bug fix, doc.HasHighlights only if file is pdf

- renamed checkFile to HasHighlights
- HasHighlights will use ghligh/document to open and then
	check for highlights only if the file specified has
	pdf magic header. This fixes bug where goroutines block
	because of hang on of document.GhlighDoc (may be caused by
	poppler low level implementation)

 Changes to be committed:
	modified:   ls.go

1 files changed, 32 insertions, 2 deletions

diff --git a/cmd/ls.go b/cmd/ls.go
index bcdbe66..cfe31be 100644
--- a/cmd/ls.go
+++ b/cmd/ls.go
@@ -4,6 +4,7 @@ Copyright © 2025 NAME HERE <EMAIL ADDRESS>
 package cmd
 
 import (
+	"bytes"
 	"context"
 	"fmt"
 	"os"
@@ -90,7 +91,34 @@ func lsArgs(args []string) []string {
 	return args
 }
 
-func checkFile(path string) bool {
+// returns true if file specified in path start with the PDF magic header
+func isPDF(path string) bool {
+	file, err := os.Open(path)
+	if err != nil {
+		// We only care about printing permissions errors
+		// and things like that
+		fmt.Fprintf(os.Stderr, "%s\n", err)
+		return false
+	}
+
+	defer file.Close()
+
+	header := make([]byte, 5)
+	_, err = file.Read(header)
+	if err != nil {
+		return false
+	}
+
+	return bytes.Equal(header, []byte("%PDF-"))
+}
+
+// returns true if file contains at least one highlight or is tagged with "ls" (is ls-able by ghligh)
+func HasHighlights(path string) bool {
+	// Ensure is a pdf file, might block for other kind of files
+	if !isPDF(path) {
+		return false
+	}
+
 	doc, err := document.Open(path)
 	if err != nil {
 		return false
@@ -134,16 +162,18 @@ var lsCmd = &cobra.Command{
 
 		var wg sync.WaitGroup
 		var found bool
+
 		for file := range ch {
 			wg.Add(1)
 			go func(f string) {
 				defer wg.Done()
-				if checkFile(f) {
+				if HasHighlights(f) {
 					found = true
 					fmt.Printf("%s\n", f)
 				}
 			}(file)
 		}
+
 		wg.Wait()
 
 		check, err := cmd.Flags().GetBool("check")