odm/include/nczarrcommon.h

#pragma once
#include "merrors.h"
#include <utility>
#include <variant>

using michlib::Error;
using michlib::int1;
using michlib::int2;
using michlib::int4;
using michlib::int8;
using michlib::int_cast;
using michlib::MString;
using michlib::RetVal;
using michlib::uint1;
using michlib::uint8;

class NcZarrTypes
{
 protected:
 using AttVT = std::variant<std::monostate, int8, uint8, double, MString, bool>;

 class ArrCounter
 {
  using VT = std::vector<size_t>;
  const VT count;
  VT       ind;
  bool     end;

  public:
  static size_t Index(const VT& i, const VT& c)
  {
   size_t out = 0;
   size_t mul = 1;
   for(size_t ii = i.size(); ii != 0; ii--)
   {
    out += mul * i[ii - 1];
    mul *= c[ii - 1];
   }
   return out;
  }

  static VT Index(size_t lind, const VT& c)
  {
   VT out(c.size());

   size_t j = lind;

   for(auto i = c.size(); i > 0; i--)
   {
    out[i - 1] = j % c[i - 1];
    j          = j / c[i - 1];
   }

   return out;
  }

  ArrCounter() = delete;
  ArrCounter(const VT& cnt): count(cnt), ind(cnt.size(), 0), end(false) {}

  size_t operator[](size_t i) const { return ind[i]; }

  ArrCounter& operator++()
  {
   size_t curind = count.size();
   while(curind != 0)
   {
    ind[curind - 1]++;
    if(ind[curind - 1] >= count[curind - 1])
    {
     ind[curind - 1] = 0;
     curind--;
    }
    else
     return *this;
   }
   ind = count;
   end = true;
   return *this;
  }

  explicit operator bool() const { return !end; }

  size_t Index() const { return Index(ind, count); }
  size_t Index(const VT& i) const { return Index(i, count); }
  VT     Index(size_t lind) const { return Index(lind, count); }

  size_t Count(size_t i) const { return count[i]; }

  const VT& VIndex() const { return ind; }
  VT        VIndex(const VT& start) const
  {
   VT out(ind.size());
   for(size_t i = 0; i < ind.size(); i++) out[i] = ind[i] + start[i];
   return out;
  }

  const auto& Count() const { return count; }

  size_t N() const
  {
   size_t out = 1;
   for(size_t i = 0; i < count.size(); i++) out *= count[i];
   return out;
  }
 };

 public:
 enum class AttType
 {
  UNDEF,
  INT,
  UINT,
  REAL,
  STRING,
  BOOL
 };
 enum class VarType
 {
  UNDEF,
  FLOAT,
  DOUBLE,
  INT1,
  INT2,
  INT4,
  INT8,
  UINT1
 };

 protected:
 template<VarType VT, class Dummy = void> struct VarType2Type;

 template<class Dummy> struct VarType2Type<VarType::FLOAT, Dummy>
 {
  using type = float;
 };
 template<class Dummy> struct VarType2Type<VarType::DOUBLE, Dummy>
 {
  using type = double;
 };
 template<class Dummy> struct VarType2Type<VarType::INT1, Dummy>
 {
  using type = int1;
 };
 template<class Dummy> struct VarType2Type<VarType::INT2, Dummy>
 {
  using type = int2;
 };
 template<class Dummy> struct VarType2Type<VarType::INT4, Dummy>
 {
  using type = int4;
 };
 template<class Dummy> struct VarType2Type<VarType::INT8, Dummy>
 {
  using type = int8;
 };
 template<class Dummy> struct VarType2Type<VarType::UINT1, Dummy>
 {
  using type = uint1;
 };

 template<VarType VT> using Type = VarType2Type<VT>::type;

 static constexpr size_t SizeOf(VarType vt)
 {
  switch(vt)
  {
  case(VarType::UNDEF): return 0;
  case(VarType::FLOAT): return sizeof(Type<VarType::FLOAT>);
  case(VarType::DOUBLE): return sizeof(Type<VarType::DOUBLE>);
  case(VarType::INT1): return sizeof(Type<VarType::INT1>);
  case(VarType::INT2): return sizeof(Type<VarType::INT2>);
  case(VarType::INT4): return sizeof(Type<VarType::INT4>);
  case(VarType::INT8): return sizeof(Type<VarType::INT8>);
  case(VarType::UINT1): return sizeof(Type<VarType::UINT1>);
  }
  return 0;
 }

 template<class T> static size_t FindInd(const MString& name, const std::vector<T>& arr)
 {
  for(size_t i = 0; i < arr.size(); i++)
   if(arr[i].Name() == name) return i;
  return arr.size();
 }

 class Attribute: public AttVT
 {
  MString name;

  public:
  Attribute(const MString& n, AttVT&& v): AttVT(std::move(v)), name(n) {}
  Attribute(const std::string& n, AttVT&& v): AttVT(std::move(v)), name(n.c_str(), n.size()) {}

  const MString& Name() const { return name; }

  AttType Type() const
  {
   if(std::holds_alternative<int8>(*this))
    return AttType::INT;
   else if(std::holds_alternative<uint8>(*this))
    return AttType::UINT;
   else if(std::holds_alternative<double>(*this))
    return AttType::REAL;
   else if(std::holds_alternative<MString>(*this))
    return AttType::STRING;
   else if(std::holds_alternative<bool>(*this))
    return AttType::BOOL;

   return AttType::UNDEF;
  }

  int8 I() const
  {
   if(std::holds_alternative<int8>(*this))
    return std::get<int8>(*this);
   else if(std::holds_alternative<uint8>(*this))
    return int_cast<int8>(std::get<uint8>(*this));
   else if(std::holds_alternative<double>(*this))
    return static_cast<int8>(std::get<double>(*this));
   else if(std::holds_alternative<MString>(*this))
    return std::get<MString>(*this).ToInteger<int8>();
   else if(std::holds_alternative<bool>(*this))
    return std::get<bool>(*this) ? 1 : 0;
   return 0;
  }

  uint8 U() const
  {
   if(std::holds_alternative<int8>(*this))
    return int_cast<uint8>(std::get<int8>(*this));
   else if(std::holds_alternative<uint8>(*this))
    return std::get<uint8>(*this);
   else if(std::holds_alternative<double>(*this))
    return static_cast<uint8>(std::get<double>(*this));
   else if(std::holds_alternative<MString>(*this))
    return std::get<MString>(*this).ToInteger<uint8>();
   else if(std::holds_alternative<bool>(*this))
    return std::get<bool>(*this) ? 1 : 0;
   return 0;
  }

  double D() const
  {
   if(std::holds_alternative<int8>(*this))
    return std::get<int8>(*this);
   else if(std::holds_alternative<uint8>(*this))
    return std::get<uint8>(*this);
   else if(std::holds_alternative<double>(*this))
    return std::get<double>(*this);
   else if(std::holds_alternative<MString>(*this))
    return michlib_internal::RealType<sizeof(double)>::String2Real(std::get<MString>(*this).Buf());
   else if(std::holds_alternative<bool>(*this))
    return std::get<bool>(*this) ? 1 : 0;
   return 0;
  }

  MString S() const
  {
   if(std::holds_alternative<int8>(*this))
    return MString().FromInt(std::get<int8>(*this));
   else if(std::holds_alternative<uint8>(*this))
    return MString().FromUInt(std::get<uint8>(*this));
   else if(std::holds_alternative<double>(*this))
    return MString().FromReal(std::get<double>(*this));
   else if(std::holds_alternative<MString>(*this))
    return std::get<MString>(*this);
   else if(std::holds_alternative<bool>(*this))
    return MString().FromBool(std::get<bool>(*this));
   return "";
  }

  bool B() const
  {
   if(std::holds_alternative<int8>(*this))
    return std::get<int8>(*this) != 0;
   else if(std::holds_alternative<uint8>(*this))
    return std::get<uint8>(*this) != 0;
   else if(std::holds_alternative<double>(*this))
    return std::get<double>(*this) != 0.0;
   else if(std::holds_alternative<MString>(*this))
    return std::get<MString>(*this).ToBool();
   else if(std::holds_alternative<bool>(*this))
    return std::get<bool>(*this);
   return false;
  }
 };

 class Dimension
 {
  MString name;
  size_t  size;

  public:
  Dimension(const MString& str, size_t num): name(str), size(num) {}
  const MString& Name() const { return name; }

  size_t Size() const { return size; }
 };

 class Variable
 {
  public:
  using FillType = std::variant<std::monostate, int8, uint8, double>;

  private:
  MString                name;
  VarType                type = VarType::UNDEF;
  std::vector<size_t>    dims;
  std::vector<Attribute> atts;
  FillType               fill;

  public:
  Variable(const MString& name_, VarType type_, std::vector<size_t>&& dims_, std::vector<Attribute>&& atts_, FillType fill_ = 0):
      name(name_), type(type_), dims(std::move(dims_)), atts(std::move(atts_)), fill(fill_)
  {
  }

  explicit operator bool() const { return type != VarType::UNDEF; }

  const auto& Dims() const { return dims; }

  size_t NDim() const { return dims.size(); }

  size_t NAtt() const { return atts.size(); }

  auto AttNames() const
  {
   std::vector<MString> out;
   std::transform(atts.cbegin(), atts.cend(), std::back_inserter(out), [](const Attribute& a) { return a.Name(); });
   return out;
  }

  AttType AttT(const MString& name) const
  {
   size_t ind = FindInd(name, atts);
   return ind < atts.size() ? atts[ind].Type() : AttType::UNDEF;
  }

  int8 AttInt(const MString& name) const
  {
   size_t ind = FindInd(name, atts);
   return ind < atts.size() ? atts[ind].I() : 0;
  }

  uint8 AttUInt(const MString& name) const
  {
   size_t ind = FindInd(name, atts);
   return ind < atts.size() ? atts[ind].U() : 0;
  }

  double AttReal(const MString& name) const
  {
   size_t ind = FindInd(name, atts);
   return ind < atts.size() ? atts[ind].D() : 0.0;
  }

  MString AttString(const MString& name) const
  {
   size_t ind = FindInd(name, atts);
   return ind < atts.size() ? atts[ind].S() : MString();
  }

  bool AttBool(const MString& name) const
  {
   size_t ind = FindInd(name, atts);
   return ind < atts.size() ? atts[ind].B() : false;
  }

  const MString& Name() const { return name; }

  auto Type() const { return type; }

  const auto& Fill() const { return fill; }
 };

 protected:
 std::vector<Attribute> gats;
 std::vector<Dimension> dims;
 std::vector<Variable>  vars;

 public:
 explicit operator bool() const { return !vars.empty(); }

 size_t NDim() const { return dims.size(); }

 size_t NDim(const MString& var) const
 {
  size_t ind = FindInd(var, vars);
  return ind < vars.size() ? vars[ind].NDim() : 0;
 }

 size_t NAtt() const { return gats.size(); }

 auto AttNames() const
 {
  std::vector<MString> out;
  std::transform(gats.cbegin(), gats.cend(), std::back_inserter(out), [](const Attribute& a) { return a.Name(); });
  return out;
 }

 size_t NAtt(const MString& var) const
 {
  if(!var.Exist()) return NAtt();
  size_t ind = FindInd(var, vars);
  return ind < vars.size() ? vars[ind].NAtt() : 0;
 }

 auto AttNames(const MString& var) const
 {
  if(!var.Exist()) return AttNames();
  size_t ind = FindInd(var, vars);
  return ind < vars.size() ? vars[ind].AttNames() : decltype(AttNames())();
 }

 auto VarNames() const
 {
  std::vector<MString> out;
  std::transform(vars.cbegin(), vars.cend(), std::back_inserter(out), [](const Variable& v) { return v.Name(); });
  return out;
 }

 VarType VarT(const MString& var) const
 {
  size_t ind = FindInd(var, vars);
  return ind < vars.size() ? vars[ind].Type() : VarType::UNDEF;
 }

 auto VarFill(const MString& var) const
 {
  size_t ind = FindInd(var, vars);
  return ind < vars.size() ? vars[ind].Fill() : Variable::FillType();
 }

 auto DimNames() const
 {
  std::vector<MString> out;
  std::transform(dims.cbegin(), dims.cend(), std::back_inserter(out), [](const Dimension& d) { return d.Name(); });
  return out;
 }

 auto DimNames(const MString& var) const
 {
  size_t ind = FindInd(var, vars);

  std::vector<MString> out;
  if(ind >= vars.size()) return out;

  auto vdims = vars[ind].Dims();
  std::transform(vdims.cbegin(), vdims.cend(), std::back_inserter(out), [&dims = std::as_const(dims)](const size_t& i) { return dims[i].Name(); });
  return out;
 }

 size_t DimSize(const MString& dim) const
 {
  size_t ind = FindInd(dim, dims);
  return ind < dims.size() ? dims[ind].Size() : 0;
 }

 AttType AttT(const MString& var, const MString& name) const
 {
  if(!var.Exist())
  {
   size_t ind = FindInd(name, gats);
   return ind < gats.size() ? gats[ind].Type() : AttType::UNDEF;
  }

  size_t ind = FindInd(var, vars);
  return ind < vars.size() ? vars[ind].AttT(name) : AttType::UNDEF;
 }

 int8 AttInt(const MString& var, const MString& name) const
 {
  if(!var.Exist())
  {
   size_t ind = FindInd(name, gats);
   return ind < gats.size() ? gats[ind].I() : 0;
  }

  size_t ind = FindInd(var, vars);
  return ind < vars.size() ? vars[ind].AttInt(name) : 0;
 }

 uint8 AttUInt(const MString& var, const MString& name) const
 {
  if(!var.Exist())
  {
   size_t ind = FindInd(name, gats);
   return ind < gats.size() ? gats[ind].U() : 0;
  }

  size_t ind = FindInd(var, vars);
  return ind < vars.size() ? vars[ind].AttUInt(name) : 0;
 }

 double AttReal(const MString& var, const MString& name) const
 {
  if(!var.Exist())
  {
   size_t ind = FindInd(name, gats);
   return ind < gats.size() ? gats[ind].D() : 0.0;
  }

  size_t ind = FindInd(var, vars);
  return ind < vars.size() ? vars[ind].AttReal(name) : 0.0;
 }

 MString AttString(const MString& var, const MString& name) const
 {
  if(!var.Exist())
  {
   size_t ind = FindInd(name, gats);
   return ind < gats.size() ? gats[ind].S() : MString();
  }

  size_t ind = FindInd(var, vars);
  return ind < vars.size() ? vars[ind].AttString(name) : MString();
 }

 bool AttBool(const MString& var, const MString& name) const
 {
  if(!var.Exist())
  {
   size_t ind = FindInd(name, gats);
   return ind < gats.size() ? gats[ind].B() : false;
  }

  size_t ind = FindInd(var, vars);
  return ind < vars.size() ? vars[ind].AttBool(name) : false;
 }

 auto AttT(const MString& name) const { return AttT("", name); }
 auto AttInt(const MString& name) const { return AttInt("", name); }
 auto AttUInt(const MString& name) const { return AttUInt("", name); }
 auto AttReal(const MString& name) const { return AttReal("", name); }
 auto AttString(const MString& name) const { return AttString("", name); }
 auto AttBool(const MString& name) const { return AttBool("", name); }

 bool HasDim(const MString& name) const { return FindInd(name, dims) < dims.size(); }
 bool HasVar(const MString& name) const { return FindInd(name, vars) < vars.size(); }
 bool HasAtt(const MString& vname, const MString& aname) const { return AttT(vname, aname) != AttType::UNDEF; }
 bool HasAtt(const MString& aname) const { return AttT(aname) != AttType::UNDEF; }

 const auto& Vars() const { return vars; }
 const auto& Dims() const { return dims; }
};

class DimReqDef
{
 protected:
 struct DimReq
 {
  static const auto fill = std::numeric_limits<size_t>::max();
  MString           name;
  size_t            beg, count;

  DimReq(): name(MString()), beg(fill), count(fill) {}
  DimReq(const char* n): name(n), beg(fill), count(fill) {}
  DimReq(const MString& n): name(n), beg(fill), count(fill) {}
  DimReq(MString&& n): name(std::move(n)), beg(fill), count(fill) {}
  DimReq(const char* n, size_t s): name(n), beg(s), count(fill) {}
  DimReq(const MString& n, size_t s): name(n), beg(s), count(fill) {}
  DimReq(MString&& n, size_t s): name(std::move(n)), beg(s), count(fill) {}
  DimReq(const char* n, size_t s, size_t c): name(n), beg(s), count(c) {}
  DimReq(const MString& n, size_t s, size_t c): name(n), beg(s), count(c) {}
  DimReq(MString&& n, size_t s, size_t c): name(std::move(n)), beg(s), count(c) {}

  const MString& Name() const { return name; }
 };
};

template<class C> class NcZarrRead: public C, public DimReqDef
{
 template<class Data> static constexpr size_t Dimensionity()
 {
  if constexpr(requires(Data& d) { d(0, 0, 0, 0); }) return 4;
  if constexpr(requires(Data& d) { d(0, 0, 0); }) return 3;
  if constexpr(requires(Data& d) { d(0, 0); }) return 2;
  if constexpr(requires(Data& d) { d(0); }) return 1;
  return 0;
 }

 template<class Data, size_t D, class Dummy = void> struct DataTypeExtractorS;

 template<class Data, class Dummy> struct DataTypeExtractorS<Data, 1, Dummy>
 {
  using type = std::decay_t<decltype(std::declval<Data>()(0))>;
 };
 template<class Data, class Dummy> struct DataTypeExtractorS<Data, 2, Dummy>
 {
  using type = std::decay_t<decltype(std::declval<Data>()(0, 0))>;
 };
 template<class Data, class Dummy> struct DataTypeExtractorS<Data, 3, Dummy>
 {
  using type = std::decay_t<decltype(std::declval<Data>()(0, 0, 0))>;
 };
 template<class Data, class Dummy> struct DataTypeExtractorS<Data, 4, Dummy>
 {
  using type = std::decay_t<decltype(std::declval<Data>()(0, 0, 0, 0))>;
 };

 template<class Data> using DataTypeExtractor = DataTypeExtractorS<Data, Dimensionity<Data>()>::type;

 template<class VType, class Data, class Transform>
 Error Read(const MString& vname, const std::vector<size_t>& transindex, Data& data, Transform transform, std::vector<DimReq> reqs) const
 {
  const size_t     indim  = reqs.size();
  constexpr size_t outdim = Dimensionity<Data>();

  std::vector<size_t> start;
  std::vector<size_t> count;

  start.resize(indim);
  count.resize(indim);
  for(size_t i = 0; i < indim; i++)
  {
   start[i] = reqs[i].beg;
   count[i] = reqs[i].count;
  }

  using DataType = DataTypeExtractor<Data>;
  DataType fillout;
  bool     havefill = C::VarFill(vname).index() > 0;
  VType    fillin   = std::visit(
      [](auto v)
      {
       if constexpr(std::is_convertible_v<decltype(v), VType>)
        return static_cast<VType>(v);
       else
        return std::numeric_limits<VType>::max();
      },
      C::VarFill(vname));

  if constexpr(requires(Data& d) { // Data have own fillvalue
                { d.Fillval() } -> std::convertible_to<DataType>;
               })
   fillout = data.Fillval();
  else // Data does'nt have own fillvalue, using variable fillvalue
   fillout = static_cast<DataType>(fillin);

  auto ret = C::template Read<VType>(vname, start.data(), count.data());
  if(!ret) return ret;
  const auto& rawdata = ret.Value();

  std::vector<size_t> mul(indim, 1);
  for(size_t i = indim - 1; i > 0; i--) mul[i - 1] = mul[i] * count[i];

  size_t inind = 0;
  for(typename C::ArrCounter i(count); i; ++i)
  {
   // TODO: Remove this testing block
   size_t cind = 0;
   for(size_t j = 0; j < indim; j++) cind += i[j] * mul[j];
   if(cind != inind) return {"NcZarrRead::Read", "Internal error"};
   if(i.Index() != inind) return {"NcZarrRead::Read", "Internal error"};
   if(inind != i.Index(i.Index(inind, count), count)) return {"NcZarrRead::Read", "Internal error"};

   DataType     out;
   const VType& in = rawdata(inind);
   if(havefill && in == fillin)
    out = fillout;
   else
    out = transform(in);

   if constexpr(outdim == 1)
    data(i[transindex[0]]) = out;
   else if constexpr(outdim == 2)
    data(i[transindex[0]], i[transindex[1]]) = out;
   else if constexpr(outdim == 3)
    data(i[transindex[0]], i[transindex[1]], i[transindex[2]]) = out;
   else if constexpr(outdim == 4)
    data(i[transindex[0]], i[transindex[1]], i[transindex[2]], i[transindex[3]]) = out;

   inind++;
  }

  return Error();
 }

 public:
 // Request is string
 template<class Data, class Transform> Error Read(const MString& vname, Data& data, Transform transform, const char* request) const
 {
  return Read(vname, data, transform, MString(request));
 }

 // Request by one dimension
 template<class Data, class Transform> Error Read(const MString& vname, Data& data, Transform transform, DimReq&& req1) const
 {
  return Read(vname, data, transform, std::vector<DimReq>{std::move(req1)});
 }
 // Request by two dimension
 template<class Data, class Transform> Error Read(const MString& vname, Data& data, Transform transform, DimReq&& req1, DimReq&& req2) const
 {
  return Read(vname, data, transform, std::vector<DimReq>{std::move(req1), std::move(req2)});
 }
 // Request by three dimension
 template<class Data, class Transform> Error Read(const MString& vname, Data& data, Transform transform, DimReq&& req1, DimReq&& req2, DimReq&& req3) const
 {
  return Read(vname, data, transform, std::vector<DimReq>{std::move(req1), std::move(req2), std::move(req3)});
 }
 // Request by four dimension
 template<class Data, class Transform> Error Read(const MString& vname, Data& data, Transform transform, DimReq&& req1, DimReq&& req2, DimReq&& req3, DimReq&& req4) const
 {
  return Read(vname, data, transform, std::vector<DimReq>{std::move(req1), std::move(req2), std::move(req3), std::move(req4)});
 }

 // Request full variable
 template<class Data, class Transform> Error Read(const MString& vname, Data& data, Transform transform) const
 {
  static const MString pref = "NcZarrRead::Read";
  if(!C::HasVar(vname)) return {pref, "Variable " + vname + " not found"};

  std::vector<struct DimReq> pdims;

  const auto vdims = C::DimNames(vname);
  std::transform(vdims.cbegin(), vdims.cend(), std::back_inserter(pdims), [this](const MString& n) -> struct DimReq { return {n, 0, C::DimSize(n)}; });

  return Read(vname, data, transform, pdims);
 }

 // Base function for all Read's
 template<class Data, class Transform> Error Read(const MString& vname, Data& data, Transform transform, const std::vector<DimReq>& reqs) const
 {
  static const MString pref = "NcZarrRead::Read";

  if(!C::HasVar(vname)) return {pref, "Variable " + vname + " not found"};

  std::vector<struct DimReq> pdims;
  {
   const auto vdims = C::DimNames(vname);
   std::transform(vdims.cbegin(), vdims.cend(), std::back_inserter(pdims), [](const MString& n) -> struct DimReq { return {n, 0, 1}; });
  }

  std::vector<size_t> transindex;

  // Parse request
  if(reqs.size() == 0) return {pref, "Empty request"};
  for(const auto& req: reqs)
  {
   size_t ind = C::FindInd(req.name, pdims);
   if(ind >= pdims.size()) return {pref, "Variable " + vname + " has no dimension " + req.name};

   for(size_t i = 0; i < transindex.size(); i++)
    if(transindex[i] == ind) return {pref, "Parameters for dimension " + req.name + " already defined"};
   transindex.push_back(ind);

   size_t dlen = C::DimSize(pdims[ind].name);
   if(req.beg == req.fill && req.count == req.fill) // Only name, so, we request full length
   {
    pdims[ind].beg   = 0;
    pdims[ind].count = dlen;
   }
   else if(req.count == req.fill) // Name and first index
   {
    pdims[ind].beg   = req.beg;
    pdims[ind].count = 1;
   }
   else // Name, first index, count
   {
    pdims[ind].beg   = req.beg;
    pdims[ind].count = req.count;
   }
   // Sanity checks
   if(pdims[ind].count <= 0) return {pref, "Error parsing request: count must be greter then zero"};
   if(pdims[ind].beg >= dlen) return {pref, MString("Error parsing request: start index ") + pdims[ind].beg + " must be lesser then " + pdims[ind].name + " size " + dlen};
   if(pdims[ind].beg + pdims[ind].count > dlen)
    return {pref, MString("Error parsing request: start index ") + pdims[ind].beg + " with count " + pdims[ind].count + " exceeds " + pdims[ind].name + " size " + dlen};

   // Ignore hyperplanes in requests for calculation of data dimensionality
   if(pdims[transindex.back()].count == 1) transindex.pop_back();
  }

  if(transindex.size() != Dimensionity<Data>())
   return {pref, MString("Output data dimensions (") + Dimensionity<Data>() + ") not corresponding request dimensions (" + transindex.size() + ")"};
  switch(C::VarT(vname))
  {
  case(C::VarType::UNDEF): return {pref, "No variable with name " + vname + " (impossible)"};
  case(C::VarType::FLOAT): return Read<typename C::template Type<C::VarType::FLOAT>>(vname, transindex, data, transform, pdims);
  case(C::VarType::DOUBLE): return Read<typename C::template Type<C::VarType::DOUBLE>>(vname, transindex, data, transform, pdims);
  case(C::VarType::INT1): return Read<typename C::template Type<C::VarType::INT1>>(vname, transindex, data, transform, pdims);
  case(C::VarType::INT2): return Read<typename C::template Type<C::VarType::INT2>>(vname, transindex, data, transform, pdims);
  case(C::VarType::INT4): return Read<typename C::template Type<C::VarType::INT4>>(vname, transindex, data, transform, pdims);
  case(C::VarType::INT8): return Read<typename C::template Type<C::VarType::INT8>>(vname, transindex, data, transform, pdims);
  case(C::VarType::UINT1): return Read<typename C::template Type<C::VarType::INT1>>(vname, transindex, data, transform, pdims);
  }

  return {pref, "Internal error (impossible)"};
 }

 // Request by string argument
 template<class Data, class Transform> Error Read(const MString& vname, Data& data, Transform transform, const MString& request) const
 {
  static const MString pref = "NcZarrRead::Read";

  std::vector<struct DimReq> pdims;

  // Parse request
  const auto dimdesc = request.Split(";, \t");
  if(dimdesc.size() == 0) return {pref, "Empty request"};
  for(const auto& dd: dimdesc)
  {
   const auto dimpar = dd.Split(":", true);

   if(dimpar.size() == 1) // Only name, so, we request full length
    pdims.emplace_back(dimpar[0]);
   else if(dimpar.size() == 2) // Name and first index
    pdims.emplace_back(dimpar[0], dimpar[1].ToInteger<size_t>());
   else if(dimpar.size() == 3) // Name, first index, count
    pdims.emplace_back(dimpar[0], dimpar[1].ToInteger<size_t>(), dimpar[2].ToInteger<size_t>());
   else
    return {pref, "Can't parse expression " + dd};
  }

  return Read(vname, data, transform, pdims);
 }

 // Request full one-dimensional variable
 template<class Type> Error Read(const MString& vname, std::vector<Type>& out) const
 {
  const auto& dnames = C::DimNames(vname);
  if(dnames.size() > 0) out.resize(C::DimSize(dnames[0]));
  auto data = [&vec = out](size_t i) -> Type& { return vec[i]; };

  return Read(vname, data, std::identity());
 }
};