Add Buffer.characterIndexForPosition

spec/atom/buffer-spec.coffee

@@ -203,3 +203,11 @@ describe 'Buffer', ->
         lineLength = buffer.lineForRow(2).length
         range = [[2,10], [4,10]]
         expect(buffer.getTextInRange(range)).toBe "ems.length <= 1) return items;\n    var pivot = items.shift(), current, left = [], right = [];\n    while("
+
+  describe ".characterIndexForPosition(position)", ->
+    it "returns the total number of charachters that precede the given position", ->
+      expect(buffer.characterIndexForPosition([0, 0])).toBe 0
+      expect(buffer.characterIndexForPosition([0, 1])).toBe 1
+      expect(buffer.characterIndexForPosition([0, 29])).toBe 29
+      expect(buffer.characterIndexForPosition([1, 0])).toBe 30
+      expect(buffer.characterIndexForPosition([2, 0])).toBe 61

src/atom/buffer.coffee

@@ -1,5 +1,6 @@
 _ = require 'underscore'
 fs = require 'fs'
+Point = require 'point'
 Range = require 'range'
 EventEmitter = require 'event-emitter'
 UndoManager = require 'undo-manager'
@@ -59,6 +60,13 @@ class Buffer
   lastLine: ->
     @lineForRow(@lastRow())
 
+  characterIndexForPosition: (position) ->
+    position = Point.fromObject(position)
+
+    index = 0
+    index += @getLineLength(row) + 1 for row in [0...position.row]
+    index + position.column
+
   deleteRow: (row) ->
     range = null
     if row == @lastRow()