from app.core import db

GROUPS = ['sum', 'avg', 'count']
FILTERS = ['$gt', '$lt', '$eq']
PERIODS = ['year', 'month', 'week', 'day']


def run_query_on(query_object, field_provider, **kwargs):
    selections, filters, groups = validate_selections(**kwargs)
    entities = []

    print('Starting with args: ' + str(kwargs))

    if selections is not None:
        for selection in selections.keys():
            entities.append(get_column(selections[selection],
                            field_provider(selection)))

        print('New entities: ' + str(entities))
        query_object = query_object.with_entities(*entities)

    if filters is not None:
        for filtered_column in filters.keys():
            for actual_filter in filters[filtered_column].keys():
                query_object = query_object.filter(
                        get_filter(field_provider(filtered_column),
                                   actual_filter,
                                   filters[filtered_column][actual_filter]))

    if groups is not None:
        for group in groups.keys():
            query_object = query_object.group_by(
                    get_group(field_provider(group), groups[group]))

    return query_object


def get_column(selection_name, field):
    if selection_name == 'value':
        return field
    if selection_name == 'sum':
        return db.func.sum(field)
    if selection_name == 'avg':
        return db.func.avg(field)
    if selection_name == 'count':
        return db.func.count(field)


def get_filter(filter_column, filter_key, filter_value):
    if filter_key == '$gt':
        return filter_column > filter_value
    if filter_key == '$lt':
        return filter_column < filter_value
    if filter_key == '$eq':
        return filter_column == filter_value


def get_group(group_column, group_value):
    if group_value == 'value':
        return group_column
    if group_value in PERIODS:
        return db.func.date_part(group_value, group_column)
    # We now expect a date format
    return db.func.to_char(group_column, group_value)


def is_group(**kwargs):
    if kwargs.get('group') is not None:
        return True


def validate_selections(**kwargs):
    selections = kwargs.get('selections')
    filters = kwargs.get('filters')
    groups = kwargs.get('groups')

    if selections is None:
        raise ValueError("Missing selections!")

    if is_group(**kwargs):
        for key in selections.keys():
            if selections[key] not in GROUPS:
                raise ValueError("Can only use sum, avg and count when\
                                 grouping!")

    if filters is not None:
        for key in filters.keys():
            for inner_key in filters[key].keys():
                if inner_key not in FILTERS:
                    raise ValueError("Unknown filter: " + str(
                        inner_key))

    return selections, filters, groups