Added option to display sequentially numbered files instead of randomly choosing, when possible

README.md

@@ -10,6 +10,14 @@ Browser history is preserved, so you can always go back to any previously displa
 
 Builds available [here](https://cdn.seedno.de/builds/roulette).
 
+## [-s, --successive]
+
+This option is tailored specifically for my own use case. When loading a new image, it checks for a successively-numbered file in the same path.
+
+For example, if the file `/mnt/photos/MyVacation001.jpg` is being displayed, clicking on the image will search for a `/mnt/photos/MyVacation002.jpg`.
+
+If a matching file is not found, it will select a random file as usual.
+
 ## Usage output
 ```
 Usage:
@@ -25,6 +33,7 @@ Flags:
   -h, --help         help for roulette
   -p, --port int     port to listen on (default 8080)
   -r, --recursive    recurse into subdirectories
+  -s, --successive   load the next sequential file, if possible
   -v, --verbose      log accessed files to stdout
 
 Use "roulette [command] --help" for more information about a command.

cmd/files.go

@@ -6,14 +6,55 @@ package cmd
 
 import (
 	"errors"
+	"fmt"
 	"math/rand"
 	"os"
 	"path/filepath"
+	"regexp"
+	"strconv"
 	"time"
 
 	"github.com/h2non/filetype"
 )
 
+func getNextFile(path string) (string, error) {
+	re := regexp.MustCompile("(.+)([0-9]{3})(\\..+)")
+
+	split := re.FindAllStringSubmatch(path, -1)
+
+	base := split[0][1]
+	number, err := strconv.Atoi(split[0][2])
+	if err != nil {
+		return "", nil
+	}
+	extension := split[0][3]
+
+	incremented := number + 1
+
+	fileName := fmt.Sprintf("%v%.3d%v", base, incremented, extension)
+
+	nextFile, err := checkNextFile(fileName)
+	if err != nil {
+		return "", err
+	}
+
+	if !nextFile {
+		return "", nil
+	}
+
+	return fileName, nil
+}
+
+func checkNextFile(path string) (bool, error) {
+	if _, err := os.Stat(path); err == nil {
+		return true, nil
+	} else if errors.Is(err, os.ErrNotExist) {
+		return false, nil
+	} else {
+		return false, err
+	}
+}
+
 func checkIfImage(path string) (bool, error) {
 	file, err := os.Open(path)
 	if err != nil {

cmd/root.go

@@ -12,6 +12,7 @@ import (
 
 var Port int
 var Recursive bool
+var Successive bool
 var Verbose bool
 
 var rootCmd = &cobra.Command{
@@ -33,6 +34,7 @@ func Execute() {
 func init() {
 	rootCmd.Flags().IntVarP(&Port, "port", "p", 8080, "port to listen on")
 	rootCmd.Flags().BoolVarP(&Recursive, "recursive", "r", false, "recurse into subdirectories")
+	rootCmd.Flags().BoolVarP(&Successive, "successive", "s", false, "load the next sequential file, if possible")
 	rootCmd.Flags().BoolVarP(&Verbose, "verbose", "v", false, "log accessed files to stdout")
 	rootCmd.Flags().SetInterspersed(true)
 }

cmd/version.go

@@ -10,7 +10,7 @@ import (
 	"github.com/spf13/cobra"
 )
 
-var Version = "0.6.3"
+var Version = "0.7.0"
 
 func init() {
 	rootCmd.AddCommand(versionCmd)

cmd/web.go

@@ -22,6 +22,16 @@ const LOGDATE string = "2006-01-02T15:04:05.000000000-07:00"
 
 const PREFIX string = "/src"
 
+func refererToUri(referer string) string {
+	parts := strings.SplitAfterN(referer, "/", 4)
+
+	if len(parts) < 4 {
+		return ""
+	}
+
+	return "/" + parts[3]
+}
+
 func serveHtml(w http.ResponseWriter, r http.Request, filePath string) error {
 	fileName := filepath.Base(filePath)
 
@@ -123,11 +133,35 @@ func serveStaticFileHandler(paths []string) http.HandlerFunc {
 func serveHtmlHandler(paths []string) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
 		if r.RequestURI == "/" {
-			filePath, err := pickFile(paths)
+			var filePath string
+			var err error
+
+			if Successive {
+				refererUri := refererToUri(r.Referer())
+				if refererUri != "" && Verbose {
+					fmt.Printf("Referer is %v\n", refererUri)
+				}
+
+				if refererUri != "" {
+					f, err := url.QueryUnescape(refererUri)
 					if err != nil {
 						log.Fatal(err)
 					}
 
+					filePath, err = getNextFile(f)
+					if err != nil {
+						log.Fatal(err)
+					}
+				}
+			}
+
+			if filePath == "" {
+				filePath, err = pickFile(paths)
+				if err != nil {
+					log.Fatal(err)
+				}
+			}
+
 			newUrl := r.URL.Host + filePath
 			http.Redirect(w, r, newUrl, http.StatusSeeOther)
 		} else {