#include "global_request_scheduler.h"
#include "runtime.h"

static struct deque_sandbox *global_request_scheduler_deque;
static pthread_mutex_t       global_request_scheduler_deque_mutex = PTHREAD_MUTEX_INITIALIZER;

/**
 * Pushes a sandbox request to the global deque
 * @param sandbox_request
 * @returns pointer to request if added. NULL otherwise
 */
static struct sandbox_request *
global_request_scheduler_deque_add(void *sandbox_request_raw)
{
	struct sandbox_request *sandbox_request = (struct sandbox_request *)sandbox_request_raw;
	int                     return_code     = 1;

	return_code = deque_push_sandbox(global_request_scheduler_deque, &sandbox_request);

	if (return_code != 0) return NULL;
	return sandbox_request_raw;
}

/**
 * Stealing from the dequeue is a lock-free, cross-core "pop", which removes the element from the end opposite to
 * "pop". Because the producer and consumer (the core stealine the sandbox request) modify different ends,
 * no locks are required, and coordination is achieved by instead retrying on inconsistent indices.
 *
 * Relevant Read: https://www.dre.vanderbilt.edu/~schmidt/PDF/work-stealing-dequeue.pdf
 *
 * @returns 0 if successfully returned a sandbox request, -ENOENT if empty, -EAGAIN if atomic instruction unsuccessful
 */
static int
global_request_scheduler_deque_remove(struct sandbox_request **removed_sandbox_request)
{
	return deque_steal_sandbox(global_request_scheduler_deque, removed_sandbox_request);
}

static int
global_request_scheduler_deque_remove_if_earlier(struct sandbox_request **removed_sandbox_request,
                                                 uint64_t                 target_deadline)
{
	panic("Deque variant does not support this call\n");
	return -1;
}

void
global_request_scheduler_deque_initialize()
{
	/* Allocate and Initialize the global deque */
	global_request_scheduler_deque = (struct deque_sandbox *)malloc(sizeof(struct deque_sandbox));
	assert(global_request_scheduler_deque);
	/* Note: Below is a Macro */
	deque_init_sandbox(global_request_scheduler_deque, RUNTIME_MAX_SANDBOX_REQUEST_COUNT);

	/* Register Function Pointers for Abstract Scheduling API */
	struct global_request_scheduler_config config = {
		.add_fn               = global_request_scheduler_deque_add,
		.remove_fn            = global_request_scheduler_deque_remove,
		.remove_if_earlier_fn = global_request_scheduler_deque_remove_if_earlier
	};

	global_request_scheduler_initialize(&config);
}