urlshort.gno

  1// Package urlshort is a simple on-chain URL alias registry.
  2//
  3// Callers register an `alias -> url` mapping they own. An alias can only be
  4// claimed once; the owner may later update the target URL, but nobody else can
  5// overwrite an alias they do not own. A per-alias click counter is bumped every
  6// time the alias is resolved through Render("/<alias>").
  7package urlshort
  8
  9import (
 10	"strings"
 11
 12	"chain"
 13	"chain/runtime/unsafe"
 14
 15	"gno.land/p/moul/kit/ui/v0"
 16	"gno.land/p/nt/avl/v0"
 17)
 18
 19// entry is the persisted record for a single alias.
 20type entry struct {
 21	url    string
 22	owner  address
 23	note   string
 24	clicks int
 25}
 26
 27// aliases maps alias (string) -> *entry, kept in an avl.Tree for deterministic
 28// iteration order in Render.
 29var aliases avl.Tree
 30
 31// isAlphanumeric reports whether s is non-empty and made only of [0-9A-Za-z].
 32func isAlphanumeric(s string) bool {
 33	if s == "" {
 34		return false
 35	}
 36	for _, c := range s {
 37		switch {
 38		case c >= '0' && c <= '9':
 39		case c >= 'a' && c <= 'z':
 40		case c >= 'A' && c <= 'Z':
 41		default:
 42			return false
 43		}
 44	}
 45	return true
 46}
 47
 48// Shorten registers `alias -> url` owned by the caller.
 49//
 50// Rules:
 51//   - alias must be non-empty and alphanumeric;
 52//   - url must be non-empty;
 53//   - if the alias is unclaimed, it is created owned by the caller;
 54//   - if it is already claimed by the caller, the url/note are updated;
 55//   - if it is claimed by someone else, the call aborts.
 56func Shorten(cur realm, alias string, url string, note string) {
 57	if !isAlphanumeric(alias) {
 58		panic("alias must be non-empty and alphanumeric")
 59	}
 60	if url == "" {
 61		panic("url must be non-empty")
 62	}
 63
 64	caller := unsafe.PreviousRealm().Address()
 65
 66	if v := aliases.Get(alias); v != nil {
 67		e := v.(*entry)
 68		if e.owner != caller {
 69			panic("alias already taken by another owner")
 70		}
 71		e.url = url
 72		e.note = note
 73		chain.Emit("AliasUpdated", "alias", alias, "owner", caller.String())
 74		return
 75	}
 76
 77	e := &entry{url: url, owner: caller, note: note, clicks: 0}
 78	aliases.Set(alias, e)
 79	chain.Emit("AliasCreated", "alias", alias, "owner", caller.String())
 80}
 81
 82// Remove deletes an alias owned by the caller. Aborts if the alias does not
 83// exist or the caller is not the owner.
 84func Remove(cur realm, alias string) {
 85	v := aliases.Get(alias)
 86	if v == nil {
 87		panic("alias not found")
 88	}
 89	e := v.(*entry)
 90	caller := unsafe.PreviousRealm().Address()
 91	if e.owner != caller {
 92		panic("only the owner can remove an alias")
 93	}
 94	aliases.Remove(alias)
 95	chain.Emit("AliasRemoved", "alias", alias, "owner", caller.String())
 96}
 97
 98// Lookup returns the target url for an alias and whether it exists. It is a
 99// read-only helper and does NOT increment the click counter.
100func Lookup(alias string) (string, bool) {
101	v := aliases.Get(alias)
102	if v == nil {
103		return "", false
104	}
105	return v.(*entry).url, true
106}
107
108// Render renders Markdown. The root path lists every alias; "/<alias>" shows a
109// single alias detail and bumps its click counter.
110func Render(path string) string {
111	if path == "" || path == "/" {
112		return renderIndex()
113	}
114
115	alias := strings.TrimPrefix(path, "/")
116	v := aliases.Get(alias)
117	if v == nil {
118		return "# URL Shortener\n\nNo alias named `" + alias + "`.\n\n[← all aliases](/)\n"
119	}
120
121	e := v.(*entry)
122	e.clicks++
123
124	var b strings.Builder
125	b.WriteString("# 🔗 " + alias + "\n\n")
126	b.WriteString("**Target:** <" + e.url + ">\n\n")
127	b.WriteString("**Owner:** " + e.owner.String() + "\n\n")
128	if e.note != "" {
129		b.WriteString("**Note:** " + e.note + "\n\n")
130	}
131	b.WriteString("**Clicks:** " + itoa(e.clicks) + "\n\n")
132	b.WriteString("[← all aliases](/)\n")
133	return b.String()
134}
135
136func renderIndex() string {
137	var b strings.Builder
138	b.WriteString("# 🔗 URL Shortener\n\n")
139
140	if aliases.Size() == 0 {
141		b.WriteString("_No aliases registered yet._\n\n")
142		b.WriteString("Call `Shorten(alias, url, note)` to register one.\n")
143		return b.String()
144	}
145
146	b.WriteString("| Alias | Target | Owner | Clicks |\n")
147	b.WriteString("|-------|--------|-------|--------|\n")
148	aliases.Iterate("", "", func(key string, value interface{}) bool {
149		e := value.(*entry)
150		b.WriteString("| [" + key + "](/" + key + ") | <" + e.url + "> | " +
151			ui.Addr(e.owner) + " | " + itoa(e.clicks) + " |\n")
152		return false
153	})
154	b.WriteString("\nTotal aliases: " + itoa(aliases.Size()) + "\n")
155	return b.String()
156}
157
158// itoa converts a non-negative int to its decimal string without importing
159// strconv (kept minimal & deterministic).
160func itoa(n int) string {
161	if n == 0 {
162		return "0"
163	}
164	neg := n < 0
165	if neg {
166		n = -n
167	}
168	var buf [20]byte
169	i := len(buf)
170	for n > 0 {
171		i--
172		buf[i] = byte('0' + n%10)
173		n /= 10
174	}
175	if neg {
176		i--
177		buf[i] = '-'
178	}
179	return string(buf[i:])
180}