/* SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later */

#include <assert.h>
#include <stdarg.h>
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#undef pr_fmt
#define pr_fmt(fmt) "core: " fmt

#include "libmctp.h"
#include "libmctp-alloc.h"
#include "libmctp-log.h"

/* Internal data structures */

struct mctp_bus {
	mctp_eid_t		eid;
	struct mctp_binding	*binding;
	bool			tx_enabled;

	struct mctp_pktbuf	*tx_queue_head;
	struct mctp_pktbuf	*tx_queue_tail;

	/* todo: routing */
};

struct mctp_msg_ctx {
	uint8_t		src;
	uint8_t		dest;
	uint8_t		tag;
	uint8_t		last_seq;
	void		*buf;
	size_t		buf_size;
	size_t		buf_alloc_size;
};

struct mctp {
	int			n_busses;
	struct mctp_bus		*busses;

	/* Message RX callback */
	mctp_rx_fn		message_rx;
	void			*message_rx_data;

	/* Message reassembly.
	 * @todo: flexible context count
	 */
	struct mctp_msg_ctx	msg_ctxs[16];

	enum {
		ROUTE_ENDPOINT,
		ROUTE_BRIDGE,
	}			route_policy;
};

#ifndef BUILD_ASSERT
#define BUILD_ASSERT(x) \
	do { (void)sizeof(char[0-(!(x))]); } while (0)
#endif

#ifndef ARRAY_SIZE
#define ARRAY_SIZE(a) (sizeof(a) / sizeof(a[0]))
#endif

static int mctp_message_tx_on_bus(struct mctp *mctp, struct mctp_bus *bus,
		mctp_eid_t src, mctp_eid_t dest, void *msg, size_t msg_len);

struct mctp_pktbuf *mctp_pktbuf_alloc(struct mctp_binding *binding, size_t len)
{
	struct mctp_pktbuf *buf;
	size_t size;

	size = binding->pkt_size + binding->pkt_pad;

	/* todo: pools */
	buf = __mctp_alloc(sizeof(*buf) + size);

	buf->size = size;
	buf->start = binding->pkt_pad;
	buf->end = buf->start + len;
	buf->mctp_hdr_off = buf->start;
	buf->next = NULL;

	return buf;
}

void mctp_pktbuf_free(struct mctp_pktbuf *pkt)
{
	__mctp_free(pkt);
}

struct mctp_hdr *mctp_pktbuf_hdr(struct mctp_pktbuf *pkt)
{
	return (void *)pkt->data + pkt->mctp_hdr_off;
}

void *mctp_pktbuf_data(struct mctp_pktbuf *pkt)
{
	return (void *)pkt->data + pkt->mctp_hdr_off + sizeof(struct mctp_hdr);
}

uint8_t mctp_pktbuf_size(struct mctp_pktbuf *pkt)
{
	return pkt->end - pkt->start;
}

void *mctp_pktbuf_alloc_start(struct mctp_pktbuf *pkt, size_t size)
{
	assert(size <= pkt->start);
	pkt->start -= size;
	return pkt->data + pkt->start;
}

void *mctp_pktbuf_alloc_end(struct mctp_pktbuf *pkt, size_t size)
{
	void *buf;

	assert(size < (pkt->size - pkt->end));
	buf = pkt->data + pkt->end;
	pkt->end += size;
	return buf;
}

int mctp_pktbuf_push(struct mctp_pktbuf *pkt, void *data, size_t len)
{
	void *p;

	if (pkt->end + len > pkt->size)
		return -1;

	p = pkt->data + pkt->end;

	pkt->end += len;
	memcpy(p, data, len);

	return 0;
}

/* Message reassembly */
static struct mctp_msg_ctx *mctp_msg_ctx_lookup(struct mctp *mctp,
		uint8_t src, uint8_t dest, uint8_t tag)
{
	unsigned int i;

	/* @todo: better lookup, if we add support for more outstanding
	 * message contexts */
	for (i = 0; i < ARRAY_SIZE(mctp->msg_ctxs); i++) {
		struct mctp_msg_ctx *ctx = &mctp->msg_ctxs[i];
		if (ctx->src == src && ctx->dest == dest && ctx->tag == tag)
			return ctx;
	}

	return NULL;
}

static struct mctp_msg_ctx *mctp_msg_ctx_create(struct mctp *mctp,
		uint8_t src, uint8_t dest, uint8_t tag)
{
	struct mctp_msg_ctx *ctx = NULL;
	unsigned int i;

	for (i = 0; i < ARRAY_SIZE(mctp->msg_ctxs); i++) {
		struct mctp_msg_ctx *tmp = &mctp->msg_ctxs[i];
		if (!tmp->src) {
			ctx = tmp;
			break;
		}
	}

	if (!ctx)
		return NULL;

	ctx->src = src;
	ctx->dest = dest;
	ctx->tag = tag;
	ctx->buf_size = 0;

	return ctx;
}

static void mctp_msg_ctx_drop(struct mctp_msg_ctx *ctx)
{
	ctx->src = 0;
}

static void mctp_msg_ctx_reset(struct mctp_msg_ctx *ctx)
{
	ctx->buf_size = 0;
}

static int mctp_msg_ctx_add_pkt(struct mctp_msg_ctx *ctx,
		struct mctp_pktbuf *pkt)
{
	size_t len;

	len = mctp_pktbuf_size(pkt) - sizeof(struct mctp_hdr);

	if (ctx->buf_size + len > ctx->buf_alloc_size) {
		size_t new_alloc_size;
		void *lbuf;

		/* @todo: finer-grained allocation, size limits */
		if (!ctx->buf_alloc_size) {
			new_alloc_size = 4096;
		} else {
			new_alloc_size = ctx->buf_alloc_size * 2;
		}

		lbuf = __mctp_realloc(ctx->buf, new_alloc_size);
		if (lbuf) {
			ctx->buf = lbuf;
			ctx->buf_alloc_size = new_alloc_size;
		} else {
			__mctp_free(ctx->buf);
			return -1;
		}
	}

	memcpy(ctx->buf + ctx->buf_size, mctp_pktbuf_data(pkt), len);
	ctx->buf_size += len;

	return 0;
}

/* Core API functions */
struct mctp *mctp_init(void)
{
	struct mctp *mctp;

	mctp = __mctp_alloc(sizeof(*mctp));
	memset(mctp, 0, sizeof(*mctp));

	return mctp;
}

int mctp_set_rx_all(struct mctp *mctp, mctp_rx_fn fn, void *data)
{
	mctp->message_rx = fn;
	mctp->message_rx_data = data;
	return 0;
}

static struct mctp_bus *find_bus_for_eid(struct mctp *mctp,
		mctp_eid_t dest __attribute__((unused)))
{
	/* for now, just use the first bus. For full routing support,
	 * we will need a table of neighbours */
	return &mctp->busses[0];
}

int mctp_register_bus(struct mctp *mctp,
		struct mctp_binding *binding,
		mctp_eid_t eid)
{
	/* todo: multiple busses */
	assert(mctp->n_busses == 0);
	mctp->n_busses = 1;
	mctp->busses = __mctp_alloc(sizeof(struct mctp_bus));
	memset(mctp->busses, 0, sizeof(struct mctp_bus));
	mctp->busses[0].binding = binding;
	mctp->busses[0].eid = eid;
	binding->bus = &mctp->busses[0];
	binding->mctp = mctp;
	mctp->route_policy = ROUTE_ENDPOINT;

	if (binding->start)
		binding->start(binding);

	return 0;
}

int mctp_bridge_busses(struct mctp *mctp,
		struct mctp_binding *b1, struct mctp_binding *b2)
{
	assert(mctp->n_busses == 0);
	mctp->busses = __mctp_alloc(2 * sizeof(struct mctp_bus));
	memset(mctp->busses, 0, 2 * sizeof(struct mctp_bus));
	mctp->n_busses = 2;
	mctp->busses[0].binding = b1;
	b1->bus = &mctp->busses[0];
	b1->mctp = mctp;
	mctp->busses[1].binding = b2;
	b2->bus = &mctp->busses[1];
	b2->mctp = mctp;

	mctp->route_policy = ROUTE_BRIDGE;

	if (b1->start)
		b1->start(b1);

	if (b2->start)
		b2->start(b2);

	return 0;
}

static void mctp_rx(struct mctp *mctp, struct mctp_bus *bus,
		mctp_eid_t src, mctp_eid_t dest, void *buf, size_t len)
{
	if (mctp->route_policy == ROUTE_ENDPOINT &&
			dest == bus->eid && mctp->message_rx)
		mctp->message_rx(src, mctp->message_rx_data, buf, len);

	if (mctp->route_policy == ROUTE_BRIDGE) {
		int i;

		for (i = 0; i < mctp->n_busses; i++) {
			struct mctp_bus *dest_bus = &mctp->busses[i];
			if (dest_bus == bus)
				continue;

			mctp_message_tx_on_bus(mctp, dest_bus,
					src, dest, buf, len);
		}

	}
}

void mctp_bus_rx(struct mctp_binding *binding, struct mctp_pktbuf *pkt)
{
	struct mctp_bus *bus = binding->bus;
	struct mctp *mctp = binding->mctp;
	uint8_t flags, exp_seq, seq, tag;
	struct mctp_msg_ctx *ctx;
	struct mctp_hdr *hdr;
	size_t len;
	void *p;
	int rc;

	assert(bus);

	hdr = mctp_pktbuf_hdr(pkt);

	/* small optimisation: don't bother reassembly if we're going to
	 * drop the packet in mctp_rx anyway */
	if (mctp->route_policy == ROUTE_ENDPOINT && hdr->dest != bus->eid)
		goto out;

	flags = hdr->flags_seq_tag & (MCTP_HDR_FLAG_SOM | MCTP_HDR_FLAG_EOM);
	tag = (hdr->flags_seq_tag >> MCTP_HDR_TAG_SHIFT) & MCTP_HDR_TAG_MASK;
	seq = (hdr->flags_seq_tag >> MCTP_HDR_SEQ_SHIFT) & MCTP_HDR_SEQ_MASK;

	switch (flags) {
	case MCTP_HDR_FLAG_SOM | MCTP_HDR_FLAG_EOM:
		/* single-packet message - send straight up to rx function,
		 * no need to create a message context */
		len = pkt->end - pkt->mctp_hdr_off - sizeof(struct mctp_hdr);
		p = pkt->data + pkt->mctp_hdr_off + sizeof(struct mctp_hdr),
		mctp_rx(mctp, bus, hdr->src, hdr->dest, p, len);
		break;

	case MCTP_HDR_FLAG_SOM:
		/* start of a new message - start the new context for
		 * future message reception. If an existing context is
		 * already present, drop it. */
		ctx = mctp_msg_ctx_lookup(mctp, hdr->src, hdr->dest, tag);
		if (ctx) {
			mctp_msg_ctx_reset(ctx);
		} else {
			ctx = mctp_msg_ctx_create(mctp,
					hdr->src, hdr->dest, tag);
		}

		rc = mctp_msg_ctx_add_pkt(ctx, pkt);
		if (rc) {
			mctp_msg_ctx_drop(ctx);
		} else {
			ctx->last_seq = seq;
		}

		break;

	case MCTP_HDR_FLAG_EOM:
		ctx = mctp_msg_ctx_lookup(mctp, hdr->src, hdr->dest, tag);
		if (!ctx)
			goto out;

		exp_seq = (ctx->last_seq + 1) % 4;

		if (exp_seq != seq) {
			mctp_prdebug(
				"Sequence number %d does not match expected %d",
				seq, exp_seq);
			mctp_msg_ctx_drop(ctx);
			goto out;
		}

		rc = mctp_msg_ctx_add_pkt(ctx, pkt);
		if (!rc)
			mctp_rx(mctp, bus, ctx->src, ctx->dest,
					ctx->buf, ctx->buf_size);

		mctp_msg_ctx_drop(ctx);
		break;

	case 0:
		/* Neither SOM nor EOM */
		ctx = mctp_msg_ctx_lookup(mctp, hdr->src,hdr->dest, tag);
		if (!ctx)
			goto out;

		exp_seq = (ctx->last_seq + 1) % 4;
		if (exp_seq != seq) {
			mctp_prdebug(
				"Sequence number %d does not match expected %d",
				seq, exp_seq);
			mctp_msg_ctx_drop(ctx);
			goto out;
		}

		rc = mctp_msg_ctx_add_pkt(ctx, pkt);
		if (rc) {
			mctp_msg_ctx_drop(ctx);
			goto out;
		}
		ctx->last_seq = seq;

		break;
	}
out:
	mctp_pktbuf_free(pkt);
}

static int mctp_packet_tx(struct mctp_bus *bus,
		struct mctp_pktbuf *pkt)
{
	if (!bus->tx_enabled)
		return -1;

	return bus->binding->tx(bus->binding, pkt);
}

static void mctp_send_tx_queue(struct mctp_bus *bus)
{
	struct mctp_pktbuf *pkt;

	while ((pkt = bus->tx_queue_head)) {
		int rc;

		rc = mctp_packet_tx(bus, pkt);
		if (rc)
			break;

		bus->tx_queue_head = pkt->next;
		mctp_pktbuf_free(pkt);
	}

	if (!bus->tx_queue_head)
		bus->tx_queue_tail = NULL;

}

void mctp_binding_set_tx_enabled(struct mctp_binding *binding, bool enable)
{
	struct mctp_bus *bus = binding->bus;
	bus->tx_enabled = enable;
	if (enable)
		mctp_send_tx_queue(bus);
}

static int mctp_message_tx_on_bus(struct mctp *mctp, struct mctp_bus *bus,
		mctp_eid_t src, mctp_eid_t dest, void *msg, size_t msg_len)
{
	size_t max_payload_len, payload_len, p;
	struct mctp_pktbuf *pkt;
	struct mctp_hdr *hdr;
	int i;

	max_payload_len = bus->binding->pkt_size - sizeof(*hdr);

	mctp_prdebug("%s: Generating packets for transmission of %zu byte message from %hhu to %hhu",
		     __func__, msg_len, src, dest);

	/* queue up packets, each of max MCTP_MTU size */
	for (p = 0, i = 0; p < msg_len; i++) {
		payload_len = msg_len - p;
		if (payload_len > max_payload_len)
			payload_len = max_payload_len;

		pkt = mctp_pktbuf_alloc(bus->binding,
				payload_len + sizeof(*hdr));
		hdr = mctp_pktbuf_hdr(pkt);

		/* todo: tags */
		hdr->ver = bus->binding->version & 0xf;
		hdr->dest = dest;
		hdr->src = src;
		hdr->flags_seq_tag = MCTP_HDR_FLAG_TO |
			(0 << MCTP_HDR_TAG_SHIFT);

		if (i == 0)
			hdr->flags_seq_tag |= MCTP_HDR_FLAG_SOM;
		if (p + payload_len >= msg_len)
			hdr->flags_seq_tag |= MCTP_HDR_FLAG_EOM;
		hdr->flags_seq_tag |=
			(i & MCTP_HDR_SEQ_MASK) << MCTP_HDR_SEQ_SHIFT;

		memcpy(mctp_pktbuf_data(pkt), msg + p, payload_len);

		/* add to tx queue */
		if (bus->tx_queue_tail)
			bus->tx_queue_tail->next = pkt;
		else
			bus->tx_queue_head = pkt;
		bus->tx_queue_tail = pkt;

		p += payload_len;
	}

	mctp_prdebug("%s: Enqueued %d packets", __func__, i);

	mctp_send_tx_queue(bus);

	return 0;
}

int mctp_message_tx(struct mctp *mctp, mctp_eid_t eid,
		void *msg, size_t msg_len)
{
	struct mctp_bus *bus;

	bus = find_bus_for_eid(mctp, eid);
	return mctp_message_tx_on_bus(mctp, bus, bus->eid, eid, msg, msg_len);
}