# Copyright 2024 The Pigweed Authors
#
# Licensed 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
#
#     https://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.
"""Binary log data functions."""

import io
import threading
from typing import Union

BIN_LOG_SYNC_START_STR = '0d99bbaa7d'
BIN_LOG_SYNC_START_BYTES = bytes.fromhex(BIN_LOG_SYNC_START_STR)


class BytearrayLoop:
    """A bytearray reader writer.

    Reads occur from the front of the buffer and remove data. Writes append to
    the end of the buffer.
    """

    def __init__(self, data: bytes = b''):
        self.buffer = bytearray(data)
        self.lock = threading.Lock()

    def read(self, size: int = -1) -> bytearray:
        """Read bytes from the start of the buffer."""
        data = b''
        with self.lock:
            if size < 0:
                size = len(self.buffer)
            data = self.buffer[:size]
            # Delete the data we just fetched
            self.buffer[:size] = b''
        return data

    def write(self, data: bytes) -> None:
        """Write bytes to the end of the buffer."""
        with self.lock:
            self.buffer.extend(data)

    def peek(self, size: int = 0) -> bytearray:
        """Peek into bytes from the start."""
        return self.buffer[:size]

    def __len__(self) -> int:
        return len(self.buffer)

    def getbuffer(self) -> bytearray:
        """Return the whole buffer."""
        return self.buffer

    def read_until(self, sub_sequece: bytes) -> bytearray:
        """Pop all data from the buffer until a subsequence is found."""
        # Return nothing if the buffer is smaller than the provided subsequence.
        if len(sub_sequece) > len(self.buffer):
            return bytearray()
        position = self.buffer.find(sub_sequece)
        # If no subsequece is found, read all data.
        if position < 0:
            return self.read()
        return self.read(position)


_RawIo = Union[io.RawIOBase, BytearrayLoop]


def decode_one_varint(stream: _RawIo) -> int:
    """Read a single varint from a byte stream."""
    # Track the amount shifted.
    shift = 0
    # Resulting varint.
    result = 0
    while True:
        # Get one byte
        b = stream.read(1)
        if not b:
            break
        # Read as an integer. Note: byte order is little endian but we are only
        # reading one byte at a time.
        i = int.from_bytes(b, byteorder='little')
        # Shift first 7 bits from this byte into the result.
        result |= (i & 0x7F) << shift
        shift += 7
        # Stop if the highest bit is not set.
        if not i & 0x80:
            break

    return result