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overleaf/services/document-updater/app/coffee/ChangesTracker.coffee
James Allen e739e86c48 Get basic ChangeTracker hooked up. WIP
2016-11-28 10:14:42 +00:00

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load = (EventEmitter) ->
class ChangesTracker 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
# {d: "bar", p: 37} # Delete 'bar' at offset 37
# We only track the inserts and deletes, not the whole document, but by being given all
# updates that are applied to a document, we can update these appropriately.
#
# Note that the set of inserts and deletes we store applies to the document as-is at the moment.
# So inserts correspond to text which is in the document, while deletes correspond to text which
# is no longer there, so their lengths do not affect the position of later offsets.
# E.g.
# this is the current text of the document
# |-----| |
# {i: "current ", p:12} -^ ^- {d: "old ", p: 31}
#
# Track changes rules (should be consistent with Word):
# * When text is inserted at a delete, the text goes to the left of the delete
# I.e. "foo|bar" -> "foobaz|bar", where | is the delete, and 'baz' is inserted
# * Deleting content flagged as 'inserted' does not create a new delete marker, it only
# removes the insert marker. E.g.
# * "abdefghijkl" -> "abfghijkl" when 'de' is deleted. No delete marker added
# |---| <- inserted |-| <- inserted
# * Deletes overlapping regular text and inserted text will insert a delete marker for the
# regular text:
# "abcdefghijkl" -> "abcdejkl" when 'fghi' is deleted
# |----| |--||
# ^- inserted 'bcdefg' \ ^- deleted 'hi'
# \--inserted 'bcde'
# * Deletes overlapping other deletes are merged. E.g.
# "abcghijkl" -> "ahijkl" when 'bcg is deleted'
# | <- delete 'def' | <- delete 'bcdefg'
# * Deletes by another user will consume deletes by the first user
# * Inserts by another user will not combine with inserts by the first user. If they are in the
# middle of a previous insert by the first user, the original insert will be split into two.
constructor: (@changes = [], @comments = []) ->
# Change objects have the following structure:
# {
# id: ... # Uniquely generated by us
# op: { # ShareJs style op tracking the offset (p) and content inserted (i) or deleted (d)
# i: "..."
# p: 42
# }
# }
#
# Ids are used to uniquely identify a change, e.g. for updating it in the database, or keeping in
# sync with Ace ranges.
@id = 0
addComment: (offset, length, metadata) ->
# TODO: Don't allow overlapping comments?
@comments.push comment = {
id: @_newId()
offset, length, metadata
}
@emit "comment:added", comment
return comment
getComment: (comment_id) ->
comment = null
for c in @comments
if c.id == comment_id
comment = c
break
return comment
resolveCommentId: (comment_id, resolved_data) ->
comment = @getComment(comment_id)
return if !comment?
comment.metadata.resolved = true
comment.metadata.resolved_data = resolved_data
@emit "comment:resolved", comment
unresolveCommentId: (comment_id) ->
comment = @getComment(comment_id)
return if !comment?
comment.metadata.resolved = false
@emit "comment:unresolved", comment
removeCommentId: (comment_id) ->
comment = @getComment(comment_id)
return if !comment?
@comments = @comments.filter (c) -> c.id != comment_id
@emit "comment:removed", comment
getChange: (change_id) ->
change = null
for c in @changes
if c.id == change_id
change = c
break
return change
removeChangeId: (change_id) ->
change = @getChange(change_id)
return if !change?
@_removeChange(change)
applyOp: (op, metadata = {}) ->
metadata.ts ?= new Date()
# Apply an op that has been applied to the document to our changes to keep them up to date
if op.i?
@applyInsertToChanges(op, metadata)
@applyInsertToComments(op)
else if op.d?
@applyDeleteToChanges(op, metadata)
@applyDeleteToComments(op)
applyInsertToComments: (op) ->
for comment in @comments
if op.p <= comment.offset
comment.offset += op.i.length
@emit "comment:moved", comment
else if op.p < comment.offset + comment.length
comment.length += op.i.length
@emit "comment:moved", comment
applyDeleteToComments: (op) ->
op_start = op.p
op_length = op.d.length
op_end = op.p + op_length
for comment in @comments
comment_end = comment.offset + comment.length
if op_end <= comment.offset
# delete is fully before comment
comment.offset -= op_length
@emit "comment:moved", comment
else if op_start >= comment_end
# delete is fully after comment, nothing to do
else
# delete and comment overlap
delete_length_before = Math.max(0, comment.offset - op_start)
delete_length_after = Math.max(0, op_end - comment_end)
delete_length_overlapping = op_length - delete_length_before - delete_length_after
comment.offset = Math.min(comment.offset, op_start)
comment.length -= delete_length_overlapping
@emit "comment:moved", comment
applyInsertToChanges: (op, metadata) ->
op_start = op.p
op_length = op.i.length
op_end = op.p + op_length
already_merged = false
previous_change = null
moved_changes = []
remove_changes = []
new_changes = []
for change in @changes
change_start = change.op.p
if change.op.d?
# Shift any deletes after this along by the length of this insert
if op_start < change_start
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
change.op.d = change.op.d.slice(op.i.length)
change.op.p += op.i.length
if change.op.d == ""
remove_changes.push change
else
moved_changes.push change
already_merged = true
else
change.op.p += op_length
moved_changes.push change
else if change.op.i?
change_end = change_start + change.op.i.length
is_change_overlapping = (op_start >= change_start and op_start <= change_end)
# Only merge inserts if they are from the same user
is_same_user = metadata.user_id == change.metadata.user_id
# 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.
# The previous op will be the delete, but it's already been shifted by this insert
#
# I.e.
# Originally: |-- existing insert --|
# | <- existing delete at same offset
#
# Now: |-- existing insert --| <- not shifted yet
# |-- this insert --|| <- existing delete shifted along to end of this op
#
# After: |-- existing insert --|
# |-- this insert --|| <- existing delete
#
# Without the delete, the inserts would be merged.
is_insert_blocked_by_delete = (previous_change? and previous_change.op.d? and previous_change.op.p == op_end)
# If the insert is overlapping another insert, either at the beginning in the middle or touching the end,
# then we merge them into one.
if @track_changes and
is_change_overlapping and
!is_insert_blocked_by_delete and
!already_merged and
is_same_user
offset = op_start - change_start
change.op.i = change.op.i.slice(0, offset) + op.i + change.op.i.slice(offset)
change.metadata.ts = metadata.ts
already_merged = true
moved_changes.push change
else if op_start <= change_start
# If we're fully before the other insert we can just shift the other insert by our length.
# If they are touching, and should have been merged, they will have been above.
# If not merged above, then it must be blocked by a delete, and will be after this insert, so we shift it along as well
change.op.p += op_length
moved_changes.push change
else if (!is_same_user or !@track_changes) and change_start < op_start < change_end
# This user is inserting inside a change by another user, so we need to split the
# other user's change into one before and after this one.
offset = op_start - change_start
before_content = change.op.i.slice(0, offset)
after_content = change.op.i.slice(offset)
# The existing change can become the 'before' change
change.op.i = before_content
moved_changes.push change
# Create a new op afterwards
after_change = {
op: {
i: after_content
p: change_start + offset + op_length
}
metadata: {}
}
after_change.metadata[key] = value for key, value of change.metadata
new_changes.push after_change
previous_change = change
if @track_changes and !already_merged
@_addOp op, metadata
for {op, metadata} in new_changes
@_addOp op, metadata
for change in remove_changes
@_removeChange change
if moved_changes.length > 0
@emit "changes:moved", moved_changes
applyDeleteToChanges: (op, metadata) ->
op_start = op.p
op_length = op.d.length
op_end = op.p + op_length
remove_changes = []
moved_changes = []
# We might end up modifying our delete op if it merges with existing deletes, or cancels out
# with an existing insert. Since we might do multiple modifications, we record them and do
# all the modifications after looping through the existing changes, so as not to mess up the
# offset indexes as we go.
op_modifications = []
for change in @changes
if change.op.i?
change_start = change.op.p
change_end = change_start + change.op.i.length
if op_end <= change_start
# Shift ops after us back by our length
change.op.p -= op_length
moved_changes.push change
else if op_start >= change_end
# Delete is after insert, nothing to do
else
# When the new delete overlaps an insert, we should remove the part of the insert that
# is now deleted, and also remove the part of the new delete that overlapped. I.e.
# the two cancel out where they overlap.
if op_start >= change_start
# |-- existing insert --|
# insert_remaining_before -> |.....||-- new delete --|
delete_remaining_before = ""
insert_remaining_before = change.op.i.slice(0, op_start - change_start)
else
# delete_remaining_before -> |.....||-- existing insert --|
# |-- new delete --|
delete_remaining_before = op.d.slice(0, change_start - op_start)
insert_remaining_before = ""
if op_end <= change_end
# |-- existing insert --|
# |-- new delete --||.....| <- insert_remaining_after
delete_remaining_after = ""
insert_remaining_after = change.op.i.slice(op_end - change_start)
else
# |-- existing insert --||.....| <- delete_remaining_after
# |-- new delete --|
delete_remaining_after = op.d.slice(change_end - op_start)
insert_remaining_after = ""
insert_remaining = insert_remaining_before + insert_remaining_after
if insert_remaining.length > 0
change.op.i = insert_remaining
change.op.p = Math.min(change_start, op_start)
change.metadata.ts = metadata.ts
moved_changes.push change
else
remove_changes.push change
# We know what we want to preserve of our delete op before (delete_remaining_before) and what we want to preserve
# afterwards (delete_remaining_before). Now we need to turn that into a modification which deletes the
# chunk in the middle not covered by these.
delete_removed_length = op.d.length - delete_remaining_before.length - delete_remaining_after.length
delete_removed_start = delete_remaining_before.length
modification = {
d: op.d.slice(delete_removed_start, delete_removed_start + delete_removed_length)
p: delete_removed_start
}
if modification.d.length > 0
op_modifications.push modification
else if change.op.d?
change_start = change.op.p
if op_end < change_start or (!@track_changes and op_end == change_start)
# Shift ops after us back by our length.
# If we're tracking changes, it must be strictly before, since we'll merge
# below if they are touching. Otherwise, touching is fine.
change.op.p -= op_length
moved_changes.push change
else if op_start <= change_start <= op_end
if @track_changes
# If we overlap a delete, add it in our content, and delete the existing change.
# It's easier to do it this way, rather than modifying the existing delete in case
# we overlap many deletes and we'd need to track that. We have a workaround to
# update the delete in place if possible below.
offset = change_start - op_start
op_modifications.push { i: change.op.d, p: offset }
remove_changes.push change
else
change.op.p = op_start
moved_changes.push change
# Copy rather than modify because we still need to apply it to comments
op = {
p: op.p
d: @_applyOpModifications(op.d, op_modifications)
}
for change in remove_changes
# This is a bit of hack to avoid removing one delete and replacing it with another.
# If we don't do this, it causes the UI to flicker
if op.d.length > 0 and change.op.d? and op.p <= change.op.p <= op.p + op.d.length
change.op.p = op.p
change.op.d = op.d
change.metadata = metadata
moved_changes.push change
op.d = "" # stop it being added
else
@_removeChange change
if @track_changes and op.d.length > 0
@_addOp op, metadata
else
# It's possible that we deleted an insert between two other inserts. I.e.
# If we delete 'user_2 insert' in:
# |-- user_1 insert --||-- user_2 insert --||-- user_1 insert --|
# it becomes:
# |-- user_1 insert --||-- user_1 insert --|
# We need to merge these together again
results = @_scanAndMergeAdjacentUpdates()
moved_changes = moved_changes.concat(results.moved_changes)
for change in results.remove_changes
@_removeChange change
moved_changes = moved_changes.filter (c) -> c != change
if moved_changes.length > 0
@emit "changes:moved", moved_changes
_newId: () ->
(@id++).toString()
_addOp: (op, metadata) ->
change = {
id: @_newId()
op: op
metadata: metadata
}
@changes.push change
# Keep ops in order of offset, with deletes before inserts
@changes.sort (c1, c2) ->
result = c1.op.p - c2.op.p
if result != 0
return result
else if c1.op.i? and c2.op.d?
return 1
else
return -1
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
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
# (Inserting first would modify the content that the delete will delete)
op_modifications.sort (a, b) ->
result = b.p - a.p
if result != 0
return result
else if a.i? and b.d?
return 1
else
return -1
for modification in op_modifications
if modification.i?
content = content.slice(0, modification.p) + modification.i + content.slice(modification.p)
else if modification.d?
if content.slice(modification.p, modification.p + modification.d.length) != modification.d
throw new Error("deleted content does not match. content: #{JSON.stringify(content)}; modification: #{JSON.stringify(modification)}")
content = content.slice(0, modification.p) + content.slice(modification.p + modification.d.length)
return content
_scanAndMergeAdjacentUpdates: () ->
# This should only need calling when deleting an update between two
# other updates. There's no other way to get two adjacent updates from the
# same user, since they would be merged on insert.
previous_change = null
remove_changes = []
moved_changes = []
for change in @changes
if previous_change?.op.i? and change.op.i?
previous_change_end = previous_change.op.p + previous_change.op.i.length
previous_change_user_id = previous_change.metadata.user_id
change_start = change.op.p
change_user_id = change.metadata.user_id
if previous_change_end == change_start and previous_change_user_id == change_user_id
remove_changes.push change
previous_change.op.i += change.op.i
moved_changes.push previous_change
else if previous_change?.op.d? and change.op.d? and previous_change.op.p == change.op.p
# Merge adjacent deletes
previous_change.op.d += change.op.d
remove_changes.push change
moved_changes.push previous_change
else # Only update to the current change if we haven't removed it.
previous_change = change
return { moved_changes, remove_changes }
if define?
define ["utils/EventEmitter"], load
else
EventEmitter = require("events").EventEmitter
module.exports = load(EventEmitter)
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