FileIO.hpp

#pragma once

#include <algorithm>
#include <cstddef>
#include <fstream>
#include <iomanip>
#include <sstream>
#include <string>

#include "gsl/gsl"

#include "MpiSubarray.hpp"
#include "Util.hpp"
#include "state.hpp"

struct HeaderInfo {
	Size GlobalSize;
	std::size_t HeaderLength;
};

struct FileIO {
	static auto ReadHeader(const std::string& path) {
		// read the header into a buf (20 should be sufficient)
		MPI_File fh;
		MPI_File_open(MPI_COMM_SELF, path.c_str(),
		              MPI_MODE_RDONLY | MPI_MODE_UNIQUE_OPEN, MPI_INFO_NULL,
		              &fh);
		constexpr auto HeaderBufSize = 20;
		std::array<char, HeaderBufSize> buf;
		MPI_File_read_all(fh, buf.data(), buf.size(), MPI_CHAR,
		                  MPI_STATUS_IGNORE);
		MPI_File_close(&fh);

		// make stream out of buf
		std::istringstream input;
		input.rdbuf()->pubsetbuf(buf.data(), buf.size());

		// parse the stream
		std::size_t noCols{};
		std::size_t noRows{};
		input >> noCols >> noRows;
		if (noCols < 1 || noRows < 1) {
			std::cerr << "File header corrupt\n";
			MPI_Abort(MPI_COMM_WORLD, EXIT_FAILURE);
		}
		std::string dummy; // skip line break
		std::getline(input, dummy);
		const auto headerLength = input.tellg();
		return HeaderInfo{
		    {noCols, noRows},
		    static_cast<std::size_t>(
		        headerLength) // should fit (is max HeaderBuf size)
		};
	}

	static auto WriteHeader(const HeaderInfo& header, const std::string& path, const MpiEnvironment& env) {
		if (!env.isMaster()) return;

		std::ostringstream ss;
		ss << header.GlobalSize.Cols << ' ' << header.GlobalSize.Rows << '\n';
		const auto buf = ss.str();

		MPI_File fh;
		MPI_File_open(MPI_COMM_SELF, path.c_str(),
		              MPI_MODE_WRONLY | MPI_MODE_CREATE, MPI_INFO_NULL, &fh);

		MPI_File_write(fh, buf.data(), buf.size(), MPI_CHAR,
		                   MPI_STATUS_IGNORE);
		MPI_File_close(&fh);
	}

	// TODO: is not an IO concern
	static auto GetTileSize(Size globalSize, Size gridSize) {
		const auto tileSizeCols = globalSize.Cols / gridSize.Cols;
		const auto tileSizeRows = globalSize.Rows / gridSize.Rows;
		return Size{tileSizeCols, tileSizeRows};
	}

	class Tile {
		static constexpr std::size_t LF = 1; // linefeed chars
		const std::string& _path;
		const std::size_t _headerLength;
		const Size _srcSize;
		const Size _gridSize;
		const std::size_t _rank;
		gsl::span<State> _buf;

		const Size _tileSize;
		const std::size_t _tileX;
		const std::size_t _tileY;
		const MpiSubarray _tileType;
		const MpiSubarray _bufType;
		const std::size_t _displ;

	  public:
		Tile(const std::string& path, HeaderInfo header, Size gridSize,
		     std::size_t rank, gsl::span<State> buf)
		    : _path(path), _headerLength(header.HeaderLength),
		      _srcSize(header.GlobalSize), _gridSize(gridSize), _rank(rank),
		      _buf(buf),
		      _tileSize(FileIO::GetTileSize(header.GlobalSize, gridSize)), //
		      _tileX(rank % gridSize.Cols),                                //
		      _tileY(rank / gridSize.Cols),                                //
		      _tileType(MpiSubarray(
		          {{header.GlobalSize.Rows, _tileSize.Rows, 0},
		           {header.GlobalSize.Cols + LF, _tileSize.Cols, 0}})),
		      _bufType(MpiSubarray({{_tileSize.Rows + 2, _tileSize.Rows, 1},
		                            {_tileSize.Cols + 2, _tileSize.Cols, 1}})),
		      _displ(header.HeaderLength +
		             (header.GlobalSize.Cols + LF) * _tileSize.Rows * _tileY +
		             _tileSize.Cols * _tileX) {}

		void Read() {
			MPI_File file;
			MPI_File_open(MPI_COMM_WORLD, _path.c_str(),
			              MPI_MODE_RDONLY | MPI_MODE_UNIQUE_OPEN, MPI_INFO_NULL,
			              &file);
			MPI_File_set_view(file, _displ, MPI_CHAR, _tileType.type(),
			                  "native", MPI_INFO_NULL);

			MPI_File_read_all(file, _buf.data(), 1, _bufType.type(),
			                  MPI_STATUS_IGNORE);
			MPI_File_close(&file);
		}

		void Write() const {
			MPI_File file;
			MPI_File_open(MPI_COMM_WORLD, _path.c_str(),
			              MPI_MODE_CREATE | MPI_MODE_WRONLY, MPI_INFO_NULL,
			              &file);
			MPI_File_set_view(file, _displ, MPI_CHAR, _tileType.type(),
			                  "native", MPI_INFO_NULL);

			MPI_File_write_all(file, _buf.data(), 1, _bufType.type(),
			                   MPI_STATUS_IGNORE);

			/// fix line feeds
			// this is done with an collective call, but only the rightmost
			// ranks actually write line feeds

			// are we a rightMost tile?
			const auto rightMost = _tileX == _gridSize.Cols - 1;
			const auto bottomMost = _tileY == _gridSize.Rows - 1;
			const auto noLfNeeded = rightMost ?                       //
			                            (bottomMost ?                 //
			                                 _tileSize.Rows - 1       //
			                                        : _tileSize.Rows) //
			                                  : 0;                    //
			const auto lfType = MpiSubarray( // subsize must be > 0
			    {{_srcSize.Rows, std::max<std::size_t>(noLfNeeded, 1), 0},
			     {_srcSize.Cols + LF, 1, 0}});
			const std::vector<char> lfs(noLfNeeded, '\n');

			const auto lfDisp = _headerLength +
			                    (_srcSize.Cols + LF) * _tileSize.Rows * _tileY +
			                    _srcSize.Cols;

			MPI_File_set_view(file, lfDisp, MPI_CHAR, lfType.type(), "native",
			                  MPI_INFO_NULL);

			// lfs is empty for non-rightmost ranks
			MPI_File_write_all(file, lfs.data(), lfs.size(), MPI_CHAR,
			                   MPI_STATUS_IGNORE);

			MPI_File_close(&file);
		}
	};
};