Image resource cleaner for Android project

cleaner.kt

import java.io.File
import java.util.regex.Pattern
import kotlin.system.exitProcess


fun findMatches(directory: File, pattern: Pattern, extensions: List<String>): Set<String> {
    val result = mutableSetOf<String>()

    directory.walkTopDown()
        .filter { it.isFile && it.extension in extensions }
        .forEach { file ->
            file.readLines().forEach { line ->
                val matcher = pattern.matcher(line)
                while (matcher.find()) {
                    val element = matcher.group()
                    result.add(element.substring(element.lastIndexOf('.') + 1))
                }

                val pat = Pattern.compile("@drawable/[0-9a-zA-Z_]*")
                val xmlMatcher = pat.matcher(line)
                while (xmlMatcher.find()) {
                    val element = xmlMatcher.group()
                    println("found in xml : $element")
                    result.add(element.substring(element.lastIndexOf('/') + 1))
                }
            }
        }
    return result
}

fun cleanFiles(directory: File, filesInUse: Set<String>, deleted: Boolean = true): List<File> {
    var size: Long = 0L
    val result = mutableListOf<File>()
    directory.walkTopDown()
        .filter {
            it.isFile && it.parentFile.isDirectory && it.parentFile.name.contains("drawable")
                    && it.extension in setOf("png", "jpg", "jpeg", "webp")
        }
        .forEach { file ->
            if (!filesInUse.contains(file.nameWithoutExtension)) {
                println("file ${file.absolutePath} is NOT in use")
                result.add(file)
                size += file.length()

                if (deleted) file.delete()
            }
        }
    println("Cleaned size : ${size / 1024} KB")
    return result
}

fun main(args: Array<String>) {
    if (args.isEmpty()) {
        System.err.println("Usage: prog <app_folder>")
        exitProcess(1)
    }

    println(">>> searching... ${args.joinToString(",")}")

    val srcPath = args[0]
    println("working dir: $srcPath")

    val targetFile = File(srcPath)

    val pattern = Pattern.compile("R\\.drawable\\.[0-9a-zA-Z_]*")
    val extensions = listOf("java", "kt", "gradle", "gradle.kts", "xml")
    val res = findMatches(targetFile, pattern, extensions)
    println("Matched Result: ${res.size}")
    println("Matched Result: \n${res.joinToString("\n")}")

    val filesToDelete = cleanFiles(targetFile, res)
    println("To be Deleted file size : ${filesToDelete.size}")
}