From 056c152d49c16a88c619f62e5cb3d81c3faf9dd6 Mon Sep 17 00:00:00 2001
From: "Timur A. Fatkhullin" <timur@sao.ru>
Date: Mon, 18 May 2026 11:24:17 +0300
Subject: [PATCH] mcc_keyvalue.h: worked

---
 include/mcc/mcc_keyvalue.h  | 139 ++++++++++++++++++++++++++----------
 tests/mcc_keyvalue_test.cpp |   6 +-
 2 files changed, 104 insertions(+), 41 deletions(-)

diff --git a/include/mcc/mcc_keyvalue.h b/include/mcc/mcc_keyvalue.h
index fd53231..432cd13 100644
--- a/include/mcc/mcc_keyvalue.h
+++ b/include/mcc/mcc_keyvalue.h
@@ -95,8 +95,9 @@ concept mcc_variant_valid_type_c = requires { !std::is_array_v<T> && !std::is_vo
 
 template <typename T>
 concept mcc_keyvalue_record_c = requires(T t) {
-    requires std::same_as<decltype(t.key), const std::string_view>;  // immutable key!!!
+    requires std::same_as<decltype(t.key), const std::string_view>;  // key name is immutable!!!
     requires mcc_variant_valid_type_c<decltype(t.value)>;
+    // requires mcc_serialization_params_c<decltype(t.serial_pars)>;
 };
 
 
@@ -122,6 +123,12 @@ template <mcc_keyvalue_desc_c DESCR_T,
 class MccKeyValueHolder
 {
 public:
+    enum OutputPolicy {
+        OPOLICY_CHANGED_ONLY,  // serialize only changed and previously deserialized (by fromCharRange method) key-value
+                               // pairs
+        OPOLICY_FULL           // serialize entire set of key-value pairs
+    };
+
     static constexpr std::string_view COMMENT_SEQ{COMM_SEQ == nullptr   ? constants::MCC_KV_COMMENT_SEQ_ARR
                                                   : COMM_SEQ[0] == '\0' ? constants::MCC_KV_COMMENT_SEQ_ARR
                                                                         : COMM_SEQ};
@@ -143,7 +150,7 @@ public:
             ((_hashes[I] = utils::FNV1aHash(std::get<I>(_keyValue).key)), ...);
         }(std::make_index_sequence<NUMBER_OF_RECORDS>());
 
-        _loadedKey.insert_range(_hashes);
+        _changedKey.insert_range(_hashes);
     }
 
 
@@ -238,7 +245,7 @@ public:
 
         _headComment.clear();
         _inlineComment.clear();
-        _loadedKey.clear();
+        _changedKey.clear();
 
         auto recs = std::views::split(buffer, std::move(rec_delim));
 
@@ -272,7 +279,7 @@ public:
                                 return MccKeyValueHolderErrorCode::ERROR_DESERIAL;
                             }
 
-                            _loadedKey.insert(key_hash);
+                            _changedKey.insert(key_hash);
 
                             return MccKeyValueHolderErrorCode::ERROR_OK;
                         });
@@ -300,7 +307,8 @@ public:
         return ec;
     }
 
-    template <traits::mcc_output_char_range R,
+    template <OutputPolicy OPOLICY = MccKeyValueHolder::OPOLICY_CHANGED_ONLY,
+              traits::mcc_output_char_range R,
               traits::mcc_input_char_range RecDelimT = std::string_view,
               mcc_serialization_params_c SerParamsT = mcc_serialization_params_t>
     std::error_code toCharRange(R& output_buffer,
@@ -311,41 +319,46 @@ public:
 
         auto write_rec = [&output_buffer, &rec_delim, &ec, &ser_params, this]<size_t I = 0>(this auto& self) {
             if constexpr (I < NUMBER_OF_RECORDS) {
-                if (_loadedKey.count(_hashes[I])) {
-                    auto key = std::get<I>(_keyValue).key;
-                    auto val = std::get<I>(_keyValue).value;
-                    using val_t = std::remove_cvref_t<decltype(val)>;
-
-                    std::string buff;
-                    auto err = MccSerializer<val_t>{}(buff, val, ser_params);
-                    if (err) {
-                        ec = MccKeyValueHolderErrorCode::ERROR_SERIAL;
+                if constexpr (OPOLICY == MccKeyValueHolder::OPOLICY_CHANGED_ONLY) {
+                    if (_changedKey.count(_hashes[I]) == 0) {
+                        self.template operator()<I + 1>();
                         return;
-                    } else {
-                        size_t hash = _hashes[I];
-                        // write head comment
-                        if (_headComment[hash].size()) {
-                            for (auto const& comm : _headComment[hash]) {
-                                if (comm.has_value()) {
-                                    std::format_to(std::back_inserter(output_buffer), "{}{}", COMM_SEQ, comm.value());
-                                }
-                                std::ranges::copy(rec_delim, std::back_inserter(output_buffer));
-                            }
-                        }
-
-                        // key and value
-                        std::format_to(std::back_inserter(output_buffer), "{}{}{}", key, KEY_VALUE_DELIM, buff);
-
-                        // inline comment
-                        if (_inlineComment[hash].size()) {
-                            std::format_to(std::back_inserter(output_buffer), " {}{}", COMMENT_SEQ,
-                                           _inlineComment[hash]);
-                        }
-
-                        // record delimiter
-                        std::ranges::copy(rec_delim, std::back_inserter(output_buffer));
                     }
                 }
+                // if (_changedKey.count(_hashes[I])) {
+                auto key = std::get<I>(_keyValue).key;
+                auto val = std::get<I>(_keyValue).value;
+                using val_t = std::remove_cvref_t<decltype(val)>;
+
+                std::string buff;
+                auto err = MccSerializer<val_t>{}(buff, val, ser_params);
+                if (err) {
+                    ec = MccKeyValueHolderErrorCode::ERROR_SERIAL;
+                    return;
+                } else {
+                    size_t hash = _hashes[I];
+                    // write head comment
+                    if (_headComment[hash].size()) {
+                        for (auto const& comm : _headComment[hash]) {
+                            if (comm.has_value()) {
+                                std::format_to(std::back_inserter(output_buffer), "{}{}", COMM_SEQ, comm.value());
+                            }
+                            std::ranges::copy(rec_delim, std::back_inserter(output_buffer));
+                        }
+                    }
+
+                    // key and value
+                    std::format_to(std::back_inserter(output_buffer), "{}{}{}", key, KEY_VALUE_DELIM, buff);
+
+                    // inline comment
+                    if (_inlineComment[hash].size()) {
+                        std::format_to(std::back_inserter(output_buffer), " {}{}", COMMENT_SEQ, _inlineComment[hash]);
+                    }
+
+                    // record delimiter
+                    std::ranges::copy(rec_delim, std::back_inserter(output_buffer));
+                }
+                // }
 
                 self.template operator()<I + 1>();
             }
@@ -367,7 +380,7 @@ protected:
     std::unordered_map<size_t, std::vector<std::optional<std::string>>>
         _headComment{};                                        // comment string/strings before key
     std::unordered_map<size_t, std::string> _inlineComment{};  // inline (after key=value pair) comment
-    std::unordered_set<size_t> _loadedKey{};                   // loaded keys (see fromCharRange)
+    std::unordered_set<size_t> _changedKey{};                  // loaded keys (see fromCharRange)
 
     //
     //  NOTE: deduced this is needed here to use "forKey" method in getter and setter (const and non-const contexts)!!!
@@ -395,6 +408,56 @@ protected:
 
         return MccKeyValueHolderErrorCode::ERROR_INVALID_KEY;
     }
+
+    template <size_t I = 0,
+              OutputPolicy OPOLICY = MccKeyValueHolder::OPOLICY_CHANGED_ONLY,
+              traits::mcc_output_char_range R,
+              traits::mcc_input_char_range RecDelimT,
+              mcc_serialization_params_c SerParamsT>
+    std::error_code writeRecord(R& output_buffer, RecDelimT rec_delim, SerParamsT const& ser_params)
+    {
+        if constexpr (I < NUMBER_OF_RECORDS) {
+            if constexpr (OPOLICY == MccKeyValueHolder::OPOLICY_CHANGED_ONLY) {
+                if (_changedKey.count(_hashes[I]) == 0) {
+                    return MccKeyValueHolderErrorCode::ERROR_OK;
+                }
+            }
+
+            auto key = std::get<I>(_keyValue).key;
+            auto val = std::get<I>(_keyValue).value;
+            using val_t = std::remove_cvref_t<decltype(val)>;
+
+            std::string buff;
+            auto err = MccSerializer<val_t>{}(buff, val, ser_params);
+            if (err) {
+                return MccKeyValueHolderErrorCode::ERROR_SERIAL;
+            } else {
+                size_t hash = _hashes[I];
+                // write head comment
+                if (_headComment[hash].size()) {
+                    for (auto const& comm : _headComment[hash]) {
+                        if (comm.has_value()) {
+                            std::format_to(std::back_inserter(output_buffer), "{}{}", COMM_SEQ, comm.value());
+                        }
+                        std::ranges::copy(rec_delim, std::back_inserter(output_buffer));
+                    }
+                }
+
+                // key and value
+                std::format_to(std::back_inserter(output_buffer), "{}{}{}", key, KEY_VALUE_DELIM, buff);
+
+                // inline comment
+                if (_inlineComment[hash].size()) {
+                    std::format_to(std::back_inserter(output_buffer), " {}{}", COMMENT_SEQ, _inlineComment[hash]);
+                }
+
+                // record delimiter
+                std::ranges::copy(rec_delim, std::back_inserter(output_buffer));
+            }
+        }
+
+        return MccKeyValueHolderErrorCode::ERROR_OK;
+    }
 };
 
 template <mcc_variant_valid_type_c T>
diff --git a/tests/mcc_keyvalue_test.cpp b/tests/mcc_keyvalue_test.cpp
index 29f54f2..58bb303 100644
--- a/tests/mcc_keyvalue_test.cpp
+++ b/tests/mcc_keyvalue_test.cpp
@@ -22,7 +22,6 @@ cc=   2026-05-15T05:53:20.921723918 # date UTC
 )--";
 
 static std::string STR1 = R"--(
-
 aaa = dewl_ewkj23+23998
 
 #
@@ -60,13 +59,14 @@ int main()
 
     std::string buff;
 
-    err = kv.toCharRange(buff);
+    err = kv.toCharRange<decltype(kv)::OPOLICY_FULL>(buff);
+    // err = kv.toCharRange(buff);
     if (err) {
         std::println("ERR = {}", err);
         return 1;
     }
 
-    std::println("--(\n{}\n)--'", buff);
+    std::println("--(\n{}\n)--", buff);
 
     std::print("KEYS: ");
     for (auto const& k : kv.keys()) {