From 9a4146535182c660f0d91248cad98d8f7fceb9e6 Mon Sep 17 00:00:00 2001
From: "Alkenso (Vladimir Vashurkin)" <alkensox@gmail.com>
Date: Thu, 19 Dec 2024 08:58:08 +0200
Subject: [PATCH] Introduce FileManager.uniqueFile to generate file with unique
 name

---
 .../Extensions - FileManager.swift            | 35 +++++++++++++++++++
 .../FileManagerTests.swift                    | 27 ++++++++++++++
 2 files changed, 62 insertions(+)
 rename Tests/SpellbookTests/{Extensions Tests => Filesystem & Bundle}/FileManagerTests.swift (64%)

diff --git a/Sources/SpellbookFoundation/Filesystem & Bundle/Extensions - FileManager.swift b/Sources/SpellbookFoundation/Filesystem & Bundle/Extensions - FileManager.swift
index 917930e..1162c1b 100644
--- a/Sources/SpellbookFoundation/Filesystem & Bundle/Extensions - FileManager.swift	
+++ b/Sources/SpellbookFoundation/Filesystem & Bundle/Extensions - FileManager.swift	
@@ -171,6 +171,41 @@ extension FileManager {
     }
 }
 
+extension FileManager {
+    /// Generates file with name based on string generated by `nameGenerator` call
+    /// and checks that the file does not exist on the file system.
+    ///
+    /// - Note: The call does NOT create any files.
+    public func uniqueFile(in directory: URL, _ nameGenerator: (_ attempt: Int) -> String) -> URL {
+        for attempt in 0..<Int.max {
+            let name = nameGenerator(attempt)
+            let location = directory.appendingPathComponent(name)
+            guard FileManager.default.fileExists(at: location) else { return location }
+        }
+        
+        // Should be impossible case.
+        return directory.appendingPathComponent(nameGenerator(-1) + ".invalid")
+    }
+    
+    /// Generates file with name based on `name` that does not exist on the file system.
+    /// If file with original `name` does not exist, it returns the URL with the same name.
+    /// Otherwise, it iterates over to find first non-existent file,
+    /// adding suffixes like `_3`to original `name`.
+    ///
+    /// - Note: The call does NOT create any files.
+    public func uniqueFile(_ name: String, in directory: URL) -> URL {
+        let pathExtension = name.pathExtension
+        return uniqueFile(in: directory) { attempt in
+            guard attempt > 0 else { return name }
+            var nextName = "\(name.deletingPathExtension)_\(attempt)"
+            if !pathExtension.isEmpty {
+                nextName += ".\(pathExtension)"
+            }
+            return nextName
+        }
+    }
+}
+
 extension stat {
     public var fileType: URLFileResourceType {
         URLFileResourceType(mode: st_mode)
diff --git a/Tests/SpellbookTests/Extensions Tests/FileManagerTests.swift b/Tests/SpellbookTests/Filesystem & Bundle/FileManagerTests.swift
similarity index 64%
rename from Tests/SpellbookTests/Extensions Tests/FileManagerTests.swift
rename to Tests/SpellbookTests/Filesystem & Bundle/FileManagerTests.swift
index 361cfe6..4518e09 100644
--- a/Tests/SpellbookTests/Extensions Tests/FileManagerTests.swift	
+++ b/Tests/SpellbookTests/Filesystem & Bundle/FileManagerTests.swift	
@@ -59,4 +59,31 @@ class FileManagerExtensionsTests: XCTestCase {
         try FileManager.default.removeXattr(at: file, name: "xa1")
         XCTAssertEqual(try FileManager.default.listXattr(at: file), ["xa2"])
     }
+    
+    func test_uniqueFile() {
+        let fm = FileManager.default
+        func createFile(_ name: String) -> Bool {
+            fm.createFile(atPath: tempDir.location.appendingPathComponent(name).path, contents: .random(20))
+        }
+        
+        XCTAssertEqual(fm.uniqueFile("test.foo", in: tempDir.location).lastPathComponent, "test.foo")
+        // Ensure it is not created.
+        XCTAssertEqual(fm.uniqueFile("test.foo", in: tempDir.location).lastPathComponent, "test.foo")
+        
+        XCTAssertTrue(createFile("test.foo"))
+        XCTAssertEqual(fm.uniqueFile("test.foo", in: tempDir.location).lastPathComponent, "test_1.foo")
+        
+        XCTAssertTrue(createFile("test.foo.bar"))
+        XCTAssertEqual(fm.uniqueFile("test.foo.bar", in: tempDir.location).lastPathComponent, "test.foo_1.bar")
+        
+        XCTAssertEqual(fm.uniqueFile("test", in: tempDir.location).lastPathComponent, "test")
+        XCTAssertTrue(createFile("test"))
+        XCTAssertTrue(createFile("test_1"))
+        XCTAssertTrue(createFile("test_3"))
+        XCTAssertEqual(fm.uniqueFile("test", in: tempDir.location).lastPathComponent, "test_2")
+        
+        XCTAssertEqual(fm.uniqueFile("dir/", in: tempDir.location).lastPathComponent, "dir")
+        XCTAssertTrue(createFile("dir"))
+        XCTAssertEqual(fm.uniqueFile("dir/", in: tempDir.location).lastPathComponent, "dir_1")
+    }
 }