"""
.. module: lemur.database
    :platform: Unix
    :synopsis: This module contains all of the database related methods
    needed for lemur to interact with a datastore

    :copyright: (c) 2018 by Netflix Inc., see AUTHORS for more
    :license: Apache, see LICENSE for more details.

.. moduleauthor:: Kevin Glisson <kglisson@netflix.com>
"""
import math
from inflection import underscore
from sqlalchemy import exc, func, distinct
from sqlalchemy.orm import make_transient, lazyload
from sqlalchemy.sql import and_, or_

from lemur.exceptions import AttrNotFound, DuplicateError
from lemur.extensions import db


def filter_none(kwargs):
    """
    Remove all `None` values froma  given dict. SQLAlchemy does not
    like to have values that are None passed to it.

    :param kwargs: Dict to filter
    :return: Dict without any 'None' values
    """
    n_kwargs = {}
    for k, v in kwargs.items():
        if v:
            n_kwargs[k] = v
    return n_kwargs


def session_query(model):
    """
    Returns a SQLAlchemy query object for the specified `model`.

    If `model` has a ``query`` attribute already, that object will be returned.
    Otherwise a query will be created and returned based on `session`.

    :param model: sqlalchemy model
    :return: query object for model
    """
    return model.query if hasattr(model, "query") else db.session.query(model)


def create_query(model, kwargs):
    """
    Returns a SQLAlchemy query object for specified `model`. Model
    filtered by the kwargs passed.

    :param model:
    :param kwargs:
    :return:
    """
    s = session_query(model)
    return s.filter_by(**kwargs)


def commit():
    """
    Helper to commit the current session.
    """
    db.session.commit()


def add(model):
    """
    Helper to add a `model` to the current session.

    :param model:
    :return:
    """
    db.session.add(model)


def get_model_column(model, field):
    if field in getattr(model, "sensitive_fields", ()):
        raise AttrNotFound(field)
    column = model.__table__.columns._data.get(field, None)
    if column is None:
        raise AttrNotFound(field)

    return column


def find_all(query, model, kwargs):
    """
    Returns a query object that ensures that all kwargs
    are present.

    :param query:
    :param model:
    :param kwargs:
    :return:
    """
    conditions = []
    kwargs = filter_none(kwargs)
    for attr, value in kwargs.items():
        if not isinstance(value, list):
            value = value.split(",")

        conditions.append(get_model_column(model, attr).in_(value))

    return query.filter(and_(*conditions))


def find_any(query, model, kwargs):
    """
    Returns a query object that allows any kwarg
    to be present.

    :param query:
    :param model:
    :param kwargs:
    :return:
    """
    or_args = []
    for attr, value in kwargs.items():
        or_args.append(or_(get_model_column(model, attr) == value))
    exprs = or_(*or_args)
    return query.filter(exprs)


def get(model, value, field="id"):
    """
    Returns one object filtered by the field and value.

    :param model:
    :param value:
    :param field:
    :return:
    """
    query = session_query(model)
    return query.filter(get_model_column(model, field) == value).scalar()


def get_all(model, value, field="id"):
    """
    Returns query object with the fields and value filtered.

    :param model:
    :param value:
    :param field:
    :return:
    """
    query = session_query(model)
    return query.filter(get_model_column(model, field) == value)


def create(model):
    """
    Helper that attempts to create a new instance of an object.

    :param model:
    :return: :raise IntegrityError:
    """
    try:
        db.session.add(model)
        commit()
    except exc.IntegrityError as e:
        raise DuplicateError(e.orig.diag.message_detail)

    db.session.refresh(model)
    return model


def update(model):
    """
    Helper that attempts to update a model.

    :param model:
    :return:
    """
    commit()
    db.session.refresh(model)
    return model


def delete(model):
    """
    Helper that attempts to delete a model.

    :param model:
    """
    if model:
        db.session.delete(model)
        db.session.commit()


def filter(query, model, terms):
    """
    Helper that searched for 'like' strings in column values.

    :param query:
    :param model:
    :param terms:
    :return:
    """
    column = get_model_column(model, underscore(terms[0]))
    return query.filter(column.ilike("%{}%".format(terms[1])))


def sort(query, model, field, direction):
    """
    Returns objects of the specified `model` in the field and direction
    given

    :param query:
    :param model:
    :param field:
    :param direction:
    """
    column = get_model_column(model, underscore(field))
    return query.order_by(column.desc() if direction == "desc" else column.asc())


def paginate(query, page, count):
    """
    Returns the items given the count and page specified. The items would be an empty list
    if page number exceeds max page number based on count per page and total number of records.

    :param query: search query
    :param page: current page number
    :param count: results per page
    """
    total = get_count(query)
    # Check if input page is higher than total number of pages based on count per page and total
    # In such a case Flask-SQLAlchemy pagination call results in 404
    if math.ceil(total / count) < page:
        return dict(items=[], total=total)
    items = query.paginate(page, count).items
    return dict(items=items, total=total)


def update_list(model, model_attr, item_model, items):
    """
    Helper that correctly updates a models items
    depending on what has changed

    :param model_attr:
    :param item_model:
    :param items:
    :param model:
    :return:
    """
    ids = []

    for i in getattr(model, model_attr):
        if i.id not in ids:
            getattr(model, model_attr).remove(i)

    for i in items:
        for item in getattr(model, model_attr):
            if item.id == i["id"]:
                break
        else:
            getattr(model, model_attr).append(get(item_model, i["id"]))

    return model


def clone(model):
    """
    Clones the given model and removes it's primary key
    :param model:
    :return:
    """
    db.session.expunge(model)
    make_transient(model)
    model.id = None
    return model


def get_count(q):
    """
    Count the number of rows in a table. More efficient than count(*)
    :param q:
    :return:
    """
    disable_group_by = False
    if len(q._entities) > 1:
        # currently support only one entity
        raise Exception("only one entity is supported for get_count, got: %s" % q)
    entity = q._entities[0]
    if hasattr(entity, "column"):
        # _ColumnEntity has column attr - on case: query(Model.column)...
        col = entity.column
        if q._group_by and q._distinct:
            # which query can have both?
            raise NotImplementedError
        if q._group_by or q._distinct:
            col = distinct(col)
        if q._group_by:
            # need to disable group_by and enable distinct - we can do this because we have only 1 entity
            disable_group_by = True
        count_func = func.count(col)
    else:
        # _MapperEntity doesn't have column attr - on case: query(Model)...
        count_func = func.count()
    if q._group_by and not disable_group_by:
        count_func = count_func.over(None)
    count_q = (
        q.options(lazyload("*"))
        .statement.with_only_columns([count_func])
        .order_by(None)
    )
    if disable_group_by:
        count_q = count_q.group_by(None)
    count = q.session.execute(count_q).scalar()
    return count


def sort_and_page(query, model, args):
    """
    Helper that allows us to combine sorting and paging

    :param query:
    :param model:
    :param args:
    :return:
    """
    sort_by = args.pop("sort_by")
    sort_dir = args.pop("sort_dir")
    page = args.pop("page")
    count = args.pop("count")

    if args.get("user"):
        user = args.pop("user")

    query = find_all(query, model, args)

    if sort_by and sort_dir:
        query = sort(query, model, sort_by, sort_dir)

    total = get_count(query)

    # offset calculated at zero
    page -= 1
    items = query.offset(count * page).limit(count).all()
    return dict(items=items, total=total)