/*  Copyright (C) CZ.NIC, z.s.p.o. <knot-resolver@labs.nic.cz>
 *  SPDX-License-Identifier: GPL-3.0-or-later
 */

#pragma once

#include "kresconfig.h"
#include "lib/defines.h"
#include "lib/utils.h"

/** Layer processing states.  Only one value at a time (but see TODO).
 *
 *  Each state represents the state machine transition,
 *  and determines readiness for the next action.
 *  See struct kr_layer_api for the actions.
 *
 *  TODO: the cookie module sometimes sets (_FAIL | _DONE) on purpose (!)
 */
enum kr_layer_state {
	KR_STATE_CONSUME = 1 << 0, /*!< Consume data. */
	KR_STATE_PRODUCE = 1 << 1, /*!< Produce data. */

	/*! Finished successfully or a special case: in CONSUME phase this can
	 * be used (by iterator) to do a transition to PRODUCE phase again,
	 * in which case the packet wasn't accepted for some reason. */
	KR_STATE_DONE    = 1 << 2,

	KR_STATE_FAIL    = 1 << 3, /*!< Error. */
	KR_STATE_YIELD   = 1 << 4, /*!< Paused, waiting for a sub-query. */
};

/** Check that a kr_layer_state makes sense.  We're not very strict ATM. */
static inline bool kr_state_consistent(enum kr_layer_state s)
{
#ifdef __clang__
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wtautological-constant-out-of-range-compare"
#pragma clang diagnostic ignored "-Wtautological-unsigned-enum-zero-compare"
#endif
	return s >= 0 && s < (1 << 5);
#ifdef __clang__
#pragma clang diagnostic pop
#endif
}

/* Forward declarations. */
struct kr_layer_api;

/** Packet processing context. */
typedef struct kr_layer {
	int state; /*!< The current state; bitmap of enum kr_layer_state. */
	struct kr_request *req; /*!< The corresponding request. */
	const struct kr_layer_api *api;
	knot_pkt_t *pkt; /*!< In glue for lua kr_layer_api it's used to pass the parameter. */
	struct sockaddr *dst; /*!< In glue for checkout layer it's used to pass the parameter. */
	bool is_stream;       /*!< In glue for checkout layer it's used to pass the parameter. */
} kr_layer_t;

/** Packet processing module API.  All functions return the new kr_layer_state.
 *
 * Lua modules are allowed to return nil/nothing, meaning the state shall not change.
 */
struct kr_layer_api {
      	/** Start of processing the DNS request. */
	int (*begin)(kr_layer_t *ctx);

	int (*reset)(kr_layer_t *ctx);

	/** Paired to begin, called both on successes and failures. */
	int (*finish)(kr_layer_t *ctx);

	/** Process an answer from upstream or from cache.
	 * Lua API: call is omitted iff (state & KR_STATE_FAIL). */
	int (*consume)(kr_layer_t *ctx, knot_pkt_t *pkt);

	/** Produce either an answer to the request or a query for upstream (or fail).
	 * Lua API: call is omitted iff (state & KR_STATE_FAIL). */
	int (*produce)(kr_layer_t *ctx, knot_pkt_t *pkt);

	/** Finalises the outbound query packet with the knowledge of the IP addresses.
	 * The checkout layer doesn't persist the state, so canceled subrequests
	 * don't affect the resolution or rest of the processing.
	 * Lua API: call is omitted iff (state & KR_STATE_FAIL). */
	int (*checkout)(kr_layer_t *ctx, knot_pkt_t *packet, struct sockaddr *dst, int type);

	/** Finalises the answer.
	 * Last chance to affect what will get into the answer, including EDNS.
	 * Not called if the packet is being dropped. */
	int (*answer_finalize)(kr_layer_t *ctx);

	/** The C module can store anything in here. */
	void *data;

	/** Internal to ./daemon/ffimodule.c. */
	int cb_slots[];
};

typedef struct kr_layer_api kr_layer_api_t;

/** Pickled layer state (api, input, state). */
struct kr_layer_pickle {
    struct kr_layer_pickle *next;
    const struct kr_layer_api *api;
    knot_pkt_t *pkt;
    unsigned state;
};