// Copyright 2018 Global Phasing Ltd.
//
// Monomer library - (Refmac) restraints dictionary,
// which is made of monomers (chemical components), links and modifications.

#ifndef GEMMI_MONLIB_HPP_
#define GEMMI_MONLIB_HPP_

#include <cctype>  // for tolower
#include <map>
#include <string>
#include <vector>
#include "calculate.hpp"  // for calculate_chiral_volume
#include "cifdoc.hpp"
#include "elem.hpp"       // for Element
#include "numb.hpp"       // for as_number
#include "fail.hpp"       // for fail, unreachable
#include "model.hpp"      // for Residue, Atom
#include "chemcomp.hpp"   // for ChemComp
#include "resinfo.hpp"    // for ResidueInfo

namespace gemmi {

typedef cif::Document (*read_cif_func)(const std::string&);

inline void add_distinct_altlocs(const Residue& res, std::string& altlocs) {
  for (const Atom& atom : res.atoms)
    if (atom.altloc && altlocs.find(atom.altloc) == std::string::npos)
      altlocs += atom.altloc;
}

struct ChemLink {
  enum class Group {
    // _chem_link.group_comp_N is one of:
    // "peptide", "P-peptide", "M-peptide", "pyranose", "DNA/RNA" or null
    // (we ignore "polymer")
    Peptide, PPeptide, MPeptide, Pyranose, DnaRna, Null
  };
  struct Side {
    std::string comp;
    std::string mod;
    Group group;
    bool matches_group(Group res) const {
      return group != Group::Null &&
             (res == group ||
              (group == Group::Peptide && (int) res <= (int) Group::MPeptide));
    }
    int specificity() const {
      if (!comp.empty())
        return 3;
      return group == Group::PPeptide || group == Group::MPeptide ? 1 : 0;
    };
  };
  std::string id;
  std::string name;
  Side side1;
  Side side2;
  Restraints rt;

  static Group read_group(const std::string& str) {
    if (str.size() >= 4) {
      const char* cstr = str.c_str();
      if ((str[0] == '\'' || str[0] == '"') && str.size() >= 6)
        ++cstr;
      switch (ialpha4_id(cstr)) {
        case ialpha4_id("pept"): return Group::Peptide;
        case ialpha4_id("l-pe"): return Group::Peptide;
        case ialpha4_id("p-pe"): return Group::PPeptide;
        case ialpha4_id("m-pe"): return Group::MPeptide;
        case ialpha4_id("pyra"): return Group::Pyranose;
        case ialpha4_id("dna/"): return Group::DnaRna;
      }
    }
    return Group::Null;
  }

  static const char* group_str(Group g) {
    switch (g) {
      case Group::Peptide: return "peptide";
      case Group::PPeptide: return "P-peptide";
      case Group::MPeptide: return "M-peptide";
      case Group::Pyranose: return "pyranose";
      case Group::DnaRna: return "DNA/RNA";
      case Group::Null: return ".";
    }
    unreachable();
  }

  static Group group_from_residue_info(const ResidueInfo& ri) {
    switch (ri.kind) {
      case ResidueInfo::UNKNOWN: return Group::Null;
      case ResidueInfo::AA:      return Group::Peptide;
      case ResidueInfo::AAD:     return Group::Peptide;
      case ResidueInfo::PAA:     return Group::PPeptide;
      case ResidueInfo::MAA:     return Group::MPeptide;
      case ResidueInfo::RNA:     return Group::DnaRna;
      case ResidueInfo::DNA:     return Group::DnaRna;
      case ResidueInfo::BUF:     return Group::Null;
      case ResidueInfo::HOH:     return Group::Null;
      case ResidueInfo::PYR:     return Group::Pyranose;
      case ResidueInfo::ELS:     return Group::Null;
    }
    unreachable();
  }

  // If multiple ChemLinks match a bond, the scores can pick the best match.
  int calculate_score(const Residue& res1, const Residue* res2,
                      char alt) const {
    int link_score = side1.specificity() + side2.specificity();
    // check chirality
    for (const Restraints::Chirality& chirality : rt.chirs)
      if (chirality.sign != ChiralityType::Both) {
        const Atom* a1 = chirality.id_ctr.get_from(res1, res2, alt);
        const Atom* a2 = chirality.id1.get_from(res1, res2, alt);
        const Atom* a3 = chirality.id2.get_from(res1, res2, alt);
        const Atom* a4 = chirality.id3.get_from(res1, res2, alt);
        if (a1 && a2 && a3 && a4) {
          double vol = calculate_chiral_volume(a1->pos, a2->pos,
                                               a3->pos, a4->pos);
          if (chirality.is_wrong(vol))
            link_score -= 10;
        }
      }
    // check fixed torsion angle (_chem_link_tor.period == 0)
    for (const Restraints::Torsion& tor : rt.torsions)
      if (tor.period == 0) {
        const Atom* a1 = tor.id1.get_from(res1, res2, alt);
        const Atom* a2 = tor.id2.get_from(res1, res2, alt);
        const Atom* a3 = tor.id3.get_from(res1, res2, alt);
        const Atom* a4 = tor.id4.get_from(res1, res2, alt);
        double z = 10.;
        if (a1 && a2 && a3 && a4)
          z = angle_z(calculate_dihedral(a1->pos, a2->pos, a3->pos, a4->pos),
                      tor);
        link_score -= (int) z;
      }
    return link_score;
  }
};

struct ChemMod {
  struct AtomMod {
    int func;
    std::string old_id;
    std::string new_id;
    Element el;
    float charge;
    std::string chem_type;
  };

  std::string id;
  std::string name;
  std::string comp_id;
  std::string group_id;
  std::vector<AtomMod> atom_mods;
  Restraints rt;

  void apply_to(ChemComp& chemcomp) const;
};


inline Restraints read_link_restraints(const cif::Block& block_) {
  auto read_aid = [](cif::Table::Row& row, int n) {
    return Restraints::AtomId{cif::as_int(row[n]), row.str(n+1)};
  };
  Restraints rt;
  cif::Block& block = const_cast<cif::Block&>(block_);
  for (auto row : block.find("_chem_link_bond.",
                             {"atom_1_comp_id", "atom_id_1",
                              "atom_2_comp_id", "atom_id_2",
                              "type",
                              "value_dist", "value_dist_esd"}))
    rt.bonds.push_back({read_aid(row, 0), read_aid(row, 2),
                        bond_type_from_string(row[4]), false,
                        cif::as_number(row[5]), cif::as_number(row[6]),
                        NAN, NAN});
  for (auto row : block.find("_chem_link_angle.",
                             {"atom_1_comp_id", "atom_id_1",
                              "atom_2_comp_id", "atom_id_2",
                              "atom_3_comp_id", "atom_id_3",
                              "value_angle", "value_angle_esd"}))
    rt.angles.push_back({read_aid(row, 0), read_aid(row, 2), read_aid(row, 4),
                         cif::as_number(row[6]), cif::as_number(row[7])});
  for (auto row : block.find("_chem_link_tor.",
                             {"id",
                              "atom_1_comp_id", "atom_id_1",
                              "atom_2_comp_id", "atom_id_2",
                              "atom_3_comp_id", "atom_id_3",
                              "atom_4_comp_id", "atom_id_4",
                              "value_angle", "value_angle_esd",
                              "period"}))
    rt.torsions.push_back({row.str(0),
                           read_aid(row, 1), read_aid(row, 3),
                           read_aid(row, 5), read_aid(row, 7),
                           cif::as_number(row[9]), cif::as_number(row[10]),
                           cif::as_int(row[11])});
  for (auto row : block.find("_chem_link_chir.",
                             {"atom_centre_comp_id", "atom_id_centre",
                              "atom_1_comp_id", "atom_id_1",
                              "atom_2_comp_id", "atom_id_2",
                              "atom_3_comp_id", "atom_id_3",
                              "volume_sign"}))
    if (row[4][0] != 'c') // ignore crossN
      rt.chirs.push_back({read_aid(row, 0), read_aid(row, 2),
                          read_aid(row, 4), read_aid(row, 6),
                          chirality_from_string(row[8])});
  for (auto row : block.find("_chem_link_plane.",
                             {"plane_id", "atom_comp_id", "atom_id",
                              "dist_esd"})) {
    Restraints::Plane& plane = rt.get_or_add_plane(row.str(0));
    if (plane.esd == 0.0)
      plane.esd = cif::as_number(row[3]);
    plane.ids.push_back(read_aid(row, 1));
  }
  return rt;
}

inline ResidueInfo::Kind chemcomp_group_to_kind(const std::string& group) {
  if (group.size() >= 3) {
    const char* str = group.c_str();
    if (group.size() > 4 && (*str == '"' || *str == '\''))
      ++str;
    switch (ialpha4_id(str)) {
      case ialpha4_id("non-"): return ResidueInfo::ELS;
      case ialpha4_id("pept"): return ResidueInfo::AA;
      case ialpha4_id("l-pe"): return ResidueInfo::AA;
      case ialpha4_id("p-pe"): return ResidueInfo::PAA;
      case ialpha4_id("m-pe"): return ResidueInfo::MAA;
      case ialpha4_id("dna"): return ResidueInfo::DNA;
      case ialpha4_id("rna"): return ResidueInfo::RNA;
      case ialpha4_id("pyra"): return ResidueInfo::PYR;
    }
  }
  return ResidueInfo::UNKNOWN;
}

template<typename T>
void insert_comp_list(const cif::Document& doc, T& ri_map) {
  if (const cif::Block* list_block = doc.find_block("comp_list")) {
    for (auto row : const_cast<cif::Block*>(list_block)->find("_chem_comp.",
                                {"id", "group", "?number_atoms_nh"})) {
      ResidueInfo ri;
      ri.kind = chemcomp_group_to_kind(row[1]);
      ri.one_letter_code = ' ';
      ri.hydrogen_count = row.has2(2) ? cif::as_int(row[2]) : 0;
      ri_map.emplace(row.str(0), ri);
    }
  }
}

inline void insert_chemlinks(const cif::Document& doc,
                             std::map<std::string,ChemLink>& links) {
  if (const cif::Block* list_block = doc.find_block("link_list")) {
    for (auto row : const_cast<cif::Block*>(list_block)->find("_chem_link.",
                                   {"id", "name",
                                    "comp_id_1", "mod_id_1", "group_comp_1",
                                    "comp_id_2", "mod_id_2", "group_comp_2"})) {
      ChemLink link;
      link.id = row.str(0);
      link.name = row.str(1);
      link.side1.comp = row.str(2);
      link.side1.mod = row.str(3);
      link.side1.group = ChemLink::read_group(row[4]);
      link.side2.comp = row.str(5);
      link.side2.mod = row.str(6);
      link.side2.group = ChemLink::read_group(row[7]);
      const cif::Block* block = doc.find_block("link_" + link.id);
      if (!block)
        fail("inconsistent data_link_list");
      link.rt = read_link_restraints(*block);
      links.emplace(link.id, link);
    }
  }
}

// Helper function. str is one of "add", "delete", "change".
inline int chem_mod_type(const std::string& str) {
  char c = str[0] | 0x20;
  if (c != 'a' && c != 'd' && c != 'c')
    fail("Unexpected value of _chem_mod_*.function: " + str);
  return c;
}

inline Restraints read_restraint_modifications(const cif::Block& block_) {
  Restraints rt;
  cif::Block& block = const_cast<cif::Block&>(block_);
  for (auto row : block.find("_chem_mod_bond.",
                             {"function", "atom_id_1", "atom_id_2",
                              "new_type",
                              "new_value_dist", "new_value_dist_esd",
                              "?new_value_dist_nucleus", "?new_value_dist_nucleus_esd"}))
    rt.bonds.push_back({{chem_mod_type(row[0]), row.str(1)}, {1, row.str(2)},
                        bond_type_from_string(row[3]), false,
                        cif::as_number(row[4]), cif::as_number(row[5]),
                        row.has(6) ? cif::as_number(row[6]) : NAN,
                        row.has(7) ? cif::as_number(row[7]) : NAN});
  for (auto row : block.find("_chem_mod_angle.",
                             {"function", "atom_id_1",
                              "atom_id_2", "atom_id_3",
                              "new_value_angle", "new_value_angle_esd"}))
    rt.angles.push_back({{chem_mod_type(row[0]), row.str(1)},
                         {1, row.str(2)}, {1, row.str(3)},
                         cif::as_number(row[4]), cif::as_number(row[5])});
  for (auto row : block.find("_chem_mod_tor.",
                              {"function", "id", "atom_id_1",
                               "atom_id_2", "atom_id_3", "atom_id_4",
                               "new_value_angle", "new_value_angle_esd",
                               "new_period"}))
    rt.torsions.push_back({row.str(1), {chem_mod_type(row[0]), row.str(2)},
                           {1, row.str(3)}, {1, row.str(4)}, {1, row.str(5)},
                           cif::as_number(row[6]), cif::as_number(row[7]),
                           cif::as_int(row[8])});
  for (auto row : block.find("_chem_mod_chir.",
                             {"function", "atom_id_centre", "atom_id_1",
                              "atom_id_2", "atom_id_3",
                              "new_volume_sign"}))
    rt.chirs.push_back({{1, row.str(1)}, {chem_mod_type(row[0]), row.str(2)},
                        {1, row.str(3)}, {1, row.str(4)},
                        chirality_from_string(row[5])});
  for (auto row : block.find("_chem_mod_plane_atom.",
                             {"function", "plane_id", "atom_id" ,
                              "new_dist_esd"})) {
    Restraints::Plane& plane = rt.get_or_add_plane(row.str(1));
    if (plane.esd == 0.0)
      plane.esd = cif::as_number(row[3]);
    plane.ids.push_back({chem_mod_type(row[0]), row.str(2)});
  }
  return rt;
}

inline void insert_chemmods(const cif::Document& doc,
                            std::map<std::string, ChemMod>& mods) {
  if (const cif::Block* list_block = doc.find_block("mod_list")) {
    for (auto row : const_cast<cif::Block*>(list_block)->find("_chem_mod.",
                                   {"id", "name", "comp_id", "group_id"})) {
      ChemMod mod;
      mod.id = row.str(0);
      mod.name = row.str(1);
      mod.comp_id = row.str(2);
      mod.group_id = row.str(3);
      const cif::Block* block = doc.find_block("mod_" + mod.id);
      if (!block)
        fail("inconsistent data_mod_list");
      for (auto ra : const_cast<cif::Block*>(block)->find("_chem_mod_atom.",
                                  {"function", "atom_id", "new_atom_id",
                                   "new_type_symbol", "new_type_energy",
                                   "?new_charge", "?new_partial_charge"}))
        mod.atom_mods.push_back({chem_mod_type(ra[0]), ra.str(1), ra.str(2),
                                 Element(ra.str(3)),
                                 (float) cif::as_number(ra.one_of(5, 6)),
                                 ra.str(4)});
      mod.rt = read_restraint_modifications(*block);
      mods.emplace(mod.id, mod);
    }
  }
}

inline void ChemMod::apply_to(ChemComp& chemcomp) const {
  // _chem_mod_atom
  for (const AtomMod& mod : atom_mods) {
    auto it = chemcomp.find_atom(mod.old_id);
    switch (mod.func) {
      case 'a':
        if (!chemcomp.has_atom(mod.new_id))
          chemcomp.atoms.push_back({mod.new_id, mod.el,
                                    std::isnan(mod.charge) ? mod.charge : 0,
                                    mod.chem_type});
        break;
      case 'd':
        if (it != chemcomp.atoms.end()) {
          chemcomp.atoms.erase(it);
          // delete restraints containing mod.old_id
          const std::string& old = mod.old_id;
          vector_remove_if(chemcomp.rt.bonds, [&](const Restraints::Bond& b) {
              return b.id1 == old || b.id2 == old;
          });
          vector_remove_if(chemcomp.rt.angles, [&](const Restraints::Angle& a) {
              return a.id1 == old || a.id2 == old || a.id3 == old;
          });
          vector_remove_if(chemcomp.rt.torsions,
              [&](const Restraints::Torsion& t) {
                return t.id1 == old || t.id2 == old || t.id3 == old ||
                       t.id4 == old;
          });
          vector_remove_if(chemcomp.rt.chirs,
              [&](const Restraints::Chirality& c) {
                return c.id_ctr == old || c.id1 == old || c.id2 == old ||
                       c.id3 == old;
          });
          for (Restraints::Plane& plane : chemcomp.rt.planes)
            vector_remove_if(plane.ids, [&](const Restraints::AtomId& a) {
                return a.atom == old;
            });
        }
        break;
      case 'c':
        if (it != chemcomp.atoms.end()) {
          if (!mod.new_id.empty())
            it->id = mod.new_id;
          if (mod.el != El::X)
            it->el = mod.el;
          if (!std::isnan(mod.charge))
            it->charge = mod.charge;
          if (!mod.chem_type.empty())
            it->chem_type = mod.chem_type;
        }
        break;
    }
  }

  // _chem_mod_bond
  for (const Restraints::Bond& mod : rt.bonds) {
    auto it = chemcomp.rt.find_bond(mod.id1.atom, mod.id2.atom);
    switch (mod.id1.comp) {
      case 'a':
        if (it == chemcomp.rt.bonds.end()) {
          chemcomp.rt.bonds.push_back(mod);
          // id1.comp was temporarily set to 'a', set it back to 1
          chemcomp.rt.bonds.back().id1.comp = 1;
        }
        break;
      case 'd':
        if (it != chemcomp.rt.bonds.end())
          chemcomp.rt.bonds.erase(it);
        break;
      case 'c':
        if (it != chemcomp.rt.bonds.end()) {
          if (mod.type != BondType::Unspec)
            it->type = mod.type;
          if (!std::isnan(mod.value))
            it->value = mod.value;
          if (!std::isnan(mod.esd))
            it->esd = mod.esd;
          if (!std::isnan(mod.value_nucleus))
            it->value_nucleus = mod.value_nucleus;
          if (!std::isnan(mod.esd_nucleus))
            it->esd_nucleus = mod.esd_nucleus;
        }
        break;
    }
  }

  // _chem_mod_angle
  for (const Restraints::Angle& mod : rt.angles) {
    auto it = chemcomp.rt.find_angle(mod.id1.atom, mod.id2.atom, mod.id3.atom);
    switch (mod.id1.comp) {
      case 'a':
        if (it == chemcomp.rt.angles.end()) {
          chemcomp.rt.angles.push_back(mod);
          chemcomp.rt.angles.back().id1.comp = 1;
        }
        break;
      case 'd':
        if (it != chemcomp.rt.angles.end())
          chemcomp.rt.angles.erase(it);
        break;
      case 'c':
        if (it != chemcomp.rt.angles.end()) {
          if (!std::isnan(mod.value))
            it->value = mod.value;
          if (!std::isnan(mod.esd))
            it->esd = mod.esd;
        }
        break;
    }
  }

  // _chem_mod_tor
  for (const Restraints::Torsion& mod : rt.torsions) {
    auto it = chemcomp.rt.find_torsion(mod.id1.atom, mod.id2.atom,
                                       mod.id3.atom, mod.id4.atom);
    switch (mod.id1.comp) {
      case 'a':
        if (it == chemcomp.rt.torsions.end()) {
          chemcomp.rt.torsions.push_back(mod);
          chemcomp.rt.torsions.back().id1.comp = 1;
        }
        break;
      case 'd':
        if (it != chemcomp.rt.torsions.end())
          chemcomp.rt.torsions.erase(it);
        break;
      case 'c':
        if (it != chemcomp.rt.torsions.end()) {
          if (!mod.label.empty())
            it->label = mod.label;
          if (!std::isnan(mod.value))
            it->value = mod.value;
          if (!std::isnan(mod.esd))
            it->esd = mod.esd;
          if (mod.period != -1)
            it->period = mod.period;
        }
        break;
    }
  }

  // _chem_mod_chir
  for (const Restraints::Chirality& mod : rt.chirs) {
    auto it = chemcomp.rt.find_chir(mod.id_ctr.atom, mod.id1.atom,
                                    mod.id2.atom, mod.id3.atom);
    switch (mod.id1.comp) {
      case 'a':
        if (it == chemcomp.rt.chirs.end()) {
          chemcomp.rt.chirs.push_back(mod);
          chemcomp.rt.chirs.back().id1.comp = 1;
        }
        break;
      case 'd':
        if (it != chemcomp.rt.chirs.end())
          chemcomp.rt.chirs.erase(it);
        break;
      case 'c':
        if (it != chemcomp.rt.chirs.end())
          it->sign = mod.sign;
        break;
    }
  }

  // _chem_mod_plane_atom
  for (const Restraints::Plane& mod : rt.planes)
    for (const Restraints::AtomId& atom_id : mod.ids) {
      if (atom_id.comp == 'a') {
        Restraints::Plane& plane = chemcomp.rt.get_or_add_plane(mod.label);
        if (plane.esd == 0.0 && !std::isnan(mod.esd))
          plane.esd = mod.esd;
        auto it = std::find(plane.ids.begin(), plane.ids.end(), atom_id.atom);
        if (it == plane.ids.end())
          plane.ids.push_back({1, atom_id.atom});
      } else if (atom_id.comp == 'd') {
        auto it = chemcomp.rt.get_plane(mod.label);
        if (it != chemcomp.rt.planes.end()) {
          auto item = std::find(it->ids.begin(), it->ids.end(), atom_id.atom);
          if (item != it->ids.end())
            it->ids.erase(item);
        }
      }
    }
}

struct MonLib {
  cif::Document mon_lib_list;
  std::map<std::string, ChemComp> monomers;
  std::map<std::string, ChemLink> links;
  std::map<std::string, ChemMod> modifications;
  std::map<std::string, ResidueInfo> residue_infos;

  const ChemLink* get_link(const std::string& link_id) const {
    auto link = links.find(link_id);
    return link != links.end() ? &link->second : nullptr;
  }
  const ChemMod* find_mod(const std::string& name) const {
    auto modif = modifications.find(name);
    return modif != modifications.end() ? &modif->second : nullptr;
  }
  const ResidueInfo* find_residue_info(const std::string& name) const {
    auto resinfo = residue_infos.find(name);
    return resinfo != residue_infos.end() ? &resinfo->second : nullptr;
  }

  // Returns the most specific link and a flag that is true
  // if the order is comp2-comp1 in the link definition.
  // We don't check chirality here (cf. calculate_score).
  std::pair<const ChemLink*, bool>
  match_link(const std::string& comp1, const std::string& atom1,
             const std::string& comp2, const std::string& atom2) const {
    const ChemLink* best_link = nullptr;
    int best_score = -1;
    bool inverted = false;
    for (auto& ml : links) {
      const ChemLink& link = ml.second;
      if (link.rt.bonds.empty())
        continue;
      // for now we don't have link definitions with >1 bonds
      const Restraints::Bond& bond = link.rt.bonds[0];
      if (bond.id1.atom == atom1 && bond.id2.atom == atom2 &&
          link_side_matches_residue(link.side1, comp1) &&
          link_side_matches_residue(link.side2, comp2)) {
        int score = link.side1.specificity() + link.side2.specificity();
        if (score > best_score) {
          best_link = &link;
          best_score = score;
          inverted = false;
        }
      }
      if (bond.id1.atom == atom2 && bond.id2.atom == atom1 &&
          link_side_matches_residue(link.side1, comp2) &&
          link_side_matches_residue(link.side2, comp1)) {
        int score = link.side1.specificity() + link.side2.specificity();
        if (score > best_score) {
          best_link = &link;
          best_score = score;
          inverted = true;
        }
      }
    }
    return {best_link, inverted};
  }

  void ensure_unique_link_name(std::string& name) const {
    size_t orig_len = name.size();
    for (int n = 0; get_link(name) != nullptr; ++n)
      name.replace(orig_len, name.size(), std::to_string(n));
  }

  void add_monomer_if_present(const cif::Block& block) {
    if (block.has_tag("_chem_comp_atom.atom_id")) {
      ChemComp cc = make_chemcomp_from_block(block);
      std::string name = cc.name;
      monomers.emplace(name, std::move(cc));
    }
  }

  void add_monomers_if_present(const cif::Document& doc) {
    for (const cif::Block& block : doc.blocks)
      add_monomer_if_present(block);
  }

  bool link_side_matches_residue(const ChemLink::Side& side,
                                 const std::string& res_name) const {
    if (side.comp != "")
      return side.comp == res_name;
    const ResidueInfo* resinfo = find_residue_info(res_name);
    return resinfo && side.matches_group(ChemLink::group_from_residue_info(*resinfo));
  }

  std::string path(const char* code=nullptr) const {
    size_t len = mon_lib_list.source.length();
    // "list/mon_lib_list.cif" has 21 characters
    if (len < 21)
      return {};
    std::string dir = mon_lib_list.source.substr(0, len-21);
    if (code)
      dir += relative_monomer_path(code);
    return dir;
  }

  static std::string relative_monomer_path(const std::string& code) {
    std::string path(1, std::tolower(code[0]));
    path += '/';  // works also on Windows
    path += code;
    // On Windows several names are reserved (CON, PRN, AUX, ...), see
    // https://docs.microsoft.com/en-us/windows/win32/fileio/naming-a-file
    // The workaround in CCP4 monomer library is to use CON_CON.cif, etc.
    if (code.size() == 3)
      switch (ialpha3_id(code.c_str())) {
        case ialpha3_id("AUX"):
        case ialpha3_id("COM"):
        case ialpha3_id("CON"):
        case ialpha3_id("LPT"):
        case ialpha3_id("PRN"):
          path += '_';
          path += code;
      }
    path += ".cif";
    return path;
  }

  void read_monomer_cif(const std::string& path, read_cif_func read_cif) {
    mon_lib_list = (*read_cif)(path);
    for (const cif::Block& block : mon_lib_list.blocks)
      add_monomer_if_present(block);
    insert_chemlinks(mon_lib_list, links);
    insert_chemmods(mon_lib_list, modifications);
    insert_comp_list(mon_lib_list, residue_infos);
  }
};

inline MonLib read_monomer_lib(std::string monomer_dir,
                               const std::vector<std::string>& resnames,
                               read_cif_func read_cif,
                               const std::string& libin="",
                               bool ignore_missing=false) {
  if (monomer_dir.empty())
    fail("read_monomer_lib: monomer_dir not specified.");
  if (monomer_dir.back() != '/' && monomer_dir.back() != '\\')
    monomer_dir += '/';
  MonLib monlib;
  if (!libin.empty())
    monlib.read_monomer_cif(libin, read_cif);
  monlib.read_monomer_cif(monomer_dir + "list/mon_lib_list.cif", read_cif);
  std::string error;
  for (const std::string& name : resnames) {
    try {
      cif::Document doc = (*read_cif)(monomer_dir + MonLib::relative_monomer_path(name));
      auto cc = make_chemcomp_from_cif(name, doc);
      monlib.monomers.emplace(name, std::move(cc));
    } catch(std::runtime_error& err) {
      if (!ignore_missing)
        error += "The monomer " + name + " could not be read: " + err.what() + ".\n";
    }
  }
  if (!error.empty())
    fail(error + "Please create definitions for missing monomers.");
  return monlib;
}


struct BondIndex {
  const Model& model;

  struct AtomImage {
    int atom_serial;
    bool same_image;
    bool operator==(const AtomImage& o) const {
      return atom_serial == o.atom_serial && same_image == o.same_image;
    }
  };
  std::map<int, std::vector<AtomImage>> index;

  BondIndex(const Model& model_) : model(model_) {
    for (const_CRA cra : model.all())
      if (!index.emplace(cra.atom->serial, std::vector<AtomImage>()).second)
        fail("duplicated serial numbers");
  }

  void add_oneway_link(const Atom& a, const Atom& b, bool same_image) {
    std::vector<AtomImage>& list_a = index.at(a.serial);
    AtomImage ai{b.serial, same_image};
    if (!in_vector(ai, list_a))
      list_a.push_back(ai);
  }

  void add_link(const Atom& a, const Atom& b, bool same_image) {
    add_oneway_link(a, b, same_image);
    add_oneway_link(b, a, same_image);
  }

  void add_monomer_bonds(MonLib& monlib) {
    for (const Chain& chain : model.chains)
      for (const Residue& res : chain.residues) {
        std::string altlocs;
        add_distinct_altlocs(res, altlocs);
        if (altlocs.empty())
          altlocs += '*';
        auto monomer = monlib.monomers.find(res.name);
        if (monomer == monlib.monomers.end())
          fail("Monomer description not found: " + res.name);
        for (const Restraints::Bond& bond : monomer->second.rt.bonds)
          for (char alt : altlocs)
            if (const Atom* at1 = res.find_atom(bond.id1.atom, alt))
              if (const Atom* at2 = res.find_atom(bond.id2.atom, alt)) {
                add_link(*at1, *at2, true);
                if (!at1->altloc && !at2->altloc)
                  break;
              }
      }
  }

  bool are_linked(const Atom& a, const Atom& b, bool same_image) const {
    return in_vector({b.serial, same_image}, index.at(a.serial));
  }

  int graph_distance(const Atom& a, const Atom& b, bool same_image,
                     int max_distance=4) const {
    std::vector<AtomImage> neighbors(1, {a.serial, true});
    for (int distance = 1; distance <= max_distance; ++distance) {
      for (size_t n = neighbors.size(); n--; ) {
        for (AtomImage ai : index.at(neighbors[n].atom_serial)) {
          if (!neighbors[n].same_image)
            ai.same_image = !ai.same_image;
          if (ai.atom_serial == b.serial && ai.same_image == same_image)
            return distance;
          if (!in_vector(ai, neighbors))
            neighbors.push_back(ai);
        }
      }
    }
    return max_distance + 1;
  }
};

} // namespace gemmi
#endif
