From a68ddf1f2ab010a82408e98fd706d519ebd86d65 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Toma=C5=BE=20Jerman?= <tomaz.jerman121@gmail.com>
Date: Thu, 9 Jun 2022 15:04:11 +0200
Subject: [PATCH] Add a resoruce indexing utility struct

The struct indexes resources which lowers set search complexity
from linear to constant.
---
 pkg/resource/resource.go      | 80 +++++++++++++++++++++++++++++++++++
 pkg/resource/resource_test.go | 78 ++++++++++++++++++++++++++++++++++
 2 files changed, 158 insertions(+)
 create mode 100644 pkg/resource/resource.go
 create mode 100644 pkg/resource/resource_test.go

diff --git a/pkg/resource/resource.go b/pkg/resource/resource.go
new file mode 100644
index 000000000..787762abc
--- /dev/null
+++ b/pkg/resource/resource.go
@@ -0,0 +1,80 @@
+package resource
+
+type (
+	IndexNode struct {
+		children map[string]*IndexNode
+
+		values []interface{}
+	}
+)
+
+func NewIndex() *IndexNode {
+	return &IndexNode{
+		children: make(map[string]*IndexNode),
+		values:   make([]interface{}, 0),
+	}
+}
+
+func (in *IndexNode) Add(value interface{}, pp ...[]string) {
+	if in == nil {
+		*in = *NewIndex()
+	}
+
+	if len(pp) == 1 {
+		for _, identifier := range pp[0] {
+			if identifier == "*" {
+				in.values = append(in.values, value)
+			} else {
+				nn := in.children[identifier]
+				if nn == nil {
+					nn = NewIndex()
+					in.children[identifier] = nn
+				}
+
+				nn.values = append(nn.values, value)
+			}
+		}
+		return
+	}
+
+	p := pp[0]
+	for _, identifier := range p {
+		if identifier == "*" {
+			in.values = append(in.values, value)
+			continue
+		}
+
+		if _, ok := in.children[identifier]; !ok {
+			in.children[identifier] = NewIndex()
+		}
+
+		in.children[identifier].Add(value, pp[1:]...)
+	}
+}
+
+func (di *IndexNode) Collect(pp ...[]string) (out []interface{}) {
+	if len(pp) == 0 {
+		if len(di.values) > 0 {
+			out = append(out, di.values...)
+		}
+		return
+	}
+
+	p := pp[0]
+	for _, identifier := range p {
+		skip := false
+		if _, ok := di.children[identifier]; ok {
+			aux := di.children[identifier].Collect(pp[1:]...)
+			out = append(out, aux...)
+
+			skip = len(aux) > 0
+		}
+
+		out = append(out, di.values...)
+		if skip {
+			break
+		}
+	}
+
+	return
+}
diff --git a/pkg/resource/resource_test.go b/pkg/resource/resource_test.go
new file mode 100644
index 000000000..56085296b
--- /dev/null
+++ b/pkg/resource/resource_test.go
@@ -0,0 +1,78 @@
+package resource
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func pathHelper(pp ...string) (out [][]string) {
+	for _, p := range pp {
+		out = append(out, []string{p})
+	}
+	return
+}
+
+func TestSimplePath(t *testing.T) {
+	n := NewIndex()
+
+	n.Add(1, pathHelper("a")...)
+
+	out := n.Collect(pathHelper("a")...)
+	require.Len(t, out, 1)
+	require.Equal(t, 1, out[0])
+}
+
+func TestSimpleLongPath(t *testing.T) {
+	n := NewIndex()
+
+	n.Add(1, pathHelper("a", "b", "c")...)
+
+	out := n.Collect(pathHelper("a", "b", "c")...)
+	require.Len(t, out, 1)
+	require.Equal(t, 1, out[0])
+}
+
+func TestWildSimplePath(t *testing.T) {
+	n := NewIndex()
+
+	n.Add(1, pathHelper("a", "*")...)
+
+	out := n.Collect(pathHelper("a", "b")...)
+	require.Len(t, out, 1)
+	require.Equal(t, 1, out[0])
+}
+
+func TestComplex(t *testing.T) {
+	n := NewIndex()
+
+	n.Add(1, pathHelper("resource", "lvl1.id1", "lvl2.id2", "res.id")...)
+	n.Add(2, pathHelper("resource", "lvl1.id1", "lvl2.id2", "*")...)
+	n.Add(3, pathHelper("resource", "lvl1.id1", "lvl2.id2", "*")...)
+	n.Add(4, pathHelper("resource", "*", "*", "*")...)
+
+	var out []interface{}
+
+	t.Run("full path", func(t *testing.T) {
+		out = n.Collect(pathHelper("resource", "lvl1.id1", "lvl2.id2", "res.id")...)
+		require.Len(t, out, 4)
+		require.Equal(t, []interface{}{1, 2, 3, 4}, out)
+	})
+
+	t.Run("full path; id not matching", func(t *testing.T) {
+		out = n.Collect(pathHelper("resource", "lvl1.id1", "lvl2.id2", "invalid")...)
+		require.Len(t, out, 3)
+		require.Equal(t, []interface{}{2, 3, 4}, out)
+	})
+
+	t.Run("partial matching path 1", func(t *testing.T) {
+		out = n.Collect(pathHelper("resource", "invald", "invalid", "invalid")...)
+		require.Len(t, out, 1)
+		require.Equal(t, []interface{}{4}, out)
+	})
+
+	t.Run("not matching path", func(t *testing.T) {
+		out = n.Collect(pathHelper("invalid", "invald", "invalid", "invalid")...)
+		require.Len(t, out, 0)
+	})
+}