Can advance byte index in byte stream

2016-03-13 11:34:53 +00:00
parent 8faed1ba29
commit 167579afaa
3 changed files with 65 additions and 0 deletions
@@ -17,5 +17,7 @@ public protocol ByteStream {
    func nextBytes(numberOfBytes: Int) -> NSData?

    func indexIsValid(index: Int) -> Bool
+    
+    func advanceBy(numberOfBytes: Int)

 }
@@ -48,4 +48,18 @@ class NSDataByteStream: ByteStream {
        return index >= 0 && index <= self.length
    }
    
+    func advanceBy(numberOfBytes: Int) {
+        
+        let finalIndex = self.currentIndex + numberOfBytes
+        
+        if finalIndex > self.length {
+            self.advancePointer(self.length - self.currentIndex)
+        } else if finalIndex < 0 {
+            self.advancePointer(-self.currentIndex)
+        } else {
+            self.advancePointer(numberOfBytes)
+        }
+        
+    }
+    
 }
@@ -84,4 +84,53 @@ class NSDataByteStreamTests: XCTestCase {
        XCTAssertEqual(bytes, NSData(byteArray: [5, 6]))
        XCTAssertEqual(byte, UInt8(7))
    }
+    
+    func testCanAdvanceForward1Byte() {
+        let byteStream = NSDataByteStream(data: NSData(byteArray: [5, 6, 7, 8]))
+        byteStream.advanceBy(1)
+        let byte = byteStream.nextByte()
+        XCTAssertEqual(byte, 6)
+    }
+    
+    func testCanAdvanceForwardMultipleBytes() {
+        let byteStream = NSDataByteStream(data: NSData(byteArray: [5, 6, 7, 8]))
+        byteStream.advanceBy(3)
+        let byte = byteStream.nextByte()
+        XCTAssertEqual(byte, 8)
+    }
+    
+    func testCanAdvanceBackward1Byte() {
+        let byteStream = NSDataByteStream(data: NSData(byteArray: [5, 6, 7, 8]))
+        
+        var byte = byteStream.nextByte()
+        XCTAssertEqual(byte, 5)
+        
+        byteStream.advanceBy(-1)
+        byte = byteStream.nextByte()
+        XCTAssertEqual(byte, 5)
+    }
+    
+    func testCanAdvanceBackwardMultipleBytes() {
+        let byteStream = NSDataByteStream(data: NSData(byteArray: [5, 6, 7, 8]))
+        
+        var byte = byteStream.nextByte()
+        byte = byteStream.nextByte()
+        XCTAssertEqual(byte, 6)
+        
+        byteStream.advanceBy(-2)
+        byte = byteStream.nextByte()
+        XCTAssertEqual(byte, 5)
+    }
+    
+    func testAdvanceForwardTooFarStopsAtEnd() {
+        let byteStream = NSDataByteStream(data: NSData(byteArray: [5, 6, 7, 8]))
+        byteStream.advanceBy(999)
+        XCTAssertEqual(byteStream.currentIndex, 4)
+    }
+    
+    func testAdvanceBackTooFarStopsAtBeggining() {
+        let byteStream = NSDataByteStream(data: NSData(byteArray: [5, 6, 7, 8]))
+        byteStream.advanceBy(-999)
+        XCTAssertEqual(byteStream.currentIndex, 0)
+    }
 }