#include <assert.h>
#include <inttypes.h> /* for PRI* */
#include <stdio.h>    /* for fprintf(), stderr */
#include <string.h>   /* for strerror() */

#include <libcr/coroutine.h>
#include <libcr_ipc/chan.h>
#include <libcr_ipc/mutex.h>
#include <libnetio/netio.h>

#include <lib9p/9p.h>
#include <lib9p/srv.h>
#include "internal.h"

/* structs ********************************************************************/

/* The hierarchy of concepts is:
 *
 *     server -> connection -> session -> request
 *
 */

/* struct lib9p_srv {} is defined in <lib9p/srv.h> */

struct lib9p_conn {
	/* immutable */
	struct lib9p_srv        *parent_srv;
	int                      fd;
	cid_t                    reader; /* the lib9p_srv_read_cr() coroutine */
	/* mutable */
	cr_mutex_t               writelock;
};

struct lib9p_sess {
	/* immutable */
	struct lib9p_conn       *parent_conn;
	enum lib9p_version       version;
	uint32_t                 max_msg_size;
	uint32_t                 rerror_overhead;
	/* mutable */
	bool                     initialized;
	unsigned int             refcount;
};

struct lib9p_req {
	/* immutable */
	struct lib9p_sess       *parent_sess;
	uint16_t                 tag;
	/* mutable */
	uint8_t                 *net_bytes; /* CONFIG_9P_MAX_MSG_SIZE-sized */
	struct lib9p_ctx         ctx;
};

/* base utilities *************************************************************/

#define nonrespond_errorf(fmt, ...) fprintf(stderr, "error: " fmt "\n" __VA_OPT__(,) __VA_ARGS__)

static uint32_t rerror_overhead_for_version(enum lib9p_version version, uint8_t *scratch) {
	struct lib9p_ctx empty_ctx = {
		.version      = version,
		.max_msg_size = CONFIG_9P_MAX_MSG_SIZE,
	};
	struct lib9p_msg_Rerror empty_error = { 0 };

	assert(!lib9p_marshal(&empty_ctx, LIB9P_TYP_Rerror, 0, &empty_error, scratch));
	uint32_t min_msg_size = decode_u32le(scratch);
	assert(min_msg_size < (UINT32_MAX - UINT16_MAX));
	assert(CONFIG_9P_MAX_MSG_SIZE >= min_msg_size);

	return min_msg_size;
}

static void respond_error(struct lib9p_req *req) {
	assert(req->ctx.err_num);
	assert(req->ctx.err_msg[0]);

	ssize_t r;
	struct lib9p_msg_Rerror host = {
		.ename = {
			.len = strnlen(req->ctx.err_msg, CONFIG_9P_MAX_ERR_SIZE),
			.utf8 = (uint8_t*)req->ctx.err_msg,
		},
		.errno = req->ctx.err_num,
	};

	/* Truncate the error-string if necessary to avoid needing to return ERANGE.  */
	if (((uint32_t)host.ename.len) + req->parent_sess->rerror_overhead > req->parent_sess->max_msg_size)
		host.ename.len = req->parent_sess->max_msg_size - req->parent_sess->rerror_overhead;

	lib9p_marshal(&req->ctx, LIB9P_TYP_Rerror, req->tag, &host, req->net_bytes);

	cr_mutex_lock(&req->parent_sess->parent_conn->writelock);
	r = netio_write(req->parent_sess->parent_conn->fd, req->net_bytes, decode_u32le(req->net_bytes));
	cr_mutex_unlock(&req->parent_sess->parent_conn->writelock);
	if (r < 0)
		nonrespond_errorf("write: %s", strerror(-r));
}

/* read coroutine *************************************************************/

static bool read_at_least(int fd, uint8_t *buf, size_t goal, size_t *done) {
	assert(buf);
	assert(goal);
	assert(done);
	while (*done < goal) {
		ssize_t r = netio_read(fd, &buf[*done], CONFIG_9P_MAX_MSG_SIZE - *done);
		if (r < 0) {
			nonrespond_errorf("read: %s", strerror(-r));
			return true;
		} else if (r == 0) {
			if (*done != 0)
				nonrespond_errorf("read: unexpected EOF");
			return true;
		}
		*done += r;
	}
	return false;
}

COROUTINE lib9p_srv_read_cr(void *_srv) {
	uint8_t buf[CONFIG_9P_MAX_MSG_SIZE];

	struct lib9p_srv *srv = _srv;
	assert(srv);
	cr_begin();

	uint32_t initial_rerror_overhead = rerror_overhead_for_version(0, buf);

	for (;;) {
		struct lib9p_conn conn = {
			.parent_srv = srv,
			.fd         = netio_accept(srv->sockfd),
			.reader     = cr_getcid(),
		};
		if (conn.fd < 0) {
			nonrespond_errorf("accept: %s", strerror(-conn.fd));
			continue;
		}
		
		struct lib9p_sess sess = {
			.parent_conn     = &conn,
			.version         = 0,
			.max_msg_size    = CONFIG_9P_MAX_MSG_SIZE,
			.rerror_overhead = initial_rerror_overhead,
			.initialized     = false,
			.refcount        = 1,
		};
		for (;;) {
			/* Read the message.  */
			size_t done = 0;
			if (read_at_least(conn.fd, buf, 4, &done))
				goto close;
			size_t goal = decode_u32le(buf);
			if (goal < 7) {
				nonrespond_errorf("T-message is impossibly small");
				goto close;
			}
			if (read_at_least(conn.fd, buf, 7, &done))
				goto close;
			struct lib9p_req req = {
				.parent_sess = &sess,
				.tag         = decode_u16le(&buf[5]),
				.net_bytes   = buf,
				.ctx         = {
					.version      = sess.version,
					.max_msg_size = sess.max_msg_size,
				},
			};
			if (goal > sess.max_msg_size) {
				lib9p_errorf(&req.ctx, LINUX_EMSGSIZE, "T-message larger than %s limit (%zu > %"PRIu32")",
				             sess.initialized ? "negotiated" : "server", goal, sess.max_msg_size);
				respond_error(&req);
				continue;
			}
			if (read_at_least(conn.fd, buf, goal, &done))
				goto close;

			/* Handle the message... in another coroutine.  */
			sess.refcount++;
			cr_chan_send(&srv->reqch, &req);
			cr_pause_and_yield(); /* wait for it to have copied req */
		}
	close:
		netio_close(conn.fd, true, (--sess.refcount) == 0);
		if (sess.refcount) {
			cr_pause_and_yield();
			assert(sess.refcount == 0);
			netio_close(conn.fd, false, true);
		}
	}

	cr_end();
}

/* write coroutine ************************************************************/

static void handle_Tversion(struct lib9p_req *ctx, struct lib9p_msg_Tversion *req, struct lib9p_msg_Rversion *resp);

COROUTINE lib9p_srv_write_cr(void *_srv) {
	uint8_t net[CONFIG_9P_MAX_MSG_SIZE];
	uint8_t host_req[CONFIG_9P_MAX_HOSTMSG_SIZE];
	uint8_t host_resp[CONFIG_9P_MAX_HOSTMSG_SIZE];

	struct lib9p_srv *srv = _srv;
	assert(srv);
	cr_begin();

	for (;;) {
		/* Receive the request from the reader coroutine.  */
		struct lib9p_req req;
		struct lib9p_req *_req_p;
		cr_chan_recv(&srv->reqch, &_req_p);
		req = *_req_p;
		memcpy(net, req.net_bytes, decode_u32le(req.net_bytes));
		req.net_bytes = net;
		cr_unpause(req.parent_sess->parent_conn->reader); /* notify that we've copied req */

		/* Unmarshal it.  */
		enum lib9p_msg_type typ = net[4];
		if (typ % 2 != 0) {
			lib9p_errorf(&req.ctx, LINUX_EOPNOTSUPP, "expected a T-message but got an R-message: message_type=%s",
			             lib9p_msg_type_str(typ));
			goto write;
		}
		ssize_t host_size = lib9p_unmarshal_size(&req.ctx, net);
		if (host_size < 0)
			goto write;
		if ((size_t)host_size > sizeof(host_req)) {
			lib9p_errorf(&req.ctx, LINUX_EMSGSIZE, "unmarshalled payload larger than server limit (%zu > %zu)",
			             host_size, sizeof(host_req));
			goto write;
		}
		lib9p_unmarshal(&req.ctx, net, &typ, &req.tag, host_req);
		
		/* Handle it.  */
		switch (typ) {
		case LIB9P_TYP_Tversion:
			handle_Tversion(&req, (struct lib9p_msg_Tversion *)host_req, (struct lib9p_msg_Rversion *)host_resp);
			break;
		case LIB9P_TYP_Tauth:
			lib9p_errorf(&req.ctx, LINUX_EOPNOTSUPP, "%s not yet implemented", lib9p_msg_type_str(typ));
			break;
		case LIB9P_TYP_Tattach:
			lib9p_errorf(&req.ctx, LINUX_EOPNOTSUPP, "%s not yet implemented", lib9p_msg_type_str(typ));
			break;
		case LIB9P_TYP_Tflush:
			lib9p_errorf(&req.ctx, LINUX_EOPNOTSUPP, "%s not yet implemented", lib9p_msg_type_str(typ));
			break;
		case LIB9P_TYP_Twalk:
			lib9p_errorf(&req.ctx, LINUX_EOPNOTSUPP, "%s not yet implemented", lib9p_msg_type_str(typ));
			break;
		case LIB9P_TYP_Topen:
			lib9p_errorf(&req.ctx, LINUX_EOPNOTSUPP, "%s not yet implemented", lib9p_msg_type_str(typ));
			break;
		case LIB9P_TYP_Tcreate:
			lib9p_errorf(&req.ctx, LINUX_EOPNOTSUPP, "%s not yet implemented", lib9p_msg_type_str(typ));
			break;
		case LIB9P_TYP_Tread:
			lib9p_errorf(&req.ctx, LINUX_EOPNOTSUPP, "%s not yet implemented", lib9p_msg_type_str(typ));
			break;
		case LIB9P_TYP_Twrite:
			lib9p_errorf(&req.ctx, LINUX_EOPNOTSUPP, "%s not yet implemented", lib9p_msg_type_str(typ));
			break;
		case LIB9P_TYP_Tclunk:
			lib9p_errorf(&req.ctx, LINUX_EOPNOTSUPP, "%s not yet implemented", lib9p_msg_type_str(typ));
			break;
		case LIB9P_TYP_Tremove:
			lib9p_errorf(&req.ctx, LINUX_EOPNOTSUPP, "%s not yet implemented", lib9p_msg_type_str(typ));
			break;
		case LIB9P_TYP_Tstat:
			lib9p_errorf(&req.ctx, LINUX_EOPNOTSUPP, "%s not yet implemented", lib9p_msg_type_str(typ));
			break;
		case LIB9P_TYP_Twstat:
			lib9p_errorf(&req.ctx, LINUX_EOPNOTSUPP, "%s not yet implemented", lib9p_msg_type_str(typ));
			break;
		case LIB9P_TYP_Tsession: /* 9P2000.e */
			lib9p_errorf(&req.ctx, LINUX_EOPNOTSUPP, "%s not yet implemented", lib9p_msg_type_str(typ));
			break;
		case LIB9P_TYP_Tsread: /* 9P2000.e */
			lib9p_errorf(&req.ctx, LINUX_EOPNOTSUPP, "%s not yet implemented", lib9p_msg_type_str(typ));
			break;
		case LIB9P_TYP_Tswrite: /* 9P2000.e */
			lib9p_errorf(&req.ctx, LINUX_EOPNOTSUPP, "%s not yet implemented", lib9p_msg_type_str(typ));
			break;
		default:
			assert(false);
		}

	write:
		if (req.ctx.err_num || req.ctx.err_msg[0])
			respond_error(&req);
		else {
			if (lib9p_marshal(&req.ctx, typ+1, req.tag, host_resp, net))
				goto write;
			cr_mutex_lock(&req.parent_sess->parent_conn->writelock);
			netio_write(req.parent_sess->parent_conn->fd, net, decode_u32le(net));
			cr_mutex_unlock(&req.parent_sess->parent_conn->writelock);
		}
		if ((--req.parent_sess->refcount) == 0)
			cr_unpause(req.parent_sess->parent_conn->reader);
	}

	cr_end();
}

static void handle_Tversion(struct lib9p_req *ctx, struct lib9p_msg_Tversion *req, struct lib9p_msg_Rversion *resp) {
	enum lib9p_version version = LIB9P_VER_unknown;

	if (req->version.len >= 6 &&
	    req->version.utf8[0] == '9' && 
	    req->version.utf8[1] == 'P' && 
	    '0' <= req->version.utf8[2] && req->version.utf8[2] <= '9' &&
	    '0' <= req->version.utf8[3] && req->version.utf8[3] <= '9' &&
	    '0' <= req->version.utf8[4] && req->version.utf8[4] <= '9' &&
	    '0' <= req->version.utf8[5] && req->version.utf8[5] <= '9' &&
	    (req->version.utf8[6] == '\0' || req->version.utf8[6] == '.')) {
		if (strcmp((char *)&req->version.utf8[6], ".u") == 0)
			version = LIB9P_VER_9P2000_u;
		else if (strcmp((char *)&req->version.utf8[6], ".e") == 0)
			version = LIB9P_VER_9P2000_e;
		else
			version = LIB9P_VER_9P2000;
	}

	uint32_t min_msg_size = rerror_overhead_for_version(version, ctx->net_bytes);
	if (req->max_msg_size < min_msg_size) {
		lib9p_errorf(&ctx->ctx, LINUX_EDOM, "requested max_msg_size is less than minimum for %s (%"PRIu32" < %"PRIu32")",
		             version, req->max_msg_size, min_msg_size);
		return;
	}

	resp->version.utf8 = (uint8_t *)lib9p_version_str(version);
	resp->version.len = strlen((char *)resp->version.utf8);
	resp->max_msg_size = (CONFIG_9P_MAX_MSG_SIZE < req->max_msg_size)
		? CONFIG_9P_MAX_MSG_SIZE
		: req->max_msg_size;
}