feat: add buildinfo package for version information

internal/buildinfo/buildinfo.go

@@ -0,0 +1,74 @@
+package buildinfo
+
+import (
+	"fmt"
+	"runtime"
+	"runtime/debug"
+	"strings"
+
+	"golang.org/x/mod/module"
+	"golang.org/x/mod/semver"
+)
+
+// devVersion is the version reported by builds that were not produced by a
+// release. Both the update check and `godeez update` refuse to run on them.
+const devVersion = "dev"
+
+var (
+	version = devVersion
+	commit  = ""
+	date    = ""
+)
+
+func Version() string {
+	if version != devVersion {
+		return version
+	}
+
+	if info, ok := debug.ReadBuildInfo(); ok {
+		if v := releaseVersion(info.Main.Version); v != "" {
+			return v
+		}
+	}
+
+	return devVersion
+}
+
+func releaseVersion(v string) string {
+	if !semver.IsValid(v) {
+		return ""
+	}
+	if semver.Build(v) != "" || module.IsPseudoVersion(v) {
+		return ""
+	}
+
+	return strings.TrimPrefix(v, "v")
+}
+
+func IsDev() bool {
+	return Version() == devVersion
+}
+
+func Commit() string {
+	if commit != "" {
+		return commit
+	}
+
+	if info, ok := debug.ReadBuildInfo(); ok {
+		for _, s := range info.Settings {
+			if s.Key == "vcs.revision" {
+				return s.Value
+			}
+		}
+	}
+
+	return ""
+}
+
+func Date() string {
+	return date
+}
+
+func UserAgent() string {
+	return fmt.Sprintf("godeez/%s (%s/%s)", Version(), runtime.GOOS, runtime.GOARCH)
+}