/*
Copyright 2014 Workiva, LLC

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

 http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package yfast

import "github.com/Workiva/go-datastructures/trie/xfast"

// iteratorExhausted is a magic value for an index to tell us
// that the iterator has been exhausted.
const iteratorExhausted = -2

// iterExhausted is a helper function to tell us if an iterator
// has been exhausted.
func iterExhausted(iter *Iterator) bool {
	return iter.index == iteratorExhausted
}

// Iterator will iterate of the results of a query.
type Iterator struct {
	xfastIterator *xfast.Iterator
	index         int
	entries       *entriesWrapper
}

// Next will return a bool indicating if another value exists
// in the iterator.
func (iter *Iterator) Next() bool {
	if iterExhausted(iter) {
		return false
	}
	iter.index++
	if iter.index >= len(iter.entries.entries) {
		next := iter.xfastIterator.Next()
		if !next {
			iter.index = iteratorExhausted
			return false
		}
		var ok bool
		iter.entries, ok = iter.xfastIterator.Value().(*entriesWrapper)
		if !ok {
			iter.index = iteratorExhausted
			return false
		}
		iter.index = 0
	}

	return true
}

// Value will return the Entry representing the iterator's current position.
// If no Entry exists at the present condition, the iterator is
// exhausted and this method will return nil.
func (iter *Iterator) Value() Entry {
	if iterExhausted(iter) {
		return nil
	}

	if iter.entries == nil || iter.index < 0 || iter.index >= len(iter.entries.entries) {
		return nil
	}

	return iter.entries.entries[iter.index]
}

// exhaust is a helper function that will exhaust this iterator
// and return a list of entries.  This is for internal use only.
func (iter *Iterator) exhaust() Entries {
	entries := make(Entries, 0, 100)
	for it := iter; it.Next(); {
		entries = append(entries, it.Value())
	}

	return entries
}

// nilIterator is an iterator that will always return false
// from Next() and nil for Value().
func nilIterator() *Iterator {
	return &Iterator{
		index: iteratorExhausted,
	}
}