From 7b84cb0b1f94fef64dc7b6f97cbfe0a80d12af61 Mon Sep 17 00:00:00 2001
From: lisyarus <lisyarus@gmail.com>
Date: Wed, 10 Mar 2021 14:12:29 +0300
Subject: [PATCH] Support non-modifying chunked_map::at

---
 libs/pcg/include/psemek/pcg/chunked_map.hpp | 22 ++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/libs/pcg/include/psemek/pcg/chunked_map.hpp b/libs/pcg/include/psemek/pcg/chunked_map.hpp
index d5312c8f..c1695567 100644
--- a/libs/pcg/include/psemek/pcg/chunked_map.hpp
+++ b/libs/pcg/include/psemek/pcg/chunked_map.hpp
@@ -5,6 +5,7 @@
 #include <psemek/geom/box.hpp>
 
 #include <unordered_map>
+#include <optional>
 
 namespace psemek::pcg
 {
@@ -19,7 +20,7 @@ namespace psemek::pcg
 			, generator_(std::move(generator))
 		{}
 
-		T const & operator()(geom::vector<int, N> p)
+		T & operator()(geom::point<int, N> p)
 		{
 			geom::vector<int, N> ip;
 			for (std::size_t i = 0; i < N; ++i)
@@ -45,6 +46,25 @@ namespace psemek::pcg
 			return it->second(t);
 		}
 
+		std::optional<T> at(geom::point<int, N> p) const
+		{
+			geom::vector<int, N> ip;
+			for (std::size_t i = 0; i < N; ++i)
+			{
+				ip[i] = (p[i] >= 0) ? (p[i] / chunk_size_) : -((- p[i] + chunk_size_ - 1) / chunk_size_);
+			}
+
+			auto it = chunks_.find(ip);
+			if (it == chunks_.end())
+				return std::nullopt;
+
+			std::array<std::size_t, N> t;
+			for (std::size_t i = 0; i < N; ++i)
+				t[i] = p[i] - ip[i] * chunk_size_;
+
+			return it->second(t);
+		}
+
 	private:
 		int const chunk_size_;
 		generator_func generator_;