import os
import sys
from contextlib import ExitStack

import numpy as np

from ase.db.core import Database, ops, lock, now
from ase.db.row import AtomsRow
from ase.io.jsonio import encode, decode
from ase.parallel import world, parallel_function


class JSONDatabase(Database):
    def __enter__(self):
        return self

    def __exit__(self, exc_type, exc_value, tb):
        pass

    def _write(self, atoms, key_value_pairs, data, id):
        Database._write(self, atoms, key_value_pairs, data)

        bigdct = {}
        ids = []
        nextid = 1

        if (isinstance(self.filename, str) and
            os.path.isfile(self.filename)):
            try:
                bigdct, ids, nextid = self._read_json()
            except (SyntaxError, ValueError):
                pass

        mtime = now()

        if isinstance(atoms, AtomsRow):
            row = atoms
        else:
            row = AtomsRow(atoms)
            row.ctime = mtime
            row.user = os.getenv('USER')

        dct = {}
        for key in row.__dict__:
            if key[0] == '_' or key in row._keys or key == 'id':
                continue
            dct[key] = row[key]

        dct['mtime'] = mtime

        if key_value_pairs:
            dct['key_value_pairs'] = key_value_pairs

        if data:
            dct['data'] = data

        constraints = row.get('constraints')
        if constraints:
            dct['constraints'] = constraints

        if id is None:
            id = nextid
            ids.append(id)
            nextid += 1
        else:
            assert id in bigdct

        bigdct[id] = dct
        self._write_json(bigdct, ids, nextid)
        return id

    def _read_json(self):
        if isinstance(self.filename, str):
            with open(self.filename) as fd:
                bigdct = decode(fd.read())
        else:
            bigdct = decode(self.filename.read())
            if self.filename is not sys.stdin:
                self.filename.seek(0)

        if not isinstance(bigdct, dict) or not ('ids' in bigdct
                                                or 1 in bigdct):
            from ase.io.formats import UnknownFileTypeError
            raise UnknownFileTypeError('Does not resemble ASE JSON database')

        ids = bigdct.get('ids')
        if ids is None:
            # Allow for missing "ids" and "nextid":
            assert 1 in bigdct
            return bigdct, [1], 2
        if not isinstance(ids, list):
            ids = ids.tolist()
        return bigdct, ids, bigdct['nextid']

    def _write_json(self, bigdct, ids, nextid):
        if world.rank > 0:
            return

        with ExitStack() as stack:
            if isinstance(self.filename, str):
                fd = stack.enter_context(open(self.filename, 'w'))
            else:
                fd = self.filename
            print('{', end='', file=fd)
            for id in ids:
                dct = bigdct[id]
                txt = ',\n '.join('"{0}": {1}'.format(key, encode(dct[key]))
                                  for key in sorted(dct.keys()))
                print('"{0}": {{\n {1}}},'.format(id, txt), file=fd)
            if self._metadata is not None:
                print('"metadata": {0},'.format(encode(self.metadata)), file=fd)
            print('"ids": {0},'.format(ids), file=fd)
            print('"nextid": {0}}}'.format(nextid), file=fd)

    @parallel_function
    @lock
    def delete(self, ids):
        bigdct, myids, nextid = self._read_json()
        for id in ids:
            del bigdct[id]
            myids.remove(id)
        self._write_json(bigdct, myids, nextid)

    def _get_row(self, id):
        bigdct, ids, nextid = self._read_json()
        if id is None:
            assert len(ids) == 1
            id = ids[0]
        dct = bigdct[id]
        dct['id'] = id
        return AtomsRow(dct)

    def _select(self, keys, cmps, explain=False, verbosity=0,
                limit=None, offset=0, sort=None, include_data=True,
                columns='all'):
        if explain:
            yield {'explain': (0, 0, 0, 'scan table')}
            return

        if sort:
            if sort[0] == '-':
                reverse = True
                sort = sort[1:]
            else:
                reverse = False

            def f(row):
                return row.get(sort, missing)

            rows = []
            missing = []
            for row in self._select(keys, cmps):
                key = row.get(sort)
                if key is None:
                    missing.append((0, row))
                else:
                    rows.append((key, row))

            rows.sort(reverse=reverse, key=lambda x: x[0])
            rows += missing

            if limit:
                rows = rows[offset:offset + limit]
            for key, row in rows:
                yield row
            return

        try:
            bigdct, ids, nextid = self._read_json()
        except IOError:
            return

        if not limit:
            limit = -offset - 1

        cmps = [(key, ops[op], val) for key, op, val in cmps]
        n = 0
        for id in ids:
            if n - offset == limit:
                return
            dct = bigdct[id]
            if not include_data:
                dct.pop('data', None)
            row = AtomsRow(dct)
            row.id = id
            for key in keys:
                if key not in row:
                    break
            else:
                for key, op, val in cmps:
                    if isinstance(key, int):
                        value = np.equal(row.numbers, key).sum()
                    else:
                        value = row.get(key)
                        if key == 'pbc':
                            assert op in [ops['='], ops['!=']]
                            value = ''.join('FT'[x] for x in value)
                    if value is None or not op(value, val):
                        break
                else:
                    if n >= offset:
                        yield row
                    n += 1

    @property
    def metadata(self):
        if self._metadata is None:
            bigdct, myids, nextid = self._read_json()
            self._metadata = bigdct.get('metadata', {})
        return self._metadata.copy()

    @metadata.setter
    def metadata(self, dct):
        bigdct, ids, nextid = self._read_json()
        self._metadata = dct
        self._write_json(bigdct, ids, nextid)
