/*
** 2013-05-15
**
** 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 SQLite extension implements a rot13() function and a rot13
** collating sequence.
*/
#include "sqlite3ext.h"
SQLITE_EXTENSION_INIT1
#include <assert.h>
#include <string.h>

/*
** Perform rot13 encoding on a single ASCII character.
*/
static unsigned char rot13(unsigned char c){
  if( c>='a' && c<='z' ){
    c += 13;
    if( c>'z' ) c -= 26;
  }else if( c>='A' && c<='Z' ){
    c += 13;
    if( c>'Z' ) c -= 26;
  }
  return c;
}

/*
** Implementation of the rot13() function.
**
** Rotate ASCII alphabetic characters by 13 character positions.  
** Non-ASCII characters are unchanged.  rot13(rot13(X)) should always
** equal X.
*/
static void rot13func(
  sqlite3_context *context,
  int argc,
  sqlite3_value **argv
){
  const unsigned char *zIn;
  int nIn;
  unsigned char *zOut;
  char *zToFree = 0;
  int i;
  char zTemp[100];
  assert( argc==1 );
  if( sqlite3_value_type(argv[0])==SQLITE_NULL ) return;
  zIn = (const unsigned char*)sqlite3_value_text(argv[0]);
  nIn = sqlite3_value_bytes(argv[0]);
  if( nIn<sizeof(zTemp)-1 ){
    zOut = zTemp;
  }else{
    zOut = zToFree = sqlite3_malloc( nIn+1 );
    if( zOut==0 ){
      sqlite3_result_error_nomem(context);
      return;
    }
  }
  for(i=0; i<nIn; i++) zOut[i] = rot13(zIn[i]);
  zOut[i] = 0;
  sqlite3_result_text(context, (char*)zOut, i, SQLITE_TRANSIENT);
  sqlite3_free(zToFree);
}

/*
** Implement the rot13 collating sequence so that if
**
**      x=y COLLATE rot13
**
** Then 
**
**      rot13(x)=rot13(y) COLLATE binary
*/
static int rot13CollFunc(
  void *notUsed,
  int nKey1, const void *pKey1,
  int nKey2, const void *pKey2
){
  const char *zA = (const char*)pKey1;
  const char *zB = (const char*)pKey2;
  int i, x;
  for(i=0; i<nKey1 && i<nKey2; i++){
    x = (int)rot13(zA[i]) - (int)rot13(zB[i]);
    if( x!=0 ) return x;
  }
  return nKey1 - nKey2;
}


#ifdef _WIN32
__declspec(dllexport)
#endif
int sqlite3_rot_init(
  sqlite3 *db, 
  char **pzErrMsg, 
  const sqlite3_api_routines *pApi
){
  int rc = SQLITE_OK;
  SQLITE_EXTENSION_INIT2(pApi);
  (void)pzErrMsg;  /* Unused parameter */
  rc = sqlite3_create_function(db, "rot13", 1, SQLITE_UTF8, 0,
                               rot13func, 0, 0);
  if( rc==SQLITE_OK ){
    rc = sqlite3_create_collation(db, "rot13", SQLITE_UTF8, 0, rot13CollFunc);
  }
  return rc;
}