#!/usr/bin/env python3
import abc
import argparse
import contextlib
import io
import os
import platform
import socket
import subprocess
import sys
import zlib

from typing import Any, Callable, Optional, Sequence, Tuple, Union, List


class ArticulatedValueError(ValueError, argparse.ArgumentTypeError):
    """ArticulatedTypeError is a ValueError that contains an error message
    displayed by argparse."""


def parse_host_and_maybe_port(host_port: str) -> Tuple[str, Optional[int]]:
    """
    parse_host_and_maybe_port splits host:port into a typed tuple.

    The tuple always contains an address but the port number may be None.  A
    ValueError is raised if the port is provided but does not represent a
    valid port number.
    """
    parts = host_port.split(":", 1)
    host = parts[0]
    port = None  # type: Optional[int]
    if len(parts) == 2:
        try:
            port = int(parts[1])
        except ValueError:
            raise ArticulatedValueError("port is not a number")
        if 0 > port > 65535:
            raise ArticulatedValueError("port not in range 0..65535")
    return (host, port)


def parse_host_and_port(host_port: str) -> Tuple[str, int]:
    """
    parse_host_and_port splits host:port into a typed tuple.

    A ValueError is raised if the format is invalid.
    """
    host, maybe_port = parse_host_and_maybe_port(host_port)
    if maybe_port is None:
        # See note in parse_host_and_maybe_port
        raise ArticulatedValueError("port number must be explicitly provided")
    return (host, maybe_port)


class Device(int):
    """
    Device is a device number with major and minor components.

    Note that this class does not attempt to mimic peculiar
    encoding used by the Linux kernel.
    """

    @classmethod
    def pack(cls, major: int, minor: int) -> "Device":
        return cls((major << 16) | (minor & (1 << 16) - 1))

    def __str__(self) -> str:
        return "{}:{}".format(self.major, self.minor)

    def __repr__(self) -> str:
        return "Device.pack({}, {})".format(self.major, self.minor)

    @property
    def major(self) -> int:
        """major is the higher 16 bits of the device number."""
        return self >> 16

    @property
    def minor(self) -> int:
        """minor is the lower 16 bits of the device number."""
        return self & ((1 << 16) - 1)


class OptionalFields(List[str]):
    def __str__(self) -> str:
        """__str__ returns the special formatting of optional fields."""
        if len(self):
            return " ".join(self) + " -"
        else:
            return "-"


class MountInfoEntry(object):
    """Single entry in /proc/pid/mointinfo, see proc(5)"""

    mount_id: int
    parent_id: int
    dev: Device
    root_dir: str
    mount_point: str
    mount_opts: str
    opt_fields: OptionalFields
    fs_type: str
    mount_source: str
    sb_opts: str

    def __init__(self) -> None:
        self.mount_id = 0
        self.parent_id = 0
        self.dev = Device.pack(0, 0)
        self.root_dir = ""
        self.mount_point = ""
        self.mount_opts = ""
        self.opt_fields = OptionalFields()
        self.fs_type = ""
        self.mount_source = ""
        self.sb_opts = ""

    def __eq__(self, other: object) -> "Union[NotImplemented, bool]":
        if not isinstance(other, MountInfoEntry):
            return NotImplemented
        return (
            self.mount_id == other.mount_id
            and self.parent_id == other.parent_id
            and self.dev == other.dev
            and self.root_dir == other.root_dir
            and self.mount_point == other.mount_point
            and self.mount_opts == other.mount_opts
            and self.opt_fields == other.opt_fields
            and self.fs_type == other.fs_type
            and self.mount_source == other.mount_source
            and self.sb_opts == other.sb_opts
        )

    @classmethod
    def parse(cls, line: str) -> "MountInfoEntry":
        it = iter(line.split())
        self = cls()
        self.mount_id = int(next(it))
        self.parent_id = int(next(it))
        dev_maj, dev_min = map(int, next(it).split(":"))
        self.dev = Device((dev_maj << 16) | dev_min)
        self.root_dir = next(it)
        self.mount_point = next(it)
        self.mount_opts = next(it)
        self.opt_fields = OptionalFields()
        for opt_field in it:
            if opt_field == "-":
                break
            self.opt_fields.append(opt_field)
        self.fs_type = next(it)
        self.mount_source = next(it)
        self.sb_opts = next(it)
        try:
            next(it)
        except StopIteration:
            pass
        else:
            raise ValueError("leftovers after parsing {!r}".format(line))
        return self

    def __str__(self) -> str:
        return (
            "{0.mount_id} {0.parent_id} {0.dev} {0.root_dir}"
            " {0.mount_point} {0.mount_opts} {0.opt_fields} {0.fs_type}"
            " {0.mount_source} {0.sb_opts}"
        ).format(self)

    def __repr__(self) -> str:
        return "MountInfoEntry.parse({!r})".format(str(self))

    @property
    def dev_maj(self) -> int:
        return self.dev.major

    @property
    def dev_min(self) -> int:
        return self.dev.minor


class ReMountReadOnly:
    """ReMountReadOnly is a context manager remounting filesystem to read-only."""

    def __init__(
        self, path: str, on_remount: Optional[Callable[[str, bool], None]] = None
    ):
        self.path = path
        self.altered = False
        self.on_remount = on_remount

    def __enter__(self) -> "Optional[ReMountReadOnly]":
        retcode = subprocess.call(["mount", "-o", "remount,ro", self.path])
        if retcode == 0:
            self.altered = True
            if self.on_remount is not None:
                self.on_remount(self.path, True)
            return self
        return None

    def __exit__(self, *exc_details: Any) -> None:
        if not self.altered:
            return
        retcode = subprocess.call(["mount", "-o", "remount,rw", self.path])
        if retcode == 0 and self.on_remount is not None:
            self.on_remount(self.path, False)


class Command(abc.ABC):
    """Command is the interface for command line commands."""

    class Args(argparse.Namespace):
        """Args describes the parsed arguments."""

    @abc.abstractproperty
    def name(self) -> str:
        """name of the command"""

    @abc.abstractproperty
    def description(self) -> str:
        """description of the command"""

    @abc.abstractmethod
    def configure_parser(self, parser: argparse.ArgumentParser) -> None:
        """configure_parser configures the parser specific to the command."""

    @abc.abstractmethod
    def invoke(self, args: Args) -> None:
        """invoke executes the command with the given arguments."""

    def say(self, msg: str) -> None:
        """say prints stuff as the command"""
        print("raspi-tool", msg)


class SendImgCmd(Command):

    name = "send-image"
    description = "send an image from this device to a remote machine"

    class Args(Command.Args):
        device: str
        addr: Tuple[str, int]

    def configure_parser(self, parser: argparse.ArgumentParser) -> None:
        parser.add_argument(
            "--device",
            metavar="DEVICE",
            default="/dev/mmcblk0",
            help="File representing SD card",
        )
        parser.add_argument(
            "addr",
            metavar="HOST:PORT",
            type=parse_host_and_port,
            help="Destination (e.g. running raspberry-pi-tool recv-image)",
        )

    def _on_remounted(self, path: str, is_ro: bool) -> None:
        self.say("{} re-mounted {}".format(path, "ro" if is_ro else "rw"))

    def invoke(self, args: Args) -> None:
        with contextlib.ExitStack() as stack:
            try:
                sink = socket.create_connection(args.addr)
            except IOError as exc:
                raise SystemExit("cannot connect to {}: {}".format(args.addr, exc))
            else:
                stack.enter_context(sink)

            with open("/proc/self/mountinfo") as stream:
                mountinfo = [MountInfoEntry.parse(line) for line in stream]
            for entry in mountinfo:
                if entry.mount_source.startswith(args.device):
                    stack.enter_context(
                        ReMountReadOnly(entry.mount_point, self._on_remounted)
                    )
            try:
                source = io.FileIO(args.device)
            except IOError as exc:
                raise SystemExit("cannot open {}: {}".format(args.device, exc))
            else:
                stack.enter_context(source)

            self.say("sending {} to {}".format(args.device, args.addr))
            packer = zlib.compressobj(level=9)
            buf = bytearray(4096)
            while True:
                n = source.readinto(buf)
                if n == 0:
                    break
                zbuf = packer.compress(buf[:n])
                sink.sendall(zbuf)
                del zbuf
            zbuf = packer.flush(zlib.Z_FINISH)
            sink.sendall(zbuf)
            del zbuf

            self.say("sent!")


class RecvImgCmd(Command):

    name = "recv-image"
    description = "receive an image a remote image and save it locally"

    class Args(Command.Args):
        img: str
        addr: Optional[Tuple[str, int]]

    def configure_parser(self, parser: argparse.ArgumentParser) -> None:
        parser.add_argument(
            "--addr",
            metavar="HOST:PORT",
            type=parse_host_and_port,
            help="Destination (e.g. running raspberry-pi-tool recv-image)",
        )
        parser.add_argument(
            "--image",
            dest="img",
            metavar="IMAGE",
            help="File representing SD card image",
            default="pi.img",
        )

    def invoke(self, args: Args) -> None:
        with contextlib.ExitStack() as stack:
            # Open the file we want to write to.
            try:
                sink = stack.enter_context(io.FileIO(args.img, "w"))
            except IOError as exc:
                raise SystemExit("cannot open {}: {}".format(args.img, exc))
            # Open a socket and find a port to bind to.
            sock = stack.enter_context(
                socket.socket(socket.AF_INET, socket.SOCK_STREAM)
            )
            host = "0.0.0.0"
            port = 12345
            if args.addr is not None:
                host, port = args.addr
                search = 1
            else:
                search = 10
            for try_port in range(port, port + search):
                try:
                    sock.bind((host, try_port))
                except OSError as exc:
                    self.say("cannot bind to {}:{}: {}".format(host, try_port, exc))
                else:
                    break
            else:
                raise SystemExit("cannot bind to port, giving up")
            # Listen for incoming connections.
            sock.listen()
            self.say("listening on {}:{}".format(host, port))
            hostname = socket.gethostname()
            hostaddr = socket.gethostbyname(hostname)
            if hostaddr.startswith("127."):
                self.say("cannot determine useful address of this machine")
            else:
                self.say("on the raspberry pi issue the following command")
                self.say("$ sudo ./raspi-tool.py send-image {}:{}".format(hostaddr, port))
            self.say("waiting for connection...")
            # Wait for client connection.
            try:
                source, remote_addr = sock.accept()
            except Exception as exc:
                raise SystemExit("cannot accept connection: {}".format(exc))

            self.say("saving image from {} to {}".format(remote_addr, args.img))
            packer = zlib.decompressobj()
            buf = bytearray(4096)
            while True:
                n = source.recv_into(buf, 0)
                if n == 0:
                    break
                zbuf = packer.decompress(buf[:n])
                sink.write(zbuf)
                del zbuf
            zbuf = packer.flush(zlib.Z_FINISH)
            sink.write(zbuf)
            del zbuf
            self.say("saved!")


def _make_parser(commands: Sequence[Command]) -> argparse.ArgumentParser:
    """_make_parser creates an argument parser with given subcommands."""
    parser = argparse.ArgumentParser(
        description="Utility for working with Raspberry Pi devices."
    )
    parser.add_argument("--version", action="version", version="0.1")
    sub = parser.add_subparsers()
    for cmd in commands:
        cmd_parser = sub.add_parser(cmd.name, help=cmd.description)
        cmd.configure_parser(cmd_parser)
        cmd_parser.set_defaults(invoke=cmd.invoke)
    return parser


def main() -> None:
    parser = _make_parser([SendImgCmd(), RecvImgCmd()])
    # On windows, when invoked without arguments, default to receiving an image.
    if platform.win32_ver()[0] != "" and len(sys.argv) == 1:
        args = parser.parse_args(["recv-image"])
    else:
        args = parser.parse_args()
    if not hasattr(args, "invoke"):
        parser.error("select command to execute")
    args.invoke(args)


if __name__ == "__main__":
    try:
        main()
    except KeyboardInterrupt:
        pass