# Copyright 2019 Joe Greener. All rights reserved.
#
# This file is part of the Biopython distribution and governed by your
# choice of the "Biopython License Agreement" or the "BSD 3-Clause License".
# Please see the LICENSE file that should have been included as part of this
# package.

"""Write a MMTF file."""

import itertools
from collections import defaultdict
from string import ascii_uppercase
from Bio.PDB.StructureBuilder import StructureBuilder
from Bio.PDB.PDBIO import Select, StructureIO
from mmtf.api.mmtf_writer import MMTFEncoder
from Bio.SeqUtils import seq1
from Bio.Data.PDBData import protein_letters_3to1_extended

_select = Select()


class MMTFIO(StructureIO):
    """Write a Structure object as a MMTF file.

    Examples
    --------
        >>> from Bio.PDB import MMCIFParser
        >>> from Bio.PDB.mmtf import MMTFIO
        >>> parser = MMCIFParser()
        >>> structure = parser.get_structure("1a8o", "PDB/1A8O.cif")
        >>> io=MMTFIO()
        >>> io.set_structure(structure)
        >>> io.save("bio-pdb-mmtf-out.mmtf")
        >>> import os
        >>> os.remove("bio-pdb-mmtf-out.mmtf")  # tidy up

    """

    def __init__(self):
        """Initialise."""
        pass

    def save(self, filepath, select=_select):
        """Save the structure to a file.

        :param filepath: output file
        :type filepath: string

        :param select: selects which entities will be written.
        :type select: object

        Typically select is a subclass of L{Select}, it should
        have the following methods:

         - accept_model(model)
         - accept_chain(chain)
         - accept_residue(residue)
         - accept_atom(atom)

        These methods should return 1 if the entity is to be
        written out, 0 otherwise.
        """
        # Similar to the PDBIO save method, we check if the filepath is a
        # string for a filepath or an open file handle
        if not isinstance(filepath, str):
            raise ValueError(
                "Writing to a file handle is not supported for MMTF, filepath must be a string"
            )
        if hasattr(self, "structure"):
            self._save_structure(filepath, select)
        else:
            raise ValueError("Use set_structure to set a structure to write out")

    def _chain_id_iterator(self):
        """Label chains sequentially: A, B, ..., Z, AA, AB etc."""
        for size in itertools.count(1):
            for s in itertools.product(ascii_uppercase, repeat=size):
                yield "".join(s)

    def _save_structure(self, filepath, select):
        count_models, count_chains, count_groups, count_atoms = 0, 0, 0, 0

        # If atom serials are missing, renumber atoms starting from 1
        atom_serials = [a.serial_number for a in self.structure.get_atoms()]
        renumber_atoms = None in atom_serials

        encoder = MMTFEncoder()
        # The counts are set to 0 here and changed later once we have the values
        encoder.init_structure(
            total_num_bonds=0,
            total_num_atoms=0,
            total_num_groups=0,
            total_num_chains=0,
            total_num_models=0,
            structure_id=self.structure.id,
        )

        encoder.set_xtal_info(space_group="", unit_cell=None)

        # The header information is missing for some structure objects
        header_dict = defaultdict(str, self.structure.header)
        if header_dict["resolution"] == "":
            header_dict["resolution"] = None
        if header_dict["structure_method"] == "":
            header_dict["structure_method"] = []
        else:
            header_dict["structure_method"] = [header_dict["structure_method"]]

        encoder.set_header_info(
            r_free=None,
            r_work=None,
            resolution=header_dict["resolution"],
            title=header_dict["name"],
            deposition_date=header_dict["deposition_date"],
            release_date=header_dict["release_date"],
            experimental_methods=header_dict["structure_method"],
        )

        # Tracks values to replace them at the end
        chains_per_model = []
        groups_per_chain = []

        for mi, model in enumerate(self.structure.get_models()):
            if not select.accept_model(model):
                continue

            chain_id_iterator = self._chain_id_iterator()

            count_models += 1
            encoder.set_model_info(
                model_id=mi,  # According to mmtf-python this is meaningless
                chain_count=0,  # Set to 0 here and changed later
            )
            for chain in model.get_chains():
                if not select.accept_chain(chain):
                    continue

                seqs = []
                seq = ""
                prev_residue_type = ""
                prev_resname = ""
                first_chain = True

                for residue in chain.get_unpacked_list():
                    if not select.accept_residue(residue):
                        continue

                    count_groups += 1
                    hetfield, resseq, icode = residue.get_id()
                    if hetfield == " ":
                        residue_type = "ATOM"
                        entity_type = "polymer"
                    elif hetfield == "W":
                        residue_type = "HETATM"
                        entity_type = "water"
                    else:
                        residue_type = "HETATM"
                        entity_type = "non-polymer"
                    resname = residue.get_resname()

                    # Check if the molecule changes within the chain
                    # This will always increment for the first residue in a
                    #  chain due to the starting values above
                    # Checking for similar entities is non-trivial from the
                    #  structure object so we treat each molecule as a separate
                    #  entity
                    if residue_type != prev_residue_type or (
                        residue_type == "HETATM" and resname != prev_resname
                    ):
                        encoder.set_entity_info(
                            chain_indices=[count_chains],
                            sequence="",  # Set to empty here and changed later
                            description="",
                            entity_type=entity_type,
                        )
                        encoder.set_chain_info(
                            chain_id=next(chain_id_iterator),
                            chain_name="\x00"
                            if len(chain.get_id().strip()) == 0
                            else chain.get_id(),
                            num_groups=0,  # Set to 0 here and changed later
                        )
                        if count_chains > 0:
                            groups_per_chain.append(
                                count_groups - sum(groups_per_chain) - 1
                            )
                        if not first_chain:
                            seqs.append(seq)
                        first_chain = False
                        count_chains += 1
                        seq = ""

                    if entity_type == "polymer":
                        seq += seq1(resname, custom_map=protein_letters_3to1_extended)

                    prev_residue_type = residue_type
                    prev_resname = resname

                    encoder.set_group_info(
                        group_name=resname,
                        group_number=residue.id[1],
                        insertion_code="\x00"
                        if residue.id[2] == " "
                        else residue.id[2],
                        group_type="",  # Value in the chemcomp dictionary, which is unknown here
                        atom_count=sum(
                            1
                            for a in residue.get_unpacked_list()
                            if select.accept_atom(a)
                        ),
                        bond_count=0,
                        single_letter_code=seq1(
                            resname, custom_map=protein_letters_3to1_extended
                        ),
                        sequence_index=len(seq) - 1 if entity_type == "polymer" else -1,
                        secondary_structure_type=-1,
                    )

                    for atom in residue.get_unpacked_list():
                        if select.accept_atom(atom):
                            count_atoms += 1
                            encoder.set_atom_info(
                                atom_name=atom.name,
                                serial_number=count_atoms
                                if renumber_atoms
                                else atom.serial_number,
                                alternative_location_id="\x00"
                                if atom.altloc == " "
                                else atom.altloc,
                                x=atom.coord[0],
                                y=atom.coord[1],
                                z=atom.coord[2],
                                occupancy=atom.occupancy,
                                temperature_factor=atom.bfactor,
                                element=atom.element,
                                charge=0,
                            )

                seqs.append(seq)
                # Now that we have the sequences, edit the entities to add them
                start_ind = len(encoder.entity_list) - len(seqs)
                for i, seq in enumerate(seqs):
                    encoder.entity_list[start_ind + i]["sequence"] = seq

            chains_per_model.append(count_chains - sum(chains_per_model))

        groups_per_chain.append(count_groups - sum(groups_per_chain))

        encoder.chains_per_model = chains_per_model
        encoder.groups_per_chain = groups_per_chain
        encoder.num_atoms = count_atoms
        encoder.num_groups = count_groups
        encoder.num_chains = count_chains
        encoder.num_models = count_models

        encoder.finalize_structure()
        encoder.write_file(filepath)
