From d7b6dee2db415fc5d0052dca47a45c44b9aaba6d Mon Sep 17 00:00:00 2001
From: "Claudius \"keldu\" Holeksa" <mail@keldu.de>
Date: Tue, 22 Apr 2025 13:35:38 +0200
Subject: Broken float decoder in forstio

---
 .nix/derivation.nix       | 11 +++++-----
 c++/config.hpp            | 53 +++++++++++++++++++++++++++++++++++++++++++++++
 c++/lbm.hpp               |  1 +
 c++/particle/particle.hpp |  1 +
 examples/config.json      |  5 +++++
 examples/meta_2d.cpp      | 19 ++++++++++++++++-
 6 files changed, 84 insertions(+), 6 deletions(-)
 create mode 100644 c++/config.hpp
 create mode 100644 examples/config.json

diff --git a/.nix/derivation.nix b/.nix/derivation.nix
index 7ce23e2..6a50475 100644
--- a/.nix/derivation.nix
+++ b/.nix/derivation.nix
@@ -20,13 +20,14 @@ stdenv.mkDerivation {
     forstio.async
     forstio.codec
     forstio.codec-unit
-	];
+    forstio.codec-json
+  ];
 
-	doCheck = true;
-	checkPhase = ''
+  doCheck = true;
+  checkPhase = ''
     scons test
-		./bin/tests
-	'';
+    ./bin/tests
+  '';
 
   outputs = [ "out" "dev" ];
 }
diff --git a/c++/config.hpp b/c++/config.hpp
new file mode 100644
index 0000000..64f7a0f
--- /dev/null
+++ b/c++/config.hpp
@@ -0,0 +1,53 @@
+#pragma once
+
+#include <forstio/codec/data.hpp>
+#include <forstio/codec/json/json.hpp>
+
+#include <fstream>
+#include <sstream>
+#include <string_view>
+#include <string>
+
+namespace kel {
+namespace lbm {
+namespace sch {
+using namespace saw::schema;
+template<typename T, typename Desc>
+using LbmConfig = Struct<
+    Member<T, "delta_x">,
+    Member<T, "kinematic_viscosity">,
+    Member<T, "delta_t">
+>;
+}
+
+template<typename T, typename Desc>
+saw::error_or<saw::data<sch::LbmConfig<T,Desc>>> load_lbm_config(std::string_view file_name){
+    std::ifstream file{std::string{file_name}};
+
+    if(!file.is_open()){
+        return saw::make_error<saw::err::not_found>("Couldn't open file");
+    }
+
+    saw::data<sch::LbmConfig<T,Desc>, saw::encode::Json> lbm_json_conf{saw::heap<saw::array_buffer>(1u)};
+
+    uint8_t ele{};
+    while(file.readsome(reinterpret_cast<char*>(&ele), 1u) > 0u){
+        auto err = lbm_json_conf.get_buffer().push(ele,1u);
+        if(err.failed()){
+            return err;
+        }
+    }
+
+    saw::data<sch::LbmConfig<T,Desc>> lbm_conf;
+    saw::codec<sch::LbmConfig<T,Desc>, saw::encode::Json> json_codec;
+    {
+        auto eov = json_codec.decode(lbm_json_conf, lbm_conf);
+        if(eov.is_error()){
+            return std::move(eov.get_error());
+        }
+    }
+
+    return lbm_conf;
+}
+}
+}
diff --git a/c++/lbm.hpp b/c++/lbm.hpp
index 9cd7296..1baaa0e 100644
--- a/c++/lbm.hpp
+++ b/c++/lbm.hpp
@@ -2,6 +2,7 @@
 
 #include "descriptor.hpp"
 #include "converter.hpp"
+#include "config.hpp"
 
 #include <forstio/codec/unit/unit_print.hpp>
 #include <iostream>
diff --git a/c++/particle/particle.hpp b/c++/particle/particle.hpp
index 58c028c..aeda17f 100644
--- a/c++/particle/particle.hpp
+++ b/c++/particle/particle.hpp
@@ -35,6 +35,7 @@ public:
 
 	void step(T time_step){
 		for(auto& iter : particles_){
+
 		}
 	}
 };
diff --git a/examples/config.json b/examples/config.json
new file mode 100644
index 0000000..dcd7f91
--- /dev/null
+++ b/examples/config.json
@@ -0,0 +1,5 @@
+{
+	"delta_x" : 0.1,
+	"delta_t" : 0.1,
+	"kinematic_viscosity" : 1e-3
+}
diff --git a/examples/meta_2d.cpp b/examples/meta_2d.cpp
index 5aa39f4..a66f0e9 100644
--- a/examples/meta_2d.cpp
+++ b/examples/meta_2d.cpp
@@ -1,14 +1,31 @@
 #include "../c++/lbm.hpp"
 
+#include <iostream>
+
 int main(int argc, char** argv){
 	using namespace kel::lbm;
+
+	auto eo_conf = load_lbm_config<sch::Float64,sch::Descriptor<2,9>>("config.json");
+	if(eo_conf.is_error()){
+		auto& err = eo_conf.get_error();
+		std::cerr<<"[Error]: "<<err.get_category();
+		auto err_msg = err.get_message();
+		if(!err_msg.empty()){
+			std::cerr<<" - "<<err_msg;
+		}
+		std::cerr<<std::endl;
+
+		return err.get_id();
+	}
+
+	auto& conf = eo_conf.get_value();
 	
 	converter<sch::Float64> conv{
 		{0.1},
 		{0.1}
 	};
 
-	print_lbm_meta<sch::Float64,sch::Descriptor<2,9>>(conv, {1e-5});
+	print_lbm_meta<sch::Float64,sch::Descriptor<2,9>>(conv, {conf.template get<"kinematic_viscosity">()});
 
 	return 0;
 }
-- 
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