last : move to its own pkg for sharing of GLOB pattern and --help, slightly overkill but consistent

last/last.go

@@ -0,0 +1,66 @@
+package last
+
+import (
+	"errors"
+	"fmt"
+	"log"
+	"path/filepath"
+
+	cmdpkg "github.com/brtholomy/um/go/cmd"
+	"github.com/brtholomy/um/go/flags"
+)
+
+const cmd = cmdpkg.Last
+
+const (
+	GLOB = "[0-9]*.md"
+	// we only care about the number group:
+	NOT_FOUND_MSG = "um files not found: " + GLOB
+)
+
+type options struct {
+	Help flags.Flag[bool]
+}
+
+func initOpts() options {
+	return options{
+		flags.Flag[bool]{"--help", "-h", false, "show help"},
+	}
+}
+
+func parseArgs(args []string) options {
+	opts := initOpts()
+	for _, arg := range args {
+		switch {
+		case arg == opts.Help.Long || arg == opts.Help.Short:
+			flags.Help(cmd, opts)
+		default:
+			flags.HelpInvalidArg(cmd, arg)
+			flags.Help(cmd, opts)
+		}
+	}
+	return opts
+}
+
+// get the lexical last file from GLOB
+func GlobLast(glob string) (string, error) {
+	// NOTE: filepath.Glob is more reliable than a manual ls call:
+	filelist, err := filepath.Glob(glob)
+	if err != nil {
+		return "", err
+	}
+	if len(filelist) == 0 {
+		return "", errors.New(NOT_FOUND_MSG)
+	}
+	return filelist[len(filelist)-1], nil
+}
+
+func Last(args []string) {
+	_ = parseArgs(args)
+	s, err := GlobLast(GLOB)
+	if err != nil {
+		log.Fatalf("um %s: %v", cmdpkg.Last, err)
+	}
+	// send to stdout, not stderr as is default for log.Print:
+	fmt.Println(s)
+}