src/main/kotlin/filesystem/FSCreator.kt

@@ -1,28 +1,36 @@
 package filesystem
 
 import java.nio.file.FileAlreadyExistsException
-import java.nio.file.Files
+import kotlin.io.path.Path
-import java.nio.file.Path
+import kotlin.io.path.createDirectory
+import kotlin.io.path.createFile
+import kotlin.io.path.writeText
 
 class FSCreator {
     /**
      * Create entry, leaving existing folders' contents, but overwriting existing files.
      * @throws CyclicFolderException Cyclic folders cannot be created.
+     * @throws DuplicateEntryNameException A folder or sub-folder contains entries with duplicate names.
      */
-    @Throws(CyclicFolderException::class)
+    @Throws(CyclicFolderException::class, DuplicateEntryNameException::class)
     fun create(
         entryToCreate: FSEntry,
         destination: String,
     ) {
         // No point in running anything if we know the input is invalid.
-        if (entryToCreate is FSFolder && entryToCreate.isCyclic()) {
+        if (entryToCreate is FSFolder) {
-            throw CyclicFolderException()
+            if (entryToCreate.isCyclic()) {
+                throw CyclicFolderException()
+            }
+            if (entryToCreate.deepHasDuplicateNames()) {
+                throw DuplicateEntryNameException()
+            }
         }
 
         val queue =
             ArrayDeque(
                 listOf(
-                    entryToCreate to Path.of(destination),
+                    entryToCreate to Path(destination),
                 ),
             )
 
@@ -31,13 +39,13 @@ class FSCreator {
             val path = dest.resolve(entry.name)
             try {
                 when (entry) {
-                    is FSFile -> Files.createFile(path)
+                    is FSFile -> path.createFile()
-                    is FSFolder -> Files.createDirectory(path)
+                    is FSFolder -> path.createDirectory()
                 }
             } catch (_: FileAlreadyExistsException) {
             } // Allow files/folders to already exist.
             when (entry) {
-                is FSFile -> Files.write(path, entry.content.toByteArray())
+                is FSFile -> path.writeText(entry.content)
                 is FSFolder -> queue.addAll(entry.entries.map { it to path })
             }
         }
@@ -45,3 +53,5 @@ class FSCreator {
 }
 
 class CyclicFolderException : Exception("Cyclic FSFolders are not supported")
+
+class DuplicateEntryNameException : Exception("Folder contains entries with duplicate names")

src/main/kotlin/filesystem/FSEntry.kt

@@ -1,8 +1,18 @@
 package filesystem
 
+import kotlin.io.path.Path
+
 // Note sealed allows for simpler logic in FSCreator by guaranteeing FSFile and FSFolder are the only possible FSEntries
 // (as we expect), and it also implicitly makes the class abstract as required.
-sealed class FSEntry(val name: String)
+sealed class FSEntry(val name: String) {
+    init {
+        val p = Path(name)
+        // Only allow single filenames (no paths or relative references (e.g. ".."))
+        if (p.toList().size != 1 || p.fileName != p.toFile().canonicalFile.toPath().fileName) {
+            throw InvalidEntryNameException(name)
+        }
+    }
+}
 
 class FSFile(name: String, val content: String) : FSEntry(name)
 
@@ -24,4 +34,26 @@ class FSFolder(name: String, val entries: List<FSEntry>) : FSEntry(name) {
         }
         return false
     }
+
+    /**
+     * Check whether a folder contains multiple entries with the same name.
+     */
+    fun hasDuplicateNames(): Boolean {
+        val seen = HashSet<String>()
+        return entries.any { !seen.add(it.name) }
+    }
+
+    internal fun deepHasDuplicateNames(): Boolean {
+        val queue = ArrayDeque(listOf(this))
+        while (queue.isNotEmpty()) {
+            val entry = queue.removeFirst()
+            if (entry.hasDuplicateNames()) {
+                return true
+            }
+            queue.addAll(entry.entries.mapNotNull { it as? FSFolder })
+        }
+        return false
+    }
 }
+
+class InvalidEntryNameException(name: String) : Exception("Invalid FSEntry name: '$name'")

src/test/kotlin/filesystem/FSCreatorTest.kt

@@ -1,9 +1,10 @@
 package filesystem
 
 import org.junit.jupiter.api.*
-import java.nio.file.Files
+import java.io.File
-import java.nio.file.Path
 import java.util.concurrent.TimeUnit
+import kotlin.io.path.Path
+import kotlin.io.path.createDirectory
 import kotlin.test.Test
 import kotlin.test.assertEquals
 
@@ -13,17 +14,26 @@ class FSCreatorTest {
     @BeforeEach
     fun `before each`() {
         assertDoesNotThrow("should create _tmp directory") {
-            Files.createDirectory(Path.of("_tmp"))
+            Path("_tmp").createDirectory()
         }
     }
 
     @AfterEach
     fun `after each`() {
         assertDoesNotThrow("should delete _tmp directory") {
-            deleteRecursive(Path.of("_tmp"))
+            File("_tmp").deleteRecursively()
         }
     }
 
+    @Test
+    fun `create file`() {
+        val file = FSFile("test.txt", "This is a file")
+        assertDoesNotThrow("should create file") {
+            creator.create(file, "_tmp")
+        }
+        assertEquals(file.content, File("_tmp/", file.name).readText())
+    }
+
     @Test
     fun `create entries`() {
         val readme = FSFile("README", "Hello World!")
@@ -61,10 +71,10 @@ class FSCreatorTest {
         }
         // If objects don't exist, these functions will throw anyway, so don't explicitly check for existence.
         // Similarly, don't explicitly check if an object is a directory.
-        assertEquals(readme.content, Files.readString(Path.of("_tmp/folder", readme.name)))
+        assertEquals(readme.content, File("_tmp/folder", readme.name).readText())
-        assertEquals(gomod.content, Files.readString(Path.of("_tmp/folder", gomod.name)))
+        assertEquals(gomod.content, File("_tmp/folder", gomod.name).readText())
-        assertEquals(maingo.content, Files.readString(Path.of("_tmp/folder", maingo.name)))
+        assertEquals(maingo.content, File("_tmp/folder", maingo.name).readText())
-        assertEquals(helloworldgo.content, Files.readString(Path.of("_tmp/folder/utils", helloworldgo.name)))
+        assertEquals(helloworldgo.content, File("_tmp/folder/utils", helloworldgo.name).readText())
     }
 
     @Test
@@ -94,6 +104,7 @@ class FSCreatorTest {
                     "folder",
                     listOf(
                         FSFolder(
+                            // Repeated name should be fine here (not throw)
                             "folder",
                             listOf(
                                 FSFolder(
@@ -111,11 +122,11 @@ class FSCreatorTest {
                 "_tmp",
             )
         }
-        assertEquals("hi", Files.readString(Path.of("_tmp/folder/sub-folder/hi")))
+        assertEquals("hi", File("_tmp/folder/sub-folder/hi").readText())
-        assertEquals("P4ssW0rd", Files.readString(Path.of("_tmp/folder/folder/secrets/secret")))
+        assertEquals("P4ssW0rd", File("_tmp/folder/folder/secrets/secret").readText())
-        assertEquals("One is a good number", Files.readString(Path.of("_tmp/folder/1.txt")))
+        assertEquals("One is a good number", File("_tmp/folder/1.txt").readText())
-        assertEquals("Two!", Files.readString(Path.of("_tmp/folder/2.txt")))
+        assertEquals("Two!", File("_tmp/folder/2.txt").readText())
-        assertEquals("Three!", Files.readString(Path.of("_tmp/folder/3.txt")))
+        assertEquals("Three!", File("_tmp/folder/3.txt").readText())
     }
 
     @Test
@@ -142,13 +153,34 @@ class FSCreatorTest {
             creator.create(folder4, "_tmp")
         }
     }
-}
 
-fun deleteRecursive(path: Path) {
+    @Test
-    if (Files.isDirectory(path)) {
+    fun `create throws on folder with duplicate names`() {
-        for (child in Files.list(path)) {
+        val folder =
-            deleteRecursive(child)
+            FSFolder(
+                "folder",
+                listOf(
+                    FSFile("README.md", "# Test File"),
+                    FSFile("hello-world.txt", "Hello World!"),
+                    FSFolder(
+                        "src",
+                        listOf(
+                            FSFile("README.md", "# Source files"),
+                            FSFolder(
+                                "solution",
+                                listOf(
+                                    FSFile("solution.py", "print('1 + 1 = 1')"),
+                                    FSFile("tmp", "A temporary file"),
+                                    FSFolder("tmp", listOf()),
+                                ),
+                            ),
+                        ),
+                    ),
+                    FSFolder("tmp", listOf()),
+                ),
+            )
+        assertThrows<DuplicateEntryNameException> {
+            creator.create(folder, "_tmp")
         }
     }
-    Files.delete(path)
 }

src/test/kotlin/filesystem/FSEntryTest.kt

@@ -1,10 +1,34 @@
 package filesystem
 
-import org.junit.jupiter.api.Test
+import org.junit.jupiter.api.*
 import kotlin.test.assertFalse
 import kotlin.test.assertTrue
 
 class FSEntryTest {
+    @Test
+    fun `valid name entries`() {
+        assertDoesNotThrow("should construct FSFile and FSFolder without throwing") {
+            FSFile("A file with a name.tar.xz", "Contents")
+            FSFolder(".a folder with a name", listOf())
+        }
+    }
+
+    @Test
+    fun `invalid name entries`() {
+        assertThrows<InvalidEntryNameException> {
+            FSFile("File/here", "Contents")
+        }
+        assertThrows<InvalidEntryNameException> {
+            FSFolder("Folder/here", listOf())
+        }
+        assertThrows<InvalidEntryNameException> {
+            FSFolder(".", listOf())
+        }
+        assertThrows<InvalidEntryNameException> {
+            FSFolder("/", listOf())
+        }
+    }
+
     @Test
     fun `non-cyclic folder`() {
         val folder =
@@ -39,4 +63,74 @@ class FSEntryTest {
         assertTrue(folder3.isCyclic())
         assertTrue(folder4.isCyclic())
     }
+
+    @Test
+    fun `no duplicate names folder`() {
+        val folder =
+            FSFolder(
+                "folder",
+                listOf(
+                    FSFile("README.md", "# Test File"),
+                    FSFile("hello-world.txt", "Hello World!"),
+                    FSFolder(
+                        "src",
+                        listOf(
+                            FSFile("README.md", "# Source files"),
+                            FSFile("solution-1.py", "print('1 + 1 = 1')"),
+                            FSFile("solution-2.py", "print('1 + 1 = 1')"),
+                        ),
+                    ),
+                    FSFolder("tmp", listOf()),
+                ),
+            )
+        assertFalse(folder.hasDuplicateNames())
+        assertFalse(folder.deepHasDuplicateNames())
+    }
+
+    @Test
+    fun `shallow duplicate names folder`() {
+        val folder =
+            FSFolder(
+                "folder",
+                listOf(
+                    FSFile("README.md", "# Test File"),
+                    FSFile("hello-world.txt", "Hello World!"),
+                    FSFolder(
+                        "src",
+                        listOf(
+                            FSFile("README.md", "# Source files"),
+                            FSFile("solution-1.py", "print('1 + 1 = 1')"),
+                            FSFile("solution-2.py", "print('1 + 1 = 1')"),
+                        ),
+                    ),
+                    FSFolder("tmp", listOf()),
+                    FSFile("tmp", "A temporary file"),
+                ),
+            )
+        assertTrue(folder.hasDuplicateNames())
+        assertTrue(folder.deepHasDuplicateNames())
+    }
+
+    @Test
+    fun `deep duplicate names folder`() {
+        val folder =
+            FSFolder(
+                "folder",
+                listOf(
+                    FSFile("README.md", "# Test File"),
+                    FSFile("hello-world.txt", "Hello World!"),
+                    FSFolder(
+                        "src",
+                        listOf(
+                            FSFile("README.md", "# Source files"),
+                            FSFile("solution-1.py", "print('1 + 1 = 1')"),
+                            FSFile("solution-1.py", "print('1 + 1 = 1')"),
+                        ),
+                    ),
+                    FSFolder("tmp", listOf()),
+                ),
+            )
+        assertFalse(folder.hasDuplicateNames())
+        assertTrue(folder.deepHasDuplicateNames())
+    }
 }