From 5b1887367680c494e27794252fee8d1aacf088ef Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Roman=20Smr=C5=BE?= <roman.smrz@seznam.cz>
Date: Sun, 8 Jan 2023 13:20:26 +0100
Subject: Property lookup helpers

---
 include/erebos/merge.h | 53 ++++++++++++++++++++++++++++++++++++++++++++++++++
 src/CMakeLists.txt     |  1 +
 src/merge.cpp          | 26 +++++++++++++++++++++++++
 3 files changed, 80 insertions(+)
 create mode 100644 src/merge.cpp

diff --git a/include/erebos/merge.h b/include/erebos/merge.h
index bef8212..9705e94 100644
--- a/include/erebos/merge.h
+++ b/include/erebos/merge.h
@@ -2,9 +2,16 @@
 
 #include <erebos/storage.h>
 
+#include <optional>
+#include <vector>
+
 namespace erebos
 {
 
+using std::nullopt;
+using std::optional;
+using std::vector;
+
 template<class T> struct Mergeable
 {
 };
@@ -17,4 +24,50 @@ template<> struct Mergeable<vector<Stored<Object>>>
 	static vector<Stored<Object>> merge(const vector<Stored<Object>> & x) { return x; }
 };
 
+vector<Stored<Object>> findPropertyObjects(const vector<Stored<Object>> & leaves, const string & prop);
+
+template<typename T>
+optional<Stored<typename Mergeable<T>::Component>> findPropertyComponent(const vector<Stored<typename Mergeable<T>::Component>> & components, const string & prop)
+{
+	vector<Stored<Object>> leaves;
+	leaves.reserve(components.size());
+
+	for (const auto & c : components)
+		leaves.push_back(Stored<Object>::load(c.ref()));
+
+	auto candidates = findPropertyObjects(leaves, prop);
+	if (!candidates.empty())
+		return Stored<typename Mergeable<T>::Component>::load(candidates[0].ref());
+	return nullopt;
+}
+
+template<typename T>
+optional<Stored<typename Mergeable<T>::Component>> findPropertyComponent(const T & x, const string & prop)
+{
+	return findPropertyComponent(x.components(), prop);
+}
+
+template<typename T>
+vector<Stored<typename Mergeable<T>::Component>> findPropertyComponents(const vector<Stored<typename Mergeable<T>::Component>> & components, const string & prop)
+{
+	vector<Stored<Object>> leaves;
+	leaves.reserve(components.size());
+
+	for (const auto & c : components)
+		leaves.push_back(Stored<Object>::load(c.ref()));
+
+	auto candidates = findPropertyObjects(leaves, prop);
+	vector<Stored<typename Mergeable<T>::Component>> result;
+	result.reserve(candidates.size());
+	for (const auto & obj : candidates)
+		result.push_back(Stored<typename Mergeable<T>::Component>::load(obj.ref()));
+	return result;
+}
+
+template<typename T>
+vector<Stored<typename Mergeable<T>::Component>> findPropertyComponents(const T & x, const string & prop)
+{
+	return findPropertyComponents(x.components(), prop);
+}
+
 }
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 72094b8..cb0db6d 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -8,6 +8,7 @@ add_library(erebos
 	contact.cpp
 	frp.cpp
 	identity.cpp
+	merge.cpp
 	message.cpp
 	network.cpp
 	pairing.cpp
diff --git a/src/merge.cpp b/src/merge.cpp
new file mode 100644
index 0000000..040ebb4
--- /dev/null
+++ b/src/merge.cpp
@@ -0,0 +1,26 @@
+#include <erebos/merge.h>
+
+namespace erebos {
+
+static void findPropertyObjects(vector<Stored<Object>> & candidates, const Stored<Object> & obj, const string & prop)
+{
+	if (auto rec = obj->asRecord()) {
+		if (rec->item(prop)) {
+			candidates.push_back(obj);
+		} else {
+			for (const auto & r : obj.ref().previous())
+				findPropertyObjects(candidates, Stored<Object>::load(r), prop);
+		}
+	}
+}
+
+vector<Stored<Object>> findPropertyObjects(const vector<Stored<Object>> & leaves, const string & prop)
+{
+	vector<Stored<Object>> candidates;
+	for (const auto & obj : leaves)
+		findPropertyObjects(candidates, obj, prop);
+	filterAncestors(candidates);
+	return candidates;
+}
+
+}
-- 
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