From e1481df76a42ff5aaff62fdb6efda08aac80e241 Mon Sep 17 00:00:00 2001
From: James Allen <james@sharelatex.com>
Date: Thu, 23 Feb 2017 11:39:19 +0100
Subject: [PATCH 1/7] Don't consume partial parts of delete when inserting a
 change

---
 services/document-updater/app/coffee/RangesTracker.coffee | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/services/document-updater/app/coffee/RangesTracker.coffee b/services/document-updater/app/coffee/RangesTracker.coffee
index 865ecf4ef6..6a07e38c0e 100644
--- a/services/document-updater/app/coffee/RangesTracker.coffee
+++ b/services/document-updater/app/coffee/RangesTracker.coffee
@@ -206,12 +206,12 @@ load = (EventEmitter) ->
 					# If this is an insert op at the end of an existing insert with a delete following, and it cancels out the following
 					# delete then we shouldn't append it to this insert, but instead only cancel the following delete.
 					# E.g.
-					#                   foo|<--- about to insert 'b' here
+					#                   foo|<--- about to insert 'bar' here
 					#  inserted 'foo'  --^ ^-- deleted 'bar'
-					# should become just 'foo' not 'foob' (with the delete marker becoming just 'ar'), .
+					# should become just 'foo' not 'foobar' (with the delete marker disappearing), .
 					next_change = @changes[i+1]
 					is_op_adjacent_to_next_delete = next_change? and next_change.op.d? and op.p == change_end and next_change.op.p == op.p
-					will_op_cancel_next_delete = is_op_adjacent_to_next_delete and next_change.op.d.slice(0, op.i.length) == op.i
+					will_op_cancel_next_delete = is_op_adjacent_to_next_delete and next_change.op.d == op.i
 					
 					# If there is a delete at the start of the insert, and we're inserting
 					# at the start, we SHOULDN'T merge since the delete acts as a partition.

From 80284e1b0141cf370ebc234c0d51871e9e373e29 Mon Sep 17 00:00:00 2001
From: James Allen <james@sharelatex.com>
Date: Fri, 24 Feb 2017 14:21:06 +0100
Subject: [PATCH 2/7] Only cancel deletes with inserts on undo and reject

---
 .../app/coffee/RangesTracker.coffee           | 82 ++++++++++++-------
 .../app/coffee/sharejs/types/text-api.coffee  | 16 ++--
 .../app/coffee/sharejs/types/text.coffee      | 33 +++++---
 .../coffee/ShareJS/TextTransformTests.coffee  | 53 +++++++++++-
 4 files changed, 133 insertions(+), 51 deletions(-)

diff --git a/services/document-updater/app/coffee/RangesTracker.coffee b/services/document-updater/app/coffee/RangesTracker.coffee
index 6a07e38c0e..a9c43e9816 100644
--- a/services/document-updater/app/coffee/RangesTracker.coffee
+++ b/services/document-updater/app/coffee/RangesTracker.coffee
@@ -1,5 +1,5 @@
-load = (EventEmitter) ->
-	class RangesTracker extends EventEmitter
+load = () ->
+	class RangesTracker
 		# The purpose of this class is to track a set of inserts and deletes to a document, like
 		# track changes in Word. We store these as a set of ShareJs style ranges:
 		#   {i: "foo", p: 42} # Insert 'foo' at offset 42
@@ -36,6 +36,7 @@ load = (EventEmitter) ->
 		#     middle of a previous insert by the first user, the original insert will be split into two.
 		constructor: (@changes = [], @comments = []) ->
 			@setIdSeed(RangesTracker.generateIdSeed())
+			@resetDirtyState()
 
 		getIdSeed: () ->
 			return @id_seed
@@ -75,7 +76,7 @@ load = (EventEmitter) ->
 			comment = @getComment(comment_id)
 			return if !comment?
 			@comments = @comments.filter (c) -> c.id != comment_id
-			@emit "comment:removed", comment
+			@_markAsDirty comment, "comment", "removed"
 		
 		getChange: (change_id) ->
 			change = null
@@ -103,7 +104,11 @@ load = (EventEmitter) ->
 				@addComment(op, metadata)
 			else
 				throw new Error("unknown op type")
-			
+
+		applyOps: (ops, metadata = {}) ->
+			for op in ops
+				@applyOp(op, metadata)
+
 		addComment: (op, metadata) ->
 			# TODO: Don't allow overlapping comments?
 			@comments.push comment = {
@@ -114,18 +119,18 @@ load = (EventEmitter) ->
 					t: op.t
 				metadata
 			}
-			@emit "comment:added", comment
+			@_markAsDirty comment, "comment", "added"
 			return comment
 		
 		applyInsertToComments: (op) ->
 			for comment in @comments
 				if op.p <= comment.op.p
 					comment.op.p += op.i.length
-					@emit "comment:moved", comment
+					@_markAsDirty comment, "comment", "moved"
 				else if op.p < comment.op.p + comment.op.c.length
 					offset = op.p - comment.op.p
 					comment.op.c = comment.op.c[0..(offset-1)] + op.i + comment.op.c[offset...]
-					@emit "comment:moved", comment
+					@_markAsDirty comment, "comment", "moved"
 
 		applyDeleteToComments: (op) ->
 			op_start = op.p
@@ -138,7 +143,7 @@ load = (EventEmitter) ->
 				if op_end <= comment_start
 					# delete is fully before comment
 					comment.op.p -= op_length
-					@emit "comment:moved", comment
+					@_markAsDirty comment, "comment", "moved"
 				else if op_start >= comment_end
 					# delete is fully after comment, nothing to do
 				else
@@ -161,12 +166,13 @@ load = (EventEmitter) ->
 					
 					comment.op.p = Math.min(comment_start, op_start)
 					comment.op.c = remaining_before + remaining_after
-					@emit "comment:moved", comment
+					@_markAsDirty comment, "comment", "moved"
 
 		applyInsertToChanges: (op, metadata) ->
 			op_start = op.p
 			op_length = op.i.length
 			op_end = op.p + op_length
+			undoing = !!op.u
 
 
 			already_merged = false
@@ -184,8 +190,9 @@ load = (EventEmitter) ->
 						change.op.p += op_length
 						moved_changes.push change
 					else if op_start == change_start
-						# If the insert matches the start of the delete, just remove it from the delete instead
-						if change.op.d.length >= op.i.length and change.op.d.slice(0, op.i.length) == op.i
+						# If we are undoing, then we want to cancel any existing delete ranges if we can.
+						# Check if the insert matches the start of the delete, and just remove it from the delete instead if so.
+						if undoing and change.op.d.length >= op.i.length and change.op.d.slice(0, op.i.length) == op.i
 							change.op.d = change.op.d.slice(op.i.length)
 							change.op.p += op.i.length
 							if change.op.d == ""
@@ -203,15 +210,15 @@ load = (EventEmitter) ->
 					# Only merge inserts if they are from the same user
 					is_same_user = metadata.user_id == change.metadata.user_id
 					
-					# If this is an insert op at the end of an existing insert with a delete following, and it cancels out the following
-					# delete then we shouldn't append it to this insert, but instead only cancel the following delete.
+					# If we are undoing, then our changes will be removed from any delete ops just after. In that case, if there is also
+					# an insert op just before, then we shouldn't append it to this insert, but instead only cancel the following delete.
 					# E.g.
-					#                   foo|<--- about to insert 'bar' here
+					#                   foo|<--- about to insert 'b' here
 					#  inserted 'foo'  --^ ^-- deleted 'bar'
-					# should become just 'foo' not 'foobar' (with the delete marker disappearing), .
+					# should become just 'foo' not 'foob' (with the delete marker becoming just 'ar'), .
 					next_change = @changes[i+1]
 					is_op_adjacent_to_next_delete = next_change? and next_change.op.d? and op.p == change_end and next_change.op.p == op.p
-					will_op_cancel_next_delete = is_op_adjacent_to_next_delete and next_change.op.d == op.i
+					will_op_cancel_next_delete = undoing and is_op_adjacent_to_next_delete and next_change.op.d.slice(0, op.i.length) == op.i
 					
 					# If there is a delete at the start of the insert, and we're inserting
 					# at the start, we SHOULDN'T merge since the delete acts as a partition.
@@ -281,8 +288,8 @@ load = (EventEmitter) ->
 			for change in remove_changes
 				@_removeChange change
 			
-			if moved_changes.length > 0
-				@emit "changes:moved", moved_changes
+			for change in moved_changes
+				@_markAsDirty change, "change", "moved"
 		
 		applyDeleteToChanges: (op, metadata) ->
 			op_start = op.p
@@ -406,8 +413,8 @@ load = (EventEmitter) ->
 					@_removeChange change
 					moved_changes = moved_changes.filter (c) -> c != change
 			
-			if moved_changes.length > 0
-				@emit "changes:moved", moved_changes
+			for change in moved_changes
+				@_markAsDirty change, "change", "moved"
 
 		_addOp: (op, metadata) ->
 			change = {
@@ -427,17 +434,11 @@ load = (EventEmitter) ->
 				else
 					return -1
 
-			if op.d?
-				@emit "delete:added", change
-			else if op.i?
-				@emit "insert:added", change
+			@_markAsDirty(change, "change", "added")
 		
 		_removeChange: (change) ->
 			@changes = @changes.filter (c) -> c.id != change.id
-			if change.op.d?
-				@emit "delete:removed", change
-			else if change.op.i?
-				@emit "insert:removed", change
+			@_markAsDirty change, "change", "removed"
 			
 		_applyOpModifications: (content, op_modifications) ->
 			# Put in descending position order, with deleting first if at the same offset 
@@ -486,13 +487,32 @@ load = (EventEmitter) ->
 					previous_change = change
 			return { moved_changes, remove_changes }
 		
+		resetDirtyState: () ->
+			@_dirtyState = {
+				comment: {
+					moved: {}
+					removed: {}
+					added: {}
+				}
+				change: {
+					moved: {}
+					removed: {}
+					added: {}
+				}
+			}
+		
+		getDirtyState: () ->
+			return @_dirtyState
+		
+		_markAsDirty: (object, type, action) ->
+			@_dirtyState[type][action][object.id] = object
+		
 		_clone: (object) ->
 			clone = {}
 			(clone[k] = v for k,v of object)
 			return clone
 
 if define?
-	define ["utils/EventEmitter"], load
+	define [], load
 else
-	EventEmitter = require("events").EventEmitter
-	module.exports = load(EventEmitter)
\ No newline at end of file
+	module.exports = load()
diff --git a/services/document-updater/app/coffee/sharejs/types/text-api.coffee b/services/document-updater/app/coffee/sharejs/types/text-api.coffee
index 96243ceffb..98bb3fd503 100644
--- a/services/document-updater/app/coffee/sharejs/types/text-api.coffee
+++ b/services/document-updater/app/coffee/sharejs/types/text-api.coffee
@@ -11,14 +11,20 @@ text.api =
   # Get the text contents of a document
   getText: -> @snapshot
 
-  insert: (pos, text, callback) ->
-    op = [{p:pos, i:text}]
+  insert: (pos, text, fromUndo, callback) ->
+    op = {p:pos, i:text}
+    if fromUndo
+      op.u = true
+    op = [op]
     
     @submitOp op, callback
     op
   
-  del: (pos, length, callback) ->
-    op = [{p:pos, d:@snapshot[pos...(pos + length)]}]
+  del: (pos, length, fromUndo, callback) ->
+    op = {p:pos, d:@snapshot[pos...(pos + length)]}
+    if fromUndo
+      op.u = true
+    op = [op]
 
     @submitOp op, callback
     op
@@ -28,5 +34,5 @@ text.api =
       for component in op
         if component.i != undefined
           @emit 'insert', component.p, component.i
-        else
+        else if component.d != undefined
           @emit 'delete', component.p, component.d
diff --git a/services/document-updater/app/coffee/sharejs/types/text.coffee b/services/document-updater/app/coffee/sharejs/types/text.coffee
index 2a3b79997d..ee7bf57043 100644
--- a/services/document-updater/app/coffee/sharejs/types/text.coffee
+++ b/services/document-updater/app/coffee/sharejs/types/text.coffee
@@ -56,6 +56,13 @@ text.apply = (snapshot, op) ->
       throw new Error "Unknown op type"
   snapshot
 
+cloneAndModify = (op, modifications) ->
+  newOp = {}
+  for k,v of op
+    newOp[k] = v
+  for k,v of modifications
+    newOp[k] = v
+  return newOp
 
 # Exported for use by the random op generator.
 #
@@ -69,10 +76,10 @@ text._append = append = (newOp, c) ->
     last = newOp[newOp.length - 1]
 
     # Compose the insert into the previous insert if possible
-    if last.i? && c.i? and last.p <= c.p <= (last.p + last.i.length)
-      newOp[newOp.length - 1] = {i:strInject(last.i, c.p - last.p, c.i), p:last.p}
-    else if last.d? && c.d? and c.p <= last.p <= (c.p + c.d.length)
-      newOp[newOp.length - 1] = {d:strInject(c.d, last.p - c.p, last.d), p:c.p}
+    if last.i? && c.i? and last.p <= c.p <= (last.p + last.i.length) and last.u == c.u
+      newOp[newOp.length - 1] = cloneAndModify(last, {i:strInject(last.i, c.p - last.p, c.i)})
+    else if last.d? && c.d? and c.p <= last.p <= (c.p + c.d.length) and last.u == c.u
+      newOp[newOp.length - 1] = cloneAndModify(last, {d:strInject(c.d, last.p - c.p, last.d), p: c.p})
     else
       newOp.push c
 
@@ -150,25 +157,25 @@ text._tc = transformComponent = (dest, c, otherC, side) ->
   checkValidOp [otherC]
 
   if c.i?
-    append dest, {i:c.i, p:transformPosition(c.p, otherC, side == 'right')}
+    append dest, cloneAndModify(c, {p:transformPosition(c.p, otherC, side == 'right')})
 
   else if c.d? # Delete
     if otherC.i? # delete vs insert
       s = c.d
       if c.p < otherC.p
-        append dest, {d:s[...otherC.p - c.p], p:c.p}
+        append dest, cloneAndModify(c, {d:s[...otherC.p - c.p]})
         s = s[(otherC.p - c.p)..]
       if s != ''
-        append dest, {d:s, p:c.p + otherC.i.length}
+        append dest, cloneAndModify(c, {d:s, p:c.p + otherC.i.length})
 
     else if otherC.d? # Delete vs delete
       if c.p >= otherC.p + otherC.d.length
-        append dest, {d:c.d, p:c.p - otherC.d.length}
+        append dest, cloneAndModify(c, {p:c.p - otherC.d.length})
       else if c.p + c.d.length <= otherC.p
         append dest, c
       else
         # They overlap somewhere.
-        newC = {d:'', p:c.p}
+        newC = cloneAndModify(c, {d:''})
         if c.p < otherC.p
           newC.d = c.d[...(otherC.p - c.p)]
         if c.p + c.d.length > otherC.p + otherC.d.length
@@ -198,18 +205,18 @@ text._tc = transformComponent = (dest, c, otherC, side) ->
       if c.p < otherC.p < c.p + c.c.length
         offset = otherC.p - c.p
         new_c = (c.c[0..(offset-1)] + otherC.i + c.c[offset...])
-        append dest, {c:new_c, p:c.p, t: c.t}
+        append dest, cloneAndModify(c, {c:new_c})
       else
-        append dest, {c:c.c, p:transformPosition(c.p, otherC, true), t: c.t}
+        append dest, cloneAndModify(c, {p:transformPosition(c.p, otherC, true)})
     
     else if otherC.d?
       if c.p >= otherC.p + otherC.d.length
-        append dest, {c:c.c, p:c.p - otherC.d.length, t: c.t}
+        append dest, cloneAndModify(c, {p:c.p - otherC.d.length})
       else if c.p + c.c.length <= otherC.p
         append dest, c
       else # Delete overlaps comment
         # They overlap somewhere.
-        newC = {c:'', p:c.p, t: c.t}
+        newC = cloneAndModify(c, {c:''})
         if c.p < otherC.p
           newC.c = c.c[...(otherC.p - c.p)]
         if c.p + c.c.length > otherC.p + otherC.d.length
diff --git a/services/document-updater/test/unit/coffee/ShareJS/TextTransformTests.coffee b/services/document-updater/test/unit/coffee/ShareJS/TextTransformTests.coffee
index 81440bfe5b..5477b47b38 100644
--- a/services/document-updater/test/unit/coffee/ShareJS/TextTransformTests.coffee
+++ b/services/document-updater/test/unit/coffee/ShareJS/TextTransformTests.coffee
@@ -27,6 +27,11 @@ describe "ShareJS text type", ->
 				dest = []
 				text._tc(dest, { i: "foo", p: 3 }, { i: "bar", p: 3 }, 'left')
 				dest.should.deep.equal [{ i: "foo", p: 3 }]
+			
+			it "should preserve the undo flag", ->
+				dest = []
+				text._tc(dest, { i: "foo", p: 9, u: true }, { i: "bar", p: 3 })
+				dest.should.deep.equal [{ i: "foo", p: 12, u: true }]
 
 		describe "insert / delete", ->
 			it "with a delete before", ->
@@ -46,9 +51,13 @@ describe "ShareJS text type", ->
 
 			it "with a delete at the same place with side == 'left'", ->
 				dest = []
-				
 				text._tc(dest, { i: "foo", p: 3 }, { d: "bar", p: 3 }, 'left')
 				dest.should.deep.equal [{ i: "foo", p: 3 }]
+			
+			it "should preserve the undo flag", ->
+				dest = []
+				text._tc(dest, { i: "foo", p: 9, u: true }, { d: "bar", p: 3 })
+				dest.should.deep.equal [{ i: "foo", p: 6, u: true }]
 
 		describe "delete / insert", ->
 			it "with an insert before", ->
@@ -75,7 +84,11 @@ describe "ShareJS text type", ->
 				dest = []
 				text._tc(dest, { d: "foo", p: 3 }, { i: "bar", p: 4 })
 				dest.should.deep.equal [{ d: "f", p: 3 }, { d: "oo", p: 6 }]
-				
+			
+			it "should preserve the undo flag", ->
+				dest = []
+				text._tc(dest, { d: "foo", p: 9, u: true }, { i: "bar", p: 3 })
+				dest.should.deep.equal [{ d: "foo", p: 12, u: true }]
 
 		describe "delete / delete", ->
 			it "with a delete before", ->
@@ -112,6 +125,11 @@ describe "ShareJS text type", ->
 				dest = []
 				text._tc(dest, { d: "foo", p: 6 }, { d: "abcfoo123", p: 3 })
 				dest.should.deep.equal []
+			
+			it "should preserve the undo flag", ->
+				dest = []
+				text._tc(dest, { d: "foo", p: 9, u: true }, { d: "bar", p: 3 })
+				dest.should.deep.equal [{ d: "foo", p: 6, u: true }]
 	
 		describe "comment / insert", ->
 			it "with an insert before", ->
@@ -210,6 +228,37 @@ describe "ShareJS text type", ->
 				text.apply("foo123bar", [{ c: "456", p: 3 }])
 			).should.throw(Error)
 	
+	describe "_append", ->
+		it "should combine adjacent inserts", ->
+			dest = [{ i: "foo", p: 3 }]
+			text._append dest, { i: "bar", p: 6 }
+			dest.should.deep.equal [{ i: "foobar", p: 3 }]
+
+		it "should combine adjacent undo inserts", ->
+			dest = [{ i: "foo", p: 3, u: true }]
+			text._append dest, { i: "bar", p: 6, u: true }
+			dest.should.deep.equal [{ i: "foobar", p: 3, u: true }]
+
+		it "should not combine an undo and a normal insert", ->
+			dest = [{ i: "foo", p: 3, u: true }]
+			text._append dest, { i: "bar", p: 6 }
+			dest.should.deep.equal [{ i: "foo", p: 3, u: true }, { i: "bar", p: 6 }]
+	
+		it "should combine adjacent deletes", ->
+			dest = [{ d: "bar", p: 6 }]
+			text._append dest, { d: "foobaz", p: 3 }
+			dest.should.deep.equal [{ d: "foobarbaz", p: 3 }]
+
+		it "should combine adjacent undo deletes", ->
+			dest = [{ d: "foo", p: 3, u: true }]
+			text._append dest, { d: "bar", p: 3, u: true }
+			dest.should.deep.equal [{ d: "foobar", p: 3, u: true }]
+
+		it "should not combine an undo and a normal insert", ->
+			dest = [{ d: "foo", p: 3, u: true }]
+			text._append dest, { d: "bar", p: 3 }
+			dest.should.deep.equal [{ d: "foo", p: 3, u: true }, { d: "bar", p: 3 }]
+	
 	describe "applying ops and comments in different orders", ->
 		it "should not matter which op or comment is applied first", ->
 			transform = (op1, op2, side) ->

From d56bb5595320cbc2a0273ed98421ea85b0f6c417 Mon Sep 17 00:00:00 2001
From: James Allen <james@sharelatex.com>
Date: Wed, 1 Mar 2017 16:49:46 +0000
Subject: [PATCH 3/7] Revert PR #19

---
 .../app/coffee/RangesTracker.coffee           | 78 +++++++------------
 .../app/coffee/sharejs/types/text-api.coffee  | 16 ++--
 .../app/coffee/sharejs/types/text.coffee      | 33 ++++----
 .../coffee/ShareJS/TextTransformTests.coffee  | 53 +------------
 4 files changed, 49 insertions(+), 131 deletions(-)

diff --git a/services/document-updater/app/coffee/RangesTracker.coffee b/services/document-updater/app/coffee/RangesTracker.coffee
index a9c43e9816..865ecf4ef6 100644
--- a/services/document-updater/app/coffee/RangesTracker.coffee
+++ b/services/document-updater/app/coffee/RangesTracker.coffee
@@ -1,5 +1,5 @@
-load = () ->
-	class RangesTracker
+load = (EventEmitter) ->
+	class RangesTracker extends EventEmitter
 		# The purpose of this class is to track a set of inserts and deletes to a document, like
 		# track changes in Word. We store these as a set of ShareJs style ranges:
 		#   {i: "foo", p: 42} # Insert 'foo' at offset 42
@@ -36,7 +36,6 @@ load = () ->
 		#     middle of a previous insert by the first user, the original insert will be split into two.
 		constructor: (@changes = [], @comments = []) ->
 			@setIdSeed(RangesTracker.generateIdSeed())
-			@resetDirtyState()
 
 		getIdSeed: () ->
 			return @id_seed
@@ -76,7 +75,7 @@ load = () ->
 			comment = @getComment(comment_id)
 			return if !comment?
 			@comments = @comments.filter (c) -> c.id != comment_id
-			@_markAsDirty comment, "comment", "removed"
+			@emit "comment:removed", comment
 		
 		getChange: (change_id) ->
 			change = null
@@ -104,11 +103,7 @@ load = () ->
 				@addComment(op, metadata)
 			else
 				throw new Error("unknown op type")
-
-		applyOps: (ops, metadata = {}) ->
-			for op in ops
-				@applyOp(op, metadata)
-
+			
 		addComment: (op, metadata) ->
 			# TODO: Don't allow overlapping comments?
 			@comments.push comment = {
@@ -119,18 +114,18 @@ load = () ->
 					t: op.t
 				metadata
 			}
-			@_markAsDirty comment, "comment", "added"
+			@emit "comment:added", comment
 			return comment
 		
 		applyInsertToComments: (op) ->
 			for comment in @comments
 				if op.p <= comment.op.p
 					comment.op.p += op.i.length
-					@_markAsDirty comment, "comment", "moved"
+					@emit "comment:moved", comment
 				else if op.p < comment.op.p + comment.op.c.length
 					offset = op.p - comment.op.p
 					comment.op.c = comment.op.c[0..(offset-1)] + op.i + comment.op.c[offset...]
-					@_markAsDirty comment, "comment", "moved"
+					@emit "comment:moved", comment
 
 		applyDeleteToComments: (op) ->
 			op_start = op.p
@@ -143,7 +138,7 @@ load = () ->
 				if op_end <= comment_start
 					# delete is fully before comment
 					comment.op.p -= op_length
-					@_markAsDirty comment, "comment", "moved"
+					@emit "comment:moved", comment
 				else if op_start >= comment_end
 					# delete is fully after comment, nothing to do
 				else
@@ -166,13 +161,12 @@ load = () ->
 					
 					comment.op.p = Math.min(comment_start, op_start)
 					comment.op.c = remaining_before + remaining_after
-					@_markAsDirty comment, "comment", "moved"
+					@emit "comment:moved", comment
 
 		applyInsertToChanges: (op, metadata) ->
 			op_start = op.p
 			op_length = op.i.length
 			op_end = op.p + op_length
-			undoing = !!op.u
 
 
 			already_merged = false
@@ -190,9 +184,8 @@ load = () ->
 						change.op.p += op_length
 						moved_changes.push change
 					else if op_start == change_start
-						# If we are undoing, then we want to cancel any existing delete ranges if we can.
-						# Check if the insert matches the start of the delete, and just remove it from the delete instead if so.
-						if undoing and change.op.d.length >= op.i.length and change.op.d.slice(0, op.i.length) == op.i
+						# If the insert matches the start of the delete, just remove it from the delete instead
+						if change.op.d.length >= op.i.length and change.op.d.slice(0, op.i.length) == op.i
 							change.op.d = change.op.d.slice(op.i.length)
 							change.op.p += op.i.length
 							if change.op.d == ""
@@ -210,15 +203,15 @@ load = () ->
 					# Only merge inserts if they are from the same user
 					is_same_user = metadata.user_id == change.metadata.user_id
 					
-					# If we are undoing, then our changes will be removed from any delete ops just after. In that case, if there is also
-					# an insert op just before, then we shouldn't append it to this insert, but instead only cancel the following delete.
+					# If this is an insert op at the end of an existing insert with a delete following, and it cancels out the following
+					# delete then we shouldn't append it to this insert, but instead only cancel the following delete.
 					# E.g.
 					#                   foo|<--- about to insert 'b' here
 					#  inserted 'foo'  --^ ^-- deleted 'bar'
 					# should become just 'foo' not 'foob' (with the delete marker becoming just 'ar'), .
 					next_change = @changes[i+1]
 					is_op_adjacent_to_next_delete = next_change? and next_change.op.d? and op.p == change_end and next_change.op.p == op.p
-					will_op_cancel_next_delete = undoing and is_op_adjacent_to_next_delete and next_change.op.d.slice(0, op.i.length) == op.i
+					will_op_cancel_next_delete = is_op_adjacent_to_next_delete and next_change.op.d.slice(0, op.i.length) == op.i
 					
 					# If there is a delete at the start of the insert, and we're inserting
 					# at the start, we SHOULDN'T merge since the delete acts as a partition.
@@ -288,8 +281,8 @@ load = () ->
 			for change in remove_changes
 				@_removeChange change
 			
-			for change in moved_changes
-				@_markAsDirty change, "change", "moved"
+			if moved_changes.length > 0
+				@emit "changes:moved", moved_changes
 		
 		applyDeleteToChanges: (op, metadata) ->
 			op_start = op.p
@@ -413,8 +406,8 @@ load = () ->
 					@_removeChange change
 					moved_changes = moved_changes.filter (c) -> c != change
 			
-			for change in moved_changes
-				@_markAsDirty change, "change", "moved"
+			if moved_changes.length > 0
+				@emit "changes:moved", moved_changes
 
 		_addOp: (op, metadata) ->
 			change = {
@@ -434,11 +427,17 @@ load = () ->
 				else
 					return -1
 
-			@_markAsDirty(change, "change", "added")
+			if op.d?
+				@emit "delete:added", change
+			else if op.i?
+				@emit "insert:added", change
 		
 		_removeChange: (change) ->
 			@changes = @changes.filter (c) -> c.id != change.id
-			@_markAsDirty change, "change", "removed"
+			if change.op.d?
+				@emit "delete:removed", change
+			else if change.op.i?
+				@emit "insert:removed", change
 			
 		_applyOpModifications: (content, op_modifications) ->
 			# Put in descending position order, with deleting first if at the same offset 
@@ -487,32 +486,13 @@ load = () ->
 					previous_change = change
 			return { moved_changes, remove_changes }
 		
-		resetDirtyState: () ->
-			@_dirtyState = {
-				comment: {
-					moved: {}
-					removed: {}
-					added: {}
-				}
-				change: {
-					moved: {}
-					removed: {}
-					added: {}
-				}
-			}
-		
-		getDirtyState: () ->
-			return @_dirtyState
-		
-		_markAsDirty: (object, type, action) ->
-			@_dirtyState[type][action][object.id] = object
-		
 		_clone: (object) ->
 			clone = {}
 			(clone[k] = v for k,v of object)
 			return clone
 
 if define?
-	define [], load
+	define ["utils/EventEmitter"], load
 else
-	module.exports = load()
+	EventEmitter = require("events").EventEmitter
+	module.exports = load(EventEmitter)
\ No newline at end of file
diff --git a/services/document-updater/app/coffee/sharejs/types/text-api.coffee b/services/document-updater/app/coffee/sharejs/types/text-api.coffee
index 98bb3fd503..96243ceffb 100644
--- a/services/document-updater/app/coffee/sharejs/types/text-api.coffee
+++ b/services/document-updater/app/coffee/sharejs/types/text-api.coffee
@@ -11,20 +11,14 @@ text.api =
   # Get the text contents of a document
   getText: -> @snapshot
 
-  insert: (pos, text, fromUndo, callback) ->
-    op = {p:pos, i:text}
-    if fromUndo
-      op.u = true
-    op = [op]
+  insert: (pos, text, callback) ->
+    op = [{p:pos, i:text}]
     
     @submitOp op, callback
     op
   
-  del: (pos, length, fromUndo, callback) ->
-    op = {p:pos, d:@snapshot[pos...(pos + length)]}
-    if fromUndo
-      op.u = true
-    op = [op]
+  del: (pos, length, callback) ->
+    op = [{p:pos, d:@snapshot[pos...(pos + length)]}]
 
     @submitOp op, callback
     op
@@ -34,5 +28,5 @@ text.api =
       for component in op
         if component.i != undefined
           @emit 'insert', component.p, component.i
-        else if component.d != undefined
+        else
           @emit 'delete', component.p, component.d
diff --git a/services/document-updater/app/coffee/sharejs/types/text.coffee b/services/document-updater/app/coffee/sharejs/types/text.coffee
index ee7bf57043..2a3b79997d 100644
--- a/services/document-updater/app/coffee/sharejs/types/text.coffee
+++ b/services/document-updater/app/coffee/sharejs/types/text.coffee
@@ -56,13 +56,6 @@ text.apply = (snapshot, op) ->
       throw new Error "Unknown op type"
   snapshot
 
-cloneAndModify = (op, modifications) ->
-  newOp = {}
-  for k,v of op
-    newOp[k] = v
-  for k,v of modifications
-    newOp[k] = v
-  return newOp
 
 # Exported for use by the random op generator.
 #
@@ -76,10 +69,10 @@ text._append = append = (newOp, c) ->
     last = newOp[newOp.length - 1]
 
     # Compose the insert into the previous insert if possible
-    if last.i? && c.i? and last.p <= c.p <= (last.p + last.i.length) and last.u == c.u
-      newOp[newOp.length - 1] = cloneAndModify(last, {i:strInject(last.i, c.p - last.p, c.i)})
-    else if last.d? && c.d? and c.p <= last.p <= (c.p + c.d.length) and last.u == c.u
-      newOp[newOp.length - 1] = cloneAndModify(last, {d:strInject(c.d, last.p - c.p, last.d), p: c.p})
+    if last.i? && c.i? and last.p <= c.p <= (last.p + last.i.length)
+      newOp[newOp.length - 1] = {i:strInject(last.i, c.p - last.p, c.i), p:last.p}
+    else if last.d? && c.d? and c.p <= last.p <= (c.p + c.d.length)
+      newOp[newOp.length - 1] = {d:strInject(c.d, last.p - c.p, last.d), p:c.p}
     else
       newOp.push c
 
@@ -157,25 +150,25 @@ text._tc = transformComponent = (dest, c, otherC, side) ->
   checkValidOp [otherC]
 
   if c.i?
-    append dest, cloneAndModify(c, {p:transformPosition(c.p, otherC, side == 'right')})
+    append dest, {i:c.i, p:transformPosition(c.p, otherC, side == 'right')}
 
   else if c.d? # Delete
     if otherC.i? # delete vs insert
       s = c.d
       if c.p < otherC.p
-        append dest, cloneAndModify(c, {d:s[...otherC.p - c.p]})
+        append dest, {d:s[...otherC.p - c.p], p:c.p}
         s = s[(otherC.p - c.p)..]
       if s != ''
-        append dest, cloneAndModify(c, {d:s, p:c.p + otherC.i.length})
+        append dest, {d:s, p:c.p + otherC.i.length}
 
     else if otherC.d? # Delete vs delete
       if c.p >= otherC.p + otherC.d.length
-        append dest, cloneAndModify(c, {p:c.p - otherC.d.length})
+        append dest, {d:c.d, p:c.p - otherC.d.length}
       else if c.p + c.d.length <= otherC.p
         append dest, c
       else
         # They overlap somewhere.
-        newC = cloneAndModify(c, {d:''})
+        newC = {d:'', p:c.p}
         if c.p < otherC.p
           newC.d = c.d[...(otherC.p - c.p)]
         if c.p + c.d.length > otherC.p + otherC.d.length
@@ -205,18 +198,18 @@ text._tc = transformComponent = (dest, c, otherC, side) ->
       if c.p < otherC.p < c.p + c.c.length
         offset = otherC.p - c.p
         new_c = (c.c[0..(offset-1)] + otherC.i + c.c[offset...])
-        append dest, cloneAndModify(c, {c:new_c})
+        append dest, {c:new_c, p:c.p, t: c.t}
       else
-        append dest, cloneAndModify(c, {p:transformPosition(c.p, otherC, true)})
+        append dest, {c:c.c, p:transformPosition(c.p, otherC, true), t: c.t}
     
     else if otherC.d?
       if c.p >= otherC.p + otherC.d.length
-        append dest, cloneAndModify(c, {p:c.p - otherC.d.length})
+        append dest, {c:c.c, p:c.p - otherC.d.length, t: c.t}
       else if c.p + c.c.length <= otherC.p
         append dest, c
       else # Delete overlaps comment
         # They overlap somewhere.
-        newC = cloneAndModify(c, {c:''})
+        newC = {c:'', p:c.p, t: c.t}
         if c.p < otherC.p
           newC.c = c.c[...(otherC.p - c.p)]
         if c.p + c.c.length > otherC.p + otherC.d.length
diff --git a/services/document-updater/test/unit/coffee/ShareJS/TextTransformTests.coffee b/services/document-updater/test/unit/coffee/ShareJS/TextTransformTests.coffee
index 5477b47b38..81440bfe5b 100644
--- a/services/document-updater/test/unit/coffee/ShareJS/TextTransformTests.coffee
+++ b/services/document-updater/test/unit/coffee/ShareJS/TextTransformTests.coffee
@@ -27,11 +27,6 @@ describe "ShareJS text type", ->
 				dest = []
 				text._tc(dest, { i: "foo", p: 3 }, { i: "bar", p: 3 }, 'left')
 				dest.should.deep.equal [{ i: "foo", p: 3 }]
-			
-			it "should preserve the undo flag", ->
-				dest = []
-				text._tc(dest, { i: "foo", p: 9, u: true }, { i: "bar", p: 3 })
-				dest.should.deep.equal [{ i: "foo", p: 12, u: true }]
 
 		describe "insert / delete", ->
 			it "with a delete before", ->
@@ -51,13 +46,9 @@ describe "ShareJS text type", ->
 
 			it "with a delete at the same place with side == 'left'", ->
 				dest = []
+				
 				text._tc(dest, { i: "foo", p: 3 }, { d: "bar", p: 3 }, 'left')
 				dest.should.deep.equal [{ i: "foo", p: 3 }]
-			
-			it "should preserve the undo flag", ->
-				dest = []
-				text._tc(dest, { i: "foo", p: 9, u: true }, { d: "bar", p: 3 })
-				dest.should.deep.equal [{ i: "foo", p: 6, u: true }]
 
 		describe "delete / insert", ->
 			it "with an insert before", ->
@@ -84,11 +75,7 @@ describe "ShareJS text type", ->
 				dest = []
 				text._tc(dest, { d: "foo", p: 3 }, { i: "bar", p: 4 })
 				dest.should.deep.equal [{ d: "f", p: 3 }, { d: "oo", p: 6 }]
-			
-			it "should preserve the undo flag", ->
-				dest = []
-				text._tc(dest, { d: "foo", p: 9, u: true }, { i: "bar", p: 3 })
-				dest.should.deep.equal [{ d: "foo", p: 12, u: true }]
+				
 
 		describe "delete / delete", ->
 			it "with a delete before", ->
@@ -125,11 +112,6 @@ describe "ShareJS text type", ->
 				dest = []
 				text._tc(dest, { d: "foo", p: 6 }, { d: "abcfoo123", p: 3 })
 				dest.should.deep.equal []
-			
-			it "should preserve the undo flag", ->
-				dest = []
-				text._tc(dest, { d: "foo", p: 9, u: true }, { d: "bar", p: 3 })
-				dest.should.deep.equal [{ d: "foo", p: 6, u: true }]
 	
 		describe "comment / insert", ->
 			it "with an insert before", ->
@@ -228,37 +210,6 @@ describe "ShareJS text type", ->
 				text.apply("foo123bar", [{ c: "456", p: 3 }])
 			).should.throw(Error)
 	
-	describe "_append", ->
-		it "should combine adjacent inserts", ->
-			dest = [{ i: "foo", p: 3 }]
-			text._append dest, { i: "bar", p: 6 }
-			dest.should.deep.equal [{ i: "foobar", p: 3 }]
-
-		it "should combine adjacent undo inserts", ->
-			dest = [{ i: "foo", p: 3, u: true }]
-			text._append dest, { i: "bar", p: 6, u: true }
-			dest.should.deep.equal [{ i: "foobar", p: 3, u: true }]
-
-		it "should not combine an undo and a normal insert", ->
-			dest = [{ i: "foo", p: 3, u: true }]
-			text._append dest, { i: "bar", p: 6 }
-			dest.should.deep.equal [{ i: "foo", p: 3, u: true }, { i: "bar", p: 6 }]
-	
-		it "should combine adjacent deletes", ->
-			dest = [{ d: "bar", p: 6 }]
-			text._append dest, { d: "foobaz", p: 3 }
-			dest.should.deep.equal [{ d: "foobarbaz", p: 3 }]
-
-		it "should combine adjacent undo deletes", ->
-			dest = [{ d: "foo", p: 3, u: true }]
-			text._append dest, { d: "bar", p: 3, u: true }
-			dest.should.deep.equal [{ d: "foobar", p: 3, u: true }]
-
-		it "should not combine an undo and a normal insert", ->
-			dest = [{ d: "foo", p: 3, u: true }]
-			text._append dest, { d: "bar", p: 3 }
-			dest.should.deep.equal [{ d: "foo", p: 3, u: true }, { d: "bar", p: 3 }]
-	
 	describe "applying ops and comments in different orders", ->
 		it "should not matter which op or comment is applied first", ->
 			transform = (op1, op2, side) ->

From b186a01c04596c38d4cf9f652d23fd8dc8225b50 Mon Sep 17 00:00:00 2001
From: Brian Gough <bjg@network-theory.co.uk>
Date: Fri, 3 Mar 2017 15:27:42 +0000
Subject: [PATCH 4/7] don't log errors from redis backend

this also picks up errors from RedisManager like "doc ops range is not
loaded in redis"
---
 services/document-updater/app/coffee/RedisBackend.coffee | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/services/document-updater/app/coffee/RedisBackend.coffee b/services/document-updater/app/coffee/RedisBackend.coffee
index 9ec479c01f..d69cd21a6e 100644
--- a/services/document-updater/app/coffee/RedisBackend.coffee
+++ b/services/document-updater/app/coffee/RedisBackend.coffee
@@ -100,7 +100,8 @@ class MultiClient
 					cb(error, result)
 		async.parallel jobs, (error, results) ->
 			if error?
-				logger.error {err: error}, "error in redis backend"
+				# suppress logging of errors
+				# logger.error {err: error}, "error in redis backend"
 			else
 				compareResults(results, "exec")
 			callback(primaryError, primaryResult)

From 3f13263ecfebbc6dd4da584031fce96df85a3f4e Mon Sep 17 00:00:00 2001
From: Brian Gough <bjg@network-theory.co.uk>
Date: Fri, 3 Mar 2017 15:32:11 +0000
Subject: [PATCH 5/7] upgrade to logger-sharelatex 1.5.3

---
 services/document-updater/package.json | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/services/document-updater/package.json b/services/document-updater/package.json
index 72a2e28121..76bb426cf4 100644
--- a/services/document-updater/package.json
+++ b/services/document-updater/package.json
@@ -11,7 +11,7 @@
     "coffee-script": "1.4.0",
     "express": "3.3.4",
     "ioredis": "^2.2.0",
-    "logger-sharelatex": "git+https://github.com/sharelatex/logger-sharelatex.git#v1.5.2",
+    "logger-sharelatex": "git+https://github.com/sharelatex/logger-sharelatex.git#v1.5.3",
     "lynx": "0.0.11",
     "metrics-sharelatex": "git+https://github.com/sharelatex/metrics-sharelatex.git#v1.5.0",
     "redis-sharelatex": "0.0.9",

From d086e0b61b032a34ecec503596c14524e96af013 Mon Sep 17 00:00:00 2001
From: Brian Gough <bjg@network-theory.co.uk>
Date: Fri, 3 Mar 2017 15:57:44 +0000
Subject: [PATCH 6/7] log doclines on hash mismatch

---
 services/document-updater/app/coffee/RedisManager.coffee | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/services/document-updater/app/coffee/RedisManager.coffee b/services/document-updater/app/coffee/RedisManager.coffee
index d822f4ef74..1ce0062fe6 100644
--- a/services/document-updater/app/coffee/RedisManager.coffee
+++ b/services/document-updater/app/coffee/RedisManager.coffee
@@ -52,7 +52,7 @@ module.exports = RedisManager =
 			# check the hash computed on the redis server
 			writeHash = result?[0]
 			if logHashWriteErrors and writeHash? and writeHash isnt docHash
-				logger.error project_id: project_id, doc_id: doc_id, writeHash: writeHash, origHash: docHash, "hash mismatch on putDocInMemory"
+				logger.error project_id: project_id, doc_id: doc_id, writeHash: writeHash, origHash: docHash, docLines:docLines, "hash mismatch on putDocInMemory"
 			# update docsInProject set
 			rclient.sadd keys.docsInProject(project_id:project_id), doc_id, callback
 
@@ -92,7 +92,7 @@ module.exports = RedisManager =
 			if docLines? and storedHash?
 				computedHash = RedisManager._computeHash(docLines)
 				if logHashReadErrors and computedHash isnt storedHash
-					logger.error project_id: project_id, doc_id: doc_id, doc_project_id: doc_project_id, computedHash: computedHash, storedHash: storedHash, "hash mismatch on retrieved document"
+					logger.error project_id: project_id, doc_id: doc_id, doc_project_id: doc_project_id, computedHash: computedHash, storedHash: storedHash, docLines:docLines, "hash mismatch on retrieved document"
 
 			try
 				docLines = JSON.parse docLines
@@ -181,7 +181,7 @@ module.exports = RedisManager =
 					# check the hash computed on the redis server
 					writeHash = result?[0]
 					if logHashWriteErrors and writeHash? and writeHash isnt newHash
-						logger.error doc_id: doc_id, writeHash: writeHash, origHash: newHash, "hash mismatch on updateDocument"
+						logger.error doc_id: doc_id, writeHash: writeHash, origHash: newHash, docLines:newDocLines, "hash mismatch on updateDocument"
 					return callback()
 
 	getDocIdsInProject: (project_id, callback = (error, doc_ids) ->) ->

From 501d907299cf8265d7d3b32e10f10d6de7fb355e Mon Sep 17 00:00:00 2001
From: Brian Gough <bjg@network-theory.co.uk>
Date: Fri, 3 Mar 2017 16:08:14 +0000
Subject: [PATCH 7/7] upgrade to logger-sharelatex 1.5.4

---
 services/document-updater/package.json | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/services/document-updater/package.json b/services/document-updater/package.json
index 76bb426cf4..9f8439ea04 100644
--- a/services/document-updater/package.json
+++ b/services/document-updater/package.json
@@ -11,7 +11,7 @@
     "coffee-script": "1.4.0",
     "express": "3.3.4",
     "ioredis": "^2.2.0",
-    "logger-sharelatex": "git+https://github.com/sharelatex/logger-sharelatex.git#v1.5.3",
+    "logger-sharelatex": "git+https://github.com/sharelatex/logger-sharelatex.git#v1.5.4",
     "lynx": "0.0.11",
     "metrics-sharelatex": "git+https://github.com/sharelatex/metrics-sharelatex.git#v1.5.0",
     "redis-sharelatex": "0.0.9",