chore(examples): update userbook example to use avl_pager (gnolang#3251)

<!-- please provide a detailed description of the changes made in this
pull request. -->

## Description

Updates the `r/demo/userbook` example to use the `avl_pager` package.

<details><summary>Contributors' checklist...</summary>

- [ ] Added new tests, or not needed, or not feasible
- [ ] Provided an example (e.g. screenshot) to aid review or the PR is
self-explanatory
- [ ] Updated the official documentation or not needed
- [ ] No breaking changes were made, or a `BREAKING CHANGE: xxx` message
was included in the description
- [ ] Added references to related issues and PRs
- [ ] Provided any useful hints for running manual tests
</details>

---------

Co-authored-by: Morgan <[email protected]>

examples/gno.land/r/demo/userbook/render.gno

@@ -0,0 +1,51 @@
+// Package userbook demonstrates a small userbook system working with gnoweb
+package userbook
+
+import (
+	"sort"
+	"strconv"
+
+	"gno.land/p/demo/avl/pager"
+	"gno.land/p/demo/ufmt"
+	"gno.land/p/moul/txlink"
+)
+
+func Render(path string) string {
+	p := pager.NewPager(signupsTree, 2)
+	page := p.MustGetPageByPath(path)
+
+	out := "# Welcome to UserBook!\n\n"
+
+	out += ufmt.Sprintf("## [Click here to sign up!](%s)\n\n", txlink.Call("SignUp"))
+	out += "---\n\n"
+
+	var sorted sortedSignups
+	for _, item := range page.Items {
+		sorted = append(sorted, item.Value.(*Signup))
+	}
+
+	sort.Sort(sorted)
+
+	for _, item := range sorted {
+		out += ufmt.Sprintf("- **User #%d - %s - signed up on %s**\n\n", item.ordinal, item.address.String(), item.timestamp.Format("02-01-2006 15:04:05"))
+	}
+
+	out += "---\n\n"
+	out += "**Page " + strconv.Itoa(page.PageNumber) + " of " + strconv.Itoa(page.TotalPages) + "**\n\n"
+	out += page.Selector() // Repeat selector for ease of navigation
+	return out
+}
+
+type sortedSignups []*Signup
+
+func (s sortedSignups) Swap(i, j int) {
+	s[i], s[j] = s[j], s[i]
+}
+
+func (s sortedSignups) Len() int {
+	return len(s)
+}
+
+func (s sortedSignups) Less(i, j int) bool {
+	return s[i].timestamp.Before(s[j].timestamp)
+}

examples/gno.land/r/demo/userbook/userbook.gno

@@ -1,158 +1,46 @@
-// This realm demonstrates a small userbook system working with gnoweb
+// Package userbook demonstrates a small userbook system working with gnoweb
 package userbook
 
 import (
 	"std"
-	"strconv"
+	"time"
 
 	"gno.land/p/demo/avl"
-	"gno.land/p/demo/mux"
 	"gno.land/p/demo/ufmt"
 )
 
 type Signup struct {
-	account string
-	height  int64
+	address   std.Address
+	ordinal   int
+	timestamp time.Time
 }
 
-// signups - keep a slice of signed up addresses efficient pagination
-var signups []Signup
+var signupsTree = avl.NewTree()
 
-// tracker - keep track of who signed up
-var (
-	tracker *avl.Tree
-	router  *mux.Router
-)
-
-const (
-	defaultPageSize = 20
-	pathArgument    = "number"
-	subPath         = "page/{" + pathArgument + "}"
-	signUpEvent     = "SignUp"
-)
+const signUpEvent = "SignUp"
 
 func init() {
-	// Set up tracker tree
-	tracker = avl.NewTree()
-
-	// Set up route handling
-	router = mux.NewRouter()
-	router.HandleFunc("", renderHelper)
-	router.HandleFunc(subPath, renderHelper)
-
-	// Sign up the deployer
-	SignUp()
+	SignUp() // Sign up the deployer
 }
 
 func SignUp() string {
 	// Get transaction caller
-	caller := std.PrevRealm().Addr().String()
-	height := std.GetHeight()
+	caller := std.PrevRealm().Addr()
 
 	// Check if the user is already signed up
-	if _, exists := tracker.Get(caller); exists {
+	if _, exists := signupsTree.Get(caller.String()); exists {
 		panic(caller + " is already signed up!")
 	}
 
+	now := time.Now()
 	// Sign up the user
-	tracker.Set(caller, struct{}{})
-	signup := Signup{
-		caller,
-		height,
-	}
-
-	signups = append(signups, signup)
-	std.Emit(signUpEvent, "SignedUpAccount", signup.account)
+	signupsTree.Set(caller.String(), &Signup{
+		std.PrevRealm().Addr(),
+		signupsTree.Size(),
+		now,
+	})
 
-	return ufmt.Sprintf("%s added to userbook up at block #%d!", signup.account, signup.height)
-}
-
-func GetSignupsInRange(page, pageSize int) ([]Signup, int) {
-	if page < 1 {
-		panic("page number cannot be less than 1")
-	}
-
-	if pageSize < 1 || pageSize > 50 {
-		panic("page size must be from 1 to 50")
-	}
-
-	// Pagination
-	// Calculate indexes
-	startIndex := (page - 1) * pageSize
-	endIndex := startIndex + pageSize
-
-	// If page does not contain any users
-	if startIndex >= len(signups) {
-		return nil, -1
-	}
-
-	// If page contains fewer users than the page size
-	if endIndex > len(signups) {
-		endIndex = len(signups)
-	}
-
-	return signups[startIndex:endIndex], endIndex
-}
-
-func renderHelper(res *mux.ResponseWriter, req *mux.Request) {
-	totalSignups := len(signups)
-	res.Write("# Welcome to UserBook!\n\n")
-
-	// Get URL parameter
-	page, err := strconv.Atoi(req.GetVar("number"))
-	if err != nil {
-		page = 1 // render first page on bad input
-	}
-
-	// Fetch paginated signups
-	fetchedSignups, endIndex := GetSignupsInRange(page, defaultPageSize)
-	// Handle empty page case
-	if len(fetchedSignups) == 0 {
-		res.Write("No users on this page!\n\n")
-		res.Write("---\n\n")
-		res.Write("[Back to Page #1](/r/demo/userbook:page/1)\n\n")
-		return
-	}
-
-	// Write page title
-	res.Write(ufmt.Sprintf("## UserBook - Page #%d:\n\n", page))
-
-	// Write signups
-	pageStartIndex := defaultPageSize * (page - 1)
-	for i, signup := range fetchedSignups {
-		out := ufmt.Sprintf("#### User #%d - %s - signed up at Block #%d\n", pageStartIndex+i, signup.account, signup.height)
-		res.Write(out)
-	}
-
-	res.Write("---\n\n")
-
-	// Write UserBook info
-	latestSignupIndex := totalSignups - 1
-	res.Write(ufmt.Sprintf("#### Total users: %d\n", totalSignups))
-	res.Write(ufmt.Sprintf("#### Latest signup: User #%d at Block #%d\n", latestSignupIndex, signups[latestSignupIndex].height))
-
-	res.Write("---\n\n")
-
-	// Write page number
-	res.Write(ufmt.Sprintf("You're viewing page #%d", page))
-
-	// Write navigation buttons
-	var prevPage string
-	var nextPage string
-	// If we are on any page that is not the first page
-	if page > 1 {
-		prevPage = ufmt.Sprintf(" - [Previous page](/r/demo/userbook:page/%d)", page-1)
-	}
-
-	// If there are more pages after the current one
-	if endIndex < totalSignups {
-		nextPage = ufmt.Sprintf(" - [Next page](/r/demo/userbook:page/%d)\n\n", page+1)
-	}
-
-	res.Write(prevPage)
-	res.Write(nextPage)
-}
+	std.Emit(signUpEvent, "SignedUpAccount", caller.String())
 
-func Render(path string) string {
-	return router.Render(path)
+	return ufmt.Sprintf("%s added to userbook! Timestamp: %s", caller.String(), now.Format(time.RFC822Z))
 }