Add pushover notifications, this should be a super basic MVP

vendor/github.com/dgraph-io/badger/trie/trie.go

@@ -0,0 +1,104 @@
+/*
+ * Copyright 2019 Dgraph Labs, Inc. and Contributors
+ *
+ * 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 trie
+
+type node struct {
+	children map[byte]*node
+	ids      []uint64
+}
+
+func newNode() *node {
+	return &node{
+		children: make(map[byte]*node),
+		ids:      []uint64{},
+	}
+}
+
+// Trie datastructure.
+type Trie struct {
+	root *node
+}
+
+// NewTrie returns Trie.
+func NewTrie() *Trie {
+	return &Trie{
+		root: newNode(),
+	}
+}
+
+// Add adds the id in the trie for the given prefix path.
+func (t *Trie) Add(prefix []byte, id uint64) {
+	node := t.root
+	for _, val := range prefix {
+		child, ok := node.children[val]
+		if !ok {
+			child = newNode()
+			node.children[val] = child
+		}
+		node = child
+	}
+	// We only need to add the id to the last node of the given prefix.
+	node.ids = append(node.ids, id)
+}
+
+// Get returns prefix matched ids for the given key.
+func (t *Trie) Get(key []byte) map[uint64]struct{} {
+	out := make(map[uint64]struct{})
+	node := t.root
+	// If root has ids that means we have subscribers for "nil/[]byte{}"
+	// prefix. Add them to the list.
+	if len(node.ids) > 0 {
+		for _, i := range node.ids {
+			out[i] = struct{}{}
+		}
+	}
+	for _, val := range key {
+		child, ok := node.children[val]
+		if !ok {
+			break
+		}
+		// We need ids of the all the node in the matching key path.
+		for _, id := range child.ids {
+			out[id] = struct{}{}
+		}
+		node = child
+	}
+	return out
+}
+
+// Delete will delete the id if the id exist in the given index path.
+func (t *Trie) Delete(index []byte, id uint64) {
+	node := t.root
+	for _, val := range index {
+		child, ok := node.children[val]
+		if !ok {
+			return
+		}
+		node = child
+	}
+	// We're just removing the id not the hanging path.
+	out := node.ids[:0]
+	for _, val := range node.ids {
+		if val != id {
+			out = append(out, val)
+		}
+	}
+	for i := len(out); i < len(node.ids); i++ {
+		node.ids[i] = 0 // garbage collecting
+	}
+	node.ids = out
+}