tools: resolve images by short references

src/main/kotlin/ImageIndex.kt

@@ -0,0 +1,29 @@
+package top.jie65535.mirai
+
+/**
+ * 会话内图片短索引：向 LLM 暴露递增整数，内部保留从原消息图片取得的精确 URL。
+ * 同一 imageId 重复出现在上下文中时复用原编号，并用最新取得的 URL 刷新映射。
+ */
+internal class ImageIndex {
+    private val imageUrlByIndex = LinkedHashMap<Int, String>()
+    private val indexByImageId = HashMap<String, Int>()
+    private var counter = 0
+
+    @Synchronized
+    fun add(imageId: String, imageUrl: String): Int {
+        require(imageId.isNotBlank()) { "图片ID不能为空" }
+        require(imageUrl.isNotBlank()) { "图片URL不能为空" }
+        indexByImageId[imageId]?.let { index ->
+            imageUrlByIndex[index] = imageUrl
+            return index
+        }
+
+        val index = ++counter
+        imageUrlByIndex[index] = imageUrl
+        indexByImageId[imageId] = index
+        return index
+    }
+
+    @Synchronized
+    fun getUrl(index: Int): String? = imageUrlByIndex[index]
+}