Upgraded: Snapshot/anchor to Snapshot/selection

Author: oscbyspro

Sources/DiffableTextKit/DiffableTextStyle.swift

@@ -89,9 +89,7 @@ public extension DiffableTextStyle {
     // MARK: Utilities
     //=------------------------------------------------------------------------=
 
-    @inlinable func update(_ cache: inout Cache) {
-        cache = self.cache()
-    }
+    @inlinable func update(_ cache: inout Cache) { cache = self.cache() }
 }
 
 //=----------------------------------------------------------------------------=

Sources/DiffableTextKit/Models/Layout.swift

@@ -13,7 +13,7 @@
 
 /// A model describing a snapshot and a selection in it.
 ///
-/// - Autocorrects selection when the snapshot changes.
+/// - Autocorrects selection when the snapshot  changes.
 /// - Autocorrects selection when the selection changes.
 ///
 @usableFromInline struct Layout {
@@ -29,8 +29,10 @@
     // MARK: Initializers
     //=------------------------------------------------------------------------=
 
-    @inlinable init(  _ snapshot: Snapshot) {
-        self.snapshot = snapshot; self.selection = .initial(snapshot) // O(n)
+    @inlinable init(_ snapshot: Snapshot) {
+        self.snapshot  = snapshot /*----------------------------*/
+        let  selection = Selection(Caret.upper(snapshot.endIndex))
+        self.selection = snapshot.resolve(selection) /*---------*/
     }
 
     //=------------------------------------------------------------------------=
@@ -69,6 +71,7 @@
             carets.upper.momentum = Direction(from: self.selection.upper, to: selection.upper)
         }
 
-        self.selection = Selection(unchecked: carets).map(snapshot.resolve(_:))
+        let  unchecked = Selection(unchecked:carets)
+        self.selection = snapshot.resolve(unchecked)
     }
 }

Sources/DiffableTextKit/Models/Selection.swift

@@ -44,11 +44,7 @@ public struct Selection<Bound: Comparable>: Equatable {
     // MARK: Initializers
     //=------------------------------------------------------------------------=
 
-    @inlinable static func initial(_ snapshot: Snapshot) -> Self where Bound == Snapshot.Index {
-        Self(snapshot.resolve(.upper(snapshot.endIndex)))
-    }
-    
-    @inlinable static func max<T>(_ collection: T) -> Self where T: Collection, T.Index == Bound {
+    @inlinable public static func max<T>(_ collection: T) -> Self where T: Collection, T.Index == Bound {
         Self(unchecked: (collection.startIndex, collection.endIndex))
     }
 

Sources/DiffableTextKit/Models/Snapshot.swift

@@ -18,18 +18,6 @@
 /// |x|o|o|x|x|o|o|o|x|x|o|o|o|x|o|x|x|x|x|~
 /// ```
 ///
-/// **Anchor**
-///
-/// Set the anchor index to select the caret represented by it. This can be
-/// desirable on snapshots containing only formatting characters. A pattern
-/// style may set the anchor at its first placeholder character, for example.
-///
-/// ```
-///    ↓ == anchor
-/// |+|#|#|_|(|#|#|#|)|_|#|#|#|-|#|#|-|#|#|~
-/// |x|x|x|x|x|x|x|x|x|x|x|x|x|x|x|x|x|x|x|~
-/// ```
-///
 /// **Attributes & Characters**
 ///
 /// The number of attributes must equal the number of joint characters in the
@@ -47,6 +35,18 @@
 /// |➖| + |➖| + |➖| + |➖| -> |➖|➖|➖|➖|~ (BAD)
 /// ```
 ///
+/// **Selection**
+///
+/// Selection is done by differentiation, but it can also be done manually. It
+/// can be appropriate on snapshots containing only formatting characters. A pattern
+/// text style may manually select its first placeholder character, for example.
+///
+/// ```
+///    ↓ == selection
+/// |+|#|#|_|(|#|#|#|)|_|#|#|#|-|#|#|-|#|#|~
+/// |x|x|x|x|x|x|x|x|x|x|x|x|x|x|x|x|x|x|x|~
+/// ```
+///
 public struct Snapshot: BidirectionalCollection, CustomStringConvertible, Equatable,
 ExpressibleByArrayLiteral, ExpressibleByStringLiteral, RangeReplaceableCollection {
 
@@ -57,9 +57,9 @@ ExpressibleByArrayLiteral, ExpressibleByStringLiteral, RangeReplaceableCollectio
     // MARK: State
     //=------------------------------------------------------------------------=
 
-    @usableFromInline var _characters: String
-    @usableFromInline var _attributes: [Attribute]
-    @usableFromInline var _anchor: Self.Index?
+    @usableFromInline private(set) var _characters: String
+    @usableFromInline private(set) var _attributes: [Attribute]
+    public var selection: Selection<Index>?
 
     //=------------------------------------------------------------------------=
     // MARK: Initializers
@@ -92,11 +92,6 @@ ExpressibleByArrayLiteral, ExpressibleByStringLiteral, RangeReplaceableCollectio
         _attributes
     }
 
-    @inlinable @inline(__always)
-    public var anchor: Index? {
-        _anchor
-    }
-    
     public var description: String {
         "\(Self.self)(\"\(_characters)\", \(_attributes))"
     }
@@ -106,13 +101,13 @@ ExpressibleByArrayLiteral, ExpressibleByStringLiteral, RangeReplaceableCollectio
     //=------------------------------------------------------------------------=
 
     @inlinable @inline(__always)
-    public mutating func anchorAtEndIndex() {
-        self._anchor = endIndex
+    public mutating func select(_  position: Index) {
+        self.selection = Selection(position)
     }
 
     @inlinable @inline(__always)
-    public mutating func anchor(at index: Index?) {
-        self._anchor = index
+    public mutating func select(_  positions: Range<Index>) {
+        self.selection = Selection(positions)
     }
 
     //=------------------------------------------------------------------------=
@@ -387,11 +382,11 @@ extension Snapshot {
     // MARK: Resolve
     //=------------------------------------------------------------------------=
 
+    @inlinable func resolve(_ selection: Selection<Caret<Index>>) -> Selection<Index> {
+        self.selection ?? selection.map(resolve)
+    }
+    
     @inlinable func resolve(_ caret: Caret<Index>) -> Index {
-        //=--------------------------------------=
-        // Anchor
-        //=--------------------------------------=
-        if let anchor { return anchor }
         //=--------------------------------------=
         // Inspect Initial Index
         //=--------------------------------------=

Sources/DiffableTextKit/Styles/Prefix.swift

@@ -17,6 +17,8 @@ public struct PrefixTextStyle<Base: DiffableTextStyle>: WrapperTextStyle {
     public typealias Cache = Base.Cache
     public typealias Value = Base.Value
 
+    @usableFromInline typealias Characters = Offset<Character>
+    
     //=------------------------------------------------------------------------=
     // MARK: State
     //=------------------------------------------------------------------------=
@@ -59,13 +61,13 @@ public struct PrefixTextStyle<Base: DiffableTextStyle>: WrapperTextStyle {
 
     @inlinable func label(_ commit: inout Commit<Value>) {
         guard !prefix.isEmpty else { return }
-        let anchor = commit.snapshot.anchor
+        let selection = commit.snapshot.selection
 
         commit.snapshot = Snapshot(prefix, as: .phantom) + commit.snapshot
 
-        guard let anchor else { return }
-        commit.snapshot.anchor(at:  commit.snapshot.index(
-        commit.snapshot.startIndex, offsetBy: prefix.count + anchor.attribute))
+        guard let selection else { return }
+        let offsets = selection.map({ Characters(prefix.count + $0.attribute) })
+        commit.snapshot.select(commit.snapshot.indices(at: offsets.positions()))
     }
 }
 

Sources/DiffableTextKitXPattern/Style.swift

@@ -117,7 +117,7 @@ extension PatternTextStyle {
         } none: {
             commit, virtuals in
             commit.snapshot.append(contentsOf: virtuals, as: .phantom)
-            commit.snapshot.anchorAtEndIndex()
+            commit.snapshot.select(commit.snapshot.endIndex)
         } done: {
             commit, virtuals, mismatches in
             //=----------------------------------=

Tests/DiffableTextKitTests/Models/Snapshot.swift

@@ -47,8 +47,8 @@ final class SnapshotTests: XCTestCase {
     // MARK: Tests x State
     //=------------------------------------------------------------------------=
 
-    func testAnchorIsNilByDefault() {
-        XCTAssertEqual(snapshot.anchor, nil)
+    func testSelectionIsNilByDefault() {
+        XCTAssertEqual(snapshot.selection, nil)
     }
 
     //=------------------------------------------------------------------------=
@@ -90,23 +90,12 @@ final class SnapshotTests: XCTestCase {
     // MARK: Tests x Transformations x Anchor
     //=------------------------------------------------------------------------=
 
-    func testAnchorAtIndex() {
-        snapshot = Snapshot("ABC")
-        let index = snapshot.index(at: C(1))
-        
-        snapshot.anchor(at: index)
-        XCTAssertEqual(snapshot.anchor, index)
-        
-        snapshot.anchor(at: nil)
-        XCTAssertEqual(snapshot.anchor, nil)
-    }
-    
-    func testAnchorAtEndIndex() {
+    func testSelectEndIndex() {
         snapshot.append(Symbol(" "))
-        snapshot.anchorAtEndIndex()
+        snapshot.select(snapshot.endIndex)
         snapshot.append(Symbol(" "))
 
-        XCTAssertEqual(snapshot.anchor, snapshot.index(at: C(1)))
+        XCTAssertEqual(snapshot.selection, Selection(snapshot.index(at: C(1))))
     }
 
     //=------------------------------------------------------------------------=