Add support for Go flags and refactor variables in youtube_test

Author: dlmw

README.md

@@ -9,7 +9,7 @@ For various reasons, you may prefer not to use your Google account but you would
 1. Download the executable from the release section or build it yourself
 1. Open a Terminal (cmd.exe on Windows)
 1. Navigate to the location of the *dplaylist(.exe)* executable
-1. Execute it by passing your text file as an argument: `./dplaylist hip-hop.txt`
+1. Execute it by passing your text file as an argument: `./dplaylist -file=hip-hop.txt`
 1. The link is generated in the console
 
 ### Valid ID

main.go

@@ -2,14 +2,29 @@ package main
 
 import (
 	"bufio"
+	"flag"
 	"log"
 	"os"
 
 	"github.com/dlmw/dplaylist/youtube"
 )
 
+var filePath string
+
+func init() {
+	const (
+		filePathShort   = "f"
+		filePathLong    = "file"
+		filePathDefault = "youtube.txt"
+		filePathUsage   = "The path of the file containing YouTube IDs. " + filePathShort + " and " + filePathLong + " are equivalent."
+	)
+
+	flag.StringVar(&filePath, filePathLong, filePathDefault, filePathUsage)
+	flag.StringVar(&filePath, filePathShort, filePathDefault, filePathUsage)
+}
+
 func main() {
-	filePath := os.Args[1]
+	flag.Parse()
 	lines, err := readLines(filePath)
 	if err != nil {
 		panic(err)

youtube/youtube_test.go

@@ -6,10 +6,10 @@ import (
 	"testing"
 )
 
-var videoIDs []string = []string{"dQw4w9WgXcQ", "TYgOlqinH7A", "mOYZaiDZ7BM"}
+var videoIDs = []string{"dQw4w9WgXcQ", "TYgOlqinH7A", "mOYZaiDZ7BM"}
 
-var youtubeLongLinkExample string = "https://www.youtube.com/watch?v=dQw4w9WgXcQ"
-var youtubeShortLinkExample string = "https://youtu.be/dQw4w9WgXcQ"
+var youtubeLongLinkExample = "https://www.youtube.com/watch?v=dQw4w9WgXcQ"
+var youtubeShortLinkExample = "https://youtu.be/dQw4w9WgXcQ"
 
 func ExampleCreatePlaylist() {
 	fmt.Println(CreatePlaylist(videoIDs))