cs660-pa/include/db/BTreeHeaderPage.h at main · teobag/cs660-pa · GitHub

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#ifndef DB_BTREE_HEADERPAGE_H
#define DB_BTREE_HEADERPAGE_H

#include <db/Page.h>
#include <db/BTreePageId.h>
#include <cstdint>

namespace db {
    /**
     * Each instance of BTreeHeaderPage stores data for one page of a BTreeFile and
     * implements the Page interface that is used by BufferPool.
     *
     * @see BTreeFile
     * @see BufferPool
     *
     */
    class BTreeHeaderPage : public Page {
        int nextPage; // next header page or 0
        int prevPage; // previous header page or 0
        const BTreePageId *pid;
        uint8_t *header;
        int numSlots;

        /**
         * Computes the number of bytes in the header while saving room for pointers
         */
        static int getHeaderSize();

    public:

        /**
         * Create a BTreeHeaderPage from a set of bytes of data read from disk.
         * The format of a BTreeHeaderPage is two pointers to the next and previous
         * header pages, followed by a set of bytes indicating which pages in the file
         * are used or available
         * @see BufferPool#getPageSize()
         *
         */
        BTreeHeaderPage(const BTreePageId *id, uint8_t *data);

        /**
         * Initially mark all slots in the header used.
         */
        void init();

        /**
         * Computes the number of slots in the header
         */
        static int getNumSlots();

        /**
         * @return the PageId associated with this page.
         */
        const BTreePageId &getId() const override;

        /**
         * 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 BTreeHeaderPage constructor and
         * have it produce an identical BTreeHeaderPage object.
         *
         * @see #BTreeHeaderPage
         * @return A byte array correspond to the bytes of this page.
         */
        void *getPageData() const override;

        /**
         * Static method to generate a byte array corresponding to an empty
         * BTreeHeaderPage.
         * Used to add new, empty pages to the file. Passing the results of
         * this method to the BTreeHeaderPage constructor will create a BTreeHeaderPage with
         * no valid data in it.
         *
         * @return The returned ByteArray.
         */
        static void *createEmptyPageData();

        /**
         * Get the page id of the previous header page
         * @return the page id of the previous header page
         */
        BTreePageId *getPrevPageId();

        /**
         * Get the page id of the next header page
         * @return the page id of the next header page
         */
        BTreePageId *getNextPageId();

        /**
         * Set the page id of the previous header page
         * @param id - the page id of the previous header page
         */
        void setPrevPageId(const BTreePageId *id);

        /**
         * Set the page id of the next header page
         * @param id - the page id of the next header page
         */
        void setNextPageId(const BTreePageId *id);

        /**
         * Returns true if the page of the BTreeFile associated with slot i is used
         */
        bool isSlotUsed(int i);

        /**
         * Abstraction to mark a page of the BTreeFile used or unused
         */
        void markSlotUsed(int i, bool value);

        /**
         * get the index of the first empty slot
         * @return the index of the first empty slot or -1 if none exists
         */
        int getEmptySlot();
    };
}

#endif