Add renaming filename patterns

app/src/main/java/org/schabi/newpipe/util/FilenameUtils.java

@@ -0,0 +1,39 @@
+package org.schabi.newpipe.util;
+
+import android.content.Context;
+import android.content.SharedPreferences;
+import android.preference.PreferenceManager;
+
+import org.schabi.newpipe.R;
+
+import java.util.regex.Pattern;
+
+public class FilenameUtils {
+
+    /**
+     * #143 #44 #42 #22: make sure that the filename does not contain illegal chars.
+     * @param context the context to retrieve strings and preferences from
+     * @param title the title to create a filename from
+     * @return the filename
+     */
+    public static String createFilename(Context context, String title) {
+        SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(context);
+        final String key = context.getString(R.string.settings_file_charset_key);
+        final String value = sharedPreferences.getString(key, context.getString(R.string.default_file_charset_value));
+        Pattern pattern = Pattern.compile(value);
+
+        final String replacementChar = sharedPreferences.getString(context.getString(R.string.settings_file_replacement_character_key), "_");
+        return createFilename(title, pattern, replacementChar);
+    }
+
+    /**
+     * Create a valid filename
+     * @param title the title to create a filename from
+     * @param invalidCharacters patter matching invalid characters
+     * @param replacementChar the replacement
+     * @return the filename
+     */
+    private static String createFilename(String title, Pattern invalidCharacters, String replacementChar) {
+        return title.replaceAll(invalidCharacters.pattern(), replacementChar);
+    }
+}