MOBILE-1955: Switch from Dwifft to CollectionDifference

Since `Dwifft` repo is not maintained and since `SimpleSource` has
iOS 13 as a minimal supported version we can switch to Swift
standard library implementation

Examples/Podfile.lock

@@ -1,11 +1,8 @@
 PODS:
-  - Dwifft (0.9)
   - Nimble (12.3.0)
   - Quick (7.3.0)
-  - SimpleSource (3.0.0):
-    - Dwifft (~> 0.9.0)
+  - SimpleSource (3.0.0)
   - SimpleSource/Tests (3.0.0):
-    - Dwifft (~> 0.9.0)
     - Nimble (~> 12.0)
     - Quick (~> 7.0)
   - SwiftyJSON (5.0.1)
@@ -17,7 +14,6 @@ DEPENDENCIES:
 
 SPEC REPOS:
   trunk:
-    - Dwifft
     - Nimble
     - Quick
     - SwiftyJSON
@@ -27,10 +23,9 @@ EXTERNAL SOURCES:
     :path: ".."
 
 SPEC CHECKSUMS:
-  Dwifft: 42912068ed2a8146077d1a1404df18625bd086e1
   Nimble: f8a8219d16f176429b951e8f7e72df5c23ceddc0
   Quick: d32871931c05547cb4e0bc9009d66a18b50d8558
-  SimpleSource: 14b1bd2028a07d7b2a71433bed85f03ca33deb37
+  SimpleSource: 611bfe53fe55132415a3c72a9a0126f9aa846d8b
   SwiftyJSON: 2f33a42c6fbc52764d96f13368585094bfd8aa5e
 
 PODFILE CHECKSUM: a5deddba5204624da3222bdb26450e64fabfabc5

SimpleSource.podspec

@@ -9,7 +9,6 @@ Pod::Spec.new do |s|
   s.swift_version        = '5.7'
   s.source               = { :git => 'https://github.com/Squarespace/simple-source.git', :tag => s.version }
   s.source_files         = 'Sources/**/*.{h,m,swift}'
-  s.dependency           'Dwifft', '~> 0.9.0'
 
   s.test_spec 'Tests' do |test_spec|
     test_spec.resource = 'Tests/Model/*.xcdatamodeld'

Sources/Utils/Diff.swift

@@ -1,5 +1,4 @@
 import Foundation
-import Dwifft
 
 private struct WrappedIdentifiableSection<T: SectionType> {
     private let value: T
@@ -38,15 +37,13 @@ struct Diff {
 
         let oldSectionIdentifiers = oldData.map { $0.sectionIdentifier }
         let newSectionIdentifiers = newData.map { $0.sectionIdentifier }
-
-        let sectionsDiff = Dwifft.diff(oldSectionIdentifiers, newSectionIdentifiers)
 
-        sectionsDiff.forEach { step in
-            switch step {
-            case .insert:
-                insertedSections.insert(step.idx)
-            case .delete:
-                deletedSections.insert(step.idx)
+        newSectionIdentifiers.difference(from: oldSectionIdentifiers).forEach { change in
+            switch change {
+            case let .remove(offset, _, _):
+                deletedSections.insert(offset)
+            case let .insert(offset, _, _):
+                insertedSections.insert(offset)
             }
         }
 
@@ -76,20 +73,17 @@ struct Diff {
                     .map { IndexPath(item: $0.offset, section: sectionIndex) }
             } else {
                 // Calculate a diff to transform the old section items into the new section items. No in-place updates will be emitted.
-                Dwifft.diff(oldSection.items, newSection.items)
-                    .forEach { step in
-                        switch step {
-                        case .insert:
-                            let indexPath = IndexPath(item: step.idx, section: sectionIndex)
-                            insertedRows.append(indexPath)
-                        case .delete:
-                            let indexPath = IndexPath(item: step.idx, section: oldSectionIndex)
-                            deletedRows.append(indexPath)
-                        }
+                newSection.items.difference(from: oldSection.items).forEach { change in
+                    switch change {
+                    case let .remove(offset, _, _):
+                        deletedRows.append(.init(item: offset, section: oldSectionIndex))
+                    case let .insert(offset, _, _):
+                        insertedRows.append(.init(item: offset, section: sectionIndex))
                     }
+                }
             }
         }
-        
+
         return .delta(
             insertedSections: insertedSections,
             updatedSections: IndexSet(),