/* Copyright (C) 2017, 2021  C. McEnroe <june@causal.agency>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <assert.h>
#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <poll.h>
#include <signal.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/file.h>
#include <sys/mman.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <sysexits.h>
#include <time.h>
#include <unistd.h>

#include "torus.h"

static struct Tile *tiles;

static void tilesMap(const char *path) {
	int fd = open(path, O_CREAT | O_RDWR, 0644);
	if (fd < 0) err(EX_CANTCREAT, "%s", path);

	int error = ftruncate(fd, TilesSize);
	if (error) err(EX_IOERR, "%s", path);

	tiles = mmap(NULL, TilesSize, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
	if (tiles == MAP_FAILED) err(EX_OSERR, "mmap");
	close(fd);

#ifdef MADV_NOCORE
	error = madvise(tiles, TilesSize, MADV_NOCORE);
	if (error) err(EX_OSERR, "madvise");
#endif
}

static struct Tile *tileGet(uint32_t tileX, uint32_t tileY) {
	struct Tile *tile = &tiles[tileY * TileRows + tileX];
	if (!tile->createTime) {
		memset(tile->cells, ' ', CellsSize);
		memset(tile->colors, ColorWhite, CellsSize);
		tile->createTime = time(NULL);
	}
	return tile;
}

static struct Tile *tileAccess(uint32_t tileX, uint32_t tileY) {
	struct Tile *tile = tileGet(tileX, tileY);
	tile->accessTime = time(NULL);
	tile->accessCount++;
#ifndef NO_DECAY
	uint8_t y = arc4random_uniform(CellRows);
	uint8_t x = arc4random_uniform(CellCols);
	uint8_t b = 1 << arc4random_uniform(8);
	if (arc4random_uniform(2)) {
		tile->cells[y][x] &= ~b;
	} else {
		tile->colors[y][x] &= ~b;
	}
#endif
	return tile;
}

static struct Tile *tileModify(uint32_t tileX, uint32_t tileY) {
	struct Tile *tile = tileGet(tileX, tileY);
	tile->modifyTime = time(NULL);
	tile->modifyCount++;
	return tile;
}

static struct Tile *tileSync(struct Tile *tile) {
	int error = msync(tile, sizeof(*tile), MS_ASYNC);
	if (error) err(EX_IOERR, "msync");
	return tile;
}

enum { ClientsCap = 256 };
static struct Client {
	int fd;
	uint32_t tileX;
	uint32_t tileY;
	uint8_t cellX;
	uint8_t cellY;
} clients[ClientsCap];
static size_t clientsLen;

static struct Client *clientAdd(int fd) {
	if (clientsLen == ClientsCap) return NULL;
	struct Client *client = &clients[clientsLen++];
	client->fd = fd;
	client->tileX = TileInitX;
	client->tileY = TileInitY;
	client->cellX = CellInitX;
	client->cellY = CellInitY;
	return client;
}

static int
clientSend(const struct Client *client, const struct ServerMessage *msg) {
	ssize_t len = send(client->fd, msg, sizeof(*msg), 0);
	if (len < 0) return -1;
	if (msg->type == ServerTile) {
		const struct Tile *tile = tileSync(
			tileAccess(client->tileX, client->tileY)
		);
		len = send(client->fd, tile, sizeof(*tile), 0);
		if (len < 0) return -1;
	}
	return 0;
}

static void
clientCast(const struct Client *source, const struct ServerMessage *msg) {
	for (size_t i = 0; i < clientsLen; ++i) {
		if (&clients[i] == source) continue;
		if (clients[i].tileX != source->tileX) continue;
		if (clients[i].tileY != source->tileY) continue;
		clientSend(&clients[i], msg);
	}
}

static void clientRemove(size_t i) {
	struct Client client = clients[i];
	clients[i] = clients[--clientsLen];
	close(client.fd);
	struct ServerMessage msg = {
		.type = ServerCursor,
		.cursor = {
			.oldCellX = client.cellX, .oldCellY = client.cellY,
			.newCellX = CursorNone, .newCellY = CursorNone,
		},
	};
	clientCast(&client, &msg);
}

static int clientCursors(const struct Client *client) {
	struct ServerMessage msg = {
		.type = ServerCursor,
		.cursor.oldCellX = CursorNone,
		.cursor.oldCellY = CursorNone,
	};
	for (size_t i = 0; i < clientsLen; ++i) {
		if (&clients[i] == client) continue;
		if (clients[i].tileX != client->tileX) continue;
		if (clients[i].tileY != client->tileY) continue;
		msg.cursor.newCellX = clients[i].cellX;
		msg.cursor.newCellY = clients[i].cellY;
		if (clientSend(client, &msg) < 0) return -1;
	}
	return 0;
}

static int clientUpdate(struct Client *new, const struct Client *old) {
	struct ServerMessage msg = {
		.type = ServerMove,
		.move.cellX = new->cellX,
		.move.cellY = new->cellY,
	};
	if (clientSend(new, &msg) < 0) return -1;

	if (new->tileX != old->tileX || new->tileY != old->tileY) {
		msg.type = ServerTile;
		if (clientSend(new, &msg) < 0) return -1;
		if (clientCursors(new) < 0) return -1;

		msg = (struct ServerMessage) {
			.type = ServerCursor,
			.cursor = {
				.oldCellX = old->cellX, .oldCellY = old->cellY,
				.newCellX = CursorNone, .newCellY = CursorNone,
			},
		};
		clientCast(old, &msg);

		msg = (struct ServerMessage) {
			.type = ServerCursor,
			.cursor = {
				.oldCellX = CursorNone, .oldCellY = CursorNone,
				.newCellX = new->cellX, .newCellY = new->cellY,
			},
		};
		clientCast(new, &msg);

	} else {
		msg = (struct ServerMessage) {
			.type = ServerCursor,
			.cursor = {
				.oldCellX = old->cellX, .oldCellY = old->cellY,
				.newCellX = new->cellX, .newCellY = new->cellY,
			},
		};
		clientCast(new, &msg);
	}
	return 0;
}

static int clientMove(struct Client *client, int8_t dx, int8_t dy) {
	struct Client old = *client;

	if (dx > CellCols - client->cellX) dx = CellCols - client->cellX;
	if (dx < -client->cellX - 1)       dx = -client->cellX - 1;
	if (dy > CellRows - client->cellY) dy = CellRows - client->cellY;
	if (dy < -client->cellY - 1)       dy = -client->cellY - 1;

	client->cellX += dx;
	client->cellY += dy;

	if (client->cellX == CellCols) {
		client->tileX++;
		client->cellX = 0;
	}
	if (client->cellX == UINT8_MAX) {
		client->tileX--;
		client->cellX = CellCols - 1;
	}
	if (client->cellY == CellRows) {
		client->tileY++;
		client->cellY = 0;
	}
	if (client->cellY == UINT8_MAX) {
		client->tileY--;
		client->cellY = CellRows - 1;
	}

	if (client->tileX == TileCols)   client->tileX = 0;
	if (client->tileX == UINT32_MAX) client->tileX = TileCols - 1;
	if (client->tileY == TileRows)   client->tileY = 0;
	if (client->tileY == UINT32_MAX) client->tileY = TileRows - 1;

	assert(client->cellX < CellCols);
	assert(client->cellY < CellRows);
	assert(client->tileX < TileCols);
	assert(client->tileY < TileRows);

	return clientUpdate(client, &old);
}

static int clientFlip(struct Client *client) {
	struct Client old = *client;
	client->tileX = (client->tileX + TileCols / 2) % TileCols;
	client->tileY = (client->tileY + TileRows / 2) % TileRows;
	return clientUpdate(client, &old);
}

static int clientPut(const struct Client *client, uint8_t color, uint8_t cell) {
	struct Tile *tile = tileModify(client->tileX, client->tileY);
	tile->colors[client->cellY][client->cellX] = color;
	tile->cells[client->cellY][client->cellX] = cell;
	tileSync(tile);
	struct ServerMessage msg = {
		.type = ServerPut,
		.put = {
			.cellX = client->cellX,
			.cellY = client->cellY,
			.color = color,
			.cell = cell,
		},
	};
	int error = clientSend(client, &msg);
	clientCast(client, &msg);
	return error;
}

static int clientMap(const struct Client *client) {
	int32_t mapY = (int32_t)client->tileY - MapRows / 2;
	int32_t mapX = (int32_t)client->tileX - MapCols / 2;

	time_t now = time(NULL);
	struct Map map = {
		.now = now,
		.min = {
			.createTime = now,
			.modifyTime = now,
			.accessTime = now,
			.modifyCount = UINT32_MAX,
			.accessCount = UINT32_MAX,
		},
	};

	for (int32_t y = 0; y < MapRows; ++y) {
		for (int32_t x = 0; x < MapCols; ++x) {
			uint32_t tileY = ((mapY + y) % TileRows + TileRows) % TileRows;
			uint32_t tileX = ((mapX + x) % TileCols + TileCols) % TileCols;
			struct Meta meta = tileMeta(&tiles[tileY * TileRows + tileX]);

			if (meta.createTime > 1) {
				if (meta.createTime < map.min.createTime) {
					map.min.createTime = meta.createTime;
				}
				if (meta.createTime > map.max.createTime) {
					map.max.createTime = meta.createTime;
				}
			}
			if (meta.modifyTime) {
				if (meta.modifyTime < map.min.modifyTime) {
					map.min.modifyTime = meta.modifyTime;
				}
				if (meta.modifyTime > map.max.modifyTime) {
					map.max.modifyTime = meta.modifyTime;
				}
			}
			if (meta.accessTime) {
				if (meta.accessTime < map.min.accessTime) {
					map.min.accessTime = meta.accessTime;
				}
				if (meta.accessTime > map.max.accessTime) {
					map.max.accessTime = meta.accessTime;
				}
			}
			if (meta.modifyCount < map.min.modifyCount) {
				map.min.modifyCount = meta.modifyCount;
			}
			if (meta.modifyCount > map.max.modifyCount) {
				map.max.modifyCount = meta.modifyCount;
			}
			if (meta.accessCount < map.min.accessCount) {
				map.min.accessCount = meta.accessCount;
			}
			if (meta.accessCount > map.max.accessCount) {
				map.max.accessCount = meta.accessCount;
			}

			map.meta[y][x] = meta;
		}
	}

	struct ServerMessage msg = { .type = ServerMap };
	if (clientSend(client, &msg) < 0) return -1;
	if (send(client->fd, &map, sizeof(map), 0) < 0) return -1;
	return 0;
}

static int clientTele(struct Client *client, uint8_t port) {
	if (port >= ARRAY_LEN(Ports)) return -1;
	struct Client old = *client;
	client->tileX = Ports[port].tileX;
	client->tileY = Ports[port].tileY;
	client->cellX = CellInitX;
	client->cellY = CellInitY;
	return clientUpdate(client, &old);
}

int main(int argc, char *argv[]) {
	int error;

	const char *dataPath = DefaultDataPath;
	const char *sockPath = DefaultSockPath;
	const char *pidPath = NULL;

	for (int opt; 0 < (opt = getopt(argc, argv, "d:p:s:"));) {
		switch (opt) {
			break; case 'd': dataPath = optarg;
			break; case 'p': pidPath = optarg;
			break; case 's': sockPath = optarg;
			break; default:  return EX_USAGE;
		}
	}

	int pidFile = -1;
	if (pidPath) {
		pidFile = open(pidPath, O_WRONLY | O_CREAT | O_CLOEXEC, 0600);
		if (pidFile < 0) err(EX_CANTCREAT, "%s", pidPath);

		error = flock(pidFile, LOCK_EX | LOCK_NB);
		if (error && errno != EWOULDBLOCK) err(EX_IOERR, "%s", pidPath);
		if (error) errx(EX_CANTCREAT, "%s: file is locked", pidPath);

		error = ftruncate(pidFile, 0);
		if (error) err(EX_IOERR, "%s", pidPath);
	}

	tilesMap(dataPath);

	int server = socket(PF_UNIX, SOCK_STREAM, 0);
	if (server < 0) err(EX_OSERR, "socket");

	error = unlink(sockPath);
	if (error && errno != ENOENT) err(EX_CANTCREAT, "%s", sockPath);

	struct sockaddr_un addr = { .sun_family = AF_UNIX };
	snprintf(addr.sun_path, sizeof(addr.sun_path), "%s", sockPath);
	error = bind(server, (struct sockaddr *)&addr, SUN_LEN(&addr));
	if (error) err(EX_CANTCREAT, "%s", sockPath);

	if (pidPath) {
		error = daemon(0, 0);
		if (error) err(EX_OSERR, "daemon");
		dprintf(pidFile, "%ju", (uintmax_t)getpid());
	}

#ifdef __OpenBSD__
	error = pledge("stdio unix", NULL);
	if (error) err(EX_OSERR, "pledge");
#endif

	error = listen(server, -1);
	if (error) err(EX_OSERR, "listen");

	signal(SIGPIPE, SIG_IGN);
	struct pollfd fds[1 + ClientsCap] = {
		{ .fd = server, .events = POLLIN },
	};
	for (;;) {
		for (size_t i = 0; i < clientsLen; ++i) {
			fds[1 + i].fd = clients[i].fd;
			fds[1 + i].events = POLLIN;
		}
		int nfds = poll(fds, 1 + clientsLen, -1);
		if (nfds < 0 && errno != EINTR) err(EX_IOERR, "poll");
		if (nfds < 0) continue;

		for (size_t i = clientsLen - 1; i < clientsLen; --i) {
			if (!fds[1 + i].revents) continue;
			if (fds[1 + i].revents & (POLLHUP | POLLERR)) {
				clientRemove(i);
				continue;
			}

			struct ClientMessage msg;
			ssize_t len = recv(clients[i].fd, &msg, sizeof(msg), 0);
			if (len != sizeof(msg)) {
				clientRemove(i);
				continue;
			}

			switch (msg.type) {
				break; case ClientMove: {
					error = clientMove(&clients[i], msg.move.dx, msg.move.dy);
				}
				break; case ClientFlip: {
					error = clientFlip(&clients[i]);
				}
				break; case ClientPut: {
					error = clientPut(&clients[i], msg.put.color, msg.put.cell);
				}
				break; case ClientMap: {
					error = clientMap(&clients[i]);
				}
				break; case ClientTele: {
					error = clientTele(&clients[i], msg.port);
				}
				break; default: error = -1;
			}
			if (error) clientRemove(i);
		}

		if (fds[0].revents) {
			int fd = accept(server, NULL, NULL);
			if (fd < 0) err(EX_IOERR, "accept");
			fcntl(fd, F_SETFL, O_NONBLOCK);

			int size = 2 * sizeof(struct Tile);
			error = setsockopt(fd, SOL_SOCKET, SO_SNDBUF, &size, sizeof(size));
			if (error) err(EX_IOERR, "setsockopt");

			struct Client *client = clientAdd(fd);
			if (!client) {
				close(fd);
				continue;
			}

			struct ServerMessage msg = { .type = ServerTile };
			error = 0
				|| clientSend(client, &msg)
				|| clientMove(client, 0, 0)
				|| clientCursors(client);
			if (error) clientRemove(clientsLen - 1);
		}
	}
}