: (dataSource, concurrency) ->
+    @dataSource = dataSource
+    # Creates a priorityQueue that calls performQuery
+    worker = (query, callback) ->
+      dataSource.performQuery(query, callback)
+    @performQueryPriorityQueue = new async.priorityQueue(worker, concurrency)
+
+  # Creates a PriorityDataSource that will then be used like a DataSource but with a priority
+  createPriorityDataSource : (priority) ->
+    return new PriorityDataSource(this, priority)
+
+  # Designed to be called by PriorityDataSource
+  performQuery: (query, cb, priority) ->
+    # Push to the priorityQueue
+    @performQueryPriorityQueue.push query, priority, cb
+
+  # Simply call the dataSource since this is not an async function
+  getImageUrl: (imageId, height) ->
+    @dataSource.getImageUrl(imageId, height)
+
+  kill: () ->
+    if @performQueryPriorityQueue?
+      @performQueryPriorityQueue.kill()

src/PriorityDataSource.coffee

@@ -0,0 +1,15 @@
+
+# Behaves like a DataSource
+# Created by a PriorityDataQueue
+# Forwards performQuery call to the PriorityDataQueue that will forward them to the DataSource
+module.exports = class PriorityDataSource
+
+  constructor: (priorityDataQueue, priority) ->
+    @priorityDataQueue = priorityDataQueue
+    @priority = priority
+
+  performQuery: (query, cb) ->
+    @priorityDataQueue.performQuery(query, cb, @priority)
+
+  getImageUrl: (imageId, height) ->
+    @priorityDataQueue.getImageUrl(imageId, height)

src/index.coffee

@@ -1,5 +1,6 @@
 exports.Schema = require './Schema'
 exports.DataSource = require './DataSource'
+exports.PriorityDataQueue = require './PriorityDataQueue'
 
 exports.ExprCleaner = require './ExprCleaner'
 exports.ExprUtils = require './ExprUtils'

test/PriorityDataQueueTests.coffee

@@ -0,0 +1,55 @@
+assert = require('chai').assert
+
+PriorityDataQueue = require '../src/PriorityDataQueue'
+DataSource = require '../src/DataSource'
+
+# Very simple DataSource implementation used for testing
+class TestDataSource extends DataSource
+  performQuery: (query, cb) ->
+    # Simply does an async callback passing back the query
+    call = () ->
+      cb(query)
+    setTimeout(call, 1)
+
+describe "PriorityDataQueue", ->
+  beforeEach ->
+    testDataSource = new TestDataSource()
+    @priorityDataQueue = new PriorityDataQueue(testDataSource, 1)
+
+  it "calling performQuery reaches the DataSource", (testCallback) ->
+    priorityDataSource = @priorityDataQueue.createPriorityDataSource(1)
+    priorityDataSource.performQuery('test', (data) ->
+      # Make sure that TestDataSource called back with the right data
+      assert.equal('test', data)
+      testCallback()
+    )
+
+  it "priorityDataQueue properly prioritize the calls", (testCallback) ->
+    counter = 0
+    callDone = (priority) ->
+      counter++
+      # Make sure that the priority is called in the right order
+      assert.equal priority, counter
+      if counter == 4
+        testCallback()
+
+    priorityDataSource1 = @priorityDataQueue.createPriorityDataSource(1)
+    priorityDataSource2 = @priorityDataQueue.createPriorityDataSource(2)
+    priorityDataSource3 = @priorityDataQueue.createPriorityDataSource(3)
+    priorityDataSource4 = @priorityDataQueue.createPriorityDataSource(4)
+    # First one needs to be done first since the query is empty and the first call will have best priority
+    priorityDataSource1.performQuery(1, (data) ->
+      callDone(1)
+    )
+    # Then call with 3
+    priorityDataSource3.performQuery(3, (data) ->
+      callDone(3)
+    )
+    # Then call with 4
+    priorityDataSource4.performQuery(4, (data) ->
+      callDone(4)
+    )
+    # Then with 2
+    priorityDataSource2.performQuery(2, (data) ->
+      callDone(2)
+    )