feat(shortcuts): regex rewrite rules for host shortcuts

shortcuts.rewrites applies regex replacements after the domain suffix
is stripped, e.g. ^([a-z]+)[0-9]+- -> $1 turns fsn1-bx1.hoster.de into
fsnbx1. The shortcut works for connecting (cached hosts), shell
aliases, and Tab completion, where it is offered when the full name
does not match the typed text. Rules are editable in netssh configure,
and netssh alias --test HOSTNAME shows a name's shortcut and the cached
hosts it matches.

The shortcut lookup only ran when domains or strip_hyphens were set;
it now also runs for rewrite-only configurations.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/shortcuts/shortcuts.go

@@ -1,13 +1,30 @@
 package shortcuts
 
 import (
+	"regexp"
 	"strings"
+	"sync"
 
 	"git.zb-server.de/Sebi/ssh-netbox-wrapper/internal/config"
 )
 
-// Normalize strips configured domain suffixes and optionally hyphens from a hostname.
-// The result is lowercased for case-insensitive comparison.
+// compiled caches rewrite patterns: Normalize runs for every cache entry on each lookup.
+var compiled sync.Map // pattern → *regexp.Regexp
+
+func rewritePattern(pattern string) *regexp.Regexp {
+	if re, ok := compiled.Load(pattern); ok {
+		return re.(*regexp.Regexp)
+	}
+	re, err := regexp.Compile(pattern)
+	if err != nil {
+		return nil // rejected by config.Load already
+	}
+	compiled.Store(pattern, re)
+	return re
+}
+
+// Normalize strips configured domain suffixes, applies rewrite rules in order, and
+// optionally strips hyphens. The result is lowercased for case-insensitive comparison.
 func Normalize(name string, cfg config.ShortcutsConfig) string {
 	s := strings.ToLower(name)
 	for _, domain := range cfg.Domains {
@@ -20,6 +37,11 @@ func Normalize(name string, cfg config.ShortcutsConfig) string {
 			break
 		}
 	}
+	for _, rewrite := range cfg.Rewrites {
+		if re := rewritePattern(rewrite.Pattern); re != nil {
+			s = re.ReplaceAllString(s, rewrite.Replace)
+		}
+	}
 	if cfg.StripHyphens {
 		s = strings.ReplaceAll(s, "-", "")
 	}
@@ -34,7 +56,7 @@ func MakeNormalizer(cfg config.ShortcutsConfig) func(string) string {
 }
 
 // AliasName returns a shell-safe alias name for the given host.
-// It normalizes the name (strips configured domains and optionally hyphens) then
+// It normalizes the name (strips configured domains, applies rewrites, optionally strips hyphens) then
 // replaces any remaining dots with underscores so the result is a valid identifier.
 func AliasName(name string, cfg config.ShortcutsConfig) string {
 	s := Normalize(name, cfg)

internal/shortcuts/shortcuts_test.go

@@ -78,3 +78,40 @@ func TestAliasName_NoConfig(t *testing.T) {
 		t.Errorf("AliasName = %q, want %q", got, want)
 	}
 }
+
+func TestNormalizeRewrites(t *testing.T) {
+	cfg := config.ShortcutsConfig{
+		Domains:  []string{".hoster.de"},
+		Rewrites: []config.ShortcutRewrite{{Pattern: `^([a-z]+)[0-9]+-`, Replace: "$1"}},
+	}
+	for input, want := range map[string]string{
+		"fsn1-bx1.hoster.de": "fsnbx1",
+		"FSN1-BX1.hoster.de": "fsnbx1",
+		"fsn1-bx1":           "fsnbx1",
+		"fsnbx1":             "fsnbx1", // the shortcut itself is left alone
+		"web01.hoster.de":    "web01",
+	} {
+		if got := shortcuts.Normalize(input, cfg); got != want {
+			t.Errorf("Normalize(%q) = %q, want %q", input, got, want)
+		}
+	}
+	if got := shortcuts.AliasName("fsn1-bx1.hoster.de", cfg); got != "fsnbx1" {
+		t.Errorf("AliasName = %q", got)
+	}
+}
+
+func TestNormalizeRewritesOrder(t *testing.T) {
+	// Rules run in order after domain stripping, before hyphen stripping.
+	cfg := config.ShortcutsConfig{
+		Domains:      []string{".hoster.de"},
+		StripHyphens: true,
+		Rewrites: []config.ShortcutRewrite{
+			{Pattern: `\.hoster\.de$`, Replace: "-never"},
+			{Pattern: `^fsn`, Replace: "f"},
+			{Pattern: `^f1`, Replace: "falkenstein"},
+		},
+	}
+	if got := shortcuts.Normalize("fsn1-bx-1.hoster.de", cfg); got != "falkensteinbx1" {
+		t.Fatalf("got %q", got)
+	}
+}