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//! An SQL-based storage manager 
//! 
//! This storage manager provides the means to save data to an SQL-based 
//! backend. 
//! 
//! For now it's mysql only, dialectization will be added at a later time. 
//! Serialization should be taken care of by the low-level SQL drivers. 
//! 
//! @note 
//!   An administrator is supposed to create the database and give 
//!   the user enough privileges to write to it. It will be care 
//!   of this driver to create the database tables itself. 
//! 
//! @thanks 
//!   Thanks to Francesco Chemolli <kinkie@@roxen.com> for the contribution. 
 
#pike __REAL_VERSION__ 
 
inherit Cache.Storage.Base; 
 
#define MAX_KEY_SIZE "255" 
#define CREATION_QUERY "create table cache ( \ 
cachekey varchar(" MAX_KEY_SIZE ") not null primary key, \ 
atime timestamp, \ 
ctime timestamp, \ 
etime timestamp, \ 
cost float unsigned DEFAULT 1.0 NOT NULL, \ 
data longblob NOT NULL, \ 
dependants longblob \ 
)" 
 
Sql.Sql db; 
int have_dependants=0; 
 
#if 0                           // set to 1 to enable debugging 
#ifdef debug 
#undef debug 
#endif // ifdef debug 
#define debug(X...) werror("Cache.Storage.mysql: "+X);werror("\n") 
#else  // 1 
#ifndef debug                   // if there's a clash, let's let it show 
#define debug(X...) /**/ 
#endif // ifndef debug 
#endif // 1 
 
 
//! Database manipulation is done externally. This class only returns 
//! values, with some lazy decoding. 
class Data { 
  inherit Cache.Data; 
  private int _size; 
  private string db_data; 
  private mixed _data; 
 
  void create (mapping q) { 
    debug("instantiating data object from %O",q); 
    db_data=q->data; 
    _size=sizeof(db_data); 
    atime=(int)q->atime; 
    ctime=(int)q->ctime; 
    etime=(int)q->etime; 
    cost=(float)q->cost; 
  } 
 
  int size() { 
    debug("object size requested"); 
    return _size; 
  } 
 
  mixed data() { 
    debug("data requested"); 
    if (_data) 
      return _data; 
    debug("lazy-decoding data"); 
    _data=decode_value(db_data); 
    db_data=0; 
    return _data; 
  } 
} 
//does MySQL support multiple outstanding resultsets? 
//we'll know now. 
//Notice: this will fail miserably with Sybase, for instance. 
//Notice: can and will throw exceptions if anything fails. 
private object(Sql.sql_result) enum_result; 
int(0..0)|string first() { 
  debug("first()"); 
  if (enum_result) 
    destruct(enum_result); 
  enum_result=db->big_query("select cachekey from cache"); 
  return next(); 
} 
 
int(0..0)|string next() { 
  debug("next()"); 
  array res; 
  if (!enum_result) 
    return 0; 
  if (res=enum_result->fetch_row()) 
    return res[0]; 
  enum_result=0;                // enumeration finished 
  return 0; 
} 
 
//unfortunately with MySQL we can't optimize much, 
//if we want to properly follow the dependencies chain. 
//also, we're taking the easy way out using encode_value rather than 
// SQL tables. With other databases it would be easier to use 
// SQL-related functions rather than doing stuff ourselves (and 
// performing plenty of queries). 
// I'll try to use a local cache to avoid multiple deletions for 
// the same value, since queries are expensive. It could prove 
// to be a problem for HUGE caches. Let's hope it won't happen.. 
void delete(string key, void|int(0..1) hard, void|multiset already_deleted) { 
  multiset dependants=0; 
 
  debug("deleting %s\n",key); 
  if (have_dependants) { 
    if (already_deleted && already_deleted[key]) // already deleted. Skip 
      return; 
    mixed rv=db->query("select dependants from cache where cachekey='%s'",key); 
    if (rv && sizeof(rv) && rv[0]->dependants) { // there are dependants 
      dependants=decode_value(rv[0]->dependants); 
    } 
    if (!already_deleted) already_deleted=(<>); 
  } 
 
  if (already_deleted) already_deleted[key]=1; 
  db->query("delete from cache where cachekey='%s'",key); 
 
  if (dependants) { 
    foreach (indices(dependants),string dep) { 
      werror("chain-deleting %s\n",dep); 
      delete(dep); 
    } 
    werror("done chain-deleting\n"); 
  } 
} 
 
void set(string key, mixed value, 
         void|int expire_time, void|float preciousness, 
         void|multiset(string) dependants) { 
  debug("setting value for key %s (e: %d, v: %f",key,expire_time, 
        preciousness?preciousness:1.0); 
  db->query("delete from cache where cachekey='%s'",key); 
  db->query("insert into cache " 
            "(cachekey,atime,ctime,etime,cost,data, dependants) " 
            "values('%s',CURRENT_TIMESTAMP,CURRENT_TIMESTAMP,%s,%s,'%s','%s')", 
            key, 
            (expire_time?"FROM_UNIXTIME("+expire_time+")":"0"), 
            (preciousness?(string)preciousness:"1"), 
            encode_value(value), 
            (dependants?encode_value(dependants):"NULL") 
            //BUG: this fails when there are no dependants. 
            ); 
  if (dependants) 
    have_dependants=1; 
} 
 
int(0..0)|Cache.Data get(string key,void|int notouch) { 
  debug("getting value for key %s (nt: %d)",key,notouch); 
  array(mapping) result=0; 
  mixed err=0; 
  catch (result=db->query("select unix_timestamp(atime) as atime," 
                          "unix_timestamp(ctime) as ctime," 
                          "unix_timestamp(etime) as etime,cost,data " 
                          "from cache where cachekey='%s'",key)); 
  if (!result || !sizeof(result)) 
    return 0; 
  if (!notouch) 
    catch(db->query("update cache set atime=CURRENT_TIMESTAMP " 
                    "where cachekey='%s'",key)); 
  return Data(result[0]); 
} 
 
void aget(string key, 
          function(string,int(0..0)|Cache.Data:void) callback) { 
  callback(key,get(key)); 
} 
 
 
//! 
void create(string sql_url) { 
  array result=0; 
  mixed err=0; 
  db=Sql.Sql(sql_url); 
  // used to determine whether there already is a DB here. 
  err=catch(result=db->query("select stamp from cache_admin")); 
  if (err || !sizeof(result)) { 
    db->query(CREATION_QUERY); 
    db->query("create table cache_admin (stamp integer primary key)"); 
    db->query("insert into cache_admin values ('1')"); 
  } 
}