feat: add cobra CLI with input/output flags and debug option

- Add --input/-i and --output/-o flags for file selection
- Add --debug flag to print intermediate JSON to stderr
- Print errors during parsing

go.mod

@@ -1,3 +1,10 @@
 module git.donadeo.net/pdonadeo/todotxt2remind
 
 go 1.24.1
+
+require github.com/spf13/cobra v1.10.1
+
+require (
+	github.com/inconshreveable/mousetrap v1.1.0 // indirect
+	github.com/spf13/pflag v1.0.9 // indirect
+)

go.sum

@@ -0,0 +1,10 @@
+github.com/cpuguy83/go-md2man/v2 v2.0.6/go.mod h1:oOW0eioCTA6cOiMLiUPZOpcVxMig6NIQQ7OS05n1F4g=
+github.com/inconshreveable/mousetrap v1.1.0 h1:wN+x4NVGpMsO7ErUn/mUI3vEoE6Jt13X2s0bqwp9tc8=
+github.com/inconshreveable/mousetrap v1.1.0/go.mod h1:vpF70FUmC8bwa3OWnCshd2FqLfsEA9PFc4w1p2J65bw=
+github.com/russross/blackfriday/v2 v2.1.0/go.mod h1:+Rmxgy9KzJVeS9/2gXHxylqXiyQDYRxCVz55jmeOWTM=
+github.com/spf13/cobra v1.10.1 h1:lJeBwCfmrnXthfAupyUTzJ/J4Nc1RsHC/mSRU2dll/s=
+github.com/spf13/cobra v1.10.1/go.mod h1:7SmJGaTHFVBY0jW4NXGluQoLvhqFQM+6XSKD+P4XaB0=
+github.com/spf13/pflag v1.0.9 h1:9exaQaMOCwffKiiiYk6/BndUBv+iRViNW+4lEMi0PvY=
+github.com/spf13/pflag v1.0.9/go.mod h1:McXfInJRrz4CZXVZOBLb0bTZqETkiAhM9Iw0y3An2Bg=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

main.go

@@ -3,29 +3,77 @@ package main
 import (
 	"encoding/json"
 	"fmt"
+	"io"
 	"os"
 
 	"git.donadeo.net/pdonadeo/todotxt2remind/internal/parser"
+	"github.com/spf13/cobra"
+)
+
+var (
+	inputFile  string
+	outputFile string
+	debug      bool
+	version    = "1"
 )
 
 func main() {
-	if len(os.Args) < 2 {
-		fmt.Fprintf(os.Stderr, "usage: example /path/to/todo.txt\n")
-		os.Exit(2)
-	}
-	f, err := os.Open(os.Args[1])
-	if err != nil {
-		panic(err)
-	}
-	defer func() { _ = f.Close() }()
+	rootCmd := &cobra.Command{
+		Use:   "todotxt2remind",
+		Short: "Convert a todo.txt file to Remind format",
+		Long:  "Reads tasks from todo.txt format and outputs Remind-compatible entries.",
+		Run: func(cmd *cobra.Command, args []string) {
+			var in io.Reader = os.Stdin
+			if inputFile != "" {
+				f, err := os.Open(inputFile)
+				if err != nil {
+					fmt.Fprintf(os.Stderr, "error opening input file: %v\n", err)
+					os.Exit(2)
+				}
+				defer func() { _ = f.Close() }()
+				in = f
+			}
 
-	tasks, errors := parser.ParseReader(f)
-	if len(errors) > 0 {
-		fmt.Fprintf(os.Stderr, "errors while parsing:\n")
-		for _, e := range errors {
-			fmt.Fprintf(os.Stderr, " - %v\n", e)
-		}
+			tasks, errors := parser.ParseReader(in)
+			if len(errors) > 0 {
+				fmt.Fprintf(os.Stderr, "errors while parsing:\n")
+				for _, e := range errors {
+					fmt.Fprintf(os.Stderr, " - %v\n", e)
+				}
+			}
+
+			if debug {
+				b, _ := json.MarshalIndent(tasks, "", "  ")
+				fmt.Fprintf(os.Stderr, "%s\n", string(b))
+			}
+
+			var out io.Writer = os.Stdout
+			if outputFile != "" {
+				f, err := os.Create(outputFile)
+				if err != nil {
+					fmt.Fprintf(os.Stderr, "error opening output file: %v\n", err)
+					os.Exit(2)
+				}
+				defer func() { _ = f.Close() }()
+				out = f
+			}
+
+			for _, t := range tasks {
+				rem := t.ToRemind()
+				if rem == "" {
+					continue
+				}
+				_, _ = fmt.Fprintf(out, "%s\n", rem)
+			}
+		},
 	}
-	b, _ := json.MarshalIndent(tasks, "", "  ")
-	fmt.Println(string(b))
+
+	rootCmd.Flags().StringVarP(&inputFile, "input", "i", "", "Input file (default: stdin)")
+	rootCmd.Flags().StringVarP(&outputFile, "output", "o", "", "Output file (default: stdout)")
+	rootCmd.Flags().BoolVar(&debug, "debug", false, "Print intermediate JSON to stderr")
+	rootCmd.Version = version
+	rootCmd.Flags().BoolP("version", "v", false, "Show version and exit")
+	rootCmd.SetVersionTemplate(fmt.Sprintf("todotxt2remind version %s\n", version))
+
+	_ = rootCmd.Execute()
 }