feat: add assertIsBoardName() function

Also changed the expression to validate board names to check that the
name starts with three letters and ends with three numbers.

This has been defined this way to match `users` realm implementation.
See: gnolang#2827

In a next iteration we can support vanity names for boards, once vanity
names are supported for the `users` realm.

examples/gno.land/r/demo/boards2/board.gno

@@ -1,6 +1,7 @@
 package boards
 
 import (
+	"regexp"
 	"std"
 	"strconv"
 	"time"
@@ -9,8 +10,9 @@ import (
 	"gno.land/p/moul/txlink"
 )
 
-//----------------------------------------
-// Board
+var reBoardName = regexp.MustCompile(`^[a-z]{3}[_a-z0-9]{0,23}[0-9]{3}$`)
+
+// TODO: Move post and board to a package to improve API and reduce realm size?
 
 type BoardID uint64
 
@@ -30,9 +32,7 @@ type Board struct {
 }
 
 func newBoard(id BoardID, url string, name string, creator std.Address) *Board {
-	if !reName.MatchString(name) {
-		panic("invalid name: " + name)
-	}
+	assertIsBoardName(name)
 	exists := gBoardsByName.Has(name)
 	if exists {
 		panic("board already exists")
@@ -58,6 +58,7 @@ func NewPrivateBoard(url string, name string, creator std.Address) *Board {
 }
 */
 
+// TODO: Do we want to support private boards? If so move forward with implementation.
 func (board *Board) IsPrivate() bool {
 	return board.id == 0
 }
@@ -89,6 +90,7 @@ func (board *Board) DeleteThread(pid PostID) {
 	}
 }
 
+// TODO: Change HasPermission to use a new authorization interface's `CanDo()`
 func (board *Board) HasPermission(addr std.Address, perm Permission) bool {
 	if board.creator == addr {
 		switch perm {
@@ -137,3 +139,9 @@ func (board *Board) GetURLFromThreadAndReplyID(threadID, replyID PostID) string
 func (board *Board) GetPostFormURL() string {
 	return txlink.URL("CreateThread", "bid", board.id.String())
 }
+
+func assertIsBoardName(name string) {
+	if !reBoardName.MatchString(name) {
+		panic("invalid board name: " + name)
+	}
+}

examples/gno.land/r/demo/boards2/boards.gno

@@ -1,22 +1,13 @@
 package boards
 
 import (
-	"regexp"
-
 	"gno.land/p/demo/avl"
 )
 
-//----------------------------------------
-// Realm (package) state
-
+// TODO: Create a Boards or App struct to handle counter and tree indexes
 var (
 	gBoards         avl.Tree    // id -> *Board
 	gBoardsCtr      int         // increments Board.id
 	gBoardsByName   avl.Tree    // name -> *Board
 	gDefaultAnonFee = 100000000 // minimum fee required if anonymous
 )
-
-//----------------------------------------
-// Constants
-
-var reName = regexp.MustCompile(`^[a-z]+[_a-z0-9]{2,29}$`)