/*
** 2016-06-29
**
** 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.
**
*************************************************************************
**
** This file demonstrates how to create a table-valued-function that
** returns the values in a C-language array.
** Examples:
**
**      SELECT * FROM carray($ptr,5)
**
** The query above returns 5 integers contained in a C-language array
** at the address $ptr.  $ptr is a pointer to the array of integers that
** has been cast to an integer.
**
** There is an optional third parameter to determine the datatype of
** the C-language array.  Allowed values of the third parameter are
** 'int32', 'int64', 'double', 'char*'.  Example:
**
**      SELECT * FROM carray($ptr,10,'char*');
**
** HOW IT WORKS
**
** The carray "function" is really a virtual table with the
** following schema:
**
**     CREATE TABLE carray(
**       value,
**       pointer HIDDEN,
**       count HIDDEN,
**       ctype TEXT HIDDEN
**     );
**
** If the hidden columns "pointer" and "count" are unconstrained, then 
** the virtual table has no rows.  Otherwise, the virtual table interprets
** the integer value of "pointer" as a pointer to the array and "count"
** as the number of elements in the array.  The virtual table steps through
** the array, element by element.
*/
#include "sqlite3ext.h"
SQLITE_EXTENSION_INIT1
#include <assert.h>
#include <string.h>

#ifndef SQLITE_OMIT_VIRTUALTABLE

/*
** Allowed datatypes
*/
#define CARRAY_INT32    0
#define CARRAY_INT64    1
#define CARRAY_DOUBLE   2
#define CARRAY_TEXT     3

/*
** Names of types
*/
static const char *azType[] = { "int32", "int64", "double", "char*" };


/* carray_cursor is a subclass of sqlite3_vtab_cursor which will
** serve as the underlying representation of a cursor that scans
** over rows of the result
*/
typedef struct carray_cursor carray_cursor;
struct carray_cursor {
  sqlite3_vtab_cursor base;  /* Base class - must be first */
  sqlite3_int64 iRowid;      /* The rowid */
  sqlite3_int64 iPtr;        /* Pointer to array of values */
  sqlite3_int64 iCnt;        /* Number of integers in the array */
  unsigned char eType;       /* One of the CARRAY_type values */
};

/*
** The carrayConnect() method is invoked to create a new
** carray_vtab that describes the carray virtual table.
**
** Think of this routine as the constructor for carray_vtab objects.
**
** All this routine needs to do is:
**
**    (1) Allocate the carray_vtab object and initialize all fields.
**
**    (2) Tell SQLite (via the sqlite3_declare_vtab() interface) what the
**        result set of queries against carray will look like.
*/
static int carrayConnect(
  sqlite3 *db,
  void *pAux,
  int argc, const char *const*argv,
  sqlite3_vtab **ppVtab,
  char **pzErr
){
  sqlite3_vtab *pNew;
  int rc;

/* Column numbers */
#define CARRAY_COLUMN_VALUE   0
#define CARRAY_COLUMN_POINTER 1
#define CARRAY_COLUMN_COUNT   2
#define CARRAY_COLUMN_CTYPE   3

  rc = sqlite3_declare_vtab(db,
     "CREATE TABLE x(value,pointer hidden,count hidden,ctype hidden)");
  if( rc==SQLITE_OK ){
    pNew = *ppVtab = sqlite3_malloc( sizeof(*pNew) );
    if( pNew==0 ) return SQLITE_NOMEM;
    memset(pNew, 0, sizeof(*pNew));
  }
  return rc;
}

/*
** This method is the destructor for carray_cursor objects.
*/
static int carrayDisconnect(sqlite3_vtab *pVtab){
  sqlite3_free(pVtab);
  return SQLITE_OK;
}

/*
** Constructor for a new carray_cursor object.
*/
static int carrayOpen(sqlite3_vtab *p, sqlite3_vtab_cursor **ppCursor){
  carray_cursor *pCur;
  pCur = sqlite3_malloc( sizeof(*pCur) );
  if( pCur==0 ) return SQLITE_NOMEM;
  memset(pCur, 0, sizeof(*pCur));
  *ppCursor = &pCur->base;
  return SQLITE_OK;
}

/*
** Destructor for a carray_cursor.
*/
static int carrayClose(sqlite3_vtab_cursor *cur){
  sqlite3_free(cur);
  return SQLITE_OK;
}


/*
** Advance a carray_cursor to its next row of output.
*/
static int carrayNext(sqlite3_vtab_cursor *cur){
  carray_cursor *pCur = (carray_cursor*)cur;
  pCur->iRowid++;
  return SQLITE_OK;
}

/*
** Return values of columns for the row at which the carray_cursor
** is currently pointing.
*/
static int carrayColumn(
  sqlite3_vtab_cursor *cur,   /* The cursor */
  sqlite3_context *ctx,       /* First argument to sqlite3_result_...() */
  int i                       /* Which column to return */
){
  carray_cursor *pCur = (carray_cursor*)cur;
  sqlite3_int64 x = 0;
  switch( i ){
    case CARRAY_COLUMN_POINTER:   x = pCur->iPtr;   break;
    case CARRAY_COLUMN_COUNT:     x = pCur->iCnt;   break;
    case CARRAY_COLUMN_CTYPE: {
      sqlite3_result_text(ctx, azType[pCur->eType], -1, SQLITE_STATIC);
      return SQLITE_OK;
    }
    default: {
      switch( pCur->eType ){
        case CARRAY_INT32: {
          int *p = (int*)pCur->iPtr;
          sqlite3_result_int(ctx, p[pCur->iRowid-1]);
          return SQLITE_OK;
        }
        case CARRAY_INT64: {
          sqlite3_int64 *p = (sqlite3_int64*)pCur->iPtr;
          sqlite3_result_int64(ctx, p[pCur->iRowid-1]);
          return SQLITE_OK;
        }
        case CARRAY_DOUBLE: {
          double *p = (double*)pCur->iPtr;
          sqlite3_result_double(ctx, p[pCur->iRowid-1]);
          return SQLITE_OK;
        }
        case CARRAY_TEXT: {
          const char **p = (const char**)pCur->iPtr;
          sqlite3_result_text(ctx, p[pCur->iRowid-1], -1, SQLITE_TRANSIENT);
          return SQLITE_OK;
        }
      }
    }
  }
  sqlite3_result_int64(ctx, x);
  return SQLITE_OK;
}

/*
** Return the rowid for the current row.  In this implementation, the
** rowid is the same as the output value.
*/
static int carrayRowid(sqlite3_vtab_cursor *cur, sqlite_int64 *pRowid){
  carray_cursor *pCur = (carray_cursor*)cur;
  *pRowid = pCur->iRowid;
  return SQLITE_OK;
}

/*
** Return TRUE if the cursor has been moved off of the last
** row of output.
*/
static int carrayEof(sqlite3_vtab_cursor *cur){
  carray_cursor *pCur = (carray_cursor*)cur;
  return pCur->iRowid>pCur->iCnt;
}

/*
** This method is called to "rewind" the carray_cursor object back
** to the first row of output.
*/
static int carrayFilter(
  sqlite3_vtab_cursor *pVtabCursor, 
  int idxNum, const char *idxStr,
  int argc, sqlite3_value **argv
){
  carray_cursor *pCur = (carray_cursor *)pVtabCursor;
  if( idxNum ){
    pCur->iPtr = sqlite3_value_int64(argv[0]);
    pCur->iCnt = sqlite3_value_int64(argv[1]);
    if( idxNum<3 ){
      pCur->eType = CARRAY_INT32;
    }else{
      unsigned char i;
      const char *zType = (const char*)sqlite3_value_text(argv[2]);
      for(i=0; i<sizeof(azType)/sizeof(azType[0]); i++){
        if( sqlite3_stricmp(zType, azType[i])==0 ) break;
      }
      if( i>=sizeof(azType)/sizeof(azType[0]) ){
        pVtabCursor->pVtab->zErrMsg = sqlite3_mprintf(
          "unknown datatype: %Q", zType);
        return SQLITE_ERROR;
      }else{
        pCur->eType = i;
      }
    }
  }else{
    pCur->iPtr = 0;
    pCur->iCnt = 0;
  }
  pCur->iRowid = 1;
  return SQLITE_OK;
}

/*
** SQLite will invoke this method one or more times while planning a query
** that uses the carray virtual table.  This routine needs to create
** a query plan for each invocation and compute an estimated cost for that
** plan.
**
** In this implementation idxNum is used to represent the
** query plan.  idxStr is unused.
**
** idxNum is 2 if the pointer= and count= constraints exist,
** 3 if the ctype= constraint also exists, and is 0 otherwise.
** If idxNum is 0, then carray becomes an empty table.
*/
static int carrayBestIndex(
  sqlite3_vtab *tab,
  sqlite3_index_info *pIdxInfo
){
  int i;                 /* Loop over constraints */
  int ptrIdx = -1;       /* Index of the pointer= constraint, or -1 if none */
  int cntIdx = -1;       /* Index of the count= constraint, or -1 if none */
  int ctypeIdx = -1;     /* Index of the ctype= constraint, or -1 if none */

  const struct sqlite3_index_constraint *pConstraint;
  pConstraint = pIdxInfo->aConstraint;
  for(i=0; i<pIdxInfo->nConstraint; i++, pConstraint++){
    if( pConstraint->usable==0 ) continue;
    if( pConstraint->op!=SQLITE_INDEX_CONSTRAINT_EQ ) continue;
    switch( pConstraint->iColumn ){
      case CARRAY_COLUMN_POINTER:
        ptrIdx = i;
        break;
      case CARRAY_COLUMN_COUNT:
        cntIdx = i;
        break;
      case CARRAY_COLUMN_CTYPE:
        ctypeIdx = i;
        break;
    }
  }
  if( ptrIdx>=0 && cntIdx>=0 ){
    pIdxInfo->aConstraintUsage[ptrIdx].argvIndex = 1;
    pIdxInfo->aConstraintUsage[ptrIdx].omit = 1;
    pIdxInfo->aConstraintUsage[cntIdx].argvIndex = 2;
    pIdxInfo->aConstraintUsage[cntIdx].omit = 1;
    pIdxInfo->estimatedCost = (double)1;
    pIdxInfo->estimatedRows = 100;
    pIdxInfo->idxNum = 2;
    if( ctypeIdx>=0 ){
      pIdxInfo->aConstraintUsage[ctypeIdx].argvIndex = 3;
      pIdxInfo->aConstraintUsage[ctypeIdx].omit = 1;
      pIdxInfo->idxNum = 3;
    }
  }else{
    pIdxInfo->estimatedCost = (double)2147483647;
    pIdxInfo->estimatedRows = 2147483647;
    pIdxInfo->idxNum = 0;
  }
  return SQLITE_OK;
}

/*
** This following structure defines all the methods for the 
** carray virtual table.
*/
static sqlite3_module carrayModule = {
  0,                         /* iVersion */
  0,                         /* xCreate */
  carrayConnect,             /* xConnect */
  carrayBestIndex,           /* xBestIndex */
  carrayDisconnect,          /* xDisconnect */
  0,                         /* xDestroy */
  carrayOpen,                /* xOpen - open a cursor */
  carrayClose,               /* xClose - close a cursor */
  carrayFilter,              /* xFilter - configure scan constraints */
  carrayNext,                /* xNext - advance a cursor */
  carrayEof,                 /* xEof - check for end of scan */
  carrayColumn,              /* xColumn - read data */
  carrayRowid,               /* xRowid - read data */
  0,                         /* xUpdate */
  0,                         /* xBegin */
  0,                         /* xSync */
  0,                         /* xCommit */
  0,                         /* xRollback */
  0,                         /* xFindMethod */
  0,                         /* xRename */
};

#endif /* SQLITE_OMIT_VIRTUALTABLE */

#ifdef _WIN32
__declspec(dllexport)
#endif
int sqlite3_carray_init(
  sqlite3 *db, 
  char **pzErrMsg, 
  const sqlite3_api_routines *pApi
){
  int rc = SQLITE_OK;
  SQLITE_EXTENSION_INIT2(pApi);
#ifndef SQLITE_OMIT_VIRTUALTABLE
  rc = sqlite3_create_module(db, "carray", &carrayModule, 0);
#endif
  return rc;
}