/*
 * exec_query_string
 *
 * This is the guts of exec_simply_query, but is also used by
 * execute_sql_string in contrib/pg_background
 */
void
exec_query_string(const char *query_string,
				  CommandDest dest, /* Where to send output */
				  MemoryContext parsecontext, /* Context we should use to parse query_string */
				  bool allow_transactions, /* Should we allow transaction statements? */
				  bool last_result_only /* If true, drop all command output except for the last command */
				  )
{
	MemoryContext oldcontext;
	List	   *parsetree_list;
	ListCell   *parsetree_item;
	bool		was_logged = false;
	bool		isTopLevel;
	char		msec_str[32];
	int			commands_remaining;

	/*
	 * Start up a transaction command.  All queries generated by the
	 * query_string will be in this same command block, *unless* we find a
	 * BEGIN/COMMIT/ABORT statement; we have to force a new xact command after
	 * one of those, else bad things will happen in xact.c. (Note that this
	 * will normally change current memory context.)
	 */
	start_xact_command();

	/*
	 * Zap any pre-existing unnamed statement.  (While not strictly necessary,
	 * it seems best to define simple-Query mode as if it used the unnamed
	 * statement and portal; this ensures we recover any storage used by prior
	 * unnamed operations.)
	 */
	drop_unnamed_stmt();

	/*
	 * Switch to appropriate context for constructing parsetrees.
	 */
	oldcontext = MemoryContextSwitchTo(MessageContext);

	/*
	 * Do basic parsing of the query or queries (this should be safe even if
	 * we are in aborted transaction state!)
	 */
	parsetree_list = pg_parse_query(query_string);
	commands_remaining = list_length(parsetree_list);

	/* Log immediately if dictated by log_statement */
	if (check_log_statement(parsetree_list))
	{
		ereport(LOG,
				(errmsg("statement: %s", query_string),
				 errhidestmt(true),
				 errdetail_execute(parsetree_list)));
		was_logged = true;
	}

	/*
	 * Switch back to transaction context to enter the loop.
	 */
	MemoryContextSwitchTo(oldcontext);

	/*
	 * We'll tell PortalRun it's a top-level command iff there's exactly one
	 * raw parsetree.  If more than one, it's effectively a transaction block
	 * and we want PreventTransactionChain to reject unsafe commands. (Note:
	 * we're assuming that query rewrite cannot add commands that are
	 * significant to PreventTransactionChain.)
	 */
	isTopLevel = (list_length(parsetree_list) == 1);

	/*
	 * Run through the raw parsetree(s) and process each one.
	 */
	foreach(parsetree_item, parsetree_list)
	{
		Node	   *parsetree = (Node *) lfirst(parsetree_item);
		bool		snapshot_set = false;
		const char *commandTag;
		char		completionTag[COMPLETION_TAG_BUFSIZE];
		List	   *querytree_list,
				   *plantree_list;
		Portal		portal;
		DestReceiver *receiver;
		int16		format;

		if (!allow_transactions && IsA(parsetree, TransactionStmt))
			/* XXX this needs to be more flexible */
			ereport(ERROR,
					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
					 errmsg("transaction control statements are not allowed in pg_background")));


		/*
		 * Get the command name for use in status display (it also becomes the
		 * default completion tag, down inside PortalRun).  Set ps_status and
		 * do any special start-of-SQL-command processing needed by the
		 * destination.
		 */
		commandTag = CreateCommandTag(parsetree);

		set_ps_display(commandTag, false);

		/* XXX what should we do here in the case of last_result_only = true? */
		BeginCommand(commandTag, dest);

		/*
		 * If we are in an aborted transaction, reject all commands except
		 * COMMIT/ABORT.  It is important that this test occur before we try
		 * to do parse analysis, rewrite, or planning, since all those phases
		 * try to do database accesses, which may fail in abort state. (It
		 * might be safe to allow some additional utility commands in this
		 * state, but not many...)
		 */
		if (IsAbortedTransactionBlockState() &&
			!IsTransactionExitStmt(parsetree))
			ereport(ERROR,
					(errcode(ERRCODE_IN_FAILED_SQL_TRANSACTION),
					 errmsg("current transaction is aborted, "
						  "commands ignored until end of transaction block"),
					 errdetail_abort()));

		/* Make sure we are in a transaction command */
		if (allow_transactions)
			start_xact_command();

		/* If we got a cancel signal in parsing or prior command, quit */
		CHECK_FOR_INTERRUPTS();

		/*
		 * Set up a snapshot if parse analysis/planning will need one.
		 */
		if (analyze_requires_snapshot(parsetree))
		{
			PushActiveSnapshot(GetTransactionSnapshot());
			snapshot_set = true;
		}

		/*
		 * OK to analyze, rewrite, and plan this query.
		 *
		 * Switch to appropriate context for constructing querytrees (again,
		 * these must outlive the execution context).
		 */
		oldcontext = MemoryContextSwitchTo(MessageContext);

		querytree_list = pg_analyze_and_rewrite(parsetree, query_string,
												NULL, 0);

		plantree_list = pg_plan_queries(querytree_list, 0, NULL);

		/* Done with the snapshot used for parsing/planning */
		if (snapshot_set)
			PopActiveSnapshot();

		/* If we got a cancel signal in analysis or planning, quit */
		CHECK_FOR_INTERRUPTS();

		/*
		 * Create unnamed portal to run the query or queries in. If there
		 * already is one, silently drop it.
		 */
		portal = CreatePortal("", true, true);
		/* Don't display the portal in pg_cursors */
		portal->visible = false;

		/*
		 * We don't have to copy anything into the portal, because everything
		 * we are passing here is in MessageContext, which will outlive the
		 * portal anyway.
		 */
		PortalDefineQuery(portal,
						  NULL,
						  query_string,
						  commandTag,
						  plantree_list,
						  NULL);

		/*
		 * Start the portal.  No parameters here.
		 */
		PortalStart(portal, NULL, 0, InvalidSnapshot);

		/*
		 * Select the appropriate output format: text unless we are doing a
		 * FETCH from a binary cursor.  (Pretty grotty to have to do this here
		 * --- but it avoids grottiness in other places.  Ah, the joys of
		 * backward compatibility...)
		 */
		format = 0;				/* TEXT is default */
		if (IsA(parsetree, FetchStmt))
		{
			FetchStmt  *stmt = (FetchStmt *) parsetree;

			if (!stmt->ismove)
			{
				Portal		fportal = GetPortalByName(stmt->portalname);

				if (PortalIsValid(fportal) &&
					(fportal->cursorOptions & CURSOR_OPT_BINARY))
					format = 1; /* BINARY */
			}
		}
		PortalSetResultFormat(portal, 1, &format);

		/*
		 * Now we can create the destination receiver object.
		 *
		 * If we sending the last result only, throw output away unless it's
		 * the last command.
		 */
		--commands_remaining;
		if (last_result_only && commands_remaining > 0)
			receiver = CreateDestReceiver(DestNone);
		else
		{
			receiver = CreateDestReceiver(dest);
			if (dest == DestRemote)
				SetRemoteDestReceiverParams(receiver, portal);
		}

		/*
		 * Switch back to transaction context for execution.
		 */
		MemoryContextSwitchTo(oldcontext);

		/*
		 * Run the portal to completion, and then drop it (and the receiver).
		 */
		(void) PortalRun(portal,
						 FETCH_ALL,
						 isTopLevel,
						 receiver,
						 receiver,
						 completionTag);

		(*receiver->rDestroy) (receiver);

		PortalDrop(portal, false);

		if (IsA(parsetree, TransactionStmt))
		{
			/*
			 * If this was a transaction control statement, commit it. We will
			 * start a new xact command for the next command (if any). Note
			 * that if allow_transactions is false then we should never get to
			 * this point.
			 */
			finish_xact_command();
		}
		else if (lnext(parsetree_item) == NULL)
		{
			/*
			 * If this is the last parsetree of the query string, close down
			 * transaction statement before reporting command-complete.  This
			 * is so that any end-of-transaction errors are reported before
			 * the command-complete message is issued, to avoid confusing
			 * clients who will expect either a command-complete message or an
			 * error, not one and then the other.  But for compatibility with
			 * historical Postgres behavior, we do not force a transaction
			 * boundary between queries appearing in a single query string.
			 */
			finish_xact_command();
		}
		else
		{
			/*
			 * We need a CommandCounterIncrement after every query, except
			 * those that start or end a transaction block.
			 */
			CommandCounterIncrement();
		}

		/*
		 * Tell client that we're done with this query.  Note we emit exactly
		 * one EndCommand report for each raw parsetree, thus one for each SQL
		 * command the client sent, regardless of rewriting. (But a command
		 * aborted by error will not send an EndCommand report at all.)
		 */
		EndCommand(completionTag, dest);
	}							/* end loop over parsetrees */

	/*
	 * Close down transaction statement, if one is open.
	 */
	finish_xact_command();

	/*
	 * If there were no parsetrees, return EmptyQueryResponse message.
	 */
	if (!parsetree_list)
		NullCommand(dest);

	/*
	 * Emit duration logging if appropriate.
	 */
	switch (check_log_duration(msec_str, was_logged))
	{
		case 1:
			ereport(LOG,
					(errmsg("duration: %s ms", msec_str),
					 errhidestmt(true)));
			break;
		case 2:
			ereport(LOG,
					(errmsg("duration: %s ms  statement: %s",
							msec_str, query_string),
					 errhidestmt(true),
					 errdetail_execute(parsetree_list)));
			break;
	}

}