page.h

#ifndef PAGE_H
#define PAGE_H

#include "error.h"

// Record ID - used to identify tuples based on page and slot number
struct RID{
  int  pageNo;
  int  slotNo;
  bool operator == (const RID & other) const
  {
    return ((other.pageNo == pageNo) && (other.slotNo == slotNo));
  }

  RID() {reset();}
  void reset() {pageNo = -1; slotNo = -1;}
};

// Record - pointer to start of tuple and length of the record
struct Record
{
  void* data;
  int length;
};

// slot structure
struct slot_t {
        short	offset;  
        short	length;  // equals -1 if slot is not in use
};

const unsigned PAGESIZE = 1024;
// DPFIXED - amount of space reserved for book-keeping. Please
// note that the Page class has 4 shorts and 3 ints which must be
// subtracted from space availale for data.
const unsigned DPFIXED= sizeof(slot_t)+4*sizeof(short)+3*sizeof(int);

// Class definition for a minirel data page.   
// The design assumes that records are kept compacted when
// deletions are performed. Notice, however, that the slot
// array cannot be compacted.  
//
// Notice, this class does not delineate records by column, 
// instead it relies on other parts of the database to ensure
// correct byte offset of the various columns

class Page {
private:
    char 	data[PAGESIZE - DPFIXED]; // all record data + slot array stored here 
    slot_t 	slot[1]; // first element of slot array - grows backwards!
    short	slotCnt; // number of slots in use;
    short	freePtr; // offset of first free byte in data[]
    short	freeSpace; // number of bytes free in data[]
    short	dummy;	// for alignment purposes
    int		prevPage; // backwards pointer
    int		nextPage; // forwards pointer
    int		curPage;  // page number of current pointer

public:
    void init(const int pageNo); // initialize a new page
    void dumpPage() const;       // dump contents of a page

    const int getNextPage() const; // returns value of nextPage
    const int getPrevPage() const; // returns value of prevPage
    void setNextPage(const int pageNo); // sets value of nextPage to pageNo
    void setPrevPage(const int pageNo); // sets value of prevPage to pageNo
    const short getFreeSpace() const; // returns amount of free space

    // inserts a new record (rec) into the page, returns RID of record 
    const Status insertRecord(const Record & rec, RID& rid);

    // delete the record with the specified rid
    const Status deleteRecord(const RID & rid);

    // returns RID of first record on page
    // returns  NORECORDS if page contains no records.  Otherwise, returns OK
    const Status firstRecord(RID& firstRid) const;

    // returns RID of next record on the page 
    // returns ENDOFPAGE if no more records exist on the page
    const Status nextRecord (const RID & curRid, RID& nextRid) const;

    // returns reference to record with RID rid
    const Status getRecord(const RID & rid, Record & rec);
};

#endif