gplib/include/gp/vfs/channel_fs.hpp

#pragma once
#include "gp/array.hpp"
#include "gp/algorithm/move.hpp"
#include "gp/vfs/fs_types.hpp"
#include "gp/allocator/aggregator.hpp"

namespace gp {
	template<typename error_function, typename pop_function>
	class self_filling_channel{
		error_function on_error;
		pop_function filler;
	public:
		gp::buffer<char>::associated_iterator push(gp::buffer<char> input) {
			on_error();
			return input.begin();
		}
		gp::buffer<char>::associated_iterator pop(gp::buffer<char> dest) {
			return filler(dest);
		}
	};

	template<size_t size, size_t count = 1, bool whole_messages = true, bool zero_out = true>
	class channel {
		gp::array<size_t, count> message_sizes;
		gp::array<
			gp::array<char, size>,
			count
		> messages;
		size_t r_offset = 0;
		size_t w_offset = 0;
		[[nodiscard]] size_t write_one(size_t loc, gp::buffer<char> message) {
			auto cond =  message.size();
			size_t idx = 0;
			for(; idx < cond; ++idx) {
				messages[loc][idx] = message[idx];
			}
			message_sizes[loc] = message.size();
			w_offset += 1;
			if constexpr (count != 1) w_offset %= size;
			if constexpr (zero_out) {
				auto ret = idx;
				for(; idx < messages[loc].size(); ++idx) {
					messages[loc] = 0;
				}
				return ret;
			}
			return idx;
		}
		[[nodiscard]] size_t read_one(size_t loc, gp::buffer<char> message) {
			size_t ret;
			size_t idx = 0;
			size_t trailer = 0;
			if(message_sizes[loc] < message.size())
			{
				for(; idx < message_sizes[loc]; ++idx) {
					message[idx] = messages[loc][idx];
				}
				r_offset += 1;
				if constexpr (count != 1) w_offset %= size;
				ret = idx;
			} else {
				for(; idx < message.size(); ++idx) {
					message[idx] = messages[loc][idx];
				}
				ret = idx;
				for(; idx < message_sizes[loc]; ++idx, ++trailer)
				{
					message[trailer] = message[idx];
				}
				message_sizes[loc] = trailer;
			}

			if constexpr (zero_out) {
				if(trailer == 0) {
					message_sizes[loc] = 0;
				}
				for(; trailer < messages[loc].size(); ++trailer)
				{
					messages[loc][trailer] = 0;
				}
			}

			return ret;
		}
	public:
		channel() {}
		gp::buffer<char>::associated_iterator push(gp::buffer<char> input) {
			if constexpr (whole_messages) {
				if(input.size() > size) {
					return input.begin();
				}
			}
			if constexpr (count == 1) {
				if(w_offset == r_offset) {
					auto to_write = gp::min(input.size(), size);
					write_one(
						0, 
						gp::buffer<char>(input.begin().data, to_write)
					);
					return input.begin()+to_write;
				} else {
					return input.begin();
				}
			} else {
				auto next_w = (w_offset+1)%count;
				auto to_consume = input;
				while(to_consume.size() && (next_w == r_offset)) {
					auto to_write = gp::min(to_consume.size(), size);
					to_write = write_one(
						w_offset, 
						to_consume.trim_start(to_write)
					);
					to_consume = to_consume.trim_start(to_write);
					next_w = (w_offset+1)%count;
				}
				return to_consume.begin();
			}
		}
		gp::buffer<char>::associated_iterator pop(gp::buffer<char> dest) {
			if(r_offset == w_offset) {
				return dest.begin();
			}
			size_t idx;
			if constexpr (count == 1) {
				idx = 0;
			} else {
				idx = r_offset;
			}
			if constexpr (whole_messages) {
				if(message_sizes[idx] > dest.size()) {
					return dest.begin();
				}
				auto sz = gp::min(message_sizes[idx], dest.size());
				read_one(idx, gp::buffer<char>(dest.begin(), sz));
				return dest.begin()+sz;
			}
			auto to_fill = dest;
			do{
				auto to_read = gp::min(to_fill.size(), size);
				to_read = read_one(
					r_offset, 
					to_fill.trim_start(to_read)
				);
				to_fill = to_fill.trim_start(to_read);
			}while(r_offset != w_offset && to_fill.size());
			return to_fill.begin();
		}
	};
}