package simpledb;
import java.util.*;

/**
 * Page is the interface used to represent pages that are resident in the
 * BufferPool.  Typically, DbFiles will read and write pages from disk.
 * <p>
 * Pages may be "dirty", indicating that they have been modified since they
 * were last written out to disk.
 *
 * For recovery purposes, pages MUST have a single constructor of the form:
 *     Page(PageId id, byte[] data)
 */
public interface Page {
    
    /**
     * Return the id of this page.  The id is a unique identifier for a page
     * that can be used to look up the page on disk or determine if the page
     * is resident in the buffer pool.
     *
     * @return the id of this page
     */
    public PageId id();

    /**
     * Returns a Java iterator that iterates through the tuples of this page.
     * The type of the Object return by each call to Iterator.getNext is
     * Tuple.
     *
     * @return The iterator.
     * @see Tuple
     */
    public Iterator iterator();

    /**
     * Returns true if this page is dirty.
     *
     * @return The id of the transaction that last dirtied this page, or null
     */
    public TransactionId isDirty();
    
  /**
   * Set the dirty state of this page as dirtied by a particular transaction
   */
    public void markDirty(boolean dirty, TransactionId tid);

  /**
   * Generates a byte array representing the contents of this page.
   * Used to serialize this page to disk.
   * <p>
   * The invariant here is that it should be possible to pass the byte array
   * generated by getPageData to the Page constructor and have it produce
   * an identical Page object.
   *
   * @return A byte array correspond to the bytes of this page.
   */

    public byte[] getPageData();

    /** Provide a representation of this page before any modifications were made
	to it.  Used by recovery.
    */
    public Page getBeforeImage();      

    /** 
     *  Return the size of the byte array returned by getPageData()
     *	@return the size of the byte array
     *  @see #getPageData
     */
    public int getPageSize();
}