/* SPDX-License-Identifier: BSD-2-Clause */
/*
 * chardev_client.c — kernel-bridge client for the daedalus-v4l2 daemon.
 */
#include "chardev_client.h"
#include "decoder.h"
#include "ffmpeg_loader.h"
#include "log.h"

#include <errno.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <poll.h>

#define CHARDEV_PATH		"/dev/daedalus-v4l2"
#define CHARDEV_READ_BUFSZ	(sizeof(struct daedalus_msg_hdr) + \
				 DAEDALUS_PROTO_MAX_PAYLOAD)

int chardev_client_open(struct chardev_client *cli,
			struct ffmpeg_loader *loader,
			volatile sig_atomic_t *stop_flag)
{
	int fd, rc;

	memset(cli, 0, sizeof(*cli));
	cli->fd		 = -1;
	cli->loader	 = loader;
	cli->stop_flag	 = stop_flag;

	fd = open(CHARDEV_PATH, O_RDWR | O_CLOEXEC);
	if (fd < 0) {
		rc = -errno;
		log_err("open(%s): %s", CHARDEV_PATH, strerror(errno));
		return rc;
	}

	cli->decoder = calloc(1, sizeof(*cli->decoder));
	if (!cli->decoder) {
		close(fd);
		return -ENOMEM;
	}
	rc = daedalus_decoder_init(cli->decoder, loader);
	if (rc < 0) {
		free(cli->decoder);
		cli->decoder = NULL;
		close(fd);
		log_err("daedalus_decoder_init: %d", rc);
		return rc;
	}

	cli->fd = fd;
	log_info("chardev: opened %s (fd %d)", CHARDEV_PATH, fd);
	return 0;
}

void chardev_client_close(struct chardev_client *cli)
{
	if (!cli)
		return;
	if (cli->decoder) {
		daedalus_decoder_cleanup(cli->decoder);
		free(cli->decoder);
		cli->decoder = NULL;
	}
	if (cli->fd >= 0) {
		close(cli->fd);
		cli->fd = -1;
	}
}

static int send_response(struct chardev_client *cli, uint32_t type,
			 uint32_t cookie, const void *payload,
			 size_t payload_len)
{
	struct daedalus_msg_hdr hdr;
	int rc;

	if (payload_len > DAEDALUS_PROTO_MAX_PAYLOAD)
		return -EMSGSIZE;

	hdr.magic	 = DAEDALUS_PROTO_MAGIC;
	hdr.version	 = DAEDALUS_PROTO_VERSION;
	hdr.type	 = type;
	hdr.cookie	 = cookie;
	hdr.payload_len	 = (uint32_t) payload_len;
	hdr.reserved	 = 0;

	/*
	 * The kernel's write() path validates count == sizeof(hdr)
	 * + hdr.payload_len in a single call, and only implements
	 * .write (not .write_iter), so a writev() lands as -EINVAL.
	 * Marshal the message into a single buffer and write() it.
	 *
	 * Response payloads are small (struct daedalus_resp_frame =
	 * 36 bytes; PONG echoes <= 64 KiB).  A short-lived heap
	 * allocation per response is fine; per-loop reuse can come
	 * later if profiling demands it.
	 */
	{
		size_t total = sizeof(hdr) + payload_len;
		uint8_t *out = malloc(total);
		ssize_t n;

		if (!out)
			return -ENOMEM;
		memcpy(out, &hdr, sizeof(hdr));
		if (payload_len)
			memcpy(out + sizeof(hdr), payload, payload_len);

		for (;;) {
			n = write(cli->fd, out, total);
			if (n >= 0) {
				if ((size_t) n != total) {
					log_err("chardev: short write %zd != %zu",
						n, total);
					rc = -EIO;
				} else {
					rc = 0;
				}
				break;
			}
			if (errno == EINTR)
				continue;
			rc = -errno;
			log_err("chardev: write: %s", strerror(errno));
			break;
		}
		free(out);
	}
	return rc;
}

static int handle_req_decode(struct chardev_client *cli,
			     const struct daedalus_msg_hdr *hdr,
			     const uint8_t *payload)
{
	struct daedalus_req_decode req;
	struct daedalus_resp_frame resp;
	int rc;

	if (hdr->payload_len < sizeof(req)) {
		log_err("REQ_DECODE cookie=%u: payload too short %u < %zu",
			hdr->cookie, hdr->payload_len, sizeof(req));
		memset(&resp, 0, sizeof(resp));
		resp.status = DAEDALUS_DECODE_ERR_RECV;
		return send_response(cli, DAEDALUS_MSG_RESP_FRAME,
				     hdr->cookie, &resp, sizeof(resp));
	}
	memcpy(&req, payload, sizeof(req));
	if ((size_t) req.bitstream_len + sizeof(req) != hdr->payload_len) {
		log_err("REQ_DECODE cookie=%u: bitstream_len %u inconsistent with payload_len %u",
			hdr->cookie, req.bitstream_len, hdr->payload_len);
		memset(&resp, 0, sizeof(resp));
		resp.status = DAEDALUS_DECODE_ERR_RECV;
		return send_response(cli, DAEDALUS_MSG_RESP_FRAME,
				     hdr->cookie, &resp, sizeof(resp));
	}

	log_info("REQ_DECODE cookie=%u codec=%u bitstream=%u bytes",
		 hdr->cookie, req.codec_id, req.bitstream_len);

	rc = daedalus_decoder_run_request(cli->decoder, &req,
					  payload + sizeof(req), &resp);
	if (rc < 0)
		return rc;

	return send_response(cli, DAEDALUS_MSG_RESP_FRAME, hdr->cookie,
			     &resp, sizeof(resp));
}

static int handle_ping(struct chardev_client *cli,
		       const struct daedalus_msg_hdr *hdr,
		       const uint8_t *payload)
{
	log_info("PING cookie=%u plen=%u — echoing PONG",
		 hdr->cookie, hdr->payload_len);
	return send_response(cli, DAEDALUS_MSG_PONG, hdr->cookie,
			     payload, hdr->payload_len);
}

static int handle_one_message(struct chardev_client *cli, uint8_t *buf)
{
	struct daedalus_msg_hdr hdr;
	ssize_t n;

	/*
	 * The kernel chardev delivers exactly one message per
	 * read().  Pass a buffer that can hold any legal message.
	 */
	for (;;) {
		n = read(cli->fd, buf, CHARDEV_READ_BUFSZ);
		if (n >= 0)
			break;
		if (errno == EINTR) {
			if (*cli->stop_flag)
				return 0;
			continue;
		}
		log_err("chardev: read: %s", strerror(errno));
		return -errno;
	}
	if (n == 0)
		return -EIO;	/* EOF / device unplugged */
	if ((size_t) n < sizeof(hdr)) {
		log_err("chardev: short read %zd < hdr", n);
		return -EBADMSG;
	}

	memcpy(&hdr, buf, sizeof(hdr));
	if (hdr.magic != DAEDALUS_PROTO_MAGIC) {
		log_err("chardev: bad magic 0x%08x", hdr.magic);
		return -EBADMSG;
	}
	if (hdr.version != DAEDALUS_PROTO_VERSION) {
		log_err("chardev: unsupported version %u", hdr.version);
		return -EPROTO;
	}
	if ((size_t) n != sizeof(hdr) + hdr.payload_len) {
		log_err("chardev: framing mismatch n=%zd expected %zu",
			n, sizeof(hdr) + hdr.payload_len);
		return -EBADMSG;
	}

	switch (hdr.type) {
	case DAEDALUS_MSG_PING:
		return handle_ping(cli, &hdr, buf + sizeof(hdr));
	case DAEDALUS_MSG_REQ_DECODE:
		return handle_req_decode(cli, &hdr, buf + sizeof(hdr));
	default:
		log_warn("chardev: unknown request type 0x%08x cookie=%u",
			 hdr.type, hdr.cookie);
		return 0;	/* skip, don't bail the loop */
	}
}

int chardev_client_run(struct chardev_client *cli)
{
	uint8_t *buf;
	int rc = 0;

	buf = malloc(CHARDEV_READ_BUFSZ);
	if (!buf)
		return -ENOMEM;

	log_info("daemon loop started; waiting for kernel requests");

	while (!*cli->stop_flag) {
		rc = handle_one_message(cli, buf);
		if (rc < 0) {
			if (rc == -EINTR)
				continue;
			log_err("chardev: handle_one_message: %d", rc);
			break;
		}
	}

	log_info("daemon loop exiting (stop=%d rc=%d)", *cli->stop_flag, rc);
	free(buf);
	return rc;
}