system updater: complete overhaul

Move system update flow to GO, with a CLI (convenient AIO tool) and
server integration. All lifecycle, scheduling, execution occurs on
backend side.

Run some backends via pkexec, some via terminal like paru/yay.

Incorporate flatpak as an option to update.

Add terminal override setting in GUI, in addition to $TERMINAL env
variable.

fixes #2307
fixes #822
fixes #1102
fixes #1812
fixes #1087
fixes #1743

core/internal/server/sysupdate/backend_flatpak.go

@@ -0,0 +1,139 @@
+package sysupdate
+
+import (
+	"context"
+	"os/exec"
+	"strings"
+)
+
+func init() {
+	RegisterOverlayBackend(func() Backend { return &flatpakBackend{} })
+}
+
+type flatpakBackend struct{}
+
+func (flatpakBackend) ID() string                         { return "flatpak" }
+func (flatpakBackend) DisplayName() string                { return "Flatpak" }
+func (flatpakBackend) Repo() RepoKind                     { return RepoFlatpak }
+func (flatpakBackend) NeedsAuth() bool                    { return false }
+func (flatpakBackend) RunsInTerminal() bool               { return false }
+func (flatpakBackend) IsAvailable(_ context.Context) bool { return commandExists("flatpak") }
+
+func (flatpakBackend) CheckUpdates(ctx context.Context) ([]Package, error) {
+	cmd := exec.CommandContext(ctx, "flatpak", "remote-ls", "--updates", "--columns=application,version,branch,commit,name")
+	out, err := cmd.Output()
+	if err != nil {
+		return nil, err
+	}
+	installed := flatpakInstalled(ctx)
+	return parseFlatpakUpdates(string(out), installed), nil
+}
+
+func flatpakInstalled(ctx context.Context) map[string]flatpakInstalledEntry {
+	out, err := exec.CommandContext(ctx, "flatpak", "list", "--columns=application,version,branch,active").Output()
+	if err != nil {
+		return nil
+	}
+	m := make(map[string]flatpakInstalledEntry)
+	for line := range strings.SplitSeq(string(out), "\n") {
+		if line == "" {
+			continue
+		}
+		fields := strings.Split(line, "\t")
+		if len(fields) == 0 || fields[0] == "" {
+			continue
+		}
+		appID := fields[0]
+		entry := flatpakInstalledEntry{}
+		if len(fields) > 1 {
+			entry.version = fields[1]
+		}
+		if len(fields) > 2 {
+			entry.branch = fields[2]
+		}
+		if len(fields) > 3 {
+			entry.commit = fields[3]
+		}
+		key := appID
+		if entry.branch != "" {
+			key = appID + "//" + entry.branch
+		}
+		m[key] = entry
+	}
+	return m
+}
+
+type flatpakInstalledEntry struct {
+	version string
+	branch  string
+	commit  string
+}
+
+func (flatpakBackend) Upgrade(ctx context.Context, opts UpgradeOptions, onLine func(string)) error {
+	argv := []string{"flatpak", "update", "-y", "--noninteractive"}
+	if opts.DryRun {
+		argv = []string{"flatpak", "update", "--no-deploy", "-y"}
+	}
+	return Run(ctx, argv, RunOptions{OnLine: onLine})
+}
+
+func parseFlatpakUpdates(text string, installed map[string]flatpakInstalledEntry) []Package {
+	if text == "" {
+		return nil
+	}
+	var pkgs []Package
+	for line := range strings.SplitSeq(text, "\n") {
+		if line == "" {
+			continue
+		}
+		fields := strings.Split(line, "\t")
+		if len(fields) == 0 || fields[0] == "" {
+			continue
+		}
+		appID := fields[0]
+		version, branch, commit := "", "", ""
+		if len(fields) > 1 {
+			version = fields[1]
+		}
+		if len(fields) > 2 {
+			branch = fields[2]
+		}
+		if len(fields) > 3 {
+			commit = fields[3]
+		}
+		display := appID
+		if len(fields) > 4 && fields[4] != "" {
+			display = fields[4]
+		}
+
+		key := appID
+		if branch != "" {
+			key = appID + "//" + branch
+		}
+		inst := installed[key]
+		from, to := flatpakVersionPair(inst.version, inst.commit, version, commit)
+
+		pkgs = append(pkgs, Package{
+			Name:        display,
+			Repo:        RepoFlatpak,
+			Backend:     "flatpak",
+			FromVersion: from,
+			ToVersion:   to,
+		})
+	}
+	return pkgs
+}
+
+func flatpakVersionPair(installedVer, installedCommit, remoteVer, remoteCommit string) (from, to string) {
+	if remoteVer != "" {
+		return installedVer, remoteVer
+	}
+	return shortCommit(installedCommit), shortCommit(remoteCommit)
+}
+
+func shortCommit(c string) string {
+	if len(c) > 8 {
+		return c[:8]
+	}
+	return c
+}