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Demo FileHostingService
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| import java.time.Instant | |
| data class File( | |
| val filename: String, | |
| val size: Int, | |
| val createdAt: Long? = null, | |
| val ttlSec: Long? = null | |
| ) { | |
| fun isAlive(timestamp: Long): Boolean { | |
| if (ttlSec == null || createdAt == null) | |
| return true | |
| val expiryDate = createdAt + (ttlSec * 1000) | |
| return expiryDate > timestamp | |
| } | |
| } | |
| class FileAlreadyExists(filename: String) : RuntimeException("File $filename already exists") | |
| class FileNotFoundException(filename: String) : RuntimeException("File $filename doesn't exist") | |
| class FileHostingService { | |
| val files = mutableMapOf<String, File>() | |
| val history = mutableListOf<Pair<Long, Map<String, File>>>() | |
| fun upload(filename: String, size: Int) { | |
| if (filename in files) { | |
| throw FileAlreadyExists(filename) | |
| } | |
| files[filename] = File(filename, size) | |
| backup() | |
| } | |
| fun uploadAt(filename: String, size: Int, timestamp: Long, ttlSec: Long? = null) { | |
| if (filename in files) { | |
| throw FileAlreadyExists(filename) | |
| } | |
| files[filename] = File(filename, size, createdAt = timestamp, ttlSec) | |
| backup(timestamp) | |
| } | |
| fun get(name: String): Int? = files[name]?.size | |
| fun getAt(name: String, timestamp: Long): Int? = | |
| files[name] | |
| ?.takeIf { it.isAlive(timestamp) } | |
| ?.size | |
| fun copy(source: String, dest: String) { | |
| val oldFile = files[source] ?: throw FileNotFoundException(source) | |
| files[dest] = oldFile | |
| backup() | |
| } | |
| fun copyAt(source: String, dest: String, timestamp: Long) { | |
| val oldFile = files[source] | |
| ?.takeIf { it.isAlive(timestamp) } | |
| ?: throw FileNotFoundException(source) | |
| files[dest] = oldFile | |
| backup(timestamp) | |
| } | |
| fun search(prefix: String): List<File> { | |
| return files | |
| .filter { it.key.startsWith(prefix) } | |
| .map { it.value } | |
| .sortedWith( | |
| compareByDescending<File> { it.size } | |
| .thenBy { it.filename } | |
| ) | |
| .take(10) | |
| } | |
| fun searchAt(prefix: String, timestamp: Long): List<File> { | |
| return files | |
| .filter { it.key.startsWith(prefix) } | |
| .map { it.value } | |
| .filter { it.isAlive(timestamp) } | |
| .sortedWith( | |
| compareByDescending<File> { it.size } | |
| .thenBy { it.filename } | |
| ) | |
| .take(10) | |
| } | |
| fun rollback(timestamp: Long) { | |
| val snapshot = history | |
| .filter { it.first <= timestamp } | |
| .maxByOrNull { it.first } | |
| ?.second ?: return | |
| files.clear() | |
| val modified = snapshot | |
| .mapValues { (_, file) -> file.copy(createdAt = timestamp) } | |
| files.putAll(modified) | |
| } | |
| private fun backup(timestamp: Long = Instant.now().toEpochMilli()) { | |
| history.add(Pair(timestamp, files.toMap())) | |
| } | |
| } | |
| fun main() { | |
| val now = Instant.now() | |
| val fh = FileHostingService() | |
| for (i in 1..15) { | |
| fh.uploadAt( | |
| "f$i", 100, | |
| now.minusSeconds(i.toLong()).toEpochMilli(), | |
| 5 | |
| ) | |
| } | |
| // fh.searchAt("f", Instant.now().toEpochMilli()) | |
| // .forEach { println(it) } | |
| val cutTime = now.plusSeconds(2) | |
| fh.uploadAt("after", 100, cutTime.plusSeconds(2).toEpochMilli(), 3) | |
| fh.files.forEach { println(it) } | |
| println("------") | |
| fh.history.forEach { println(it) } | |
| println("------") | |
| fh.rollback(cutTime.minusSeconds(6).toEpochMilli()) | |
| fh.files.forEach { println(it) } | |
| val words = arrayOf("apple", "tisane") | |
| words | |
| .mapIndexed { index, w -> index to w } | |
| .filter { (_, w) -> | |
| w.startsWith("a") && w.endsWith("e") | |
| } | |
| .maxByOrNull { (index, _) -> index } ?: -1 | |
| } | |
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