1package awsrulesfn
 2
 3import (
 4	"strings"
 5)
 6
 7// ARN provides AWS ARN components broken out into a data structure.
 8type ARN struct {
 9	Partition  string
10	Service    string
11	Region     string
12	AccountId  string
13	ResourceId OptionalStringSlice
14}
15
16const (
17	arnDelimiters      = ":"
18	resourceDelimiters = "/:"
19	arnSections        = 6
20	arnPrefix          = "arn:"
21
22	// zero-indexed
23	sectionPartition = 1
24	sectionService   = 2
25	sectionRegion    = 3
26	sectionAccountID = 4
27	sectionResource  = 5
28)
29
30// ParseARN returns an [ARN] value parsed from the input string provided. If
31// the ARN cannot be parsed nil will be returned, and error added to
32// [ErrorCollector].
33func ParseARN(input string) *ARN {
34	if !strings.HasPrefix(input, arnPrefix) {
35		return nil
36	}
37
38	sections := strings.SplitN(input, arnDelimiters, arnSections)
39	if numSections := len(sections); numSections != arnSections {
40		return nil
41	}
42
43	if sections[sectionPartition] == "" {
44		return nil
45	}
46	if sections[sectionService] == "" {
47		return nil
48	}
49	if sections[sectionResource] == "" {
50		return nil
51	}
52
53	return &ARN{
54		Partition:  sections[sectionPartition],
55		Service:    sections[sectionService],
56		Region:     sections[sectionRegion],
57		AccountId:  sections[sectionAccountID],
58		ResourceId: splitResource(sections[sectionResource]),
59	}
60}
61
62// splitResource splits the resource components by the ARN resource delimiters.
63func splitResource(v string) []string {
64	var parts []string
65	var offset int
66
67	for offset <= len(v) {
68		idx := strings.IndexAny(v[offset:], "/:")
69		if idx < 0 {
70			parts = append(parts, v[offset:])
71			break
72		}
73		parts = append(parts, v[offset:idx+offset])
74		offset += idx + 1
75	}
76
77	return parts
78}
79
80// OptionalStringSlice provides a helper to safely get the index of a string
81// slice that may be out of bounds. Returns pointer to string if index is
82// valid. Otherwise returns nil.
83type OptionalStringSlice []string
84
85// Get returns a string pointer of the string at index i if the index is valid.
86// Otherwise returns nil.
87func (s OptionalStringSlice) Get(i int) *string {
88	if i < 0 || i >= len(s) {
89		return nil
90	}
91
92	v := s[i]
93	return &v
94}