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 ++++++++++++++++++++++++++++++++++++++++++++++
 include/erebos/identity.h |   2 +
 include/erebos/network.h  |   1 +
 include/erebos/storage.h  |  26 ++++++
 src/CMakeLists.txt        |   1 +
 src/frp.cpp               | 133 +++++++++++++++++++++++++++
 src/identity.cpp          |  10 ++
 src/network.cpp           |   6 ++
 src/network.h             |   1 +
 9 files changed, 410 insertions(+)
 create mode 100644 include/erebos/frp.h
 create mode 100644 src/frp.cpp

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;
+}
+
+}
diff --git a/include/erebos/identity.h b/include/erebos/identity.h
index aeddd08..f7b17b8 100644
--- a/include/erebos/identity.h
+++ b/include/erebos/identity.h
@@ -24,6 +24,8 @@ public:
 	Stored<class PublicKey> keyMessage() const;
 
 	bool sameAs(const Identity &) const;
+	bool operator==(const Identity & other) const;
+	bool operator!=(const Identity & other) const;
 
 	std::optional<Ref> ref() const;
 
diff --git a/include/erebos/network.h b/include/erebos/network.h
index 5a1fca6..f2ae191 100644
--- a/include/erebos/network.h
+++ b/include/erebos/network.h
@@ -17,6 +17,7 @@ public:
 	~Server();
 
 	const Head<LocalState> & localHead() const;
+	const Bhv<LocalState> & localState() const;
 
 	const Identity & identity() const;
 	template<class S> S & svc();
diff --git a/include/erebos/storage.h b/include/erebos/storage.h
index 7ec73ab..2d00cc3 100644
--- a/include/erebos/storage.h
+++ b/include/erebos/storage.h
@@ -1,5 +1,6 @@
 #pragma once
 
+#include <erebos/frp.h>
 #include <erebos/time.h>
 #include <erebos/uuid.h>
 
@@ -496,6 +497,8 @@ public:
 	std::optional<Head<T>> update(const std::function<Stored<T>(const Stored<T> &)> &) const;
 	WatchedHead<T> watch(const std::function<void(const Head<T> &)> &) const;
 
+	Bhv<T> behavior() const;
+
 private:
 	UUID mid;
 	Stored<T> mstored;
@@ -526,6 +529,23 @@ public:
 	~WatchedHead();
 };
 
+template<class T>
+class HeadBhv : public BhvSource<T>
+{
+public:
+	HeadBhv(const Head<T> & head):
+		whead(head.watch([this] (const Head<T> & cur) {
+			BhvCurTime ctime;
+			whead = cur;
+			BhvImplBase::updated(ctime);
+		})) {}
+
+	T get(const BhvCurTime &, const std::monostate &) const { return *whead; }
+
+private:
+	WatchedHead<T> whead;
+};
+
 template<typename T>
 std::optional<Head<T>> Storage::head(UUID id) const
 {
@@ -583,6 +603,12 @@ WatchedHead<T> Head<T>::watch(const std::function<void(const Head<T> &)> & watch
 	return WatchedHead<T>(*this, wid);
 }
 
+template<typename T>
+Bhv<T> Head<T>::behavior() const
+{
+	return make_shared<HeadBhv<T>>(*this);
+}
+
 template<class T>
 WatchedHead<T>::~WatchedHead()
 {
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 61f491f..8f65555 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -5,6 +5,7 @@ include_directories(
 add_library(erebos
 	attach
 	channel
+	frp
 	identity
 	message
 	network
diff --git a/src/frp.cpp b/src/frp.cpp
new file mode 100644
index 0000000..142fcd4
--- /dev/null
+++ b/src/frp.cpp
@@ -0,0 +1,133 @@
+#include <erebos/frp.h>
+
+#include <condition_variable>
+#include <mutex>
+
+using namespace erebos;
+
+using std::condition_variable;
+using std::move;
+using std::mutex;
+using std::nullopt;
+using std::unique_lock;
+using std::weak_ptr;
+
+mutex bhvTimeMutex;
+condition_variable bhvTimeCond;
+bool bhvTimeRunning = false;
+uint64_t bhvTimeLast = 0;
+
+BhvCurTime::BhvCurTime()
+{
+	unique_lock lock(bhvTimeMutex);
+	bhvTimeCond.wait(lock, []{ return !bhvTimeRunning; });
+
+	bhvTimeRunning = true;
+	t = BhvTime(++bhvTimeLast);
+}
+
+BhvCurTime::~BhvCurTime()
+{
+	if (t) {
+		unique_lock lock(bhvTimeMutex);
+		bhvTimeRunning = false;
+		lock.unlock();
+		bhvTimeCond.notify_one();
+	}
+}
+
+BhvCurTime::BhvCurTime(BhvCurTime && other)
+{
+	t = other.t;
+	other.t = nullopt;
+}
+
+BhvCurTime & BhvCurTime::operator=(BhvCurTime && other)
+{
+	t = other.t;
+	other.t = nullopt;
+	return *this;
+}
+
+
+BhvImplBase::~BhvImplBase() = default;
+
+void BhvImplBase::dependsOn(shared_ptr<BhvImplBase> other)
+{
+	depends.push_back(other);
+	other->rdepends.push_back(shared_from_this());
+}
+
+void BhvImplBase::updated(const BhvCurTime & ctime)
+{
+	vector<shared_ptr<BhvImplBase>> toUpdate;
+	markDirty(ctime, toUpdate);
+
+	for (auto & bhv : toUpdate)
+		bhv->updateDirty(ctime);
+}
+
+void BhvImplBase::markDirty(const BhvCurTime & ctime, vector<shared_ptr<BhvImplBase>> & toUpdate)
+{
+	if (dirty)
+		return;
+
+	if (!needsUpdate(ctime))
+		return;
+
+	dirty = true;
+	toUpdate.push_back(shared_from_this());
+
+	bool prune = false;
+	for (const auto & w : rdepends) {
+		if (auto b = w.lock())
+			b->markDirty(ctime, toUpdate);
+		else
+			prune = true;
+	}
+
+	if (prune) {
+		decltype(rdepends) pruned;
+		for (const auto & w : rdepends)
+			if (!w.expired())
+				pruned.push_back(move(w));
+		rdepends = move(pruned);
+	}
+}
+
+void BhvImplBase::updateDirty(const BhvCurTime & ctime)
+{
+	if (!dirty)
+		return;
+
+	for (auto & d : depends)
+		d->updateDirty(ctime);
+
+	doUpdate(ctime);
+	dirty = false;
+
+	bool prune = false;
+	for (const auto & wcb : watchers) {
+		if (auto cb = wcb.lock())
+			(*cb)(ctime);
+		else
+			prune = true;
+	}
+
+	if (prune) {
+		decltype(watchers) pruned;
+		for (const auto & w : watchers)
+			if (!w.expired())
+				pruned.push_back(move(w));
+		watchers = move(pruned);
+	}
+}
+
+bool BhvImplBase::needsUpdate(const BhvCurTime &) const
+{
+	return true;
+}
+
+void BhvImplBase::doUpdate(const BhvCurTime &)
+{
+}
diff --git a/src/identity.cpp b/src/identity.cpp
index 374a872..a4c12f2 100644
--- a/src/identity.cpp
+++ b/src/identity.cpp
@@ -77,6 +77,16 @@ bool Identity::sameAs(const Identity & other) const
 		other.p->data[0]->data->keyIdentity;
 }
 
+bool Identity::operator==(const Identity & other) const
+{
+	return p->data == other.p->data;
+}
+
+bool Identity::operator!=(const Identity & other) const
+{
+	return p->data != other.p->data;
+}
+
 optional<Ref> Identity::ref() const
 {
 	if (p->data.size() == 1)
diff --git a/src/network.cpp b/src/network.cpp
index f33c097..259ae5e 100644
--- a/src/network.cpp
+++ b/src/network.cpp
@@ -38,6 +38,11 @@ const Head<LocalState> & Server::localHead() const
 	return p->localHead;
 }
 
+const Bhv<LocalState> & Server::localState() const
+{
+	return p->localState;
+}
+
 const Identity & Server::identity() const
 {
 	return p->self;
@@ -203,6 +208,7 @@ Server::Priv::Priv(const Head<LocalState> & local, const Identity & self,
 		vector<unique_ptr<Service>> && svcs):
 	self(self),
 	// Watching needs to start after self is initialized
+	localState(local.behavior()),
 	localHead(local.watch(std::bind(&Priv::handleLocalHeadChange, this, std::placeholders::_1))),
 	services(std::move(svcs))
 {
diff --git a/src/network.h b/src/network.h
index 6ebd60c..fe7d7b4 100644
--- a/src/network.h
+++ b/src/network.h
@@ -158,6 +158,7 @@ struct Server::Priv : enable_shared_from_this<Server::Priv>
 	bool finish = false;
 
 	Identity self;
+	Bhv<LocalState> localState;
 	WatchedHead<LocalState> localHead;
 	vector<unique_ptr<Service>> services;
 
-- 
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