diff --git a/src/klotski_core/group/CMakeLists.txt b/src/klotski_core/group/CMakeLists.txt
index 45df20a..e23a160 100644
--- a/src/klotski_core/group/CMakeLists.txt
+++ b/src/klotski_core/group/CMakeLists.txt
@@ -1,3 +1,3 @@
 cmake_minimum_required(VERSION 3.0)
 
-add_library(group OBJECT group.cc build_cases.cc block_num.cc)
+add_library(group OBJECT group.cc block_num.cc build_cases.cc group_info.cc)
diff --git a/src/klotski_core/group/build_cases.cc b/src/klotski_core/group/build_cases.cc
index fa91e04..42c95f6 100644
--- a/src/klotski_core/group/build_cases.cc
+++ b/src/klotski_core/group/build_cases.cc
@@ -74,6 +74,11 @@ std::vector<RawCode> Group::group_cases(const RawCode &seed) {
     return result;
 }
 
+// TODO: test this function
+std::vector<RawCode> Group::group_cases(const CommonCode &seed) {
+    return group_cases(RawCode::from_common_code(seed));
+}
+
 std::vector<CommonCode> Group::build_group(uint32_t type_id, uint32_t group_id) {
     uint32_t group_num = 0;
     auto all_cases = Group::all_cases(type_id); // load all cases of type_id
diff --git a/src/klotski_core/group/group.h b/src/klotski_core/group/group.h
index b2fb9e5..a540c8e 100644
--- a/src/klotski_core/group/group.h
+++ b/src/klotski_core/group/group.h
@@ -9,7 +9,7 @@ namespace klotski {
 const uint32_t TYPE_ID_LIMIT = 203;
 
 class Group {
-/// ---------------------------- block statistics -----------------------------
+/// -------------------------------- block statistics ---------------------------------
 public:
     /// 1. n_1x1 + (n_1x2 + n_2x1) * 2 <= 14
     /// 2. (n_1x1 != 0) && (n_2x1 != 7)
@@ -29,13 +29,14 @@ public:
     static block_num_t block_num(const RawCode &raw_code);
     static block_num_t block_num(const CommonCode &common_code);
 
-/// ----------------------------- cases expansion -----------------------------
+/// --------------------------------- cases expansion ---------------------------------
 
     /// Search for all cases of the specified type_id.
     static std::vector<CommonCode> all_cases(uint32_t type_id);
 
     /// Search for all derivatives that a case can produce.
     static std::vector<RawCode> group_cases(const RawCode &seed);
+    static std::vector<RawCode> group_cases(const CommonCode &seed);
 
     /// Calculate all groups in the specified type_id.
     static std::vector<std::vector<CommonCode>> build_groups(uint32_t type_id);
@@ -43,15 +44,34 @@ public:
     /// Calculate the specified group using type_id and group_id.
     static std::vector<CommonCode> build_group(uint32_t type_id, uint32_t group_id);
 
-/// ---------------------------- xxxxxxxxxxxxxxxxx ----------------------------
+/// ----------------------------------- group info ------------------------------------
 
+    struct group_info_t {
+        uint16_t type_id;
+        uint16_t group_id;
+        uint32_t group_index;
+    };
+
+    /// Get group info according to RawCode.
+    static group_info_t group_info(const RawCode &raw_code);
+
+    /// Get group info according to CommonCode.
+    static group_info_t group_info(const CommonCode &common_code);
+
+    /// Get the CommonCode according to the group info.
+    static CommonCode group_case(const group_info_t &group_info);
+
+/// -------------------------------- xxxxxxxxxxxxxxxxx --------------------------------
+
+    // TODO: update max_group_size in TYPE_ID_MAX_GROUP
 
 //    static uint32_t max_group_size(uint32_t type_id);
+
     static uint32_t max_group_size(const RawCode &raw_code) {
         return 65535 * 8;
     };
 
-
+//    static uint32_t max_group_size(const CommonCode &common_code);
 
 };
 
diff --git a/src/klotski_core/group/group_info.cc b/src/klotski_core/group/group_info.cc
new file mode 100644
index 0000000..cc103be
--- /dev/null
+++ b/src/klotski_core/group/group_info.cc
@@ -0,0 +1,26 @@
+#include "group.h"
+
+namespace klotski {
+
+Group::group_info_t Group::group_info(const RawCode &raw_code) {
+
+    // TODO: function body
+
+    return Group::group_info_t();
+}
+
+Group::group_info_t Group::group_info(const CommonCode &common_code) {
+
+    // TODO: function body
+
+    return Group::group_info_t();
+}
+
+CommonCode Group::group_case(const Group::group_info_t &group_info) {
+
+    // TODO: function body
+
+    return CommonCode(0);
+}
+
+} // namespace klotski
diff --git a/src/klotski_core/group/type_id.h b/src/klotski_core/group/type_id.h
index 034c029..1478e98 100644
--- a/src/klotski_core/group/type_id.h
+++ b/src/klotski_core/group/type_id.h
@@ -47,4 +47,7 @@ const uint32_t TYPE_ID_SIZE[203] = {
       1036,    464,    342,
 };
 
+// TODO: TYPE_ID_MAX_GROUP_SIZE
+// TODO: TYPE_ID_GROUP_NUM
+
 } // namespace klotski