Implement Math view

Sources/SwiftUIMath/Internal/Display/DisplayProvider.swift

@@ -0,0 +1,118 @@
+import Foundation
+
+extension Math {
+  final class DisplayProvider: Sendable {
+    private struct Cache {
+      struct Key: Hashable {
+        let latex: String
+        let font: Font
+        let style: TypesettingStyle
+        let proposedWidth: CGFloat
+      }
+
+      let atomList = NSCache<NSString, AtomList>()
+      let displayNode = NSCache<KeyBox<Key>, DisplayNode>()
+    }
+
+    static let shared = DisplayProvider()
+
+    private let cache = ReadWriteLockIsolated<Cache>(Cache())
+
+    func sizeThatFits(
+      proposedWidth width: CGFloat,
+      latex: String,
+      font: Font,
+      style: TypesettingStyle
+    ) -> CGSize {
+      display(
+        for: latex,
+        font: font,
+        style: style,
+        proposedWidth: width
+      )?.bounds.size ?? .zero
+    }
+
+    func display(
+      for latex: String,
+      font: Font,
+      style: TypesettingStyle,
+      proposedWidth: CGFloat
+    ) -> DisplayNode? {
+      cache.withValue { cache in
+        let roundedWidth = proposedWidth.halfPointRounded()
+        let key = KeyBox(
+          Cache.Key(
+            latex: latex,
+            font: font,
+            style: style,
+            proposedWidth: roundedWidth
+          )
+        )
+
+        if let displayNode = cache.displayNode.object(forKey: key) {
+          return displayNode
+        }
+
+        guard
+          let atomList = atomList(for: latex, cache: &cache),
+          let displayNode = Typesetter.createLineForMathList(
+            atomList,
+            font: .init(font: font),
+            style: .init(style),
+            maxWidth: roundedWidth
+          )
+        else {
+          return nil
+        }
+
+        cache.displayNode.setObject(displayNode, forKey: key)
+
+        if displayNode.width != roundedWidth {
+          // Cache the measured width to avoid a miss between layout and draw passes
+          let secondaryKey = KeyBox(
+            Cache.Key(
+              latex: latex,
+              font: font,
+              style: style,
+              proposedWidth: displayNode.width.halfPointRounded()
+            )
+          )
+          cache.displayNode.setObject(displayNode, forKey: secondaryKey)
+        }
+
+        return displayNode
+      }
+    }
+
+    private func atomList(for latex: String, cache: inout Cache) -> AtomList? {
+      if let atomList = cache.atomList.object(forKey: latex as NSString) {
+        return atomList
+      }
+
+      guard let atomList = Parser.build(fromString: latex) else {
+        return nil
+      }
+
+      cache.atomList.setObject(atomList, forKey: latex as NSString)
+      return atomList
+    }
+  }
+}
+
+extension Math.Style.Level {
+  fileprivate init(_ typesettingStyle: Math.TypesettingStyle) {
+    switch typesettingStyle {
+    case .display:
+      self = .display
+    case .text:
+      self = .text
+    }
+  }
+}
+
+extension CGFloat {
+  fileprivate func halfPointRounded() -> CGFloat {
+    guard self > 0 else { return 0 }
+    return (self * 2).rounded() / 2
+  }
+}