chore: move jsoncons path code into dedicated files (#2666)

It's only a code move, without functional changes.
This is in preparation to implementing the same path functionality
for flexbuffers objects.

Signed-off-by: Roman Gershman <roman@dragonflydb.io>

src/core/dash_internal.h

@@ -1,4 +1,4 @@
-// Copyright 2022, DragonflyDB authors.  All rights reserved.
+// Copyright 2024, DragonflyDB authors.  All rights reserved.
 // See LICENSE for licensing terms.
 //
 

src/core/json/CMakeLists.txt

@@ -4,7 +4,8 @@ gen_bison(jsonpath_grammar)
 cur_gen_dir(gen_dir)
 
 add_library(jsonpath lexer_impl.cc driver.cc path.cc
-            ${gen_dir}/jsonpath_lexer.cc ${gen_dir}/jsonpath_grammar.cc json_object.cc)
+            ${gen_dir}/jsonpath_lexer.cc ${gen_dir}/jsonpath_grammar.cc json_object.cc
+            detail/jsoncons_dfs.cc)
 target_link_libraries(jsonpath base absl::strings TRDP::reflex TRDP::jsoncons)
 
 cxx_test(jsonpath_test jsonpath LABELS DFLY)

src/core/json/detail/common.h

@@ -0,0 +1,13 @@
+// Copyright 2024, DragonflyDB authors.  All rights reserved.
+// See LICENSE for licensing terms.
+//
+
+#pragma once
+
+namespace dfly::json::detail {
+enum MatchStatus {
+  OUT_OF_BOUNDS,
+  MISMATCH,
+};
+
+}

src/core/json/detail/jsoncons_dfs.cc

@@ -0,0 +1,184 @@
+// Copyright 2024, DragonflyDB authors.  All rights reserved.
+// See LICENSE for licensing terms.
+//
+
+// clang-format off
+#include <glog/logging.h>
+// clang-format on
+
+#include "core/json/detail/jsoncons_dfs.h"
+
+namespace dfly::json::detail {
+
+using namespace std;
+using nonstd::make_unexpected;
+
+inline bool IsRecursive(jsoncons::json_type type) {
+  return type == jsoncons::json_type::object_value || type == jsoncons::json_type::array_value;
+}
+
+void Dfs::Traverse(absl::Span<const PathSegment> path, const JsonType& root, const Cb& callback) {
+  DCHECK(!path.empty());
+  if (path.size() == 1) {
+    PerformStep(path[0], root, callback);
+    return;
+  }
+
+  using ConstItem = JsonconsDfsItem<true>;
+  vector<ConstItem> stack;
+  stack.emplace_back(&root);
+
+  do {
+    unsigned segment_index = stack.back().segment_idx();
+    const auto& path_segment = path[segment_index];
+
+    // init or advance the current object
+    ConstItem::AdvanceResult res = stack.back().Advance(path_segment);
+    if (res && res->first != nullptr) {
+      const JsonType* next = res->first;
+      DVLOG(2) << "Handling now " << next->type() << " " << next->to_string();
+
+      // We descent only if next is object or an array.
+      if (IsRecursive(next->type())) {
+        unsigned next_seg_id = res->second;
+
+        if (next_seg_id + 1 < path.size()) {
+          stack.emplace_back(next, next_seg_id);
+        } else {
+          // terminal step
+          // TODO: to take into account MatchStatus
+          // for `json.set foo $.a[10]` or for `json.set foo $.*.b`
+          PerformStep(path[next_seg_id], *next, callback);
+        }
+      }
+    } else {
+      stack.pop_back();
+    }
+  } while (!stack.empty());
+}
+
+void Dfs::Mutate(absl::Span<const PathSegment> path, const MutateCallback& callback,
+                 JsonType* json) {
+  DCHECK(!path.empty());
+  if (path.size() == 1) {
+    MutateStep(path[0], callback, json);
+    return;
+  }
+
+  using Item = detail::JsonconsDfsItem<false>;
+  vector<Item> stack;
+  stack.emplace_back(json);
+
+  do {
+    unsigned segment_index = stack.back().segment_idx();
+    const auto& path_segment = path[segment_index];
+
+    // init or advance the current object
+    Item::AdvanceResult res = stack.back().Advance(path_segment);
+    if (res && res->first != nullptr) {
+      JsonType* next = res->first;
+      DVLOG(2) << "Handling now " << next->type() << " " << next->to_string();
+
+      // We descent only if next is object or an array.
+      if (IsRecursive(next->type())) {
+        unsigned next_seg_id = res->second;
+
+        if (next_seg_id + 1 < path.size()) {
+          stack.emplace_back(next, next_seg_id);
+        } else {
+          MutateStep(path[next_seg_id], callback, next);
+        }
+      }
+    } else {
+      stack.pop_back();
+    }
+  } while (!stack.empty());
+}
+
+auto Dfs::PerformStep(const PathSegment& segment, const JsonType& node, const Cb& callback)
+    -> nonstd::expected<void, MatchStatus> {
+  switch (segment.type()) {
+    case SegmentType::IDENTIFIER: {
+      if (!node.is_object())
+        return make_unexpected(MISMATCH);
+
+      auto it = node.find(segment.identifier());
+      if (it != node.object_range().end()) {
+        DoCall(callback, it->key(), it->value());
+      }
+    } break;
+    case SegmentType::INDEX: {
+      if (!node.is_array())
+        return make_unexpected(MISMATCH);
+      if (segment.index() >= node.size()) {
+        return make_unexpected(OUT_OF_BOUNDS);
+      }
+      DoCall(callback, nullopt, node[segment.index()]);
+    } break;
+
+    case SegmentType::DESCENT:
+    case SegmentType::WILDCARD: {
+      if (node.is_object()) {
+        for (const auto& k_v : node.object_range()) {
+          DoCall(callback, k_v.key(), k_v.value());
+        }
+      } else if (node.is_array()) {
+        for (const auto& val : node.array_range()) {
+          DoCall(callback, nullopt, val);
+        }
+      }
+    } break;
+    default:
+      LOG(DFATAL) << "Unknown segment " << SegmentName(segment.type());
+  }
+  return {};
+}
+
+auto Dfs::MutateStep(const PathSegment& segment, const MutateCallback& cb, JsonType* node)
+    -> nonstd::expected<void, MatchStatus> {
+  switch (segment.type()) {
+    case SegmentType::IDENTIFIER: {
+      if (!node->is_object())
+        return make_unexpected(MISMATCH);
+
+      auto it = node->find(segment.identifier());
+      if (it != node->object_range().end()) {
+        if (Mutate(cb, it->key(), &it->value())) {
+          node->erase(it);
+        }
+      }
+    } break;
+    case SegmentType::INDEX: {
+      if (!node->is_array())
+        return make_unexpected(MISMATCH);
+      if (segment.index() >= node->size()) {
+        return make_unexpected(OUT_OF_BOUNDS);
+      }
+      auto it = node->array_range().begin() + segment.index();
+      if (Mutate(cb, nullopt, &*it)) {
+        node->erase(it);
+      }
+    } break;
+
+    case SegmentType::DESCENT:
+    case SegmentType::WILDCARD: {
+      if (node->is_object()) {
+        auto it = node->object_range().begin();
+        while (it != node->object_range().end()) {
+          it = Mutate(cb, it->key(), &it->value()) ? node->erase(it) : it + 1;
+        }
+      } else if (node->is_array()) {
+        auto it = node->array_range().begin();
+        while (it != node->array_range().end()) {
+          it = Mutate(cb, nullopt, &*it) ? node->erase(it) : it + 1;
+        }
+      }
+    } break;
+    case SegmentType::FUNCTION:
+      LOG(DFATAL) << "Function segment is not supported for mutation";
+      break;
+  }
+  return {};
+}
+
+}  // namespace dfly::json::detail