#include "sqlite_hecl_vfs.h"

#include "sqlite3.h"
#include <assert.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

/*
 * Modified test_onefile.c VFS for sqlite3
 *
 * This VFS gets registered with sqlite to access an in-memory,
 * block-compressed LBA. It's designed for read-only access of
 * a packed object-database.
 *
 * Journal and temp read/write is unsupported and will call abort
 * if attempted.
 */

/*
 * App-supplied callback called when file is closed (ready to access)
 */
static TCloseCallback CLOSE_CALLBACK = NULL;
static void* CLOSE_CTX = NULL;

typedef struct mem_file mem_file;
struct mem_file
{
    sqlite3_file base;
    int nSize;
    int nAlloc;
    char* zAlloc;
};

/*
** Method declarations for mem_file.
*/
static int memClose(sqlite3_file*);
static int memRead(sqlite3_file*, void*, int iAmt, sqlite3_int64 iOfst);
static int memWrite(sqlite3_file*, const void*, int iAmt, sqlite3_int64 iOfst);
static int memTruncate(sqlite3_file*, sqlite3_int64 size);
static int memSync(sqlite3_file*, int flags);
static int memFileSize(sqlite3_file*, sqlite3_int64* pSize);
static int memLock(sqlite3_file*, int);
static int memUnlock(sqlite3_file*, int);
static int memCheckReservedLock(sqlite3_file*, int* pResOut);
static int memFileControl(sqlite3_file*, int op, void* pArg);
static int memSectorSize(sqlite3_file*);
static int memDeviceCharacteristics(sqlite3_file*);

/*
** Method declarations for fs_vfs.
*/
static int memOpen(sqlite3_vfs*, const char*, sqlite3_file*, int , int*);
static int memDelete(sqlite3_vfs*, const char* zName, int syncDir);
static int memAccess(sqlite3_vfs*, const char* zName, int flags, int*);
static int memFullPathname(sqlite3_vfs*, const char* zName, int nOut, char* zOut);
static void* memDlOpen(sqlite3_vfs*, const char* zFilename);
static void memDlError(sqlite3_vfs*, int nByte, char* zErrMsg);
static void (*memDlSym(sqlite3_vfs*, void*, const char* zSymbol))(void);
static void memDlClose(sqlite3_vfs*, void*);
static int memRandomness(sqlite3_vfs*, int nByte, char* zOut);
static int memSleep(sqlite3_vfs*, int microseconds);
static int memCurrentTime(sqlite3_vfs*, double*);

static sqlite3_vfs mem_vfs =
{
    1,                                          /* iVersion */
    0,                                          /* szOsFile */
    0,                                          /* mxPathname */
    0,                                          /* pNext */
    "hecl_mem",                                 /* zName */
    0,                                          /* pAppData */
    memOpen,                                     /* xOpen */
    memDelete,                                   /* xDelete */
    memAccess,                                   /* xAccess */
    memFullPathname,                             /* xFullPathname */
    memDlOpen,                                   /* xDlOpen */
    memDlError,                                  /* xDlError */
    memDlSym,                                    /* xDlSym */
    memDlClose,                                  /* xDlClose */
    memRandomness,                               /* xRandomness */
    memSleep,                                    /* xSleep */
    memCurrentTime,                              /* xCurrentTime */
    0                                           /* xCurrentTimeInt64 */
};

static sqlite3_io_methods mem_io_methods =
{
    1,                            /* iVersion */
    memClose,                     /* xClose */
    memRead,                      /* xRead */
    memWrite,                     /* xWrite */
    memTruncate,                  /* xTruncate */
    memSync,                      /* xSync */
    memFileSize,                  /* xFileSize */
    memLock,                      /* xLock */
    memUnlock,                    /* xUnlock */
    memCheckReservedLock,         /* xCheckReservedLock */
    memFileControl,               /* xFileControl */
    memSectorSize,                /* xSectorSize */
    memDeviceCharacteristics,     /* xDeviceCharacteristics */
    0,                            /* xShmMap */
    0,                            /* xShmLock */
    0,                            /* xShmBarrier */
    0,                            /* xShmUnmap */
    0,
    0
};

/* Useful macros used in several places */
#define MIN(x,y) ((x)<(y)?(x):(y))
#define MAX(x,y) ((x)>(y)?(x):(y))


/*
** Close a mem-file.
*/
static int memClose(sqlite3_file* pFile)
{
    mem_file* pTmp = (mem_file*)pFile;
    if(CLOSE_CALLBACK)
        CLOSE_CALLBACK(pTmp->zAlloc, pTmp->nSize, CLOSE_CTX);
    else
        sqlite3_free(pTmp->zAlloc);
    return SQLITE_OK;
}

/*
** Read data from a mem-file.
*/
static int memRead(
    sqlite3_file* pFile,
    void* zBuf,
    int iAmt,
    sqlite_int64 iOfst
)
{
    mem_file* pTmp = (mem_file*)pFile;
    if((iAmt + iOfst) > pTmp->nSize)
        return SQLITE_IOERR_SHORT_READ;
    memcpy(zBuf, &pTmp->zAlloc[iOfst], iAmt);
    return SQLITE_OK;
}

/*
** Write data to a mem-file.
*/
static int memWrite(
    sqlite3_file* pFile,
    const void* zBuf,
    int iAmt,
    sqlite_int64 iOfst
)
{
    mem_file* pTmp = (mem_file*)pFile;
    if((iAmt + iOfst) > pTmp->nAlloc)
    {
        int nNew = (int)(2 * (iAmt + iOfst + pTmp->nAlloc));
        char* zNew = sqlite3_realloc(pTmp->zAlloc, nNew);
        if(!zNew)
            return SQLITE_NOMEM;
        pTmp->zAlloc = zNew;
        pTmp->nAlloc = nNew;
    }
    memcpy(&pTmp->zAlloc[iOfst], zBuf, iAmt);
    pTmp->nSize = (int)MAX(pTmp->nSize, iOfst + iAmt);
    return SQLITE_OK;
}

/*
** Truncate a mem-file.
*/
static int memTruncate(sqlite3_file* pFile, sqlite_int64 size)
{
    mem_file* pTmp = (mem_file*)pFile;
    pTmp->nSize = (int)MIN(pTmp->nSize, size);
    return SQLITE_OK;
}

/*
** Sync a mem-file.
*/
static int memSync(sqlite3_file* pFile, int flags)
{
    return SQLITE_OK;
}

/*
** Return the current file-size of a mem-file.
*/
static int memFileSize(sqlite3_file* pFile, sqlite_int64* pSize)
{
    mem_file* pTmp = (mem_file*)pFile;
    *pSize = pTmp->nSize;
    return SQLITE_OK;
}

/*
** Lock a mem-file.
*/
static int memLock(sqlite3_file* pFile, int eLock)
{
    return SQLITE_OK;
}

/*
** Unlock a mem-file.
*/
static int memUnlock(sqlite3_file* pFile, int eLock)
{
    return SQLITE_OK;
}

/*
** Check if another file-handle holds a RESERVED lock on a mem-file.
*/
static int memCheckReservedLock(sqlite3_file* pFile, int* pResOut)
{
    *pResOut = 0;
    return SQLITE_OK;
}

/*
** File control method. For custom operations on a mem-file.
*/
static int memFileControl(sqlite3_file* pFile, int op, void* pArg)
{
    return SQLITE_OK;
}

/*
** Return the sector-size in bytes for a mem-file.
*/
static int memSectorSize(sqlite3_file* pFile)
{
    return 0;
}

/*
** Return the device characteristic flags supported by a mem-file.
*/
static int memDeviceCharacteristics(sqlite3_file* pFile)
{
    return 0;
}

/*
** Open an mem file handle.
*/
static int memOpen(
    sqlite3_vfs* pVfs,
    const char* zName,
    sqlite3_file* pFile,
    int flags,
    int* pOutFlags
)
{
    if ((flags & SQLITE_OPEN_MAIN_DB) != SQLITE_OPEN_MAIN_DB)
    {
        fprintf(stderr, "the sqlite hecl mem VFS only supports main-db reading/writing\n");
        return SQLITE_CANTOPEN;
    }
    mem_file* p2 = (mem_file*)pFile;
    memset(p2, 0, sizeof(*p2));
    p2->base.pMethods = &mem_io_methods;
    return SQLITE_OK;
}

/*
** Delete the file located at zPath. If the dirSync argument is true,
** ensure the file-system modifications are synced to disk before
** returning.
*/
static int memDelete(sqlite3_vfs* pVfs, const char* zPath, int dirSync)
{
    return SQLITE_OK;
}

/*
** Test for access permissions. Return true if the requested permission
** is available, or false otherwise.
*/
static int memAccess(
    sqlite3_vfs* pVfs,
    const char* zPath,
    int flags,
    int* pResOut
)
{
    if(flags & SQLITE_ACCESS_READ | SQLITE_ACCESS_READWRITE)
        return 1;
    return 0;
}

/*
** Populate buffer zOut with the full canonical pathname corresponding
** to the pathname in zPath. zOut is guaranteed to point to a buffer
** of at least (FS_MAX_PATHNAME+1) bytes.
*/
static int memFullPathname(
    sqlite3_vfs* pVfs,            /* Pointer to vfs object */
    const char* zPath,            /* Possibly relative input path */
    int nOut,                     /* Size of output buffer in bytes */
    char* zOut)                   /* Output buffer */
{
    strncpy(zOut, zPath, nOut);
    return SQLITE_OK;
}

/*
** Open the dynamic library located at zPath and return a handle.
*/
static void* memDlOpen(sqlite3_vfs* pVfs, const char* zPath)
{
    return NULL;
}

/*
** Populate the buffer zErrMsg (size nByte bytes) with a human readable
** utf-8 string describing the most recent error encountered associated
** with dynamic libraries.
*/
static void memDlError(sqlite3_vfs* pVfs, int nByte, char* zErrMsg)
{
}

/*
** Return a pointer to the symbol zSymbol in the dynamic library pHandle.
*/
static void (*memDlSym(sqlite3_vfs* pVfs, void* pH, const char* zSym))(void)
{
}

/*
** Close the dynamic library handle pHandle.
*/
static void memDlClose(sqlite3_vfs* pVfs, void* pHandle)
{
}

/*
** Populate the buffer pointed to by zBufOut with nByte bytes of
** random data.
*/
static int memRandomness(sqlite3_vfs* pVfs, int nByte, char* zBufOut)
{
    for(int i = 0 ; i < nByte ; ++i)
        zBufOut[i] = rand();
    return nByte;
}

/*
** Sleep for nMicro microseconds. Return the number of microseconds
** actually slept.
*/
static int memSleep(sqlite3_vfs* pVfs, int nMicro)
{
    int seconds = (nMicro + 999999) / 1000000;
    sleep(seconds);
    return seconds * 1000000;
}

/*
** Return the current time as a Julian Day number in *pTimeOut.
*/
static int memCurrentTime(sqlite3_vfs* pVfs, double* pTimeOut)
{
    *pTimeOut = 0.0;
    return 0;
}

/*
** This procedure registers the mem vfs with SQLite. If the argument is
** true, the mem vfs becomes the new default vfs. It is the only publicly
** available function in this file.
*/
int sqlite_hecl_mem_vfs_register(TCloseCallback closeCb, void* ctx)
{
    CLOSE_CALLBACK = closeCb;
    CLOSE_CTX = ctx;
    if(mem_vfs.szOsFile) return SQLITE_OK;
    mem_vfs.szOsFile = sizeof(mem_file);
    return sqlite3_vfs_register(&mem_vfs, 0);
}