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/*! \libinternal \file
 *
 * \brief This file makes declarations used for storing bitfields
 * describing each atom so that other modules can efficiently process
 * them.
 *
 * \inlibraryapi
 */

#ifndef GMX_MDTYPES_ATOMINFO_H
#define GMX_MDTYPES_ATOMINFO_H

#include <vector>

namespace gmx
{

/*! \brief Constants whose bit describes a property of an atom in
 * AtomInfoWithinMoleculeBlock.atomInfo.
 *
 * No bit should exceed 1 << 63, so that it fits into a 64-bit
 * integer.
 *
 * Since the tpx format support max 256 energy groups, we do the same
 * here, reserving bits 0-7 for the energy-group ID.
 */
//! \{
static constexpr int64_t sc_atomInfo_FreeEnergyPerturbation = 1 << 15;
static constexpr int64_t sc_atomInfo_HasPerturbedCharge     = 1 << 16;
static constexpr int64_t sc_atomInfo_Exclusion              = 1 << 17;
static constexpr int64_t sc_atomInfo_Constraint             = 1 << 20;
static constexpr int64_t sc_atomInfo_Settle                 = 1 << 21;
static constexpr int64_t sc_atomInfo_BondCommunication      = 1 << 22;
static constexpr int64_t sc_atomInfo_HasVdw                 = 1 << 23;
static constexpr int64_t sc_atomInfo_HasCharge              = 1 << 24;
//! \}
//! The first 8 bits are reserved for energy-group ID
static constexpr int64_t sc_atomInfo_EnergyGroupIdMask = 0b11111111;

/*! \internal
 *  \brief Contains information about each atom in a molecule block of the global topology.
 */
struct AtomInfoWithinMoleculeBlock
{
    //! Index within the system of the first atom in the molecule block
    int indexOfFirstAtomInMoleculeBlock = 0;
    //! Index within the system of the last atom in the molecule block
    int indexOfLastAtomInMoleculeBlock = 0;
    /*! \brief Atom info for each atom in the block.
     *
     * The typical case is that all atoms are identical for each
     * molecule of the block, and if so this vector has size equal to
     * the number of atoms in the molecule.
     *
     * An example of an atypical case is QM/MM, where multiple
     * molecules might be present and different molecules have
     * different atoms within any one QM group or region. Now there are
     * multiple kinds of molecules with the same connectivity, so we simply
     * write out the atom info for the entire molecule block. Then the
     * size equals the product of the number of atoms in the
     * molecule and the number of molecules.
     *
     * The vector needs to be indexed accordingly.
     */
    std::vector<int64_t> atomInfo;
};

} // namespace gmx

#endif
