# Licensed to the Apache Software Foundation (ASF) under one
# or more contributor license agreements.  See the NOTICE file
# distributed with this work for additional information
# regarding copyright ownership.  The ASF licenses this file
# to you under the Apache License, Version 2.0 (the
# "License"); you may not use this file except in compliance
# with the License.  You may obtain a copy of the License at
#
#   http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing,
# software distributed under the License is distributed on an
# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
# KIND, either express or implied.  See the License for the
# specific language governing permissions and limitations
# under the License.

import collections
from typing import Callable, List, Optional

from pypaimon.read.reader.iface.record_iterator import RecordIterator
from pypaimon.read.reader.iface.record_reader import RecordReader


class ConcatRecordReader(RecordReader):

    def __init__(self, reader_suppliers: List[Callable]):
        self.queue: collections.deque[Callable] = collections.deque(reader_suppliers)
        self.current_reader: Optional[RecordReader] = None

    def read_batch(self) -> Optional[RecordIterator]:
        while True:
            if self.current_reader is not None:
                iterator = self.current_reader.read_batch()
                if iterator is not None:
                    return iterator
                self.current_reader.close()
                self.current_reader = None
            elif self.queue:
                supplier = self.queue.popleft()
                self.current_reader = supplier()
            else:
                return None

    def close(self) -> None:
        if self.current_reader:
            self.current_reader.close()
            self.current_reader = None
        self.queue.clear()
