// User-level IPC library routines

#include <inc/lib.h>
// Receive a value via IPC and return it.
// If 'pg' is nonnull, then any page sent by the sender will be mapped at
//	that address.
// If 'fromenv' is nonnull, then store the IPC sender's envid in *fromenv.
// If 'perm' is nonnull, then store the IPC sender's page permission in *perm
//	(this is nonzero iff a page was successfully transferred to 'pg').
// If the system call fails, then store 0 in *fromenv and *perm (if
//	they're nonnull) and return the error.
//
// Hint:
//   Use 'env' to discover the value and who sent it.
//   If 'pg' is null, pass sys_ipc_recv a value that it will understand
//   as meaning "no page".  (Zero is not the right value.)
int32_t
ipc_recv(envid_t *from_env_store, void *pg, int *perm_store)
{
	// LAB 4: Your code here.
	int32_t return_value;

	if (pg == NULL) {
		//want to receive value
		if ((return_value = sys_ipc_recv((void *)UTOP)) < 0) {
			cprintf("sys_ipc_recv for UTOP (no page) failed\n");
			*from_env_store = 0;
			*perm_store = 0;
			return return_value;
		}
		if (from_env_store != NULL) {
			*from_env_store = env->env_ipc_from;
		}
		if (perm_store != NULL) {
			*perm_store = env->env_ipc_perm;
		}
		return env->env_ipc_value;
	} else {
		//want to receive page
		if ((return_value = sys_ipc_recv(pg)) < 0) {
			cprintf("sys_ipc_recv for UTOP (no page) failed\n");
			*from_env_store = 0;
			*perm_store = 0;
			return return_value;
		}

		if (from_env_store != NULL) {
			*from_env_store = env->env_ipc_from;
		}
		if (perm_store != NULL) {
			*perm_store = env->env_ipc_perm;
		}
		return env->env_ipc_value;
		
		
	}
	panic("should not get here \n");
	return 0;
}

// Send 'val' (and 'pg' with 'perm', assuming 'pg' is nonnull) to 'toenv'.
// This function keeps trying until it succeeds.
// It should panic() on any error other than -E_IPC_NOT_RECV.
//
// Hint:
//   Use sys_yield() to be CPU-friendly.
//   If 'pg' is null, pass sys_ipc_recv a value that it will understand
//   as meaning "no page".  (Zero is not the right value.)
void
ipc_send(envid_t to_env, uint32_t val, void *pg, int perm)
{
	// LAB 4: Your code here.
	int error;

	while ((error = sys_ipc_try_send(to_env, val, pg == NULL ? (void *)UTOP : pg, perm)) == -E_IPC_NOT_RECV) {
		sys_yield();
	}
	if (error < 0) {
		panic("problem in sys_ipc_try_send\n");
	}
	
}