Repo // Megrez v2.0.3 update.

Source/Modules/LanguageParsers/Megrez/6_Node.swift

@@ -140,6 +140,43 @@ extension Array where Element == Megrez.Compositor.Node {
   /// 從一個節點陣列當中取出目前的索引鍵陣列。
   public var keys: [String] { map(\.key) }
 
+  /// 返回一連串的節點起點。結果為 (Result A, Result B) 辭典陣列
+  /// Result A 以索引查座標，Result B 以座標查索引。
+  public var nodeBorderPointDictPair: ([Int: Int], [Int: Int]) {
+    // Result A 以索引查座標，Result B 以座標查索引。
+    var resultA = [Int: Int]()
+    var resultB = [Int: Int]()
+    var i = 0
+    for (j, neta) in enumerated() {
+      resultA[j] = i
+      neta.keyArray.forEach { _ in
+        resultB[i] = j
+        i += 1
+      }
+    }
+    resultA[resultA.count] = i
+    resultB[i] = resultB.count
+    return (resultA, resultB)
+  }
+
+  /// 總讀音單元數量，也就是總幅位長度。
+  public var totalKeyCount: Int { map(\.keyArray.count).reduce(0, +) }
+
+  /// 根據給定的游標，返回其前後最近的邊界點。
+  /// - Parameter cursor: 給定的游標。
+  public func contextRange(ofGivenCursor cursor: Int) -> Range<Int> {
+    guard !isEmpty else { return 0..<0 }
+    let lastSpanningLength = reversed()[0].keyArray.count
+    var nilReturn = (totalKeyCount - lastSpanningLength)..<totalKeyCount
+    if cursor >= totalKeyCount { return nilReturn }  // 防呆
+    let cursor = Swift.max(0, cursor)  // 防呆
+    nilReturn = cursor..<cursor
+    guard let rearNodeID = nodeBorderPointDictPair.1[cursor] else { return nilReturn }  // 應該不會出現 nilReturn
+    guard let rearIndex = nodeBorderPointDictPair.0[rearNodeID] else { return nilReturn }  // 應該不會出現 nilReturn
+    guard let frontIndex = nodeBorderPointDictPair.0[rearNodeID + 1] else { return nilReturn }  // 應該不會出現 nilReturn
+    return rearIndex..<frontIndex
+  }
+
   /// 在陣列內以給定游標位置找出對應的節點。
   /// - Parameters:
   ///   - cursor: 給定游標位置。
@@ -147,30 +184,11 @@ extension Array where Element == Megrez.Compositor.Node {
   /// - Returns: 查找結果。
   public func findNode(at cursor: Int, target outCursorPastNode: inout Int) -> Megrez.Compositor.Node? {
     guard !isEmpty else { return nil }
-    let cursor = Swift.max(0, Swift.min(cursor, keys.count))
-
-    if cursor == 0, let theFirst = first {
-      outCursorPastNode = theFirst.spanLength
-      return theFirst
-    }
-
-    // 同時應對「游標在右端」與「游標離右端還差一個位置」的情形。
-    if cursor >= keys.count - 1, let theLast = last {
-      outCursorPastNode = keys.count
-      return theLast
-    }
-
-    var accumulated = 0
-    for neta in self {
-      accumulated += neta.spanLength
-      if accumulated > cursor {
-        outCursorPastNode = accumulated
-        return neta
-      }
-    }
-
-    // 下述情形本不應該出現。
-    return nil
+    let cursor = Swift.min(Swift.max(0, cursor), totalKeyCount - 1)  // 防呆
+    let range = contextRange(ofGivenCursor: cursor)
+    outCursorPastNode = range.upperBound
+    guard let rearNodeID = nodeBorderPointDictPair.1[cursor] else { return nil }
+    return count - 1 >= rearNodeID ? self[rearNodeID] : nil
   }
 
   /// 在陣列內以給定游標位置找出對應的節點。