queuelib/queue.py

from __future__ import annotations

import json
import os
import sqlite3
import struct
from abc import abstractmethod
from collections import deque
from contextlib import suppress
from pathlib import Path
from typing import Any, BinaryIO, Literal, cast


class _BaseQueueMeta(type):
    """
    Metaclass to check queue classes against the necessary interface
    """

    def __instancecheck__(cls, instance: Any) -> bool:
        return cls.__subclasscheck__(  # pylint: disable=no-value-for-parameter
            type(instance)
        )

    def __subclasscheck__(cls, subclass: Any) -> bool:
        return (
            hasattr(subclass, "push")
            and callable(subclass.push)
            and hasattr(subclass, "pop")
            and callable(subclass.pop)
            and hasattr(subclass, "peek")
            and callable(subclass.peek)
            and hasattr(subclass, "close")
            and callable(subclass.close)
            and hasattr(subclass, "__len__")
            and callable(subclass.__len__)
        )


class BaseQueue(metaclass=_BaseQueueMeta):
    @abstractmethod
    def push(self, obj: Any) -> None:
        raise NotImplementedError

    @abstractmethod
    def pop(self) -> Any | None:
        raise NotImplementedError

    @abstractmethod
    def peek(self) -> Any | None:
        raise NotImplementedError

    @abstractmethod
    def __len__(self) -> int:
        raise NotImplementedError

    def close(self) -> None:
        pass


class FifoMemoryQueue:
    """In-memory FIFO queue, API compliant with FifoDiskQueue."""

    def __init__(self) -> None:
        self.q: deque[Any] = deque()

    def push(self, obj: Any) -> None:
        self.q.append(obj)

    def pop(self) -> Any | None:
        return self.q.popleft() if self.q else None

    def peek(self) -> Any | None:
        return self.q[0] if self.q else None

    def close(self) -> None:
        pass

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


class LifoMemoryQueue(FifoMemoryQueue):
    """In-memory LIFO queue, API compliant with LifoDiskQueue."""

    def pop(self) -> Any | None:
        return self.q.pop() if self.q else None

    def peek(self) -> Any | None:
        return self.q[-1] if self.q else None


class FifoDiskQueue:
    """Persistent FIFO queue."""

    szhdr_format = ">L"
    szhdr_size = struct.calcsize(szhdr_format)

    def __init__(self, path: str | os.PathLike[str], chunksize: int = 100000) -> None:
        self.path = str(path)
        if not Path(path).exists():
            Path(path).mkdir(parents=True)
        self.info = self._loadinfo(chunksize)
        self.chunksize = self.info["chunksize"]
        self.headf = self._openchunk(self.info["head"][0], "ab+")
        self.tailf = self._openchunk(self.info["tail"][0])
        os.lseek(self.tailf.fileno(), self.info["tail"][2], os.SEEK_SET)

    def push(self, string: bytes) -> None:
        if not isinstance(string, bytes):
            raise TypeError(f"Unsupported type: {type(string).__name__}")
        hnum, hpos = self.info["head"]
        hpos += 1
        szhdr = struct.pack(self.szhdr_format, len(string))
        os.write(self.headf.fileno(), szhdr + string)
        if hpos == self.chunksize:
            hpos = 0
            hnum += 1
            self.headf.close()
            self.headf = self._openchunk(hnum, "ab+")
        self.info["size"] += 1
        self.info["head"] = [hnum, hpos]

    def _openchunk(self, number: int, mode: Literal["rb", "ab+"] = "rb") -> BinaryIO:
        return Path(self.path, f"q{number:05d}").open(mode)

    def pop(self) -> bytes | None:
        tnum, tcnt, toffset = self.info["tail"]
        if [tnum, tcnt] >= self.info["head"]:
            return None
        tfd = self.tailf.fileno()
        szhdr = os.read(tfd, self.szhdr_size)
        if not szhdr:
            return None
        (size,) = struct.unpack(self.szhdr_format, szhdr)
        data = os.read(tfd, size)
        tcnt += 1
        toffset += self.szhdr_size + size
        if tcnt == self.chunksize and tnum <= self.info["head"][0]:
            tcnt = toffset = 0
            tnum += 1
            self.tailf.close()
            Path(self.tailf.name).unlink()
            self.tailf = self._openchunk(tnum)
        self.info["size"] -= 1
        self.info["tail"] = [tnum, tcnt, toffset]
        return data

    def peek(self) -> bytes | None:
        tnum, tcnt, _ = self.info["tail"]
        if [tnum, tcnt] >= self.info["head"]:
            return None
        tfd = self.tailf.fileno()
        tfd_initial_pos = os.lseek(tfd, 0, os.SEEK_CUR)
        szhdr = os.read(tfd, self.szhdr_size)
        if not szhdr:
            return None
        (size,) = struct.unpack(self.szhdr_format, szhdr)
        data = os.read(tfd, size)
        os.lseek(tfd, tfd_initial_pos, os.SEEK_SET)
        return data

    def close(self) -> None:
        self.headf.close()
        self.tailf.close()
        self._saveinfo(self.info)
        if len(self) == 0:
            self._cleanup()

    def __len__(self) -> int:
        return cast(int, self.info["size"])

    def _loadinfo(self, chunksize: int) -> dict[str, Any]:
        infopath = self._infopath()
        if infopath.exists():
            info = cast(dict[str, Any], json.loads(infopath.read_text()))
        else:
            info = {
                "chunksize": chunksize,
                "size": 0,
                "tail": [0, 0, 0],
                "head": [0, 0],
            }
        return info

    def _saveinfo(self, info: dict[str, Any]) -> None:
        self._infopath().write_text(json.dumps(info))

    def _infopath(self) -> Path:
        return Path(self.path, "info.json")

    def _cleanup(self) -> None:
        for x in Path(self.path).glob("q*"):
            x.unlink()
        Path(self.path, "info.json").unlink()
        with suppress(OSError):
            Path(self.path).rmdir()


class LifoDiskQueue:
    """Persistent LIFO queue."""

    SIZE_FORMAT = ">L"
    SIZE_SIZE = struct.calcsize(SIZE_FORMAT)

    def __init__(self, path: str | os.PathLike[str]) -> None:
        self.size: int
        self.path = str(path)
        if Path(path).exists():
            self.f = Path(path).open("rb+")  # noqa: SIM115
            qsize = self.f.read(self.SIZE_SIZE)
            (self.size,) = struct.unpack(self.SIZE_FORMAT, qsize)
            self.f.seek(0, os.SEEK_END)
        else:
            self.f = Path(path).open("wb+")  # noqa: SIM115
            self.f.write(struct.pack(self.SIZE_FORMAT, 0))
            self.size = 0

    def push(self, string: bytes) -> None:
        if not isinstance(string, bytes):
            raise TypeError(f"Unsupported type: {type(string).__name__}")
        self.f.write(string)
        ssize = struct.pack(self.SIZE_FORMAT, len(string))
        self.f.write(ssize)
        self.size += 1

    def pop(self) -> bytes | None:
        if not self.size:
            return None
        self.f.seek(-self.SIZE_SIZE, os.SEEK_END)
        (size,) = struct.unpack(self.SIZE_FORMAT, self.f.read())
        self.f.seek(-size - self.SIZE_SIZE, os.SEEK_END)
        data = self.f.read(size)
        self.f.seek(-size, os.SEEK_CUR)
        self.f.truncate()
        self.size -= 1
        return data

    def peek(self) -> bytes | None:
        if not self.size:
            return None
        self.f.seek(-self.SIZE_SIZE, os.SEEK_END)
        (size,) = struct.unpack(self.SIZE_FORMAT, self.f.read())
        self.f.seek(-size - self.SIZE_SIZE, os.SEEK_END)
        return self.f.read(size)

    def close(self) -> None:
        if self.size:
            self.f.seek(0)
            self.f.write(struct.pack(self.SIZE_FORMAT, self.size))
        self.f.close()
        if not self.size:
            Path(self.path).unlink()

    def __len__(self) -> int:
        return self.size


class FifoSQLiteQueue:
    _sql_create = "CREATE TABLE IF NOT EXISTS queue (id INTEGER PRIMARY KEY AUTOINCREMENT, item BLOB)"
    _sql_size = "SELECT COUNT(*) FROM queue"
    _sql_push = "INSERT INTO queue (item) VALUES (?)"
    _sql_pop = "SELECT id, item FROM queue ORDER BY id LIMIT 1"
    _sql_del = "DELETE FROM queue WHERE id = ?"

    def __init__(self, path: str | os.PathLike[str]) -> None:
        self._path = Path(path).resolve()
        self._db = sqlite3.Connection(self._path, timeout=60)
        self._db.text_factory = bytes
        with self._db as conn:
            conn.execute(self._sql_create)

    def push(self, item: bytes) -> None:
        if not isinstance(item, bytes):
            raise TypeError(f"Unsupported type: {type(item).__name__}")
        with self._db as conn:
            conn.execute(self._sql_push, (item,))

    def pop(self) -> bytes | None:
        with self._db as conn:
            for id_, item in conn.execute(self._sql_pop):
                conn.execute(self._sql_del, (id_,))
                return cast(bytes, item)
        return None

    def peek(self) -> bytes | None:
        with self._db as conn:
            for _, item in conn.execute(self._sql_pop):
                return cast(bytes, item)
        return None

    def close(self) -> None:
        size = len(self)
        self._db.close()
        if not size:
            self._path.unlink()

    def __len__(self) -> int:
        with self._db as conn:
            return cast(int, next(conn.execute(self._sql_size))[0])


class LifoSQLiteQueue(FifoSQLiteQueue):
    _sql_pop = "SELECT id, item FROM queue ORDER BY id DESC LIMIT 1"