cmd/app: find next unused identity

This is a lot easier than grepping around. Verbose output is equivalent to assertion in the deprecated nix code.

Signed-off-by: Ophestra <cat@gensokyo.uk>

1 files changed, 75 insertions, 0 deletions

diff --git a/cmd/app/main.go b/cmd/app/main.go
index 41a513d5..ff932bdd 100644
--- a/cmd/app/main.go
+++ b/cmd/app/main.go
@@ -14,7 +14,9 @@ import (
 	"os/exec"
 	"os/signal"
 	"path/filepath"
+	"slices"
 	"strconv"
+	"strings"
 	"syscall"
 
 	"hakurei.app/check"
@@ -229,6 +231,79 @@ func main() {
 		},
 	)
 
+	c.NewCommand(
+		"next", "Find next unused identity",
+		func([]string) error {
+			var names []string
+			if dents, err := os.ReadDir(base.Append("app").String()); err != nil {
+				return err
+			} else {
+				names = make([]string, 0, len(dents))
+				for _, dent := range dents {
+					name := dent.Name()
+					if dent.IsDir() || (len(name) > 0 && name[0] == '.') {
+						continue
+					}
+					names = append(names, name)
+				}
+			}
+
+			apps := make([]*hst.Config, len(names))
+			for i, name := range names {
+				r, err := os.Open(base.Append("app", name).String())
+				if err != nil {
+					return err
+				}
+
+				apps[i], err = parse(name, base, r, nil)
+				if closeErr := r.Close(); err == nil {
+					err = closeErr
+				}
+				if err != nil {
+					return err
+				}
+			}
+
+			p := make(map[int][]*hst.Config)
+			for _, config := range apps {
+				p[config.Identity] = append(p[config.Identity], config)
+			}
+
+			identities := make([]int, 0, len(p))
+			for identity, a := range p {
+				identities = append(identities, identity)
+				if msg.IsVerbose() && len(a) != 1 {
+					ids := make([]string, len(a))
+					for i, config := range a {
+						ids[i] = config.ID
+					}
+					slices.Sort(ids)
+					msg.Verbosef(
+						"%s shares identity %d",
+						strings.Join(ids, ", "), identity,
+					)
+				}
+			}
+
+			if len(identities) == 0 {
+				// 0 is the reserved identity
+				fmt.Println(1)
+				return nil
+			}
+
+			slices.Sort(identities)
+			next := identities[0] - 1
+			for _, identity := range identities {
+				if identity != next+1 {
+					break
+				}
+				next = identity
+			}
+			fmt.Println(next + 1)
+			return nil
+		},
+	)
+
 	c.MustParse(os.Args[1:], func(err error) {
 		if e, ok := errors.AsType[*exec.ExitError](err); ok && e != nil {
 			os.Exit(e.ExitCode())