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CausalTreeStringWrapper.swift
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CausalTreeStringWrapper.swift
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//
// CausalTreeStringWrapper.swift
// CloudKitRealTimeCollabTest
//
// Created by Alexei Baboulevitch on 2017-10-20.
// Copyright © 2017 Alexei Baboulevitch. All rights reserved.
//
import Foundation
// AB: The extra cache in this class on top of the existing cache in the slice adds extra complexity.
class CausalTreeStringWrapper: NSMutableString
{
// MARK: - Model -
private(set) weak var crdt: CausalTreeString!
var revision: CausalTreeString.WeftT?
{
didSet
{
if revision != oldValue
{
_slice = nil
}
}
}
// MARK: - Caches -
private var _slice: CausalTreeString.WeaveT.AtomsSlice?
private var slice: CausalTreeString.WeaveT.AtomsSlice
{
if let revision = self.revision
{
if _slice == nil || _slice!.invalid
{
_slice = crdt.weave.weave(withWeft: crdt.convert(weft: revision))
assert(_slice != nil, "could not convert revision to local weft")
updateCache()
}
return _slice!
}
else
{
if _slice == nil || _slice!.invalid
{
_slice = crdt.weave.weave(withWeft: nil)
updateCache()
}
return _slice!
}
}
private var _visibleCharacters: [WeaveIndex] = []
private var visibleCharacters: [WeaveIndex]
{
let _ = self.slice //ensures that all our caches are up to date
return _visibleCharacters
}
// MARK: - Lifecycle -
func initialize(crdt: CausalTreeString, revision: CausalTreeString.WeftT? = nil)
{
self.crdt = crdt
self.revision = revision
updateCache()
}
// O(N), so use sparingly
private func updateCache()
{
let weave = self.slice
_visibleCharacters.removeAll()
var i = 0
while i < weave.count
{
if case .insert(_) = weave[i].value
{
var j = 0
while (i + j + 1) < weave.count
{
if case .delete = weave[i + j + 1].value
{
j += 1
}
else
{
break
}
}
if j == 0 //not deleted
{
_visibleCharacters.append(WeaveIndex(i))
}
i += (j + 1)
}
else
{
i += 1
}
}
}
func atomForCharacterAtIndex(_ i: Int) -> AtomId?
{
if i > visibleCharacters.count || i < 0
{
return nil
}
if i == 0
{
return slice[0].id
}
else
{
return slice[Int(visibleCharacters[i - 1])].id
}
}
// TODO: PERF: this is currently O(SxN), and will need tuning before production use
func characterIndexForAtom(_ a: AtomId) -> Int?
{
if a == slice[0].id
{
return 0
}
for c in 0..<visibleCharacters.count
{
if slice[Int(visibleCharacters[c])].id == a
{
return c + 1
}
}
return nil
}
// MARK: - Essential Overrides -
override var length: Int
{
return self.visibleCharacters.count
}
override func character(at index: Int) -> unichar
{
let i = self.visibleCharacters[index]
if case .insert(let char) = self.slice[Int(i)].value
{
return char
}
else
{
assert(false)
return 0
}
}
// TODO: PERF: batch deletes and inserts, otherwise it's O(N^2) per length of insert, which is egregious for pastes
override func replaceCharacters(in range: NSRange, with aString: String)
{
let anchor: AtomId
if range.location == 0
{
anchor = slice[0].id
}
else
{
let index = visibleCharacters[range.location - 1]
anchor = slice[Int(index)].id
}
var atomsToDelete: [AtomId] = []
for i in range.lowerBound..<range.upperBound
{
let index = visibleCharacters[i]
atomsToDelete.append(slice[Int(index)].id)
}
insert: do
{
var prevChar = anchor
for char in aString.utf16
{
prevChar = crdt.weave.addAtom(withValue: StringCharacterAtom(insert: char), causedBy: prevChar)!.0
}
}
delete: do
{
for a in atomsToDelete
{
let _ = crdt.weave.addAtom(withValue: StringCharacterAtom.init(withDelete: true), causedBy: a)
}
}
// PERF: cache update after this point is slow, should delta-update
//updateCache()
}
}