feat: enhance extract_cache_creation_tokens function to support three formats[#41] (#42)

- Updated the function to prioritize nested format, followed by flat new format, and finally old format for cache creation tokens.
- Added fallback logic for cases where the preferred formats return zero.
- Expanded unit tests to cover new format scenarios and ensure proper functionality across all formats.

Co-authored-by: heweimin <heweimin@retaileye.ai>

tests/api/handlers/base/test_utils.py

@@ -8,86 +8,116 @@ from src.api.handlers.base.utils import build_sse_headers, extract_cache_creatio
 class TestExtractCacheCreationTokens:
     """测试 extract_cache_creation_tokens 函数"""
 
-    def test_new_format_only(self) -> None:
-        """测试只有新格式字段"""
+    # === 嵌套格式测试（优先级最高）===
+
+    def test_nested_cache_creation_format(self) -> None:
+        """测试嵌套格式正常情况"""
+        usage = {
+            "cache_creation": {
+                "ephemeral_5m_input_tokens": 456,
+                "ephemeral_1h_input_tokens": 100,
+            }
+        }
+        assert extract_cache_creation_tokens(usage) == 556
+
+    def test_nested_cache_creation_with_old_format_fallback(self) -> None:
+        """测试嵌套格式为 0 时回退到旧格式"""
+        usage = {
+            "cache_creation": {
+                "ephemeral_5m_input_tokens": 0,
+                "ephemeral_1h_input_tokens": 0,
+            },
+            "cache_creation_input_tokens": 549,
+        }
+        assert extract_cache_creation_tokens(usage) == 549
+
+    def test_nested_has_priority_over_flat(self) -> None:
+        """测试嵌套格式优先于扁平格式"""
+        usage = {
+            "cache_creation": {
+                "ephemeral_5m_input_tokens": 100,
+                "ephemeral_1h_input_tokens": 200,
+            },
+            "claude_cache_creation_5_m_tokens": 999,  # 应该被忽略
+            "claude_cache_creation_1_h_tokens": 888,  # 应该被忽略
+            "cache_creation_input_tokens": 777,  # 应该被忽略
+        }
+        assert extract_cache_creation_tokens(usage) == 300
+
+    # === 扁平格式测试（优先级第二）===
+
+    def test_flat_new_format_still_works(self) -> None:
+        """测试扁平新格式兼容性"""
         usage = {
             "claude_cache_creation_5_m_tokens": 100,
             "claude_cache_creation_1_h_tokens": 200,
         }
         assert extract_cache_creation_tokens(usage) == 300
 
-    def test_new_format_5m_only(self) -> None:
-        """测试只有 5 分钟缓存"""
+    def test_flat_new_format_with_old_format_fallback(self) -> None:
+        """测试扁平格式为 0 时回退到旧格式"""
+        usage = {
+            "claude_cache_creation_5_m_tokens": 0,
+            "claude_cache_creation_1_h_tokens": 0,
+            "cache_creation_input_tokens": 549,
+        }
+        assert extract_cache_creation_tokens(usage) == 549
+
+    def test_flat_new_format_5m_only(self) -> None:
+        """测试只有 5 分钟扁平缓存"""
         usage = {
             "claude_cache_creation_5_m_tokens": 150,
             "claude_cache_creation_1_h_tokens": 0,
         }
         assert extract_cache_creation_tokens(usage) == 150
 
-    def test_new_format_1h_only(self) -> None:
-        """测试只有 1 小时缓存"""
+    def test_flat_new_format_1h_only(self) -> None:
+        """测试只有 1 小时扁平缓存"""
         usage = {
             "claude_cache_creation_5_m_tokens": 0,
             "claude_cache_creation_1_h_tokens": 250,
         }
         assert extract_cache_creation_tokens(usage) == 250
 
+    # === 旧格式测试（优先级第三）===
+
     def test_old_format_only(self) -> None:
-        """测试只有旧格式字段"""
+        """测试只有旧格式"""
         usage = {
-            "cache_creation_input_tokens": 500,
+            "cache_creation_input_tokens": 549,
         }
-        assert extract_cache_creation_tokens(usage) == 500
+        assert extract_cache_creation_tokens(usage) == 549
 
-    def test_both_formats_prefers_new(self) -> None:
-        """测试同时存在时优先使用新格式"""
-        usage = {
-            "claude_cache_creation_5_m_tokens": 100,
-            "claude_cache_creation_1_h_tokens": 200,
-            "cache_creation_input_tokens": 999,  # 应该被忽略
-        }
-        assert extract_cache_creation_tokens(usage) == 300
+    # === 边界情况测试 ===
 
-    def test_empty_usage(self) -> None:
-        """测试空字典"""
+    def test_no_cache_creation_tokens(self) -> None:
+        """测试没有任何缓存字段"""
         usage = {}
         assert extract_cache_creation_tokens(usage) == 0
 
-    def test_all_zeros(self) -> None:
-        """测试所有字段都为 0"""
+    def test_all_formats_zero(self) -> None:
+        """测试所有格式都为 0"""
         usage = {
+            "cache_creation": {
+                "ephemeral_5m_input_tokens": 0,
+                "ephemeral_1h_input_tokens": 0,
+            },
             "claude_cache_creation_5_m_tokens": 0,
             "claude_cache_creation_1_h_tokens": 0,
             "cache_creation_input_tokens": 0,
         }
         assert extract_cache_creation_tokens(usage) == 0
 
-    def test_partial_new_format_with_old_format_fallback(self) -> None:
-        """测试新格式字段不存在时回退到旧格式"""
-        usage = {
-            "cache_creation_input_tokens": 123,
-        }
-        assert extract_cache_creation_tokens(usage) == 123
-
-    def test_new_format_zero_should_not_fallback(self) -> None:
-        """测试新格式字段存在但为 0 时，不应 fallback 到旧格式"""
-        usage = {
-            "claude_cache_creation_5_m_tokens": 0,
-            "claude_cache_creation_1_h_tokens": 0,
-            "cache_creation_input_tokens": 456,
-        }
-        # 新格式字段存在，即使值为 0 也应该使用新格式（返回 0）
-        # 而不是 fallback 到旧格式（返回 456）
-        assert extract_cache_creation_tokens(usage) == 0
-
     def test_unrelated_fields_ignored(self) -> None:
         """测试忽略无关字段"""
         usage = {
             "input_tokens": 1000,
             "output_tokens": 2000,
             "cache_read_input_tokens": 300,
-            "claude_cache_creation_5_m_tokens": 50,
-            "claude_cache_creation_1_h_tokens": 75,
+            "cache_creation": {
+                "ephemeral_5m_input_tokens": 50,
+                "ephemeral_1h_input_tokens": 75,
+            },
         }
         assert extract_cache_creation_tokens(usage) == 125