pferd/PFERD/crawler.py

from abc import ABC, abstractmethod
from contextlib import asynccontextmanager
from datetime import datetime
from pathlib import Path, PurePath
# TODO In Python 3.9 and above, AsyncContextManager is deprecated
from typing import (Any, AsyncContextManager, AsyncIterator, Awaitable,
                    Callable, Dict, Optional, TypeVar)

import aiohttp
from rich.markup import escape

from .authenticator import Authenticator
from .conductor import ProgressBar, TerminalConductor
from .config import Config, Section
from .limiter import Limiter
from .output_dir import FileSink, OnConflict, OutputDirectory, Redownload
from .transformer import RuleParseException, Transformer
from .version import __version__


class CrawlerLoadException(Exception):
    pass


Wrapped = TypeVar("Wrapped", bound=Callable[..., None])


def noncritical(f: Wrapped) -> Wrapped:
    """
    Warning: Must only be applied to member functions of the Crawler class!

    Catches all exceptions occuring during the function call. If an exception
    occurs, the crawler's error_free variable is set to False.
    """

    def wrapper(self: "Crawler", *args: Any, **kwargs: Any) -> None:
        try:
            f(self, *args, **kwargs)
        except Exception as e:
            self.print(f"[red]Something went wrong: {escape(str(e))}")
            self.error_free = False
    return wrapper  # type: ignore


def repeat(attempts: int) -> Callable[[Wrapped], Wrapped]:
    """
    Warning: Must only be applied to member functions of the Crawler class!

    If an exception occurs during the function call, retries the function call
    a set amount of times. Exceptions that occur during the last attempt are
    not caught and instead passed on upwards.
    """

    def decorator(f: Wrapped) -> Wrapped:
        def wrapper(self: "Crawler", *args: Any, **kwargs: Any) -> None:
            for _ in range(attempts - 1):
                try:
                    f(self, *args, **kwargs)
                    return
                except Exception:
                    pass
            f(self, *args, **kwargs)
        return wrapper  # type: ignore
    return decorator


AWrapped = TypeVar("AWrapped", bound=Callable[..., Awaitable[None]])


def anoncritical(f: AWrapped) -> AWrapped:
    """
    An async version of @noncritical.
    Warning: Must only be applied to member functions of the Crawler class!

    Catches all exceptions occuring during the function call. If an exception
    occurs, the crawler's error_free variable is set to False.
    """

    async def wrapper(self: "Crawler", *args: Any, **kwargs: Any) -> None:
        try:
            await f(self, *args, **kwargs)
        except Exception as e:
            self.print(f"[red]Something went wrong: {escape(str(e))}")
            self.error_free = False
    return wrapper  # type: ignore


def arepeat(attempts: int) -> Callable[[AWrapped], AWrapped]:
    """
    An async version of @noncritical.
    Warning: Must only be applied to member functions of the Crawler class!

    If an exception occurs during the function call, retries the function call
    a set amount of times. Exceptions that occur during the last attempt are
    not caught and instead passed on upwards.
    """

    def decorator(f: AWrapped) -> AWrapped:
        async def wrapper(self: "Crawler", *args: Any, **kwargs: Any) -> None:
            for _ in range(attempts - 1):
                try:
                    await f(self, *args, **kwargs)
                    return
                except Exception:
                    pass
            await f(self, *args, **kwargs)
        return wrapper  # type: ignore
    return decorator


class CrawlerSection(Section):
    def output_dir(self, name: str) -> Path:
        # TODO Use removeprefix() after switching to 3.9
        if name.startswith("crawl:"):
            name = name[len("crawl:"):]
        return Path(self.s.get("output_dir", name)).expanduser()

    def redownload(self) -> Redownload:
        value = self.s.get("redownload", "never-smart")
        try:
            return Redownload.from_string(value)
        except ValueError as e:
            self.invalid_value(
                "redownload",
                value,
                str(e).capitalize(),
            )

    def on_conflict(self) -> OnConflict:
        value = self.s.get("on_conflict", "prompt")
        try:
            return OnConflict.from_string(value)
        except ValueError as e:
            self.invalid_value(
                "on_conflict",
                value,
                str(e).capitalize(),
            )

    def transform(self) -> str:
        return self.s.get("transform", "")

    def max_concurrent_tasks(self) -> int:
        value = self.s.getint("max_concurrent_tasks", fallback=1)
        if value <= 0:
            self.invalid_value("max_concurrent_tasks", value,
                               "Must be greater than 0")
        return value

    def max_concurrent_downloads(self) -> int:
        tasks = self.max_concurrent_tasks()
        value = self.s.getint("max_concurrent_downloads", fallback=None)
        if value is None:
            return tasks
        if value <= 0:
            self.invalid_value("max_concurrent_downloads", value,
                               "Must be greater than 0")
        if value > tasks:
            self.invalid_value("max_concurrent_downloads", value,
                               "Must not be greater than max_concurrent_tasks")
        return value

    def delay_between_tasks(self) -> float:
        value = self.s.getfloat("delay_between_tasks", fallback=0.0)
        if value < 0:
            self.invalid_value("delay_between_tasks", value,
                               "Must not be negative")
        return value

    def auth(self, authenticators: Dict[str, Authenticator]) -> Authenticator:
        value = self.s.get("auth")
        if value is None:
            self.missing_value("auth")
        auth = authenticators.get(value)
        if auth is None:
            self.invalid_value("auth", value, "No such auth section exists")
        return auth


class Crawler(ABC):
    def __init__(
            self,
            name: str,
            section: CrawlerSection,
            config: Config,
            conductor: TerminalConductor,
    ) -> None:
        """
        Initialize a crawler from its name and its section in the config file.

        If you are writing your own constructor for your own crawler, make sure
        to call this constructor first (via super().__init__).

        May throw a CrawlerLoadException.
        """

        self.name = name
        self._conductor = conductor
        self.error_free = True

        self._limiter = Limiter(
            task_limit=section.max_concurrent_tasks(),
            download_limit=section.max_concurrent_downloads(),
            task_delay=section.delay_between_tasks(),
        )

        try:
            self._transformer = Transformer(section.transform())
        except RuleParseException as e:
            e.pretty_print()
            raise CrawlerLoadException()

        self._output_dir = OutputDirectory(
            config.working_dir / section.output_dir(name),
            section.redownload(),
            section.on_conflict(),
            self._conductor,
        )

    def print(self, text: str) -> None:
        """
        Print rich markup to the terminal. Crawlers *must* use this function to
        print things unless they are holding an exclusive output context
        manager! Be careful to escape all user-supplied strings.
        """

        self._conductor.print(text)

    def exclusive_output(self) -> AsyncContextManager[None]:
        """
        Acquire exclusive rights™ to the terminal output. While this context
        manager is held, output such as printing and progress bars from other
        threads is suspended and the current thread may do whatever it wants
        with the terminal. However, it must return the terminal to its original
        state before exiting the context manager.

        No two threads can hold this context manager at the same time.

        Useful for password or confirmation prompts as well as running other
        programs while crawling (e. g. to get certain credentials).
        """

        return self._conductor.exclusive_output()

    @asynccontextmanager
    async def crawl_bar(
            self,
            path: PurePath,
            total: Optional[int] = None,
    ) -> AsyncIterator[ProgressBar]:
        desc = f"[bold bright_cyan]Crawling[/] {escape(str(path))}"
        async with self._limiter.limit_crawl():
            with self._conductor.progress_bar(desc, total=total) as bar:
                yield bar

    @asynccontextmanager
    async def download_bar(
            self,
            path: PurePath,
            total: Optional[int] = None,
    ) -> AsyncIterator[ProgressBar]:
        desc = f"[bold bright_cyan]Downloading[/] {escape(str(path))}"
        async with self._limiter.limit_download():
            with self._conductor.progress_bar(desc, total=total) as bar:
                yield bar

    def should_crawl(self, path: PurePath) -> bool:
        return self._transformer.transform(path) is not None

    async def download(
            self,
            path: PurePath,
            mtime: Optional[datetime] = None,
            redownload: Optional[Redownload] = None,
            on_conflict: Optional[OnConflict] = None,
    ) -> Optional[AsyncContextManager[FileSink]]:
        transformed_path = self._transformer.transform(path)
        if transformed_path is None:
            return None

        return await self._output_dir.download(
            transformed_path, mtime, redownload, on_conflict)

    async def cleanup(self) -> None:
        await self._output_dir.cleanup()

    async def run(self) -> None:
        """
        Start the crawling process. Call this function if you want to use a
        crawler.
        """

        async with self._conductor:
            await self.crawl()

    @abstractmethod
    async def crawl(self) -> None:
        """
        Overwrite this function if you are writing a crawler.

        This function must not return before all crawling is complete. To crawl
        multiple things concurrently, asyncio.gather can be used.
        """

        pass


class HttpCrawler(Crawler):
    COOKIE_FILE = PurePath(".cookies")

    def __init__(
            self,
            name: str,
            section: CrawlerSection,
            config: Config,
            conductor: TerminalConductor,
    ) -> None:
        super().__init__(name, section, config, conductor)

        self._cookie_jar_path = self._output_dir.resolve(self.COOKIE_FILE)
        self._output_dir.register_reserved(self.COOKIE_FILE)

    async def run(self) -> None:
        cookie_jar = aiohttp.CookieJar()

        try:
            cookie_jar.load(self._cookie_jar_path)
        except Exception:
            pass

        async with aiohttp.ClientSession(
                headers={"User-Agent": f"pferd/{__version__}"},
                cookie_jar=cookie_jar,
        ) as session:
            self.session = session
            try:
                await super().run()
            finally:
                del self.session

        try:
            cookie_jar.save(self._cookie_jar_path)
        except Exception:
            self.print(
                "[bold red]Warning:[/] Failed to save cookies to "
                + escape(str(self.COOKIE_FILE))
            )