Start on TextEditorPresenter with lines state

spec/text-editor-presenter-spec.coffee

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+TextBuffer = require 'text-buffer'
+TextEditor = require '../src/text-editor'
+TextEditorPresenter = require '../src/text-editor-presenter'
+
+describe "TextEditorPresenter", ->
+  [buffer, editor] = []
+
+  beforeEach ->
+    buffer = new TextBuffer(filePath: require.resolve('./fixtures/sample.js'))
+    editor = new TextEditor({buffer})
+    waitsForPromise -> buffer.load()
+
+  afterEach ->
+    editor.destroy()
+    buffer.destroy()
+
+  expectValues = (actual, expected) ->
+    for key, value of expected
+      expect(actual[key]).toBe value
+
+  describe "lines", ->
+    describe "on initialization", ->
+      it "contains the lines that are visible on screen, plus the overdraw margin", ->
+        presenter = new TextEditorPresenter(model: editor, clientHeight: 25, scrollTop: 0, lineHeight: 10, lineOverdrawMargin: 1)
+
+        line0 = editor.tokenizedLineForScreenRow(0)
+        expectValues presenter.state.lines[line0.id], {
+          screenRow: 0
+          tokens: line0.tokens
+          top: 10 * 0
+        }
+
+        line1 = editor.tokenizedLineForScreenRow(1)
+        expectValues presenter.state.lines[line1.id], {
+          screenRow: 1
+          tokens: line1.tokens
+          top: 10 * 1
+        }
+
+        line2 = editor.tokenizedLineForScreenRow(2)
+        expectValues presenter.state.lines[line2.id], {
+          screenRow: 2
+          tokens: line2.tokens
+          top: 10 * 2
+        }
+
+        # this row is rendered due to the overdraw margin
+        line3 = editor.tokenizedLineForScreenRow(3)
+        expectValues presenter.state.lines[line3.id], {
+          screenRow: 3
+          tokens: line3.tokens
+          top: 10 * 3
+        }
+
+      it "contains the lines that are visible on screen, minus the overdraw margin", ->
+        presenter = new TextEditorPresenter(model: editor, clientHeight: 25, scrollTop: 115, lineHeight: 10, lineOverdrawMargin: 1)
+
+        # this row is rendered due to the overdraw margin
+        line10 = editor.tokenizedLineForScreenRow(10)
+        expectValues presenter.state.lines[line10.id], {
+          screenRow: 10
+          tokens: line10.tokens
+          top: 10 * 10
+        }
+
+        line11 = editor.tokenizedLineForScreenRow(11)
+        expectValues presenter.state.lines[line11.id], {
+          screenRow: 11
+          tokens: line11.tokens
+          top: 10 * 11
+        }
+
+        line12 = editor.tokenizedLineForScreenRow(12)
+        expectValues presenter.state.lines[line12.id], {
+          screenRow: 12
+          tokens: line12.tokens
+          top: 10 * 12
+        }
+
+        # rows beyond the end of the content are not rendered

src/text-editor-presenter.coffee

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+module.exports =
+class TextEditorPresenter
+  constructor: ({@model, @clientHeight, @scrollTop, @lineHeight, @lineOverdrawMargin}) ->
+    @state = {}
+    @buildLinesState()
+
+  buildLinesState: ->
+    @state.lines = {}
+    startRow = Math.floor(@scrollTop / @lineHeight) - @lineOverdrawMargin
+    startRow = Math.max(0, startRow)
+    endRow = startRow + Math.ceil(@clientHeight / @lineHeight) + @lineOverdrawMargin
+    endRow = Math.min(@model.getScreenLineCount(), endRow)
+
+    for line, i in @model.tokenizedLinesForScreenRows(startRow, endRow)
+      row = startRow + i
+      @state.lines[line.id] = {
+        screenRow: row
+        tokens: line.tokens
+        top: row * @lineHeight
+      }