1 files changed, 123 insertions, 0 deletions
diff --git a/src/main/java/io/trygvis/btree/HeapPage.java b/src/main/java/io/trygvis/btree/HeapPage.java
new file mode 100644
index 0000000..499a244
--- /dev/null
+++ b/src/main/java/io/trygvis/btree/HeapPage.java
@@ -0,0 +1,123 @@
+package io.trygvis.btree;
+
+import java.nio.ByteBuffer;
+import java.util.Iterator;
+import java.util.NoSuchElementException;
+
+public class HeapPage {
+    public static final int headerSize = 4;
+    public static final int FREE_POSITION_INDEX = 0;
+
+    public static final int itemSize = 4;
+
+    // The page number in a heap file
+    final long pageNumber;
+    final ByteBuffer bytes;
+    int freePosition;
+
+    private HeapPage(long pageNumber, ByteBuffer bytes, int freePosition) {
+        this.pageNumber = pageNumber;
+        this.bytes = bytes;
+        this.freePosition = freePosition;
+    }
+
+    public static HeapPage heapPageFromBytes(int pageNumber, ByteBuffer bytes) {
+        int freePosition = bytes.getInt();
+        return new HeapPage(pageNumber, bytes, freePosition);
+    }
+
+    public static HeapPage blankHeapPage(ByteBuffer bytes) {
+        return new HeapPage(-1, bytes, bytes.capacity());
+    }
+
+    public void append(byte[] item) {
+//        System.out.println("io.trygvis.btree.HeapPage.append");
+
+        int bytesFree = bytesFree();
+        int bytesRequested = item.length;
+
+        if (bytesRequested > bytesFree) {
+            throw new PageOverflowException(bytesFree, bytesRequested);
+        }
+
+        freePosition -= itemSize;
+        bytes.position(freePosition);
+        bytes.putInt(item.length);
+        freePosition -= bytesRequested;
+        bytes.position(freePosition);
+        bytes.put(item);
+
+        bytes.putInt(FREE_POSITION_INDEX, freePosition);
+    }
+
+    public int bytesFree() {
+        return freePosition - headerSize;
+    }
+
+    public Iterable<ByteBuffer> bufferIterator() {
+        return new Iterable<ByteBuffer>() {
+            @Override
+            public Iterator<ByteBuffer> iterator() {
+                return new Iterator<ByteBuffer>() {
+                    private int position;
+
+                    private ByteBuffer next;
+
+                    {
+                        position = bytes.capacity();
+                        next = findNext();
+                    }
+
+                    private ByteBuffer findNext() {
+                        if (position == headerSize) {
+                            return null;
+                        }
+
+                        int size = bytes.getInt(position - itemSize);
+
+                        if (size == 0) {
+                            return null;
+                        }
+
+                        position -= itemSize + size;
+                        ByteBuffer copy = bytes.duplicate();
+                        copy.position(position);
+                        copy.limit(position + size);
+                        return copy.slice();
+                    }
+
+                    public boolean hasNext() {
+                        return next != null;
+                    }
+
+                    @Override
+                    public ByteBuffer next() {
+                        if (next == null) {
+                            throw new NoSuchElementException();
+                        }
+
+                        ByteBuffer n = next;
+                        next = findNext();
+                        return n;
+                    }
+
+                    @Override
+                    public void remove() {
+                        throw new UnsupportedOperationException();
+                    }
+                };
+            }
+        };
+    }
+
+    public static class PageOverflowException extends RuntimeException {
+        public final int bytesFree;
+        public final int bytesRequested;
+
+        public PageOverflowException(int bytesFree, int bytesRequested) {
+            super("Not enough room on page, bytes free=" + bytesFree + ", requested = " + bytesRequested);
+            this.bytesFree = bytesFree;
+            this.bytesRequested = bytesRequested;
+        }
+    }
+}