Added support for diminished exp for repeatables. Needs tweaking though.

app/lib/utils.coffee

@@ -75,3 +75,12 @@ module.exports.getByPath = (target, path) ->
     return undefined unless piece of obj
     obj = obj[piece]
   obj
+
+module.exports.round = _.curry (digits, n) ->
+  n = +n.toFixed(digits)
+
+module.exports.createLinearFunc = (params) ->
+  (x) -> (params.a or 1) * x + (params.b or 0)
+
+module.exports.createLogFunc = (params) ->
+  (x) -> (params.a or 1) * Math.log((params.b or 1) * (x + (params.c or 0)))

app/models/Achievement.coffee

@@ -1,4 +1,5 @@
 CocoModel = require './CocoModel'
+util = require '../lib/utils'
 
 module.exports = class Achievement extends CocoModel
   @className: 'Achievement'
@@ -6,4 +7,11 @@ module.exports = class Achievement extends CocoModel
   urlRoot: '/db/achievement'
 
   isRepeatable: ->
-    @get('proportionalTo')?
+    @get('proportionalTo')?
+
+  # TODO logic is duplicated in Mongoose Achievement schema
+  getExpFunction: ->
+    kind = @get('function')?.kind or @schema.function.default.kind
+    parameters = @get('function')?.parameters or @schema.function.default.parameters
+    funcCreator = if kind is 'linear' then util.createLinearFunc else if kind is 'logarithmic' then utils.createLogFunc
+    return funcCreator(parameters) if funcCreator?

app/schemas/models/achievement.coffee

@@ -52,22 +52,17 @@ _.extend(AchievementSchema.properties,
     description: 'For repeatables only. Denotes the field a repeatable achievement needs for its calculations'
   function:
     type: 'object'
-    oneOf: [
-      linear:
+    properties:
+      kind: {enum: ['linear', 'logarithmic'], default: 'linear'}
+      parameters:
         type: 'object'
-        properties:
-          a: {type: 'number', default: 1},
-          required: ['a']
-        description: 'f(x) = a * x'
-      logarithmic:
-        type:'object'
         properties:
           a: {type: 'number', default: 1}
           b: {type: 'number', default: 1}
-        required: ['a', 'b']
-        description: 'f(x) = a * ln(1/b * (x + b))'
-    ]
-    default: linear: a: 1
+          c: {type: 'number', default: 1}
+    default: {kind: 'linear', parameters: a: 1}
+    required: ['kind', 'parameters']
+    additionalProperties: false
 )
 
 AchievementSchema.definitions = {}

app/schemas/models/earned_achievement.coffee

@@ -20,15 +20,10 @@ module.exports =
               href: '/db/achievement/{($)}'
             }
           ]
-      collection:
-        type: 'string'
-      achievementName:
-        type: 'string'
-      created:
-        type: 'date'
-      changed:
-        type: 'date'
-      achievedAmount:
-        type: 'number'
-      notified:
-        type: 'boolean'
+      collection: type: 'string'
+      achievementName: type: 'string'
+      created: type: 'date'
+      changed: type: 'date'
+      achievedAmount: type: 'number'
+      previouslyAchievedAmount: {type: 'number', default: 0}
+      notified: type: 'boolean'

app/views/kinds/RootView.coffee

@@ -41,20 +41,23 @@ module.exports = class RootView extends CocoView
       #test = new Achievement(_id:'537ce4855c91b8d1dda7fda8')
       #test.fetch(success:@showNewAchievement)
 
-  showNewAchievement: (achievement) ->
+  showNewAchievement: (achievement, earnedAchievement) ->
     currentLevel = me.level()
     nextLevel = currentLevel + 1
     currentLevelExp = User.expForLevel(currentLevel)
     nextLevelExp = User.expForLevel(nextLevel)
     totalExpNeeded = nextLevelExp - currentLevelExp
+    expFunction = achievement.getExpFunction()
     currentExp = me.get('points')
-    worth = achievement.get('worth')
-    leveledUp = currentExp - worth < currentLevelExp
-    alreadyAchievedPercentage = 100 * (currentExp - currentLevelExp - worth) / totalExpNeeded
-    newlyAchievedPercentage = if currentLevelExp is currentExp then 0 else 100 * worth / totalExpNeeded
+    previousExp = currentExp - achievement.get('worth')
+    previousExp = expFunction(earnedAchievement.get('previouslyAchievedAmount')) * achievement.get('worth') if achievement.isRepeatable()
+    achievedExp = currentExp - previousExp
+    leveledUp = currentExp - achievedExp < currentLevelExp
+    alreadyAchievedPercentage = 100 * (previousExp - currentLevelExp) / totalExpNeeded
+    newlyAchievedPercentage = if leveledUp then 100 * (currentExp - currentLevelExp) / totalExpNeeded else  100 * achievedExp / totalExpNeeded
 
     console.debug "Current level is #{currentLevel} (#{currentLevelExp} xp), next level is #{nextLevel} (#{nextLevelExp} xp)."
-    console.debug "Need a total of #{nextLevelExp - currentLevelExp}, already had #{currentExp - currentLevelExp - worth} and just now earned #{worth} totalling on #{currentExp}"
+    console.debug "Need a total of #{nextLevelExp - currentLevelExp}, already had #{previousExp} and just now earned #{achievedExp} totalling on #{currentExp}"
 
     alreadyAchievedBar = $("<div class='progress-bar progress-bar-warning' style='width:#{alreadyAchievedPercentage}%'></div>")
     newlyAchievedBar = $("<div data-toggle='tooltip' class='progress-bar progress-bar-success' style='width:#{newlyAchievedPercentage}%'></div>")
@@ -63,7 +66,7 @@ module.exports = class RootView extends CocoView
     message = if (currentLevel isnt 1) and leveledUp then "Reached level #{currentLevel}!" else null
 
     alreadyAchievedBar.tooltip(title: "#{currentExp} XP in total")
-    newlyAchievedBar.tooltip(title: "#{worth} XP earned")
+    newlyAchievedBar.tooltip(title: "#{achievedExp} XP earned")
     emptyBar.tooltip(title: "#{nextLevelExp - currentExp} XP until level #{nextLevel}")
 
     # TODO a default should be linked here
@@ -73,7 +76,7 @@ module.exports = class RootView extends CocoView
       image: $("<img src='#{imageURL}' />")
       description: achievement.get('description')
       progressBar: progressBar
-      earnedExp: "+ #{worth} XP"
+      earnedExp: "+ #{achievedExp} XP"
       message: message
 
     options =
@@ -87,13 +90,11 @@ module.exports = class RootView extends CocoView
     $.notify( data, options )
 
   handleNewAchievements: (earnedAchievements) ->
-    console.debug 'Got new earned achievements'
-    # TODO performance?
     _.each(earnedAchievements.models, (earnedAchievement) =>
       achievement = new Achievement(_id: earnedAchievement.get('achievement'))
       console.log achievement
       achievement.fetch(
-        success: @showNewAchievement
+        success: (achievement) => @showNewAchievement(achievement, earnedAchievement)
       )
     )
 

server/achievements/Achievement.coffee

@@ -1,6 +1,7 @@
 mongoose = require('mongoose')
 jsonschema = require('../../app/schemas/models/achievement')
 log = require 'winston'
+util = require '../../app/lib/utils'
 
 # `pre` and `post` are not called for update operations executed directly on the database,
 # including `Model.update`,`.findByIdAndUpdate`,`.findOneAndUpdate`, `.findOneAndRemove`,and `.findByIdAndRemove`.order
@@ -11,16 +12,22 @@ AchievementSchema = new mongoose.Schema({
   userField: String
 }, {strict: false})
 
-AchievementSchema.methods.objectifyQuery = () ->
+AchievementSchema.methods.objectifyQuery = ->
   try
     @set('query', JSON.parse(@get('query'))) if typeof @get('query') == "string"
   catch error
     log.error "Couldn't convert query string to object because of #{error}"
     @set('query', {})
 
-AchievementSchema.methods.stringifyQuery = () ->
+AchievementSchema.methods.stringifyQuery = ->
   @set('query', JSON.stringify(@get('query'))) if typeof @get('query') != "string"
 
+AchievementSchema.methods.getExpFunction = ->
+  kind = @get('function.kind') or jsonschema.function.default.kind
+  parameters = @get('function.parameters') or jsonschema.function.default.parameters
+  funcCreator = if kind is 'linear' then util.createLinearFunc else if kind is 'logarithmic' then util.createLogFunc
+  return funcCreator(parameters) if funcCreator?
+
 AchievementSchema.post('init', (doc) -> doc.objectifyQuery())
 
 AchievementSchema.pre('save', (next) ->

server/achievements/EarnedAchievement.coffee

@@ -13,7 +13,11 @@ EarnedAchievementSchema = new mongoose.Schema({
     default: false
 }, {strict:false})
 
+EarnedAchievementSchema.pre 'save', (next) ->
+  @set('changed', Date.now())
+  next()
+
 EarnedAchievementSchema.index({user: 1, achievement: 1}, {unique: true, name: 'earned achievement index'})
 EarnedAchievementSchema.index({user: 1, changed: -1}, {name: 'latest '})
 
-module.exports = EarnedAchievement = mongoose.model('EarnedAchievement', EarnedAchievementSchema)
+module.exports = EarnedAchievement = mongoose.model('EarnedAchievement', EarnedAchievementSchema)

server/achievements/achievement_handler.coffee

@@ -5,7 +5,7 @@ class AchievementHandler extends Handler
   modelClass: Achievement
 
   # Used to determine which properties requests may edit
-  editableProperties: ['name', 'query', 'worth', 'collection', 'description', 'userField', 'proportionalTo', 'icon']
+  editableProperties: ['name', 'query', 'worth', 'collection', 'description', 'userField', 'proportionalTo', 'icon', 'function']
   jsonSchema = require '../../app/schemas/models/achievement.coffee'
 
   hasAccess: (req) ->

server/plugins/achievements.coffee

@@ -54,6 +54,8 @@ module.exports = AchievablePlugin = (schema, options) ->
             achievement: achievement._id.toHexString()
             achievementName: achievement.get 'name'
           }
+
+          worth = achievement.get('worth')
           earnedPoints = 0
           wrapUp = ->
             # Update user's experience points
@@ -68,22 +70,23 @@ module.exports = AchievablePlugin = (schema, options) ->
             newAmount = docObj[proportionalTo]
 
             if originalAmount isnt newAmount
+              expFunction = achievement.getExpFunction()
               earned.notified = false
               earned.achievedAmount = newAmount
-              earned.changed = Date.now()
+              earned.previouslyAchievedAmount = originalAmount
               EarnedAchievement.findOneAndUpdate({achievement:earned.achievement, user:earned.user}, earned, upsert:true, (err, docs) ->
                   return log.debug err if err?
               )
 
-              earnedPoints = achievement.get('worth') * (newAmount - originalAmount)
+              earnedPoints = (expFunction(newAmount) - expFunction(originalAmount)) * worth
+              log.debug earnedPoints
               wrapUp()
 
           else # not alreadyAchieved
             log.debug 'Creating a new earned achievement called \'' + (achievement.get 'name') + '\' for ' + userID
             (new EarnedAchievement(earned)).save (err, doc) ->
               return log.debug err if err?
-
-              earnedPoints = achievement.get('worth')
+              earnedPoints = worth
               wrapUp()
 
     delete before[doc.id] unless isNew # This assumes everything we patch has a _id