Improve LinesYardstick design

We have shifted the responsibility of orchestrating state updates and
measurements to the yardstick. The presenter still needs to be updated to make
use of these new capabilities.

spec/lines-yardstick-spec.coffee

@@ -1,8 +1,8 @@
 LinesYardstick = require '../src/lines-yardstick'
-MockLineNodesProvider = require './mock-line-nodes-provider'
+MockLinesComponent = require './mock-lines-component'
 
 describe "LinesYardstick", ->
-  [editor, mockLineNodesProvider, builtLineNodes, linesYardstick] = []
+  [editor, mockPresenter, mockLinesComponent, linesYardstick] = []
 
   beforeEach ->
     waitsForPromise ->
@@ -12,14 +12,23 @@ describe "LinesYardstick", ->
       atom.project.open('sample.js').then (o) -> editor = o
 
     runs ->
-      mockLineNodesProvider = new MockLineNodesProvider(editor)
-      linesYardstick = new LinesYardstick(editor, mockLineNodesProvider)
+      mockPresenter = {getStateForMeasurements: jasmine.createSpy()}
+      mockLinesComponent = new MockLinesComponent(editor)
+      linesYardstick = new LinesYardstick(editor, mockPresenter, mockLinesComponent)
+
+      mockLinesComponent.setDefaultFont("14px monospace")
 
   afterEach ->
-    mockLineNodesProvider.dispose()
+    doSomething = true
 
   it "converts screen positions to pixel positions", ->
-    mockLineNodesProvider.setDefaultFont("14px monospace")
+    stubState = {anything: {}}
+    mockPresenter.getStateForMeasurements.andReturn(stubState)
+
+    linesYardstick.prepareScreenRowsForMeasurement([0, 1, 2])
+
+    expect(mockPresenter.getStateForMeasurements).toHaveBeenCalledWith([0, 1, 2])
+    expect(mockLinesComponent.updateSync).toHaveBeenCalledWith(stubState)
 
     conversionTable = [
       [[0, 0], {left: 0, top: editor.getLineHeightInPixels() * 0}]
@@ -37,7 +46,7 @@ describe "LinesYardstick", ->
         linesYardstick.pixelPositionForScreenPosition(point)
       ).toEqual(position)
 
-    mockLineNodesProvider.setFontForScopes(
+    mockLinesComponent.setFontForScopes(
       ["source.js", "storage.modifier.js"], "16px monospace"
     )
     linesYardstick.clearCache()
@@ -57,19 +66,3 @@ describe "LinesYardstick", ->
       expect(
         linesYardstick.pixelPositionForScreenPosition(point)
       ).toEqual(position)
-
-  it "does not compute the same position twice unless the cache gets cleared", ->
-    mockLineNodesProvider.setDefaultFont("14px monospace")
-
-    oldPosition1 = linesYardstick.pixelPositionForScreenPosition([0, 5])
-    oldPosition2 = linesYardstick.pixelPositionForScreenPosition([1, 4])
-
-    mockLineNodesProvider.setDefaultFont("16px monospace")
-
-    expect(linesYardstick.pixelPositionForScreenPosition([0, 5])).toEqual(oldPosition1)
-    expect(linesYardstick.pixelPositionForScreenPosition([1, 4])).toEqual(oldPosition2)
-
-    linesYardstick.clearCache()
-
-    expect(linesYardstick.pixelPositionForScreenPosition([0, 5])).not.toEqual(oldPosition1)
-    expect(linesYardstick.pixelPositionForScreenPosition([1, 4])).not.toEqual(oldPosition2)

spec/mock-lines-component.coffee

@@ -1,8 +1,8 @@
 TokenIterator = require '../src/token-iterator'
 
 module.exports =
-class MockLineNodesProvider
-  constructor: (@editor) ->
+class MockLinesComponent
+  constructor: (@model) ->
     @defaultFont = ""
     @fontsByScopes = {}
     @tokenIterator = new TokenIterator
@@ -11,14 +11,12 @@ class MockLineNodesProvider
   dispose: ->
     node.remove() for node in @builtLineNodes
 
-  setFontForScopes: (scopes, font) -> @fontsByScopes[scopes] = font
-
-  setDefaultFont: (font) -> @defaultFont = font
+  updateSync: jasmine.createSpy()
 
   lineNodeForLineIdAndScreenRow: (id, screenRow) ->
     lineNode = document.createElement("div")
     lineNode.style.whiteSpace = "pre"
-    lineState = @editor.tokenizedLineForScreenRow(screenRow)
+    lineState = @model.tokenizedLineForScreenRow(screenRow)
 
     @tokenIterator.reset(lineState)
     while @tokenIterator.next()
@@ -32,3 +30,7 @@ class MockLineNodesProvider
     document.body.appendChild(lineNode)
 
     lineNode
+
+  setFontForScopes: (scopes, font) -> @fontsByScopes[scopes] = font
+
+  setDefaultFont: (font) -> @defaultFont = font

spec/text-editor-presenter-spec.coffee

@@ -5,7 +5,7 @@ TextBuffer = require 'text-buffer'
 TextEditor = require '../src/text-editor'
 TextEditorPresenter = require '../src/text-editor-presenter'
 LinesYardstick = require '../src/lines-yardstick'
-MockLineNodesProvider = require './mock-line-nodes-provider'
+MockLineNodesProvider = require './mock-lines-component'
 
 describe "TextEditorPresenter", ->
   # These `describe` and `it` blocks mirror the structure of the ::state object.

src/lines-yardstick.coffee

@@ -4,14 +4,18 @@ AcceptFilter = {acceptNode: -> NodeFilter.FILTER_ACCEPT}
 
 module.exports =
 class LinesYardstick
-  constructor: (@model, @lineNodesProvider) ->
+  constructor: (@model, @presenter, @lineNodesProvider) ->
+    @cachedPositionsByLineId = {}
     @tokenIterator = new TokenIterator
     @rangeForMeasurement = document.createRange()
-    @cachedPositionsByLineId = {}
 
   clearCache: ->
     @cachedPositionsByLineId = {}
 
+  prepareScreenRowsForMeasurement: (screenRows) ->
+    state = @presenter.getStateForMeasurements(screenRows)
+    @lineNodesProvider.updateSync(state)
+
   pixelPositionForScreenPosition: (screenPosition, clip=true) ->
     screenPosition = Point.fromObject(screenPosition)
     screenPosition = @model.clipScreenPosition(screenPosition) if clip