diff --git a/src/core/fast_cal/fast_cal.h b/src/core/fast_cal/fast_cal.h
index f50d188..5b7aef8 100644
--- a/src/core/fast_cal/fast_cal.h
+++ b/src/core/fast_cal/fast_cal.h
@@ -109,17 +109,39 @@ private:
 
 namespace klotski::fast_cal {
 
-class FCDemo {
+class FastCalPro {
 public:
-    explicit FCDemo(RawCode raw_code);
+    FastCalPro() = delete;
 
-    std::optional<RawCode> DoCal();
+    explicit FastCalPro(RawCode raw_code);
 
-    std::vector<RawCode> DoCalMulti();
+    // ------------------------------------------------------------------------------------- //
 
-    std::vector<RawCode> DoCalFurthest();
+    /// Calculate the case with minimum steps.
+    std::optional<RawCode> solve();
+
+    /// Calculate the cases with maximum steps.
+    std::vector<RawCode> furthest();
+
+    /// Calculate all of the minimum-step cases.
+    std::vector<RawCode> solve_multi();
+
+    /// Calculate the first case that meets the requirement.
+    std::optional<RawCode> achieve(std::function<bool(RawCode)> &&match);
+
+    // ------------------------------------------------------------------------------------- //
 
 private:
+    // ------------------------------------------------------------------------------------- //
+
+    /// Search next step cases and pop current.
+    KLSK_INLINE void spawn_next(MaskMover &mover);
+
+    /// Try to emplace the searched info into the cache.
+    KLSK_INLINE bool try_emplace(uint64_t code, uint64_t mask);
+
+    // ------------------------------------------------------------------------------------- //
+
     struct data_t {
         uint64_t mask;
         uint64_t back;
@@ -127,6 +149,8 @@ private:
 
     LayerQueue<uint64_t> codes_;
     phmap::flat_hash_map<uint64_t, data_t> cases_;
+
+    // ------------------------------------------------------------------------------------- //
 };
 
 } // namespace klotski::fast_cal
diff --git a/src/core/fast_cal/internal/demo.cc b/src/core/fast_cal/internal/demo.cc
index fef2285..f1dacf3 100644
--- a/src/core/fast_cal/internal/demo.cc
+++ b/src/core/fast_cal/internal/demo.cc
@@ -16,64 +16,63 @@ using klotski::cases::RangesUnion;
 using klotski::mover::MaskMover;
 using klotski::cases::GroupUnion;
 
-using klotski::fast_cal::FCDemo;
-
-std::optional<RawCode> FCDemo::DoCal() {
-    uint64_t result = 0;
-    auto core = MaskMover([this, &result](uint64_t code, uint64_t mask) {
-        if (const auto match = cases_.find(code); match != cases_.end()) {
-            match->second.mask |= mask; // update mask
-            return;
-        }
-        cases_.emplace(code, data_t {
-            .mask = mask,
-            .back = codes_.current(),
-        });
-        codes_.emplace(code);
-
-        if (((code >> 39) & 0b111) == 0b100) {
-            result = code;
+using klotski::fast_cal::FastCalPro;
+
+static KLSK_INLINE bool is_solved(uint64_t raw_code) {
+    return ((raw_code >> 39) & 0b111) == 0b100;
+}
+
+std::optional<RawCode> FastCalPro::solve() {
+    // TODO: check root case
+
+    uint64_t solution = 0;
+    auto mover = MaskMover([this, &solution](uint64_t code, uint64_t mask) {
+        if (try_emplace(code, mask) && is_solved(code)) {
+            solution = code;
         }
     });
-
     while (!codes_.is_ending()) {
-        auto curr = codes_.current();
-        core.next_cases(curr, cases_.find(curr)->second.mask);
+        spawn_next(mover);
+        if (solution != 0) {
+            return RawCode::unsafe_create(solution);
+        }
+    }
+    return std::nullopt;
+}
+
+std::optional<RawCode> FastCalPro::achieve(std::function<bool(RawCode)> &&match) {
+    // TODO: check root case
 
-        codes_.next();
-        if (result != 0) {
-            return RawCode::unsafe_create(result);
+    uint64_t target = 0;
+    auto mover = MaskMover([this, &target, match = std::move(match)](uint64_t code, uint64_t mask) {
+        if (try_emplace(code, mask) && match(RawCode::unsafe_create(code))) {
+            target = code;
+        }
+    });
+    while (!codes_.is_ending()) {
+        spawn_next(mover);
+        if (target != 0) {
+            return RawCode::unsafe_create(target);
         }
     }
     return std::nullopt;
 }
 
-std::vector<RawCode> FCDemo::DoCalMulti() {
+std::vector<RawCode> FastCalPro::solve_multi() {
+    // TODO: check root case
+
     bool stop_flag = false;
     std::vector<RawCode> results {};
 
-    auto core = MaskMover([this, &stop_flag, &results](uint64_t code, uint64_t mask) {
-        if (const auto match = cases_.find(code); match != cases_.end()) {
-            match->second.mask |= mask; // update mask
-            return;
-        }
-        cases_.emplace(code, data_t {
-            .mask = mask,
-            .back = codes_.current(),
-        });
-        codes_.emplace(code);
-
-        if (((code >> 39) & 0b111) == 0b100) {
+    auto mover = MaskMover([this, &stop_flag, &results](uint64_t code, uint64_t mask) {
+        if (try_emplace(code, mask) && is_solved(code)) {
             stop_flag = true;
             results.emplace_back(RawCode::unsafe_create(code));
         }
     });
 
     while (!codes_.is_ending()) {
-        auto curr = codes_.current();
-        core.next_cases(curr, cases_.find(curr)->second.mask);
-
-        codes_.next();
+        spawn_next(mover);
         if (codes_.is_new_layer() && stop_flag) {
             // TODO: fix when solutions at last layer
             return results;
@@ -83,24 +82,12 @@ std::vector<RawCode> FCDemo::DoCalMulti() {
     return {};
 }
 
-std::vector<RawCode> FCDemo::DoCalFurthest() {
-    auto core = MaskMover([this](uint64_t code, uint64_t mask) {
-        if (const auto match = cases_.find(code); match != cases_.end()) {
-            match->second.mask |= mask; // update mask
-            return;
-        }
-        cases_.emplace(code, data_t {
-            .mask = mask,
-            .back = codes_.current(),
-        });
-        codes_.emplace(code);
+std::vector<RawCode> FastCalPro::furthest() {
+    auto mover = MaskMover([this](uint64_t code, uint64_t mask) {
+        try_emplace(code, mask);
     });
-
     while (true) {
-        auto curr = codes_.current();
-        core.next_cases(curr, cases_.find(curr)->second.mask);
-
-        codes_.next();
+        spawn_next(mover);
         if (codes_.is_ending()) {
             return codes_.layer_cases() | std::views::transform([](uint64_t code) {
                 return RawCode::unsafe_create(code);
@@ -110,21 +97,26 @@ std::vector<RawCode> FCDemo::DoCalFurthest() {
 }
 
 RawCode FastCal_demo(RawCode raw_code) {
-    klotski::fast_cal::FCDemo fc {raw_code};
-//    return fc.DoCal().value();
+    klotski::fast_cal::FastCalPro fc {raw_code};
+    return fc.solve().value();
 
-//    auto tmp = fc.DoCal();
+//    auto tmp = fc.solve();
 //    std::cout << tmp.value().to_common_code() << std::endl;
 
-//    auto tmp = fc.DoCalMulti();
+//    auto tmp = fc.solve_multi();
 //    for (const auto x : tmp) {
 //        std::cout << x.to_common_code() << std::endl;
 //    }
 
-    auto tmp = fc.DoCalFurthest();
+//    auto tmp = fc.furthest();
 //    for (const auto x : tmp) {
 //        std::cout << x.to_common_code() << std::endl;
 //    }
 
-    return RawCode::unsafe_create(0);
+//    auto tmp = fc.achieve([](RawCode r) {
+//        return r == 0x7F87E0E5BFFF492;
+//    });
+//    std::cout << tmp.value().to_common_code() << std::endl;
+
+//    return RawCode::unsafe_create(0);
 }
diff --git a/src/core/fast_cal/internal/fast_cal.inl b/src/core/fast_cal/internal/fast_cal.inl
index b0c40ba..463a679 100644
--- a/src/core/fast_cal/internal/fast_cal.inl
+++ b/src/core/fast_cal/internal/fast_cal.inl
@@ -2,11 +2,30 @@
 
 namespace klotski::fast_cal {
 
-inline FCDemo::FCDemo(RawCode raw_code) : codes_(cases::GroupUnion::from_raw_code(raw_code).max_group_size(), {raw_code.unwrap()}) {
+inline FastCalPro::FastCalPro(RawCode raw_code) : codes_(cases::GroupUnion::from_raw_code(raw_code).max_group_size(), {raw_code.unwrap()}) {
 //    auto reserve = cases::GroupUnion::from_raw_code(raw_code).max_group_size();
     cases_.reserve(static_cast<size_t>(25955 * 1.56));
 //    cases_.reserve(static_cast<size_t>(reserve * 1.56));
     cases_.emplace(raw_code, data_t {0, 0}); // without mask
 }
 
+inline KLSK_INLINE bool FastCalPro::try_emplace(uint64_t code, uint64_t mask) {
+    if (const auto match = cases_.find(code); match != cases_.end()) {
+        match->second.mask |= mask; // update mask
+        return false;
+    }
+    cases_.emplace(code, data_t {
+        .mask = mask,
+        .back = codes_.current(),
+    });
+    codes_.emplace(code);
+    return true;
+}
+
+inline KLSK_INLINE void FastCalPro::spawn_next(MaskMover &mover) {
+    auto curr = codes_.current();
+    mover.next_cases(curr, cases_.find(curr)->second.mask);
+    codes_.next();
+}
+
 } // namespace klotski::fast_cal