//
//  ClockReceiver.hpp
//  Clock Signal
//
//  Created by Thomas Harte on 22/07/2017.
//  Copyright 2017 Thomas Harte. All rights reserved.
//

#pragma once

#include "ForceInline.hpp"

#include <algorithm>
#include <concepts>
#include <cassert>
#include <cstdint>
#include <limits>

constexpr bool is_power_of_two(const int v) {
	return !(v & (v - 1));
}

/*!
	Provides a class that wraps a plain int, providing most of the basic arithmetic and
	Boolean operators, but forcing callers and receivers to be explicit as to usage.
*/
template <int ClockDenominator>
requires (is_power_of_two(ClockDenominator))
class Clocks {
public:
	static constexpr int Denominator = ClockDenominator;
	using IntType = int64_t;

	constexpr Clocks(const IntType rhs) noexcept : length_(rhs) {}
	constexpr Clocks() noexcept : length_(0) {}

	// Assignments are implemented anywhere they can't lose data.
	template <typename SourceClocks>
	requires (SourceClocks::Denominator <= Denominator)
	constexpr Clocks(const SourceClocks rhs) noexcept {
		*this = rhs.template reduce<Clocks>();
	}

	Clocks operator +=(const Clocks rhs)	{	length_ += rhs.length_;	return *this;	}
	Clocks operator -=(const Clocks rhs)	{	length_ -= rhs.length_;	return *this;	}
	Clocks operator ++() 					{	++length_;	return *this;	}
	Clocks operator --()					{	--length_;	return *this;	}

	Clocks operator ++(int) {
		const Clocks result = *this;
		++length_;
		return result;
	}
	Clocks operator --(int) {
		const Clocks result = *this;
		--length_;
		return result;
	}

	Clocks operator *=(const Clocks rhs) 	{	*this = Clocks(length_ * rhs.length_);	return *this;	}
	Clocks operator /=(const Clocks rhs) 	{	*this = Clocks(length_ / rhs.length_);	return *this;	}
	Clocks operator %=(const Clocks rhs) 	{	*this = Clocks(length_ % rhs.length_);	return *this;	}
	Clocks operator &=(const Clocks rhs) 	{	*this = Clocks(length_ & rhs.length_);	return *this;	}

	constexpr Clocks operator +(const Clocks rhs) const		{	return Clocks(length_ + rhs.length_);	}
	constexpr Clocks operator -(const Clocks rhs) const		{	return Clocks(length_ - rhs.length_);	}

	constexpr Clocks operator *(const Clocks rhs) const		{	return Clocks(length_ * rhs.length_);	}
	constexpr Clocks operator /(const Clocks rhs) const		{	return Clocks(length_ / rhs.length_);	}

	constexpr Clocks operator %(const Clocks rhs) const		{	return Clocks(length_ % rhs.length_);	}
	constexpr Clocks operator &(const Clocks rhs) const		{	return Clocks(length_ & rhs.length_);	}

	constexpr Clocks operator -() const						{	return Clocks(-length_);				}

	auto operator <=>(const Clocks &) const = default;

	constexpr bool operator !() const					{	return !length_;				}
	// bool operator () is not supported because it offers an implicit cast to int,
	// which is prone silently to permit misuse.

	/// @returns The underlying int, converted to a numeric type of your choosing, clamped to that type's range.
	template <typename Type = IntType>
	requires std::integral<Type> || std::floating_point<Type>
	constexpr Type as() const {
		// TODO: adopt std::saturate_cast if/when this is a C++26 project.

		const IntType value = get();
		if constexpr (std::is_floating_point_v<Type>) {
			// Floating point: the caller takes responsibility for loss of precision;
			// acceptable range can be assumed.
			return Type(value);
		} else {
			assert(std::is_signed_v<IntType>);

			if constexpr (std::is_signed_v<Type>) {
				// Casting to another signed type; either it's large enough that range can't be exceeded,
				// or it's a lesser range that can safely be clamped to.
				if constexpr (sizeof(Type) >= sizeof(IntType)) {
					return Type(value);
				} else {
					return Type(std::clamp<IntType>(value, IntType(std::numeric_limits<Type>::min()), IntType(std::numeric_limits<Type>::max())));
				}
			} else {
				// Casting to an unsigned type: negative numbers map straight to 0, everything positive
				// either unambiguously fits, or can be subject to an in-IntType min.
				if(value <= 0) {
					return 0;
				}
				if constexpr (sizeof(Type) >= sizeof(IntType)) {
					return Type(value);
				} else {
					return Type(std::min<IntType>(value, IntType(std::numeric_limits<Type>::max())));
				}
			}
		}
	}

	/// @returns The underlying int, in its native form, potentially scaled upward.
	template <int GetDenominator = Denominator>
	requires (GetDenominator >= Denominator)
	constexpr IntType get() const {
		return length_ << (GetDenominator - Denominator);
	}

	/// @returns This value, optionally converted to another time base. Potentially loses precision.
	template <typename TargetClocks>
	constexpr TargetClocks reduce() const {
		if constexpr (TargetClocks::Denominator >= Denominator) {
			return TargetClocks(length_ << (TargetClocks::Denominator - Denominator));
		} else {
			return TargetClocks(length_ >> (Denominator - TargetClocks::Denominator));
		}
	}

	// operator int() is deliberately not provided, to avoid accidental subtitution of
	// classes that use this template.

	/*!
		Performs the net division necessary to: (i) convert from Clocks to DestinationClocks; and (ii) further to divide by divider.
		Returns the number of DestinationClocks. Keeps here any remainder after subtracting the returned amount.

		So e.g. `HalfCycles.divide<Cycles>(n)` with n = 1 will return a conversion from HalfCycles to Cycles for the same duration.
		Wth n = 2 will return a length in Cycles that is half the duration. Etc.
	*/
	template <typename DestinationClocks = Clocks>
	requires (DestinationClocks::Denominator <= Denominator)
	DestinationClocks divide(const Clocks divider) {
		// Apply the clock division.
		const auto native_period = length_ / divider.length_;
		length_ %= divider.length_;

		// Also accumulate some potential wastage if there's a type conversion.
		static constexpr auto Shift = Denominator - DestinationClocks::Denominator;
		if constexpr (Shift != 0) {
			const auto further_residue = native_period & ((1 << Shift) - 1);
			length_ += further_residue * divider.length_;
			// Logic: whatever part of native period isn't going to be converted is quantity lost after
			// applying the divider. So unapply it to get back to what wasn't extracted from the original.
		}

		return DestinationClocks(native_period >> Shift);
	}

	/*!
		Extracts a whole number of `DestinationClock`s from `*this`.
		Leaves the residue here.
	*/
	template <typename DestinationClocks = Clocks>
	DestinationClocks flush() {
		if constexpr (DestinationClocks::Denominator >= Denominator) {
			const auto result = DestinationClocks(get<DestinationClocks::Denominator>());
			length_ = 0;
			return result;
		} else {
			static constexpr int Shift = Denominator - DestinationClocks::Denominator;
			static constexpr IntType ResidueMask = (1 << Shift) - 1;
			const auto result = DestinationClocks(length_ >> Shift);
			length_ &= ResidueMask;
			return result;
		}
	}

	static Clocks max() { return Clocks(std::numeric_limits<IntType>::max()); }
	static Clocks min() { return Clocks(std::numeric_limits<IntType>::min()); }

private:
	IntType length_;
};

/// Reasons Clocks into being a count of querter cycles, building half- and whole-cycles from there.
using Cycles = Clocks<1>;
using HalfCycles = Clocks<2>;
using QuarterCycles = Clocks<4>;

/*!
	Provides automated boilerplate for connecting an owner that works in one clock base to a receiver that works in another.
*/
template <typename TargetT, typename SourceClocks, typename DestinationClocks>
class ConvertedClockReceiver: public TargetT {
public:
	using TargetT::TargetT;

	void run_for(const SourceClocks duration) {
		source_ += duration;
		TargetT::run_for(source_.template flush<DestinationClocks>());
	}

private:
	SourceClocks source_;
};