Convert newpipe/util/FilenameUtils.java to kotlin

Co-authored-by: Aayush Gupta <aayushgupta219@gmail.com>

Author: Yevhen Babiichuk (DustDFG)

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

@@ -0,0 +1,65 @@
+/*
+ * SPDX-FileCopyrightText: 2018-2025 NewPipe contributors <https://newpipe.net>
+ * SPDX-FileCopyrightText: 2025 NewPipe e.V. <https://newpipe-ev.de>
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+package org.schabi.newpipe.util
+
+import android.content.Context
+import androidx.preference.PreferenceManager
+import org.schabi.newpipe.R
+import org.schabi.newpipe.ktx.getStringSafe
+import java.util.regex.Matcher
+
+object FilenameUtils {
+    private const val CHARSET_MOST_SPECIAL = "[\\n\\r|?*<\":\\\\>/']+"
+    private const val CHARSET_ONLY_LETTERS_AND_DIGITS = "[^\\w\\d]+"
+
+    /**
+     * #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
+     */
+    @JvmStatic
+    fun createFilename(context: Context, title: String): String {
+        val sharedPreferences = PreferenceManager.getDefaultSharedPreferences(context)
+
+        val charsetLd = context.getString(R.string.charset_letters_and_digits_value)
+        val charsetMs = context.getString(R.string.charset_most_special_value)
+        val defaultCharset = context.getString(R.string.default_file_charset_value)
+
+        val replacementChar = sharedPreferences.getStringSafe(
+            context.getString(R.string.settings_file_replacement_character_key), "_"
+        )
+        val selectedCharset = sharedPreferences.getStringSafe(
+            context.getString(R.string.settings_file_charset_key), ""
+        ).ifEmpty { defaultCharset }
+
+        val charset = when (selectedCharset) {
+            charsetLd -> CHARSET_ONLY_LETTERS_AND_DIGITS
+            charsetMs -> CHARSET_MOST_SPECIAL
+            else -> selectedCharset // Is the user using a custom charset?
+        }
+
+        return createFilename(title, charset, Matcher.quoteReplacement(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 fun createFilename(
+        title: String,
+        invalidCharacters: String,
+        replacementChar: String
+    ): String {
+        return title.replace(invalidCharacters.toRegex(), replacementChar)
+    }
+}