Add simple error management + manage invalid cookies file

Closes #2

src/main/kotlin/bandcampcollectiondownloader/BandcampCollectionDownloader.kt

@@ -102,10 +102,13 @@ fun downloadFile(fileURL: String, saveDir: Path, optionalFileName: String = ""):
 /**
  * Core function called from the main
  */
-fun downloadAll(cookiesFile: String, bandcampUser: String, downloadFormat: String, downloadFolder: Path) {
+fun downloadAll(cookiesFile: Path, bandcampUser: String, downloadFormat: String, downloadFolder: Path) {
     // Parse JSON cookies (obtained with "Cookie Quick Manager" Firefox addon)
     val gson = Gson()
-    val jsonData = String(Files.readAllBytes(Paths.get(cookiesFile)))
+    if (!Files.exists(cookiesFile)) {
+        throw BandCampDownloaderError("Cookies file '$cookiesFile' cannot be found.")
+    }
+    val jsonData = String(Files.readAllBytes(cookiesFile))
     val parsedCookies = gson.fromJson(jsonData, Array<ParsedCookie>::class.java)
     val cookies = parsedCookiesToMap(parsedCookies)
 
@@ -146,6 +149,10 @@ fun downloadAll(cookiesFile: String, bandcampUser: String, downloadFormat: Strin
     }
 }
 
+class BandCampDownloaderError : Exception {
+    constructor(s: String) : super(s)
+}
+
 fun downloadAlbum(artistFolderPath: Path?, albumFolderPath: Path, albumtitle: String, url: String, cookies: Map<String, String>, gson: Gson, isSingleTrack: Boolean, artid: String) {
     // If the artist folder does not exist, we create it
     if (!Files.exists(artistFolderPath)) {

src/main/kotlin/bandcampcollectiondownloader/Main.kt

@@ -14,7 +14,7 @@ data class Args(
                 description = arrayOf("A JSON file with valid bandcamp credential cookies.",
                         """"Cookie Quick Manager" can be used to obtain this file after logging into bandcamp.""",
                         "(visit https://addons.mozilla.org/en-US/firefox/addon/cookie-quick-manager/)."))
-        var pathToCookiesFile: String? = null,
+        var pathToCookiesFile: Path? = null,
 
         @CommandLine.Option(names = arrayOf("--audio-format", "-f"), required = false,
                 description = arrayOf("The chosen audio format of the files to download (default: \${DEFAULT-VALUE}).",
@@ -40,19 +40,32 @@ fun main(args: Array<String>) {
     val parsedArgs: Args =
             try {
                 CommandLine.populateCommand<Args>(Args(), *args)
-            } catch (e: CommandLine.MissingParameterException) {
+            }
+
+            // If the wrong arguments are given, show help + error message
+            catch (e: CommandLine.MissingParameterException) {
                 CommandLine.usage(Args(), System.out)
                 System.err.println(e.message)
                 return
             }
+
+    // If --help, then only show help and quit
     if (parsedArgs.help) {
         CommandLine.usage(Args(), System.out)
-    } else {
+    }
+
+    // Else, parse arguments and run
+    else {
         val bandcampUser = parsedArgs.bandcampUser
         val cookiesFile = parsedArgs.pathToCookiesFile!!
         val downloadFormat = parsedArgs.audioFormat
         val downloadFolder = parsedArgs.pathToDownloadFolder
-        downloadAll(cookiesFile, bandcampUser, downloadFormat, downloadFolder)
+        try {
+            downloadAll(cookiesFile, bandcampUser, downloadFormat, downloadFolder)
+        } catch (e : BandCampDownloaderError) {
+            System.err.println("ERROR: ${e.message}")
+        }
+
     }
 
 }