Implement cli argument for file path, path validation, file type validation

cmd/zona/main.go

@@ -1,9 +1,57 @@
 package main
 
 import (
+	"errors"
+	"flag"
 	"fmt"
+	"os"
+
+	"github.com/ficcdaf/zona/internal/util"
 )
 
-func main() {
-	fmt.Println("Hello, world!")
+// validateFile checks whether a given path
+// is a valid file && matches an expected extension
+func validateFile(path, ext string) bool {
+	return (util.CheckExtension(path, ext) == nil) && (util.PathIsValid(path, true))
+}
+
+func main() {
+	mdPath := flag.String("file", "", "Path to the markdown file.")
+	flag.Parse()
+	if *mdPath == "" {
+		// no flag provided, check for positional argument instead
+		n := flag.NArg()
+		var e error
+		switch n {
+		case 1:
+			// we read the positional arg
+			arg := flag.Arg(0)
+			// mdPath wants a pointer so we get arg's address
+			mdPath = &arg
+		case 0:
+			// in case of no flag and no arg, we fail
+			e = errors.New("Required argument missing!")
+		default:
+			// more args than expected is also fail
+			e = errors.New("Unexpected arguments!")
+		}
+		if e != nil {
+			fmt.Printf("Error: %s\n", e.Error())
+			os.Exit(1)
+		}
+
+	}
+	if !validateFile(*mdPath, ".md") {
+		fmt.Println("File validation failed!")
+		os.Exit(1)
+	}
+
+	file, err := os.Open(*mdPath)
+	if err != nil {
+		fmt.Println("Error reading file:", err)
+		os.Exit(1)
+	}
+	defer file.Close()
+
+	fmt.Println("File opened :)")
 }