# bsv - Backup, Synchronization, Versioning
# Copyright (C) 2023  Simon Boyé
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU Affero General Public License for more details.
#
# You should have received a copy of the GNU Affero General Public License
# along with this program.  If not, see <https://www.gnu.org/licenses/>.
from __future__ import annotations

from abc import ABC, abstractmethod
from datetime import UTC, datetime as DateTime, timedelta as TimeDelta
import os
from pathlib import Path
import platform
import stat
from typing import BinaryIO


EPOCH = DateTime(1970, 1, 1, tzinfo=UTC)


def time_from_timestamp_us(timestamp: int) -> DateTime:
    return EPOCH + TimeDelta(microseconds=timestamp)

def timestamp_us_from_time(time: DateTime) -> int:
    return (time.astimezone(UTC) - EPOCH) // TimeDelta(microseconds=1)


def read_exact(stream: BinaryIO, num_bytes: int) -> bytes:
    data = stream.read(num_bytes)
    if len(data) != num_bytes:
        raise IOError(f"expected {num_bytes} bytes, got {len(data)}")
    return data

def read_exact_or_eof(stream: BinaryIO, num_bytes: int) -> bytes | None:
    data = stream.read(num_bytes)
    if not data:
        return None
    if len(data) != num_bytes:
        raise IOError(f"expected {num_bytes} bytes, got {len(data)}")
    return data


def is_bsv_repository(path: Path) -> bool:
    return (path / "bsv_repository.config").is_file()


def object_type_from_path(path: Path) -> bytes:
    return object_type_from_mode(path.stat(follow_symlinks=False).st_mode)

def object_type_from_mode(mode: int) -> bytes:
    if stat.S_ISLNK(mode):
        return b"slnk"
    elif stat.S_ISDIR(mode):
        return b"tree"
    elif stat.S_ISREG(mode):
        return b"blob"
    return b""


def default_bsv_config_path() -> Path:
    path = Path(os.environ.get("BSV_CONFIG", ""))
    if path and path.is_absolute() and path.is_file():
        return path
    for path in user_config_dirs():
        if path.is_file():
            return path
    return user_config_home() / "bsv/config"

def default_local_repository_path() -> Path:
    return user_data_home() / "bsv"


def user_data_home() -> Path:
    if platform.system() in ("Windows", "Darwin", "Java"):
        raise NotImplemented(f"{platform.system()} support not implemented yet")
    else:   # Assume Unix
        path = Path(os.environ.get("XDG_DATA_HOME", ""))
        if path and path.is_absolute():
            return path
        return Path.home() / ".local/share"

def user_config_home() -> Path:
    if platform.system() in ("Windows", "Darwin", "Java"):
        raise NotImplemented(f"{platform.system()} support not implemented yet")
    else:   # Assume Unix
        path = Path(os.environ.get("XDG_CONFIG_HOME", ""))
        if path and path.is_absolute():
            return path
        return Path.home() / ".config"

def user_config_dirs() -> list[Path]:
    if platform.system() in ("Windows", "Darwin", "Java"):
        raise NotImplemented(f"{platform.system()} support not implemented yet")
    else:   # Assume Unix
        paths = list(filter(Path.is_absolute, map(Path, (os.environ.get("XDG_CONFIG_DIRS") or "/etc/xdg").split(":"))))
        return [user_config_home()] + paths


class Hash(ABC):
    name: str
    digest_size: int

    @abstractmethod
    def update(self, *data: bytes | bytearray | memoryview):
        ...

    @abstractmethod
    def digest(self) -> bytes:
        ...