From 9aaba1211c95dc7e08437a7cca73452181e296d6 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Roman=20Smr=C5=BE?= <roman.smrz@seznam.cz>
Date: Sun, 18 Apr 2021 22:25:17 +0200
Subject: Initial support for FRP behaviors

---
 include/erebos/frp.h | 230 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 230 insertions(+)
 create mode 100644 include/erebos/frp.h

(limited to 'include/erebos/frp.h')

diff --git a/include/erebos/frp.h b/include/erebos/frp.h
new file mode 100644
index 0000000..587d2b6
--- /dev/null
+++ b/include/erebos/frp.h
@@ -0,0 +1,230 @@
+#pragma once
+
+#include <functional>
+#include <memory>
+#include <optional>
+#include <functional>
+#include <type_traits>
+#include <tuple>
+#include <variant>
+
+namespace erebos {
+
+using std::enable_if_t;
+using std::function;
+using std::is_same_v;
+using std::make_shared;
+using std::monostate;
+using std::optional;
+using std::shared_ptr;
+using std::static_pointer_cast;
+using std::tuple;
+using std::vector;
+using std::weak_ptr;
+
+class BhvTime
+{
+	BhvTime(uint64_t t): t(t) {}
+	friend class BhvCurTime;
+public:
+
+private:
+	uint64_t t;
+};
+
+class BhvCurTime
+{
+public:
+	BhvCurTime();
+	~BhvCurTime();
+	BhvCurTime(const BhvCurTime &) = delete;
+	BhvCurTime(BhvCurTime &&);
+
+	BhvCurTime & operator=(const BhvCurTime &) = delete;
+	BhvCurTime & operator=(BhvCurTime &&);
+
+private:
+	optional<BhvTime> t;
+};
+
+template<typename T>
+class Watched
+{
+public:
+	Watched(shared_ptr<function<void(const BhvCurTime &)>> && cb):
+		cb(move(cb)) {}
+	~Watched();
+
+private:
+	shared_ptr<function<void(const BhvCurTime &)>> cb;
+};
+
+template<typename T>
+Watched<T>::~Watched()
+{
+	BhvCurTime ctime;
+	cb.reset();
+}
+
+class BhvImplBase : public std::enable_shared_from_this<BhvImplBase>
+{
+public:
+	virtual ~BhvImplBase();
+
+protected:
+	void dependsOn(shared_ptr<BhvImplBase> other);
+	void updated(const BhvCurTime &);
+	virtual bool needsUpdate(const BhvCurTime &) const;
+	virtual void doUpdate(const BhvCurTime &);
+
+	vector<weak_ptr<function<void(const BhvCurTime &)>>> watchers;
+private:
+	void markDirty(const BhvCurTime &, vector<shared_ptr<BhvImplBase>> &);
+	void updateDirty(const BhvCurTime &);
+
+	bool dirty = false;
+	vector<shared_ptr<BhvImplBase>> depends;
+	vector<weak_ptr<BhvImplBase>> rdepends;
+
+	template<typename A, typename B> friend class BhvFun;
+};
+
+template<typename A, typename B>
+class BhvImpl : public BhvImplBase
+{
+public:
+	virtual B get(const BhvCurTime &, const A &) const = 0;
+};
+
+template<typename A>
+using BhvSource = BhvImpl<monostate, A>;
+
+template<typename A, typename B>
+class BhvFun
+{
+public:
+	BhvFun(shared_ptr<BhvImpl<A, B>> impl):
+		impl(move(impl)) {}
+
+	template<typename T> BhvFun(shared_ptr<T> impl):
+		BhvFun(static_pointer_cast<BhvImpl<A, B>>(impl)) {}
+
+	B get(const A & x) const
+	{
+		BhvCurTime ctime;
+		return impl->get(ctime, x);
+	}
+
+	const shared_ptr<BhvImpl<A, B>> impl;
+};
+
+template<typename A>
+class BhvFun<monostate, A>
+{
+public:
+	BhvFun(shared_ptr<BhvSource<A>> impl):
+		impl(move(impl)) {}
+
+	template<typename T> BhvFun(shared_ptr<T> impl):
+		BhvFun(static_pointer_cast<BhvSource<A>>(impl)) {}
+
+	A get() const
+	{
+		BhvCurTime ctime;
+		return impl->get(ctime, monostate());
+	}
+	Watched<A> watch(function<void(const A &)>);
+
+	const shared_ptr<BhvSource<A>> impl;
+};
+
+template<typename A>
+using Bhv = BhvFun<monostate, A>;
+
+template<typename A>
+Watched<A> Bhv<A>::watch(function<void(const A &)> f)
+{
+	auto cb = make_shared<function<void(const BhvCurTime &)>>(
+			[impl = BhvFun<monostate, A>::impl, f] (const BhvCurTime & ctime) {
+				f(impl->get(ctime, monostate()));
+			});
+	BhvFun<monostate, A>::impl->watchers.push_back(cb);
+	return Watched<A>(move(cb));
+}
+
+
+template<typename A, typename B>
+class BhvLambda : public BhvImpl<A, B>
+{
+public:
+	BhvLambda(function<B(const A &)> f): f(f) {}
+
+	B get(const BhvCurTime &, const A & x) const override
+	{ return f(x); }
+
+private:
+	function<B(const A &)> f;
+};
+
+template<typename A, typename B>
+BhvFun<A, B> bfun(function<B(const A &)> f)
+{
+	return make_shared<BhvLambda<A, B>>(f);
+}
+
+
+template<typename A, typename B, typename C> class BhvComp;
+template<typename A, typename B, typename C>
+BhvFun<A, C> operator>>(const BhvFun<A, B> & f, const BhvFun<B, C> & g);
+
+template<typename A, typename B, typename C>
+class BhvComp : public BhvImpl<A, C>
+{
+public:
+	BhvComp(const BhvFun<A, B> & f, const BhvFun<B, C>):
+		f(f), g(g) {}
+
+	C get(const BhvCurTime & ctime, const A & x) const override
+	{ return g.impl.get(ctime, f.impl.get(ctime, x)); }
+
+private:
+	BhvFun<A, B> f;
+	BhvFun<B, C> g;
+
+	friend BhvFun<A, C> operator>> <A, B, C>(const BhvFun<A, B> &, const BhvFun<B, C> &);
+};
+
+template<typename B, typename C>
+class BhvComp<monostate, B, C> : public BhvSource<C>
+{
+public:
+	BhvComp(const BhvFun<monostate, B> & f, const BhvFun<B, C> & g):
+		f(f), g(g) {}
+
+	bool needsUpdate(const BhvCurTime & ctime) const override
+	{ return !x || g.impl->get(ctime, f.impl->get(ctime, monostate())) != x.value(); }
+
+	void doUpdate(const BhvCurTime & ctime) override
+	{ x = g.impl->get(ctime, f.impl->get(ctime, monostate())); }
+
+	C get(const BhvCurTime & ctime, const monostate & m) const override
+	{ return x ? x.value() : g.impl->get(ctime, f.impl->get(ctime, m)); }
+
+private:
+	BhvFun<monostate, B> f;
+	BhvFun<B, C> g;
+	optional<C> x;
+
+	friend BhvFun<monostate, C> operator>> <monostate, B, C>(const BhvFun<monostate, B> &, const BhvFun<B, C> &);
+};
+
+template<typename A, typename B, typename C>
+BhvFun<A, C> operator>>(const BhvFun<A, B> & f, const BhvFun<B, C> & g)
+{
+	auto impl = make_shared<BhvComp<A, B, C>>(f, g);
+	impl->dependsOn(f.impl);
+	impl->dependsOn(g.impl);
+	return impl;
+}
+
+}
-- 
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