odm/include/cache.h

#pragma once
#include "GPL.h"
#include <functional>
#include <libpq-fe.h>
#include <sqlite3.h>
#include <time.h>
#include <variant>

using michlib::GPL;
using michlib::int_cast;
using michlib::MString;
using michlib::pointer_cast;

class SQLiteConnection
{
 public:
 using DBType   = sqlite3*;
 using FuncType = std::function<void(DBType)>;

 private:
 static DBType                db;
 static size_t                count;
 static std::vector<FuncType> destructs;

 public:
 SQLiteConnection()
 {
  count++;
  if(db == nullptr)
  {
   MString oldprefix = GPL.UsePrefix("SQLITE");
   MString name      = GPL.ParameterSValue("db", "");
   GPL.UsePrefix(oldprefix);

   auto ret = sqlite3_open(name.Buf(), &db);
   if(ret != SQLITE_OK)
   {
    sqlite3_close(db);
    db = nullptr;
   }
  }
 }

 SQLiteConnection([[maybe_unused]] const SQLiteConnection& sq): SQLiteConnection() {}
 SQLiteConnection(SQLiteConnection&&) = default;

 SQLiteConnection& operator=([[maybe_unused]] const SQLiteConnection& sq)
 {
  *this = {};
  return *this;
 }
 SQLiteConnection& operator=(SQLiteConnection&&) = default;

 ~SQLiteConnection()
 {
  if(count == 0) michlib::errmessage("Destructor of SQLiteConnection called on count==0");
  if(count > 1)
   count--;
  else
  {
   count = 0;
   if(db != nullptr)
   {
    for(const auto& f: destructs) f(db);
    sqlite3_close(db);
   }
   db = nullptr;
  }
 }

 static void AddDestructor(FuncType&& f) { destructs.emplace_back(std::move(f)); }

 operator DBType() const { return db; }

 static DBType GetDB() { return db; }

 explicit operator bool() const { return db != nullptr; }
};

class PostgreSQLConnection
{
 public:
 using DBType   = PGconn*;
 using FuncType = std::function<void(DBType)>;

 private:
 static DBType                conn;
 static size_t                count;
 static std::vector<FuncType> destructs;

 public:
 PostgreSQLConnection()
 {
  count++;
  if(conn == nullptr)
  {
   MString oldprefix = GPL.UsePrefix("POSTGRES");
   MString name      = GPL.ParameterSValue("connection", "");
   GPL.UsePrefix(oldprefix);

   conn = PQconnectdb(name.Buf());
   if(PQstatus(conn) != CONNECTION_OK)
   {
    michlib::errmessage(PQerrorMessage(conn));
    PQfinish(conn);
    conn = nullptr;
   }
  }
 }

 PostgreSQLConnection([[maybe_unused]] const PostgreSQLConnection& pq): PostgreSQLConnection() {}
 PostgreSQLConnection(PostgreSQLConnection&&) = default;

 PostgreSQLConnection& operator=([[maybe_unused]] const PostgreSQLConnection& pq)
 {
  *this = {};
  return *this;
 }
 PostgreSQLConnection& operator=(PostgreSQLConnection&&) = default;

 ~PostgreSQLConnection()
 {
  if(count == 0) michlib::errmessage("Destructor of PostgreSQLConnection called on count==0");
  if(count > 1)
   count--;
  else
  {
   count = 0;
   if(conn != nullptr)
   {
    for(const auto& f: destructs) f(conn);
    PQfinish(conn);
   }
   conn = nullptr;
  }
 }

 static void AddDestructor(FuncType&& f) { destructs.emplace_back(std::move(f)); }

 operator DBType() const { return conn; }

 static DBType GetDB() { return conn; }

 explicit operator bool() const { return conn != nullptr; }
};

class GenericCache
{
 public:
 virtual bool                     Put(const MString& key, const MString& value, size_t ttl) const = 0;
 virtual std::pair<MString, bool> Get(const MString& key) const                                   = 0;
 virtual ~GenericCache() {}
};

class FakeCache: public GenericCache
{
 public:
 virtual bool                     Put([[maybe_unused]] const MString& key, [[maybe_unused]] const MString& value, [[maybe_unused]] size_t ttl) const override { return false; }
 virtual std::pair<MString, bool> Get([[maybe_unused]] const MString& key) const override { return {"", false}; }
 virtual ~FakeCache() override {}
};

class SQLiteCache: public GenericCache
{
 static bool regdest;

 SQLiteConnection db;

 public:
 bool Init()
 {
  if(!db) return false;

  if(!regdest)
  {
   // Create table
   sqlite3_stmt* sqst;
   int           i;

   i = sqlite3_prepare_v2(db,
                          "CREATE TABLE IF NOT EXISTS `cache`('key' TEXT PRIMARY KEY ON CONFLICT REPLACE NOT NULL ON CONFLICT FAIL, 'value' BLOB NOT NULL ON CONFLICT FAIL, "
                          "'exptime' INTEGER NOT NULL ON CONFLICT FAIL) WITHOUT ROWID, STRICT;",
                          -1, &sqst, 0);
   i = sqlite3_step(sqst);
   if(i != SQLITE_DONE)
   {
    sqlite3_finalize(sqst);
    return false;
   }
   sqlite3_finalize(sqst);
   sqlite3_busy_timeout(db, 1000);

   db.AddDestructor(
       [](SQLiteConnection::DBType db)
       {
        sqlite3_stmt* sqst = nullptr;
        int           i    = SQLITE_OK;

        if(i == SQLITE_OK) i = sqlite3_prepare_v2(db, "DELETE from `cache` WHERE exptime<?1;", -1, &sqst, 0);
        if(i == SQLITE_OK) i = sqlite3_bind_int64(sqst, 1, time(nullptr));
        if(i == SQLITE_OK) i = sqlite3_step(sqst);
        sqlite3_finalize(sqst);
       });
   regdest = true;
  }
  return true;
 }

 virtual bool Put(const MString& key, const MString& value, size_t ttl) const override
 {
  if(!*this) return false;
  sqlite3_stmt* sqst = nullptr;
  int           i    = SQLITE_OK;

  if(i == SQLITE_OK) i = sqlite3_prepare_v2(db, "INSERT OR REPLACE into `cache` VALUES(?1,?2,?3);", -1, &sqst, 0);
  if(i == SQLITE_OK) i = sqlite3_bind_text(sqst, 1, key.Buf(), -1, SQLITE_STATIC);
  if(i == SQLITE_OK) i = sqlite3_bind_blob64(sqst, 2, value.Buf(), value.Len(), SQLITE_STATIC);
  if(i == SQLITE_OK) i = sqlite3_bind_int64(sqst, 3, time(nullptr) + ttl);
  if(i == SQLITE_OK) i = sqlite3_step(sqst);
  sqlite3_finalize(sqst);

  return i == SQLITE_OK;
 }

 virtual std::pair<MString, bool> Get(const MString& key) const override
 {
  if(!*this) return {"", false};

  sqlite3_stmt* sqst = nullptr;
  int           i    = SQLITE_OK;

  if(i == SQLITE_OK) i = sqlite3_prepare_v2(db, "SELECT value from `cache` WHERE key=?1 AND exptime>?2;", -1, &sqst, 0);
  if(i == SQLITE_OK) i = sqlite3_bind_text(sqst, 1, key.Buf(), -1, SQLITE_STATIC);
  if(i == SQLITE_OK) i = sqlite3_bind_int64(sqst, 2, time(nullptr));
  if(i == SQLITE_OK) i = sqlite3_step(sqst);
  if(i == SQLITE_ROW)
  {
   auto p  = sqlite3_column_blob(sqst, 0);
   auto sz = sqlite3_column_bytes(sqst, 0);
   if(p != nullptr)
   {
    MString out(p, sz);
    sqlite3_finalize(sqst);
    return {std::move(out), true};
   }
  }
  sqlite3_finalize(sqst);
  return {"", false};
 }

 virtual ~SQLiteCache() override = default;

 explicit operator bool() const { return db != nullptr; }
};

class PostgreSQLHelpers
{
 static constexpr time_t postgresepoch = 946648800;

 class PGResultRAIIDT
 {
  public:
  // TODO: make static
  void operator()(PGresult* res) { PQclear(res); }
 };

 protected:
 PostgreSQLConnection conn;

 // Convert Postgres binary representation of timestamp to Unix epoch seconds. Microseconds ignored
 static time_t raw2epoch(time_t raw) { return Invert(raw) / 1000000 + postgresepoch; }

 // Convert Unix epoch time to Postres binary representation
 static time_t epoch2raw(time_t epoch) { return Invert((epoch - postgresepoch) * 1000000); }

 class PGresultRAII: public std::unique_ptr<PGresult, PGResultRAIIDT>
 {
  public:
  PGresultRAII() = default;
  PGresultRAII(PGresult* res): std::unique_ptr<PGresult, PGResultRAIIDT>(res) {}

  operator PGresult*() const { return get(); }
 };

 bool CheckCon() const
 {
  if(!*this) return false;
  if(PQstatus(conn) == CONNECTION_OK) return true;
  PQreset(conn);
  return PQstatus(conn) == CONNECTION_OK;
 }

 template<class D> static D Invert(D d)
 {
  using michlib::int1;
  D out;
  Invert(&d, &out, sizeof(D));
  return out;
 }

 static void Invert(const void* src, void* dst, size_t sz)
 {
  if(sz == 0) return;
  const int1* pin  = pointer_cast<const int1*>(src);
  int1*       pout = pointer_cast<int1*>(dst);
  for(size_t i = 0; i < sz; i++) pout[sz - i - 1] = pin[i];
 }

 public:
 explicit operator bool() const { return conn != nullptr; }
};

class PostgreSQLCache: public GenericCache, public PostgreSQLHelpers
{
 static bool regdest;

 public:
 bool Init()
 {
  if(!conn) return false;

  if(!regdest)
  {
   PGresultRAII res;

   // Create table
   res = PQexec(conn, "SET client_min_messages=WARNING;");
   res = PQexec(conn, "CREATE TABLE IF NOT EXISTS cache(key TEXT PRIMARY KEY NOT NULL, value BYTEA, exptime TIMESTAMP(0) NOT NULL);");
   if(PQresultStatus(res) != PGRES_COMMAND_OK)
   {
    michlib::errmessage(PQresStatus(PQresultStatus(res)));
    michlib::errmessage(PQerrorMessage(conn));
   }

   res = PQexec(conn, "SET client_min_messages=NOTICE;");

   conn.AddDestructor([](PostgreSQLConnection::DBType conn) { PGresultRAII res = PQexec(conn, "DELETE FROM cache WHERE exptime<localtimestamp;"); });

   regdest = true;
  }
  return true;
 }

 virtual bool Put(const MString& key, const MString& value, size_t ttl) const override
 {
  if(!CheckCon()) return false;

  auto          interval  = michlib::int_cast<michlib::int8>(ttl);
  michlib::int8 rinterval = Invert(interval);
  const char*   params[]  = {key.Buf(), value.Buf(), pointer_cast<const char*>(&rinterval)};
  int           plens[]   = {int_cast<int>(key.Len()), int_cast<int>(value.Len()), sizeof(rinterval)};
  int           pfor[]    = {0, 1, 1};

  PGresultRAII res = PQexecParams(conn,
                                  "INSERT INTO cache(key,value,exptime) VALUES($1,$2,localtimestamp + ($3::bigint ||' seconds')::interval)"
                                  "ON CONFLICT(key) DO UPDATE SET value=EXCLUDED.value, exptime=EXCLUDED.exptime;",
                                  3, nullptr, params, plens, pfor, 1);
  if(PQresultStatus(res) != PGRES_COMMAND_OK)
  {
   michlib::errmessage(PQresStatus(PQresultStatus(res)));
   michlib::errmessage(PQerrorMessage(conn));
   return false;
  }
  return true;
 }

 virtual std::pair<MString, bool> Get(const MString& key) const override
 {
  if(!CheckCon()) return {"", false};

  const char* params[] = {key.Buf()};
  int         plens[]  = {int_cast<int>(key.Len())};
  int         pfor[]   = {0};

  PGresultRAII res = PQexecParams(conn, "SELECT value from cache WHERE key=$1::text AND exptime>localtimestamp;", 1, nullptr, params, plens, pfor, 1);
  if(PQresultStatus(res) != PGRES_TUPLES_OK)
  {
   michlib::errmessage(PQresStatus(PQresultStatus(res)));
   michlib::errmessage(PQerrorMessage(conn));
   return {"", false};
  }
  else if(PQntuples(res) == 0)
   return {"", false};

  MString val(PQgetvalue(res, 0, 0), PQgetlength(res, 0, 0));
  return {std::move(val), true};
 }

 virtual ~PostgreSQLCache() override = default;
};

inline GenericCache* CreateCache(const MString& cachedesc)
{
 auto i    = cachedesc.GetPos(':');
 auto name = i == 0 ? cachedesc : cachedesc.SubStr(1, i - 1);
 auto par  = i == 0 ? "" : cachedesc.SubStr(i + 1, cachedesc.Len() - i);

 if(name == "no") return new FakeCache;

 if(name == "sqlite")
 {
  auto ret = new SQLiteCache;
  ret->Init();
  if(*ret) return ret;
  delete ret;
 }

 if(name == "postgre" || name == "postgres" || name == "postgresql")
 {
  auto ret = new PostgreSQLCache;
  ret->Init();
  if(*ret) return ret;
  delete ret;
 }

 return nullptr;
}