#include <camellia/errno.h>
#include <camellia/flags.h>
#include <kernel/malloc.h>
#include <kernel/panic.h>
#include <kernel/proc.h>
#include <kernel/vfs/request.h>
#include <shared/mem.h>

/** Checks if the request flags don't contradict each other.
 * While this could be done by caller of vfsreq_dispatchcopy, as currently
 * there's only one of them per operation, doing this here means that any
 * potential future callers can't forget those checks.
 * Doing this so late is kinda inefficient but I don't really care. */
static bool
vfsreq_isvalid(VfsReq *r)
{
	/* Notable omissions:
	 * - Simplifying the path for open(). Already done when resolving the mount.
	 * - Checking the handle permissions. We don't have access to it.
	 * */
	if (r->type == VFSOP_OPEN && !(r->flags & OPEN_WRITE) && (r->flags & OPEN_CREATE)) {
		return false;
	}

	// XXX if i add a handle field to vfs_request, check ->readable ->writeable here
	return true;
}

void
vfsreq_dispatchcopy(VfsReq tmpl)
{
	VfsReq *req;
	VfsBackend *backend;

	/* allocate memory for the request and move it there */
	req = kmalloc(sizeof *req, "VfsReq");
	memcpy(req, &tmpl, sizeof *req);
	backend = req->backend;
	if (backend) {
		assert(backend->usehcnt > 0);
		backend->usehcnt++;
	}

	if (req->caller) {
		proc_setstate(req->caller, PS_WAITS4FS);
		req->caller->reqslot = req;
	}

	/* Check request validity. Doing this after the memcpy means that it
	 * doesn't need to be special cased in vfsreq_finish. */
	if (!vfsreq_isvalid(req)) {
		vfsreq_finish_short(req, -EINVAL);
		return;
	}
	assert(req->queue_next == NULL);
	assert(req->postqueue_next == NULL);

	if (backend == NULL) {
		/* null mount - probably never had a real backend */
		vfsreq_finish_short(req, -ENOENT);
	} else if (backend->is_user) {
		vfsback_useraccept(req);
	} else { /* kernel backend */
		assert(backend->kern.accept);
		backend->kern.accept(req);
	}
}

void
vfsreq_finish(VfsReq *req, char __user *stored, long ret, int flags, Proc *handler)
{
	if (req->type == VFSOP_OPEN && ret >= 0) {
		Handle *h;
		if (!(flags & FSR_DELEGATE)) {
			/* default behavior - create a new handle for the file, wrap the id */
			h = handle_init(HANDLE_FILE);
			h->backend = req->backend;
			req->backend->usehcnt++;
			h->file_id = stored;
			h->readable = OPEN_READABLE(req->flags);
			h->writeable = OPEN_WRITEABLE(req->flags);
		} else {
			/* delegating - moving a handle to the caller */
			assert(handler);
			h = hs_take(handler->hs, ret);
			if (h) {
				h->readable = h->readable && OPEN_READABLE(req->flags);
				h->writeable = h->writeable && OPEN_WRITEABLE(req->flags);
			}
		}

		if (h) {
			// TODO write tests for caller getting killed while opening a file
			if (!req->caller) panic_unimplemented();
			ret = hs_put(req->caller->hs, h);
			if (ret < 0) ret = -EMFILE;
		} else {
			ret = -1;
		}
	}

	if (req->type == VFSOP_READ && ret >= 0) {
		assert((size_t)ret <= req->output.len);
	}

	if (req->input.kern) {
		kfree(req->input.buf_kern);
	}

	if (req->backend) {
		vfsback_userdown(req->backend);
	}

	assert(req->queue_next == NULL);
	assert(req->postqueue_next == NULL);

	if (req->caller) {
		assert(req->caller->state == PS_WAITS4FS);
		regs_savereturn(&req->caller->regs, ret);
		proc_setstate(req->caller, PS_RUNNING);
	}
	kfree(req);
}

void
vfsback_useraccept(VfsReq *req)
{
	VfsBackend *backend;
	Proc *handler;
	struct ufs_request res = {0};
	int len;

	assert(req != NULL);
	backend = req->backend;
	assert(backend);
	assert(backend->is_user);
	if (backend->provhcnt == 0) {
		vfsreq_finish_short(req, -EPIPE);
		return;
	} else if (backend->user.handler == NULL) {
		/* queue the request up */
		// TODO use postqueue
		VfsReq **it = &backend->queue;
		while (*it != NULL) { /* find a free spot in queue */
			it = &(*it)->queue_next;
		}
		*it = req;
		return;
	}

	handler = backend->user.handler;
	assert(handler->state == PS_WAITS4REQUEST);

	// the pcpy calls aren't present in all kernel backends
	// it's a way to tell apart kernel and user backends apart
	// TODO check validity of memory regions somewhere else

	if (req->input.buf) {
		__user void *buf = handler->awaited_req.buf;
		len = min(req->input.len, handler->awaited_req.max_len);
		if (req->input.kern) {
			pcpy_to(handler, buf, req->input.buf_kern, len);
		} else {
			len = pcpy_bi(
				handler, buf,
				req->caller, req->input.buf, len
			);
		}
	} else {
		len = req->output.len;
	}

	res.len      = len;
	res.capacity = req->output.len;
	res.id       = req->id;
	res.offset   = req->offset;
	res.flags    = req->flags;
	res.op       = req->type;

	if (pcpy_to(handler, handler->awaited_req.res, &res, sizeof res) < sizeof(res))
	{
		panic_unimplemented();
	}

	Handle *h;
	hid_t hid = hs_hinit(handler->hs, HANDLE_FS_REQ, &h);
	if (hid < 0) panic_unimplemented();
	h->req = req;
	proc_setstate(handler, PS_RUNNING);
	regs_savereturn(&handler->regs, hid);
	req->backend->user.handler = NULL;
}

static void
vfsback_checkfree(VfsBackend *b)
{
	if (b->usehcnt == 0 && b->provhcnt == 0) {
		assert(!b->queue);
		kfree(b);
	}
}

void
vfsback_userdown(VfsBackend *b)
{
	assert(b);
	assert(0 < b->usehcnt);
	b->usehcnt--;
	if (b->usehcnt == 0) {
		if (!b->is_user && b->kern.cleanup) {
			b->kern.cleanup(b);
		}
		if (b->is_user && b->user.handler) {
			/* tell the process that the filesystem won't receive any more
			 * requests */
			Proc *p = b->user.handler;
			b->user.handler = NULL;
			assert(p->state == PS_WAITS4REQUEST);
			regs_savereturn(&p->regs, -EPIPE);
			proc_setstate(p, PS_RUNNING);
		}
	}
	vfsback_checkfree(b);
}

void
vfsback_provdown(VfsBackend *b)
{
	assert(b);
	assert(0 < b->provhcnt);
	b->provhcnt--;
	if (b->provhcnt == 0) {
		/* discard everything in the queue */
		VfsReq *q = b->queue;
		while (q) {
			VfsReq *q2 = q->queue_next;
			q->queue_next = NULL;
			vfsreq_finish_short(q, -EPIPE);
			q = q2;
		}
		b->queue = NULL;
	}
	vfsback_checkfree(b);
}