Ketcher needs to correctly serialize/deserialize attachment point information for super atoms for mol v3000 & ket format

[kaluginserg]

Background

At the moment Ketcher does not parse "SAP" (Superatom Attachment Point) instructions for s-group attachment points from MOL v3000.

Connected to Ketcher issue (v2000): epam/ketcher#2467

Solution

1. deserialization SAP instruction for v3000 mol files should be supported (reading from file)
2. serialization SAP instruction for v3000 mol files should be supported (saving to file)
3. implement serialization / deserialization for attachment point based on ket specification (specification will be added under this issue: Introduce to .ket file specification attachment point information for super atoms ketcher#2765 )

Notes

Link to the CTFiles format explanation: http://c4.cabrillo.edu/404/ctfile.pdf (2005)
"SAP" Section, page 91

Example of mol v3000 with SAP instruction

  Mrv2308 06142310432D          

  0  0  0     0  0            999 V3000
M  V30 BEGIN CTAB
M  V30 COUNTS 3 2 1 0 0
M  V30 BEGIN ATOM
M  V30 1 C -8.1671 3.1242 0 0
M  V30 2 C -6.8333 2.3542 0 0
M  V30 3 O -5.4998 3.1242 0 0
M  V30 END ATOM
M  V30 BEGIN BOND
M  V30 1 1 1 2
M  V30 2 2 2 3
M  V30 END BOND
M  V30 BEGIN SGROUP
M  V30 1 SUP 0 ATOMS=(3 1 2 3) SAP=(3 2 0 1) LABEL=Ac ESTATE=E
M  V30 END SGROUP
M  V30 END CTAB
M  END

[kaluginserg]

@even1024 please could you provide schema proposal for ket format for sgroup attachment points, thanks