/*
** 2014年11月10日
**
** 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 SQL function eval() which runs
** SQL statements recursively.
*/
#include "sqlite3ext.h"
SQLITE_EXTENSION_INIT1
#include <string.h>

/*
** Structure used to accumulate the output
*/
struct EvalResult {
 char *z; /* Accumulated output */
 const char *zSep; /* Separator */
 int szSep; /* Size of the separator string */
 sqlite3_int64 nAlloc; /* Number of bytes allocated for z[] */
 sqlite3_int64 nUsed; /* Number of bytes of z[] actually used */
};

/*
** Callback from sqlite_exec() for the eval() function.
*/
static int callback(void *pCtx, int argc, char **argv, char **colnames){
 struct EvalResult *p = (struct EvalResult*)pCtx;
 int i; 
 if( argv==0 ) return 0;
 for(i=0; i<argc; i++){
 const char *z = argv[i] ? argv[i] : "";
 size_t sz = strlen(z);
 if( (sqlite3_int64)sz+p->nUsed+p->szSep+1 > p->nAlloc ){
 char *zNew;
 p->nAlloc = p->nAlloc*2 + sz + p->szSep + 1;
 /* Using sqlite3_realloc64() would be better, but it is a recent
 ** addition and will cause a segfault if loaded by an older version
 ** of SQLite. */
 zNew = p->nAlloc<=0x7fffffff ? sqlite3_realloc64(p->z, p->nAlloc) : 0;
 if( zNew==0 ){
 sqlite3_free(p->z);
 memset(p, 0, sizeof(*p));
 return 1;
 }
 p->z = zNew;
 }
 if( p->nUsed>0 ){
 memcpy(&p->z[p->nUsed], p->zSep, p->szSep);
 p->nUsed += p->szSep;
 }
 memcpy(&p->z[p->nUsed], z, sz);
 p->nUsed += sz;
 }
 return 0;
}

/*
** Implementation of the eval(X) and eval(X,Y) SQL functions.
**
** Evaluate the SQL text in X. Return the results, using string
** Y as the separator. If Y is omitted, use a single space character.
*/
static void sqlEvalFunc(
 sqlite3_context *context,
 int argc,
 sqlite3_value **argv
){
 const char *zSql;
 sqlite3 *db;
 char *zErr = 0;
 int rc;
 struct EvalResult x;

 memset(&x, 0, sizeof(x));
 x.zSep = " ";
 zSql = (const char*)sqlite3_value_text(argv[0]);
 if( zSql==0 ) return;
 if( argc>1 ){
 x.zSep = (const char*)sqlite3_value_text(argv[1]);
 if( x.zSep==0 ) return;
 }
 x.szSep = (int)strlen(x.zSep);
 db = sqlite3_context_db_handle(context);
 rc = sqlite3_exec(db, zSql, callback, &x, &zErr);
 if( rc!=SQLITE_OK ){
 sqlite3_result_error(context, zErr, -1);
 sqlite3_free(zErr);
 }else if( x.zSep==0 ){
 sqlite3_result_error_nomem(context);
 sqlite3_free(x.z);
 }else{
 sqlite3_result_text(context, x.z, (int)x.nUsed, sqlite3_free);
 }
}


#ifdef _WIN32
__declspec(dllexport)
#endif
int sqlite3_eval_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, "eval", 1, 
 SQLITE_UTF8|SQLITE_DIRECTONLY, 0,
 sqlEvalFunc, 0, 0);
 if( rc==SQLITE_OK ){
 rc = sqlite3_create_function(db, "eval", 2,
 SQLITE_UTF8|SQLITE_DIRECTONLY, 0,
 sqlEvalFunc, 0, 0);
 }
 return rc;
}