Add clipScreenPosition to LineFolder & LineMap

spec/atom/line-folder-spec.coffee

@@ -32,7 +32,6 @@ describe "LineFolder", ->
       [[range]] = unfoldHandler.argsForCall
       expect(range).toEqual foldRange
 
-
     describe "when there is a single fold spanning multiple lines", ->
       it "replaces folded lines with a single line containing a placeholder and emits a change event", ->
         [line4, line5] = folder.linesForScreenRows(4, 5)
@@ -313,3 +312,23 @@ describe "LineFolder", ->
         expect(folder.bufferPositionForScreenPosition([4, 5])).toEqual [4, 5]
         expect(folder.bufferPositionForScreenPosition([4, 13])).toEqual [4, 15]
         expect(folder.bufferPositionForScreenPosition([4, 18])).toEqual [4, 20]
+  describe ".clipScreenPosition(screenPosition)", ->
+    beforeEach ->
+      folder.createFold(new Range([4, 29], [7, 4]))
+
+    it "returns the nearest valid position based on the current screen lines", ->
+      expect(folder.clipScreenPosition([-1, -1])).toEqual [0, 0]
+      expect(folder.clipScreenPosition([0, -1])).toEqual [0, 0]
+      expect(folder.clipScreenPosition([1, 10000])).toEqual [1, 30]
+      expect(folder.clipScreenPosition([2, 15])).toEqual [2, 15]
+      expect(folder.clipScreenPosition([4, 32])).toEqual [4, 32]
+      expect(folder.clipScreenPosition([4, 1000])).toEqual [4, 33]
+      expect(folder.clipScreenPosition([1000, 1000])).toEqual [10, 2]
+
+    it "clips positions inside a placeholder to the beginning of the placeholder", ->
+      expect(folder.clipScreenPosition([4, 30])).toEqual [4, 29]
+      expect(folder.clipScreenPosition([4, 31])).toEqual [4, 29]
+
+
+
+

src/atom/line-folder.coffee

@@ -136,6 +136,9 @@ class LineFolder
   bufferPositionForScreenPosition: (screenPosition) ->
     @lineMap.bufferPositionForScreenPosition(screenPosition)
 
+  clipScreenPosition: (screenPosition) ->
+    @lineMap.clipScreenPosition(screenPosition)
+
   screenRangeForBufferRange: (bufferRange) ->
     @lineMap.screenRangeForBufferRange(bufferRange)
 

src/atom/line-map.coffee

@@ -135,3 +135,18 @@ class LineMap
     end = @screenPositionForBufferPosition(bufferRange.end)
     new Range(start, end)
 
+  clipScreenPosition: (screenPosition) ->
+    screenPosition = Point.fromObject(screenPosition)
+    screenPosition = new Point(Math.max(0, screenPosition.row), Math.max(0, screenPosition.column))
+
+    screenDelta = new Point
+    for screenLine in @screenLines
+      nextDelta = screenDelta.add(screenLine.screenDelta)
+      break if nextDelta.isGreaterThan(screenPosition)
+      screenDelta = nextDelta
+
+    maxColumn = screenDelta.column + screenLine.lengthForClipping()
+    screenDelta.column = Math.min(maxColumn, screenPosition.column)
+
+    screenDelta
+