From a4587c08547a3050ab54fe9e3cbadbbd454eeb94 Mon Sep 17 00:00:00 2001
From: ShikiSuen <shikisuen@outlook.com>
Date: Tue, 7 Mar 2023 10:15:05 +0800
Subject: [PATCH] Fix an issue that update() can ruin a span unit object. (#97)

---
 Sources/Megrez/1_Compositor.swift      |  2 +-
 Sources/Megrez/4_SpanUnit.swift        | 19 +++++++++++++++----
 Tests/MegrezTests/LMDataForTests.swift |  5 ++++-
 Tests/MegrezTests/MegrezTests.swift    |  8 ++++++++
 4 files changed, 28 insertions(+), 6 deletions(-)

diff --git a/Sources/Megrez/1_Compositor.swift b/Sources/Megrez/1_Compositor.swift
index 863c2c6..7c3c7a2 100644
--- a/Sources/Megrez/1_Compositor.swift
+++ b/Sources/Megrez/1_Compositor.swift
@@ -291,7 +291,7 @@ extension Megrez.Compositor {
           // 自動銷毀無效的節點。
           if unigrams.isEmpty {
             if theNode.keyArray.count == 1 { continue }
-            spans[position].nodes.removeAll { $0 == theNode }
+            spans[position].nullify(node: theNode)
           } else {
             theNode.syncingUnigrams(from: unigrams)
           }
diff --git a/Sources/Megrez/4_SpanUnit.swift b/Sources/Megrez/4_SpanUnit.swift
index c74d271..27c3c81 100644
--- a/Sources/Megrez/4_SpanUnit.swift
+++ b/Sources/Megrez/4_SpanUnit.swift
@@ -24,10 +24,7 @@ extension Megrez.Compositor {
 
     /// 清除該幅位單元的全部的節點，且重設最長節點長度為 0，然後再在節點陣列內預留空位。
     public func clear() {
-      nodes.removeAll()
-      for _ in 0 ..< maxSpanLength {
-        nodes.append(nil)
-      }
+      nodes = .init(repeating: nil, count: maxSpanLength)
       maxLength = 0
     }
 
@@ -43,6 +40,18 @@ extension Megrez.Compositor {
       return true
     }
 
+    /// 丟掉任何與給定節點完全雷同的節點。
+    /// - Remark: Swift 不像 C# 那樣有容量鎖定型陣列，
+    /// 對某個位置的內容的刪除行為都可能會導致其它內容錯位、繼發其它不可知故障。
+    /// 於是就提供了這個專門的工具函式。
+    /// - Parameter node: 要參照的節點。
+    public func nullify(node givenNode: Node) {
+      nodes.enumerated().forEach { index, theNode in
+        guard theNode == givenNode else { return }
+        nodes[index] = nil
+      }
+    }
+
     /// 丟掉任何不小於給定幅位長度的節點。
     /// - Parameter length: 給定的幅位長度。
     /// - Returns: 該操作是否成功執行。
@@ -51,12 +60,14 @@ extension Megrez.Compositor {
         return false
       }
       for i in length ... maxSpanLength {
+        guard (0 ..< nodes.count).contains(i - 1) else { continue } // 防呆
         nodes[i - 1] = nil
       }
       maxLength = 0
       guard length > 1 else { return false }
       let maxR = length - 2
       for i in 0 ... maxR {
+        guard (0 ..< nodes.count).contains(maxR - i) else { continue } // 防呆
         if nodes[maxR - i] == nil { continue }
         maxLength = maxR - i + 1
         break
diff --git a/Tests/MegrezTests/LMDataForTests.swift b/Tests/MegrezTests/LMDataForTests.swift
index 6f9445a..61a1386 100644
--- a/Tests/MegrezTests/LMDataForTests.swift
+++ b/Tests/MegrezTests/LMDataForTests.swift
@@ -40,7 +40,10 @@ class SimpleLM: LangModelProtocol {
   func trim(key: String, value: String) {
     guard var arr = mutDatabase[key] else { return }
     arr = arr.compactMap { $0.value == value ? nil : $0 }
-    guard !arr.isEmpty else { return }
+    guard !arr.isEmpty else {
+      mutDatabase[key] = nil
+      return
+    }
     mutDatabase[key] = arr
   }
 }
diff --git a/Tests/MegrezTests/MegrezTests.swift b/Tests/MegrezTests/MegrezTests.swift
index 27daf0c..44e4c6b 100644
--- a/Tests/MegrezTests/MegrezTests.swift
+++ b/Tests/MegrezTests/MegrezTests.swift
@@ -537,5 +537,13 @@ final class MegrezTests: XCTestCase {
     let newResult = compositor.walk().0.values.joined()
     print(newResult)
     XCTAssertEqual([oldResult, newResult], ["年中獎金", "年終獎金"])
+    compositor.cursor = 4
+    compositor.dropKey(direction: .rear)
+    compositor.dropKey(direction: .rear)
+    theLM.trim(key: "nian2zhong1", value: "年終")
+    compositor.update(updateExisting: true)
+    let newResult2 = compositor.walk().0.values
+    print(newResult2)
+    XCTAssertEqual(newResult2, ["年", "中"])
   }
 }