import filecmp
import os
import random
import shutil
import string
from contextlib import contextmanager
from dataclasses import dataclass
from datetime import datetime
from enum import Enum
from pathlib import Path, PurePath
# TODO In Python 3.9 and above, AsyncContextManager is deprecated
from typing import AsyncContextManager, BinaryIO, Iterator, Optional, Tuple

from rich.markup import escape

from .logging import log
from .report import MarkConflictException, MarkDuplicateException, Report
from .utils import ReusableAsyncContextManager, prompt_yes_no

SUFFIX_CHARS = string.ascii_lowercase + string.digits
SUFFIX_LENGTH = 6
TRIES = 5


class OutputDirException(Exception):
    pass


class Redownload(Enum):
    NEVER = "never"
    NEVER_SMART = "never-smart"
    ALWAYS = "always"
    ALWAYS_SMART = "always-smart"

    @staticmethod
    def from_string(string: str) -> "Redownload":
        try:
            return Redownload(string)
        except ValueError:
            raise ValueError("must be one of 'never', 'never-smart',"
                             " 'always', 'always-smart'")


class OnConflict(Enum):
    PROMPT = "prompt"
    LOCAL_FIRST = "local-first"
    REMOTE_FIRST = "remote-first"
    NO_DELETE = "no-delete"

    @staticmethod
    def from_string(string: str) -> "OnConflict":
        try:
            return OnConflict(string)
        except ValueError:
            raise ValueError("must be one of 'prompt', 'local-first',"
                             " 'remote-first', 'no-delete'")


@dataclass
class Heuristics:
    mtime: Optional[datetime]


class FileSink:
    def __init__(self, file: BinaryIO):
        self._file = file
        self._done = False

    @property
    def file(self) -> BinaryIO:
        return self._file

    def done(self) -> None:
        self._done = True

    def is_done(self) -> bool:
        return self._done


@dataclass
class DownloadInfo:
    path: PurePath
    local_path: Path
    tmp_path: Path
    heuristics: Heuristics
    on_conflict: OnConflict
    success: bool = False


class FileSinkToken(ReusableAsyncContextManager[FileSink]):
    # Whenever this class is entered, it creates a new temporary file and
    # returns a corresponding FileSink.
    #
    # When it is exited again, the file is closed and information about the
    # download handed back to the OutputDirectory.

    def __init__(
            self,
            output_dir: "OutputDirectory",
            path: PurePath,
            local_path: Path,
            heuristics: Heuristics,
            on_conflict: OnConflict,
    ):
        super().__init__()

        self._output_dir = output_dir
        self._path = path
        self._local_path = local_path
        self._heuristics = heuristics
        self._on_conflict = on_conflict

    async def _on_aenter(self) -> FileSink:
        tmp_path, file = await self._output_dir._create_tmp_file(self._local_path)
        sink = FileSink(file)

        async def after_download() -> None:
            await self._output_dir._after_download(DownloadInfo(
                self._path,
                self._local_path,
                tmp_path,
                self._heuristics,
                self._on_conflict,
                sink.is_done(),
            ))

        self._stack.push_async_callback(after_download)
        self._stack.enter_context(file)

        return sink


class OutputDirectory:
    def __init__(
            self,
            root: Path,
            redownload: Redownload,
            on_conflict: OnConflict,
    ):
        self._root = root
        self._redownload = redownload
        self._on_conflict = on_conflict

        self._report = Report()

    def register_reserved(self, path: PurePath) -> None:
        self._report.mark_reserved(path)

    def _mark(self, path: PurePath) -> None:
        """
        May throw an OutputDirException
        """

        try:
            self._report.mark(path)
        except MarkDuplicateException:
            raise OutputDirException("Another file has already been placed here.")
        except MarkConflictException as e:
            raise OutputDirException(f"Collides with other file: {e.collides_with}")

    def resolve(self, path: PurePath) -> Path:
        """
        May throw an OutputDirException.
        """

        if ".." in path.parts:
            raise OutputDirException(f"Path {path} contains forbidden '..'")
        return self._root / path

    def _should_download(
            self,
            local_path: Path,
            heuristics: Heuristics,
            redownload: Redownload,
    ) -> bool:
        # If we don't have a *file* at the local path, we'll always redownload
        # since we know that the remote is different from the local files. This
        # includes the case where no local file exists.
        if not local_path.is_file():
            # TODO Don't download if on_conflict is LOCAL_FIRST or NO_DELETE
            return True

        if redownload == Redownload.NEVER:
            return False
        elif redownload == Redownload.ALWAYS:
            return True

        stat = local_path.stat()

        remote_newer = None
        if mtime := heuristics.mtime:
            remote_newer = mtime.timestamp() > stat.st_mtime

        if redownload == Redownload.NEVER_SMART:
            if remote_newer is None:
                return False
            else:
                return remote_newer
        elif redownload == Redownload.ALWAYS_SMART:
            if remote_newer is None:
                return True
            else:
                return not remote_newer

        # This should never be reached
        raise ValueError(f"{redownload!r} is not a valid redownload policy")

    # The following conflict resolution functions all return False if the local
    # file(s) should be kept and True if they should be replaced by the remote
    # files.

    async def _conflict_lfrf(
            self,
            on_conflict: OnConflict,
            path: PurePath,
    ) -> bool:
        if on_conflict == OnConflict.PROMPT:
            async with log.exclusive_output():
                prompt = f"Replace {path} with remote file?"
                return await prompt_yes_no(prompt, default=False)
        elif on_conflict == OnConflict.LOCAL_FIRST:
            return False
        elif on_conflict == OnConflict.REMOTE_FIRST:
            return True
        elif on_conflict == OnConflict.NO_DELETE:
            return True

        # This should never be reached
        raise ValueError(f"{on_conflict!r} is not a valid conflict policy")

    async def _conflict_ldrf(
            self,
            on_conflict: OnConflict,
            path: PurePath,
    ) -> bool:
        if on_conflict == OnConflict.PROMPT:
            async with log.exclusive_output():
                prompt = f"Recursively delete {path} and replace with remote file?"
                return await prompt_yes_no(prompt, default=False)
        elif on_conflict == OnConflict.LOCAL_FIRST:
            return False
        elif on_conflict == OnConflict.REMOTE_FIRST:
            return True
        elif on_conflict == OnConflict.NO_DELETE:
            return False

        # This should never be reached
        raise ValueError(f"{on_conflict!r} is not a valid conflict policy")

    async def _conflict_lfrd(
            self,
            on_conflict: OnConflict,
            path: PurePath,
            parent: PurePath,
    ) -> bool:
        if on_conflict == OnConflict.PROMPT:
            async with log.exclusive_output():
                prompt = f"Delete {parent} so remote file {path} can be downloaded?"
                return await prompt_yes_no(prompt, default=False)
        elif on_conflict == OnConflict.LOCAL_FIRST:
            return False
        elif on_conflict == OnConflict.REMOTE_FIRST:
            return True
        elif on_conflict == OnConflict.NO_DELETE:
            return False

        # This should never be reached
        raise ValueError(f"{on_conflict!r} is not a valid conflict policy")

    async def _conflict_delete_lf(
            self,
            on_conflict: OnConflict,
            path: PurePath,
    ) -> bool:
        if on_conflict == OnConflict.PROMPT:
            async with log.exclusive_output():
                prompt = f"Delete {path}?"
                return await prompt_yes_no(prompt, default=False)
        elif on_conflict == OnConflict.LOCAL_FIRST:
            return False
        elif on_conflict == OnConflict.REMOTE_FIRST:
            return True
        elif on_conflict == OnConflict.NO_DELETE:
            return False

        # This should never be reached
        raise ValueError(f"{on_conflict!r} is not a valid conflict policy")

    def _tmp_path(self, base: Path, suffix_length: int) -> Path:
        prefix = "" if base.name.startswith(".") else "."
        suffix = "".join(random.choices(SUFFIX_CHARS, k=suffix_length))
        name = f"{prefix}{base.name}.tmp.{suffix}"
        return base.parent / name

    async def _create_tmp_file(
            self,
            local_path: Path,
    ) -> Tuple[Path, BinaryIO]:
        """
        May raise an OutputDirException.
        """

        # Create tmp file
        for attempt in range(TRIES):
            suffix_length = SUFFIX_LENGTH + 2 * attempt
            tmp_path = self._tmp_path(local_path, suffix_length)
            try:
                return tmp_path, open(tmp_path, "xb")
            except FileExistsError:
                pass  # Try again

        raise OutputDirException(f"Failed to create temporary file {tmp_path}")

    async def download(
            self,
            path: PurePath,
            mtime: Optional[datetime] = None,
            redownload: Optional[Redownload] = None,
            on_conflict: Optional[OnConflict] = None,
    ) -> Optional[AsyncContextManager[FileSink]]:
        """
        May throw an OutputDirException.
        """

        heuristics = Heuristics(mtime)
        redownload = self._redownload if redownload is None else redownload
        on_conflict = self._on_conflict if on_conflict is None else on_conflict
        local_path = self.resolve(path)

        self._mark(path)

        if not self._should_download(local_path, heuristics, redownload):
            return None

        # Detect and solve local-dir-remote-file conflict
        if local_path.is_dir():
            if await self._conflict_ldrf(on_conflict, path):
                shutil.rmtree(local_path)
            else:
                return None

        # Detect and solve local-file-remote-dir conflict
        for parent in path.parents:
            local_parent = self.resolve(parent)
            if local_parent.exists() and not local_parent.is_dir():
                if await self._conflict_lfrd(on_conflict, path, parent):
                    local_parent.unlink()
                    break
                else:
                    return None

        # Ensure parent directory exists
        local_path.parent.mkdir(parents=True, exist_ok=True)

        return FileSinkToken(self, path, local_path, heuristics, on_conflict)

    def _update_metadata(self, info: DownloadInfo) -> None:
        if mtime := info.heuristics.mtime:
            mtimestamp = mtime.timestamp()
            os.utime(info.local_path, times=(mtimestamp, mtimestamp))

    @contextmanager
    def _ensure_deleted(self, path: Path) -> Iterator[None]:
        try:
            yield
        finally:
            path.unlink(missing_ok=True)

    async def _after_download(self, info: DownloadInfo) -> None:
        with self._ensure_deleted(info.tmp_path):
            changed = False

            if not info.success:
                return

            # Solve conflicts arising from existing local file
            if info.local_path.exists():
                changed = True

                if filecmp.cmp(info.local_path, info.tmp_path):
                    self._update_metadata(info)
                    return

                if not await self._conflict_lfrf(info.on_conflict, info.path):
                    return

            info.tmp_path.replace(info.local_path)
            self._update_metadata(info)

            if changed:
                log.action(f"[bold bright_yellow]Changed[/] {escape(str(info.path))}")
                self._report.change_file(info.path)
            else:
                log.action(f"[bold bright_green]Added[/] {escape(str(info.path))}")
                self._report.add_file(info.path)

    async def cleanup(self) -> None:
        await self._cleanup_dir(self._root, PurePath())

    async def _cleanup(self, path: Path, pure: PurePath) -> None:
        if path.is_dir():
            await self._cleanup_dir(path, pure)
        elif path.is_file():
            await self._cleanup_file(path, pure)

    async def _cleanup_dir(self, path: Path, pure: PurePath) -> None:
        for child in path.iterdir():
            pure_child = pure / child.name
            await self._cleanup(child, pure_child)

        try:
            path.rmdir()
        except OSError:
            pass

    async def _cleanup_file(self, path: Path, pure: PurePath) -> None:
        if self._report.is_marked(pure):
            return

        if await self._conflict_delete_lf(self._on_conflict, pure):
            try:
                path.unlink()
                log.action(f"[bold bright_magenta]Deleted[/] {escape(str(path))}")
                self._report.delete_file(pure)
            except OSError:
                pass