/*************************************************************************
** File-system interface.
*/
typedef struct bt_env bt_env;
typedef struct bt_file bt_file;




struct bt_env {
  void *pVfsCtx;
  int (*xFullpath)(sqlite4_env*,bt_env*, const char *, char **);
  int (*xOpen)(sqlite4_env*,bt_env*, const char *, int flags, bt_file**);

  int (*xRead)(bt_file*, i64, void *, int);
  int (*xWrite)(bt_file*, i64, void *, int);
  int (*xTruncate)(bt_file*, i64);
  int (*xSync)(bt_file*);
  int (*xSectorSize)(bt_file*);
  int (*xClose)(bt_file*);
  int (*xUnlink)(sqlite4_env*,bt_env*, const char *);
................................................................................

/* Find the default VFS */
bt_env *sqlite4BtEnvDefault(void);

/*
** End of file system interface.
*************************************************************************/

/*************************************************************************
** File-system interface.
*/
typedef struct bt_env bt_env;
typedef struct bt_file bt_file;

/*
** xFullpath:
*/
struct bt_env {
  void *pVfsCtx;
  int (*xFullpath)(sqlite4_env*,bt_env*, const char *, char **);
  int (*xOpen)(sqlite4_env*,bt_env*, const char *, int flags, bt_file**);
  int (*xSize)(bt_file*, i64*);
  int (*xRead)(bt_file*, i64, void *, int);
  int (*xWrite)(bt_file*, i64, void *, int);
  int (*xTruncate)(bt_file*, i64);
  int (*xSync)(bt_file*);
  int (*xSectorSize)(bt_file*);
  int (*xClose)(bt_file*);
  int (*xUnlink)(sqlite4_env*,bt_env*, const char *);
................................................................................

/* Find the default VFS */
bt_env *sqlite4BtEnvDefault(void);

/*
** End of file system interface.
*************************************************************************/

/*
** 2013 September 14
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
*/

#include "btInt.h"

/* By default pages are 1024 bytes in size. */
#define BT_DEFAULT_PGSZ 1024

typedef struct BtPageHash BtPageHash;
typedef struct BtDbhdr BtDbhdr;

/*
** Hash table for page references currently in memory. Manipulated using
** the following functions:
**
**     btHashAdd()
**     btHashRemove()
**     btHashSearch()
**     btHashClear()
*/
struct BtPageHash {
  int nEntry;                     /* Number of entries in hash table */
  int nHash;                      /* Size of aHash[] array */
  BtPage **aHash;                 /* Hash array */
};

struct BtPage {
  BtPager *pPager;                /* Pager object that owns this page handle */
  u32 pgno;                       /* Current page number */
  int nRef;                       /* Number of references to this page */
  int flags;                      /* Mask of BTPAGE_XXX flags */
  u8 *aData;                      /* Pointer to current data */
  BtPage *pNextHash;              /* Next entry with same hash key */
  BtPage *pNextDirty;             /* Next page in BtPager.pDirty list */
};

/*
** Candidate values for BtPage.flags
*/
#define BT_PAGE_DIRTY 0x0001      /* Set for pages in BtPager.pDirty list */

/*
** Pager object.
*/
struct BtPager {
  sqlite4_env *pEnv;              /* SQLite environment */
  bt_env *pVfs;                   /* Bt environment */
  int iTransactionLevel;          /* Current transaction level (see bt.h) */
  char *zFile;                    /* Database file name */
  int nFile;                      /* Length of string zFile in bytes */
  bt_file *pFd;                   /* Database file */
  BtPageHash hash;                /* Hash table */
  BtPage *pDirty;                 /* List of all dirty pages */
};

/*
** Database header.
*/
struct BtDbhdr {
  u32 pgsz;                       /* Page size in bytes */
  u32 nPg;                        /* Number of pages in database */
  u32 cookie;                     /* User cookie value */
};



/**************************************************************************
** Interface to BtPageHash object.
*/

/*
** Return the hash key for page number pgno in a hash table with nHash
** buckets.
*/
static int hashkey(int nHash, u32 pgno){
  return (pgno % nHash);
}

/*
** Add page pPg to the hash table.
*/
static int btHashAdd(BtPager *p, BtPage *pPg){
  BtPage **pp;
  int h;

  /* If required, increase the number of buckets in the hash table. */
  if( p->hash.nEntry>=p->hash.nHash/2 ){
    int i;
    int nNew = (p->hash.nHash ? p->hash.nHash*2 : 256);
    BtPage **aNew;
    BtPage **aOld = p->hash.aHash;

    aNew = (BtPage **)sqlite4_malloc(p->pEnv, nNew*sizeof(BtPage*));
    if( aNew==0 ) return SQLITE4_NOMEM;
    memset(aNew, 0, nNew*sizeof(BtPage*));
    for(i=0; i<p->hash.nHash; i++){
      while( aOld[i] ){
        BtPage *pShift = aOld[i];
        aOld[i] = pShift->pNextHash;
        h = hashkey(nNew, pPg->pgno);
        pShift->pNextHash = aNew[h];
        aNew[h] = pShift;
      }
    }
    p->hash.aHash = aNew;
    p->hash.nHash = nNew;
    sqlite4_free(p->pEnv, aOld);
  }

  /* Add the new entry to the hash table. */
  assert( pPg->pNextHash==0 );
  h = hashkey(p->hash.nHash, pPg->pgno);
  pPg->pNextHash = p->hash.aHash[h];
  p->hash.aHash[h] = pPg;
  p->hash.nEntry++;
}

/*
** Remove page pPg from the hash table.
*/
static void btHashRemove(BtPager *p, BtPage *pPg){
  BtPage **pp;
  int h = hashkey(p->hash.nHash, pPg->pgno);
  for(pp=&p->hash.aHash[h]; *pp!=pPg; pp = &((*pp)->pNextHash));
  *pp = pPg->pNextHash;
  p->hash.nEntry--;
}

/*
** Search the hash table for a page with page number pgno. If found, return
** a pointer to the BtPage object. Otherwise, return NULL.
*/
static BtPage *btHashSearch(BtPager *p, u32 pgno){
  int h = hashkey(p->hash.nHash, pgno);
  BtPage *pRet;
  for(pRet=p->hash.aHash[h]; pRet && pRet->pgno!=pgno; pRet=pRet->pNextHash);
  return pRet;
}

/*
** Remove all entries from the hash-table. And free any allocations made
** by earlier calls to btHashAdd().
*/
static void btHashClear(BtPager *p){
  sqlite4_free(p->pEnv, p->hash.aHash);
  memset(&p->hash, 0, sizeof(BtPageHash));
}
/*
** End of BtPageHash object interface.
**************************************************************************/

/*
** Open a new pager database handle.
*/
int sqlite4BtPagerNew(sqlite4_env *pEnv, int nExtra, BtPager **pp){
  BtPager *p;
  int nByte;

  nByte = sizeof(BtPager) + nExtra;
  p = (BtPager*)sqlite4_malloc(pEnv, nByte);
  if( !p ) return SQLITE4_NOMEM; 
  memset(0, p, nByte);

  p->pEnv = pEnv;
  p->pVfs = sqlite4BtEnvDefault();
  *pp = p;
  return SQLITE4_OK;
}

/*
** Close a pager database handle.
*/
int sqlite4BtPagerClose(BtPager *p){
  if( p->pFd ){
    p->pVfs->xClose(p->pFd);
  }
  btHashClear(p);
  sqlite4_free(p->pEnv, p->zFile);
  sqlite4_free(p->pEnv, p);
  return SQLITE4_OK;
}

/*
** Return a pointer to the nExtra bytes of space allocated by PagerNew().
*/
void *sqlite4BtPagerExtra(BtPager *p){
  return (void*)&p[1];
}

/*
** Attach a database file to a pager object.
**
** This function may only be called once for each BtPager object. If it
** fails, the BtPager is rendered unusable (and must be closed by the
** caller using BtPagerClose()).
**
** If successful, SQLITE4_OK is returned. Otherwise, an SQLite error code.
*/
int sqlite4BtPagerOpen(BtPager *p, const char *zFilename){
  int flags = 0;                  /* Flags to pass to xOpen() */
  sqlite4_env *pEnv = p->pEnv;
  bt_env *pVfs = p->pVfs;

  assert( p->pFd==0 && p->zFilename==0 );

  rc = pVfs->xFullpath(pEnv, pVfs, zFilename, &p->zFile);
  if( rc==SQLITE4_OK ){
    p->nFile = strlen(p->zFile);
    rc = pVfs->xOpen(pEnv, pVfs, zFilename, flags, &p->pFd);
  }

  assert( (rc==SQLITE4_OK)==(p->pFd!=0) );
  return rc;
}

/*
** Open a read-transaction.
*/
static int btOpenReadTransaction(BtPager *p){
  int rc;
  i64 nByte;                      /* Size of db file in bytes */

  assert( p->iTransactionLevel==0 );
  assert( p->pFd );

  rc = p->pVfs->xSize(p->pFd, &nByte);
  if( rc==SQLITE4_OK && nByte>0 ){
    rc = p->pVfs->xRead(p->pFd, 0, &p->dbhdr, sizeof(p->dbhdr));
  }else{
    memset(&p->dbhdr, 0, sizeof(p->dbhdr));
    p->dbhdr.pgsz = BT_DEFAULT_PGSZ;
  }

  return rc;
}

static int btCommitTransaction(BtPager *p){
  int rc = SQLITE4_OK;
  BtPage *pPg;
  BtPage *pNext;
  assert( p->iTransactionLevel>=2 );

  for(pPg=p->pDirty; pPg; pPg=pNext){
    pNext = pPg->pNextDirty;
    pPg->flags &= ~(BT_PAGE_DIRTY);
    pPg->pNextDirty = 0;
    if( rc==SQLITE4_OK ){
      i64 iOff = (i64)p->dbhdr.pgsz * (i64)(pPg->pgno-1);
      rc = p->pVfs->xWrite(p->pFd, iOff, pPg->aData, p->dbhdr.pgsz);
    }
  }
  p->pDirty = 0;

  if( rc==SQLITE4_OK ){
    rc = p->pVfs->xWrite(p->pFd, 0, (void*)&p->dbhdr, sizeof(BtDbhdr));
  }

  return rc;
}

/*
** Transactions. These methods are more or less the same as their 
** counterparts in bt.h.
*/
int sqlite4BtPagerBegin(BtPager *p, int iLevel){
  int rc = SQLITE4_OK;
  assert( p->pFd );

  if( p->iTransactionLevel<iLevel ){
    /* Open a read transaction if one is not already open */
    if( p->iTransactionLevel==0 ){
      rc = btOpenReadTransaction(p);
    }

    if( rc==SQLITE4_OK ){
      assert( p->iTransactionLevel>=1 && iLevel>=p->iTransactionLevel );
      p->iTransactionLevel = iLevel;
    }
  }

  return rc;
}

int sqlite4BtPagerCommit(BtPager *p, int iLevel){
  int rc = SQLITE4_OK;

  assert( p->pFd );
  if( p->iTransactionLevel>=iLevel ){
    if( p->iTransactionLevel>=2 && iLevel<2 ){
      /* Commit the main write transaction. */
      rc = btCommitTransaction(p);
    }
    p->iTransactionLevel = iLevel;
  }
  return rc;
}

int sqlite4BtPagerRollback(BtPager *p, int iLevel){
  assert( p->pFd );
  if( p->iTransactionLevel>=iLevel ){
  }
}

int sqlite4BtPagerRevert(BtPager *p, int iLevel){
  assert( p->pFd );
  rc = sqlite4BtPagerRollback(p, iLevel);
  if( rc==SQLITE4_OK && iLevel>=2 && p->iTransactionLevel==iLevel ){
    /* Rollback (but do not close) transaction iLevel */
  }
}

/*
** Return the current transaction level.
*/
int sqlite4BtPagerTransactionLevel(BtPager *p){
  return p->iTransactionLevel;
}

/*
** Query for the database page size. Requires an open read transaction.
*/
int sqlite4BtPagerPagesize(BtPager *p, int *pnByte){
  assert( p->iTransactionLevel>=1 && p->pFd );
  *pnByte = (int)p->dbhdr.pgsz;
  return SQLITE4_OK;
}

/* 
** Query for the root page number. Requires an open read transaction.
*/
int sqlite4BtPagerRootpgno(BtPager *p, u32 *piRoot){
  assert( p->iTransactionLevel>=1 && p->pFd );
  *piRoot = 2;
  return SQLITE4_OK;
}

static int btAllocatePage(BtPager *p, BtPage **ppPg){
  BtPage *pRet;
  u8 *aData;

  pRet = (BtPage*)sqlite4_malloc(p->pEnv, sizeof(BtPage));
  aData = (u8*)sqlite4_malloc(p->pEnv, p->dbhdr.pgsz);

  if( pRet && aData ){
    memset(pRet, 0, sizeof(BtPage));
    pRet->aData = aData;
    pRet->pPager = p;
    rc = SQLITE4_OK;
  }else{
    sqlite4_free(p->pEnv, pRet);
    sqlite4_free(p->pEnv, aData);
    rc = SQLITE4_NOMEM;
    pRet = 0;
  }

  *ppPg = pRet;
  return rc;
}

static void btFreePage(BtPager *p, BtPage *pPg){
  if( pPg ){
    sqlite4_free(p->pEnv, pPg->aData);
    sqlite4_free(p->pEnv, pPg);
  }
}

/*
** Read, write and trim existing database pages.
*/
int sqlite4BtPageGet(BtPager *p, u32 pgno, BtPage **ppPg){
  int rc = SQLITE4_OK;            /* Return code */
  BtPage *pRet;                   /* Returned page handle */

  /* Search the cache for an existing page. */
  pRet = btHashSearch(p, pgno);

  /* If the page is not in the cache, load it from disk */
  if( pRet==0 ){
    rc = btAllocatePage(p, &pRet);
    if( rc==SQLITE4_OK ){
      pRet->pgno = pgno;
      if( pgno<=p->dbhdr.nPg ){
        i64 iOff = (i64)p->dbhdr.pgsz * (i64)(pgno-1);
        rc = p->pVfs->xRead(p->pFd, iOff, pRet->aData, p->dbhdr.pgsz);
      }else{
        memset(pRet->aData, 0, p->dbhdr.pgsz);
      }

      if( rc==SQLITE4_OK ){
        rc = btHashAdd(p, pRet);
      }
      if( rc!=SQLITE4_OK ){
        btFreePage(p, pRet);
        pRet = 0;
      }
    }
  }

  if( rc==SQLITE4_OK ){
    pRet->nRef++;
    *ppPg = pRet;
  }
  return rc;
}

int sqlite4BtPageWrite(BtPage *pPg){
  if( (pPg->flags & BT_PAGE_DIRTY)==0 ){
    pPg->flags |= BT_PAGE_DIRTY;
    pPg->pNextDirty = pPg->pPager->pDirty;
    pPg->pPager->pDirty = pPg;
  }
  return SQLITE4_OK;
}

int sqlite4BtPageTrim(BtPage *pPg){
  assert( !"todo" );
  return SQLITE4_OK;
}

int sqlite4BtPageRelease(BtPage *pPg){
  assert( pPg->nRef>=1 );
  pPg->nRef--;
  return SQLITE4_OK;
}

/*
** Allocate a new database page and return a writable reference to it.
*/
int sqlite4BtPageAllocate(BtPager *p, BtPage **ppPg){
  BtPage *pPg = 0;
  int rc;
  u32 pgno = p->dbhdr.nPg;

  rc = sqlite4BtPageGet(p, pgno, &pPg);
  if( rc==SQLITE4_OK ){
    rc = sqlite4BtPageWrite(pPg);
    if( rc!=SQLITE4_OK ){
      sqlite4BtPageRelease(pPg);
      pPg = 0;
    }else{
      p->dbhdr.nPg = pgno+1;
    }
  }

  *ppPg = pPg;
  return rc;
}

/*
** Return the current page number of the argument page reference.
*/
u32 sqlite4BtPagePgno(BtPage *pPg){
  return pPg->pgno;
}

/*
** Return a pointer to the data buffer associated with page pPg.
*/
void *sqlite4BtPageData(BtPage *pPg){
  return pPg->aData;
}

/* 
** Read the schema cookie value. Requires an open read-transaction.
*/
int sqlite4BtPagerSetCookie(BtPager *p, u32 iVal){
  assert( p->iTransactionLevel>=2 );
  p->dbhdr.cookie = iVal;
}

/* 
** Set the schema cookie value. Requires an open write-transaction.
*/
int sqlite4BtPagerGetCookie(BtPager *p, u32 *piVal){
  assert( p->iTransactionLevel>=1 );
  *piVal = p->dbhdr.cookie;
}

      rc = btErrorBkpt(SQLITE4_IOERR);
    }
  }

  *ppFile = (bt_file*)p;
  return rc;
}















static int btPosixOsWrite(
  bt_file *pFile,                 /* File to write to */
  i64 iOff,                       /* Offset to write to */
  void *pData,                    /* Write data from this buffer */
  int nData                       /* Bytes of data to write */
){
................................................................................
  }else{
    ssize_t prc = read(p->fd, pData, (size_t)nData);
    if( prc<0 ){ 
      rc = btErrorBkpt(SQLITE4_IOERR);
    }else if( prc<nData ){
      memset(&((u8 *)pData)[prc], 0, nData - prc);
    }

  }

  return rc;
}

static int btPosixOsSync(bt_file *pFile){
  int rc = SQLITE4_OK;
................................................................................
}

bt_env *sqlite4BtEnvDefault(void){
  static bt_env posix_env = {
    0,                            /* pVfsCtx */
    btPosixOsFullpath,            /* xFullpath */
    btPosixOsOpen,                /* xOpen */

    btPosixOsRead,                /* xRead */
    btPosixOsWrite,               /* xWrite */
    btPosixOsTruncate,            /* xTruncate */
    btPosixOsSync,                /* xSync */
    btPosixOsSectorSize,          /* xSectorSize */
    btPosixOsClose,               /* xClose */
    btPosixOsUnlink,              /* xUnlink */

      rc = btErrorBkpt(SQLITE4_IOERR);
    }
  }

  *ppFile = (bt_file*)p;
  return rc;
}

static int btPosixOsSize(bt_file *pFile, i64 *pnByte){
  int rc = SQLITE4_OK;
  PosixFile *p = (PosixFile *)pFile;
  struct stat sBuf;

  if( fstat(p->fd, &sBuf)!=0 ){
    rc = SQLITE4_IOERR_FSTAT;
  }else{
    *pnByte = sBuf.st_size;
  }

  return rc;
}

static int btPosixOsWrite(
  bt_file *pFile,                 /* File to write to */
  i64 iOff,                       /* Offset to write to */
  void *pData,                    /* Write data from this buffer */
  int nData                       /* Bytes of data to write */
){
................................................................................
  }else{
    ssize_t prc = read(p->fd, pData, (size_t)nData);
    if( prc<0 ){ 
      rc = btErrorBkpt(SQLITE4_IOERR);
    }else if( prc<nData ){
      memset(&((u8 *)pData)[prc], 0, nData - prc);
    }

  }

  return rc;
}

static int btPosixOsSync(bt_file *pFile){
  int rc = SQLITE4_OK;
................................................................................
}

bt_env *sqlite4BtEnvDefault(void){
  static bt_env posix_env = {
    0,                            /* pVfsCtx */
    btPosixOsFullpath,            /* xFullpath */
    btPosixOsOpen,                /* xOpen */
    btPosixOsSize,                /* xSize */
    btPosixOsRead,                /* xRead */
    btPosixOsWrite,               /* xWrite */
    btPosixOsTruncate,            /* xTruncate */
    btPosixOsSync,                /* xSync */
    btPosixOsSectorSize,          /* xSectorSize */
    btPosixOsClose,               /* xClose */
    btPosixOsUnlink,              /* xUnlink */