/*
 * Copyright (c) 2021 IBM Corp and others.
 *
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v2.0
 * and Eclipse Distribution License v1.0 which accompany this distribution.
 *
 * The Eclipse Public License is available at
 *    https://www.eclipse.org/legal/epl-2.0/
 * and the Eclipse Distribution License is available at
 *   http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * Contributors:
 *    Seth Hoenig
 *    Allan Stockdill-Mander
 *    Mike Robertson
 */

package mqtt

import (
	"errors"
	"strings"
)

// ErrInvalidQos is the error returned when an packet is to be sent
// with an invalid Qos value
var ErrInvalidQos = errors.New("invalid QoS")

// ErrInvalidTopicEmptyString is the error returned when a topic string
// is passed in that is 0 length
var ErrInvalidTopicEmptyString = errors.New("invalid Topic; empty string")

// ErrInvalidTopicMultilevel is the error returned when a topic string
// is passed in that has the multi level wildcard in any position but
// the last
var ErrInvalidTopicMultilevel = errors.New("invalid Topic; multi-level wildcard must be last level")

// Topic Names and Topic Filters
// The MQTT v3.1.1 spec clarifies a number of ambiguities with regard
// to the validity of Topic strings.
// - A Topic must be between 1 and 65535 bytes.
// - A Topic is case sensitive.
// - A Topic may contain whitespace.
// - A Topic containing a leading forward slash is different than a Topic without.
// - A Topic may be "/" (two levels, both empty string).
// - A Topic must be UTF-8 encoded.
// - A Topic may contain any number of levels.
// - A Topic may contain an empty level (two forward slashes in a row).
// - A TopicName may not contain a wildcard.
// - A TopicFilter may only have a # (multi-level) wildcard as the last level.
// - A TopicFilter may contain any number of + (single-level) wildcards.
// - A TopicFilter with a # will match the absence of a level
//     Example:  a subscription to "foo/#" will match messages published to "foo".

func validateSubscribeMap(subs map[string]byte) ([]string, []byte, error) {
	if len(subs) == 0 {
		return nil, nil, errors.New("invalid subscription; subscribe map must not be empty")
	}

	var topics []string
	var qoss []byte
	for topic, qos := range subs {
		if err := validateTopicAndQos(topic, qos); err != nil {
			return nil, nil, err
		}
		topics = append(topics, topic)
		qoss = append(qoss, qos)
	}

	return topics, qoss, nil
}

func validateTopicAndQos(topic string, qos byte) error {
	if len(topic) == 0 {
		return ErrInvalidTopicEmptyString
	}

	levels := strings.Split(topic, "/")
	for i, level := range levels {
		if level == "#" && i != len(levels)-1 {
			return ErrInvalidTopicMultilevel
		}
	}

	if qos > 2 {
		return ErrInvalidQos
	}
	return nil
}