Initial QSfera import

Server/vendor/github.com/open-policy-agent/opa/v1/util/queue.go

@@ -0,0 +1,113 @@
+// Copyright 2017 The OPA Authors.  All rights reserved.
+// Use of this source code is governed by an Apache2
+// license that can be found in the LICENSE file.
+
+package util
+
+// LIFO represents a simple LIFO queue.
+type LIFO struct {
+	top  *queueNode
+	size int
+}
+
+type queueNode struct {
+	v    T
+	next *queueNode
+}
+
+// NewLIFO returns a new LIFO queue containing elements ts starting with the
+// left-most argument at the bottom.
+func NewLIFO(ts ...T) *LIFO {
+	s := &LIFO{}
+	for i := range ts {
+		s.Push(ts[i])
+	}
+	return s
+}
+
+// Push adds a new element onto the LIFO.
+func (s *LIFO) Push(t T) {
+	node := &queueNode{v: t, next: s.top}
+	s.top = node
+	s.size++
+}
+
+// Peek returns the top of the LIFO. If LIFO is empty, returns nil, false.
+func (s *LIFO) Peek() (T, bool) {
+	if s.top == nil {
+		return nil, false
+	}
+	return s.top.v, true
+}
+
+// Pop returns the top of the LIFO and removes it. If LIFO is empty returns
+// nil, false.
+func (s *LIFO) Pop() (T, bool) {
+	if s.top == nil {
+		return nil, false
+	}
+	node := s.top
+	s.top = node.next
+	s.size--
+	return node.v, true
+}
+
+// Size returns the size of the LIFO.
+func (s *LIFO) Size() int {
+	return s.size
+}
+
+// FIFO represents a simple FIFO queue.
+type FIFO struct {
+	front *queueNode
+	back  *queueNode
+	size  int
+}
+
+// NewFIFO returns a new FIFO queue containing elements ts starting with the
+// left-most argument at the front.
+func NewFIFO(ts ...T) *FIFO {
+	s := &FIFO{}
+	for i := range ts {
+		s.Push(ts[i])
+	}
+	return s
+}
+
+// Push adds a new element onto the LIFO.
+func (s *FIFO) Push(t T) {
+	node := &queueNode{v: t, next: nil}
+	if s.front == nil {
+		s.front = node
+		s.back = node
+	} else {
+		s.back.next = node
+		s.back = node
+	}
+	s.size++
+}
+
+// Peek returns the top of the LIFO. If LIFO is empty, returns nil, false.
+func (s *FIFO) Peek() (T, bool) {
+	if s.front == nil {
+		return nil, false
+	}
+	return s.front.v, true
+}
+
+// Pop returns the top of the LIFO and removes it. If LIFO is empty returns
+// nil, false.
+func (s *FIFO) Pop() (T, bool) {
+	if s.front == nil {
+		return nil, false
+	}
+	node := s.front
+	s.front = node.next
+	s.size--
+	return node.v, true
+}
+
+// Size returns the size of the LIFO.
+func (s *FIFO) Size() int {
+	return s.size
+}