add compatibility mode for NSIS args

AT-LAST-I2PBROWSER.md

@@ -2,6 +2,7 @@ At last, an I2P Browser you might want to use
 =============================================
 
 1. I2P can only grow if it's easily accessible to people
-2. I2P and Tor have different, unique strengths
+2. I2P and Tor have different, unique strengths and can be more powerful when combined in a considered way
 3. Anonymity is a collaborative effort
-4. Leeching is rude, if we use something we should try to improve it or give something back
+4. Leeching is rude, if we use something we should try to improve it or give something back
+

main.go

@@ -176,6 +176,10 @@ var snowflake *bool
 var client *tbserve.Client
 
 func main() {
+	if err := NSISCompat(); err != nil {
+		log.Println("NSIS compat mode failure", err)
+		os.Exit(0)
+	}
 	filename := filepath.Base(os.Args[0])
 	SnowflakeFlag()
 	usage := flag.Usage

nsis.go

@@ -0,0 +1,57 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+)
+
+func NSISCompat() error {
+	// check if no flags(args beginning with '-') were passed
+	if len(os.Args) == 1 {
+		return nil
+	}
+	for _, arg := range os.Args[1:] {
+		if arg[0] == '-' {
+			return nil
+		}
+	}
+	var convertArgs = []string{}
+	// check if any args beginning with /S or /D
+	for _, arg := range os.Args[1:] {
+		if strings.HasPrefix(arg, "/S") {
+			log.Println("/S flag was passed, we're operating in NSIS installer compatibility mode")
+		}
+		if strings.HasPrefix(arg, "/D") {
+			if len(arg) > 3 {
+				return fmt.Errorf("/D flag was passed with a directory argument in NSIS compatibility mode")
+			}
+			log.Println("/D flag was passed, we're operating in NSIS installer compatibility mode")
+			convertArgs = append(convertArgs, "--directory="+arg[2:])
+		}
+	}
+	if len(convertArgs) == 0 {
+		return nil
+	}
+	// if we're here, we're operating in NSIS compatibility mode
+	// re-run ourselves with the converted args
+	// start by getting the path to our executable
+	exePath, err := os.Executable()
+	if err != nil {
+		return err
+	}
+	// forumulate our new command
+	cmd := exec.Command(exePath, convertArgs...)
+	// set the current working directory to the same as our executable
+	cmd.Dir = filepath.Dir(exePath)
+	// run the command
+	err = cmd.Run()
+	if err != nil {
+		return err
+	}
+	// if we're here, we're done
+	return nil
+}