Optimize QueryResultSet so offset lookups are O[1] after initial scan

src/flux/models/mutable-query-result-set.coffee

@@ -30,6 +30,7 @@ class MutableQueryResultSet extends QueryResultSet
 
     models = @models()
     @_modelsHash = {}
+    @_idToIndexHash = null
     @replaceModel(m) for m in models
 
   addModelsInRange: (rangeModels, range) ->
@@ -39,6 +40,7 @@ class MutableQueryResultSet extends QueryResultSet
   addIdsInRange: (rangeIds, range) ->
     if @_offset is null or range.isInfinite()
       @_ids = rangeIds
+      @_idToIndexHash = null
       @_offset = range.offset
     else
       currentEnd = @_offset + @_ids.length
@@ -58,18 +60,21 @@ class MutableQueryResultSet extends QueryResultSet
         existingAfter = @_ids.slice(rangeIdsEnd - @_offset)
 
       @_ids = [].concat(existingBefore, rangeIds, existingAfter)
+      @_idToIndexHash = null
       @_offset = Math.min(@_offset, range.offset)
 
   replaceModel: (item) ->
     return unless item
     @_modelsHash[item.clientId] = item
     @_modelsHash[item.id] = item
+    @_idToIndexHash = null
 
   removeModelAtOffset: (item, offset) ->
     idx = offset - @_offset
     delete @_modelsHash[item.clientId]
     delete @_modelsHash[item.id]
     @_ids.splice(idx, 1)
+    @_idToIndexHash = null
 
   setQuery: (query) ->
     @_query = query.clone()

src/flux/models/query-result-set.coffee

@@ -31,6 +31,7 @@ class QueryResultSet
       throw new Error("setByApplyingModels: A hash of models is required.")
     set = set.clone()
     set._modelsHash = models
+    set._idToIndexHash = null
     set
 
   constructor: (other = {}) ->
@@ -38,11 +39,13 @@ class QueryResultSet
     @_offset = other._offset ? null
     @_query = other._query ? null
     @_ids = other._ids ? []
+    @_idToIndexHash = other._idToIndexHash ? null
 
   clone: ->
     new @constructor({
       _ids: [].concat(@_ids)
       _modelsHash: _.extend({}, @_modelsHash)
+      _idToIndexHash: _.extend({}, @_idToIndexHash)
       _query: @_query
       _offset: @_offset
     })
@@ -82,15 +85,20 @@ class QueryResultSet
   modelWithId: (id) ->
     @_modelsHash[id]
 
+  buildIdToIndexHash: ->
+    @_idToIndexHash = {}
+    for id, idx in @_ids
+      @_idToIndexHash[id] = idx
+      model = @_modelsHash[id]
+      @_idToIndexHash[model.clientId] = idx if model
+
   offsetOfId: (id) ->
-    idx = @_ids.indexOf(id)
+    if @_idToIndexHash is null
+      @buildIdToIndexHash()
 
-    # If we can't find the item, try to match against client ids as well. Some
-    # items in the models() array may not be loaded, but we can try our best.
-    if idx is -1
-      idx = _.findIndex @models(), (m) -> m and (m.id is id or m.clientId is id)
-
-    return -1 if idx is -1
-    return @_offset + idx
+    if @_idToIndexHash[id]
+      return @_idToIndexHash[id] + @_offset
+    else
+      return -1
 
 module.exports = QueryResultSet