#pragma once
#include <kernel/types.h>
#include <shared/ring.h>
#include <stdbool.h>
#include <stddef.h>

struct ReqQueue {
	VfsReq *head;
	VfsReq **slot; /* points to the place where new entries should be placed */
};

struct VfsBackend {
	/* amount of using references
	 *  VfsMount
	 *  VfsReq
	 *  Handle
	 * once it reaches 0, it'll never increase */
	size_t usehcnt; /* VfsMount */

	bool is_user;
	union {
		struct {
			Proc *handler;
			ReqQueue queue; /* kernel backends keep their own queues */
			/* amount of processes that control this backend
			 * won't ever increase if it becomes 0 */
			size_t provhcnt;
		} user;
		struct {
			void (*accept)(VfsReq *);
			void (*cleanup)(VfsBackend *);
			void *data;
		} kern;
	};
};

/* describes an in-progress vfs call */
struct VfsReq {
	enum vfs_op type;

	/* "kernel" input - an allocation owned by this struct, contains a NUL
	 * terminated string. the NUL isn't counted in the kinlen (for compat
	 * with old code). used for the path in open() */
	char *kin;
	size_t kinlen;

	/* user inputs and outputs - just point to some buffer in the caller */
	char __user *uin;
	size_t uinlen;
	char __user *out;
	size_t outlen;

	/* those correspond to handle.file.id
	 * id2 is used for duplex() */
	void __user *id, *id2;
	long offset;
	int flags;

	Proc *caller;
	VfsBackend *backend;

	VfsReq *reqqueue_next;
};

/** Assigns the vfs_request to the caller, and dispatches the call */
void vfsreq_dispatchcopy(VfsReq);
void vfsreq_finish(VfsReq*, char __user *stored, long ret, int flags, Proc *handler);

static inline void vfsreq_finish_short(VfsReq *req, long ret) {
	vfsreq_finish(req, (void __user *)ret, ret, 0, NULL);
}

/** Try to accept an enqueued request */
void vfsback_useraccept(VfsReq *);

/** Decrements the "user" reference count. */
void vfsback_userdown(VfsBackend *);

/** Decrements the "provider" reference count. */
void vfsback_provdown(VfsBackend *);

void reqqueue_init(ReqQueue *q);
void reqqueue_join(ReqQueue *q, VfsReq *req);
VfsReq *reqqueue_pop(ReqQueue *q);

/** If there are any pending read requests, and the ring buffer isn't empty,
 *  fulfill them all with a single read. */
void reqqueue_ringreadall(ReqQueue *q, ring_t *r);