from __future__ import annotations

import asyncio
import base64
import hashlib
import hmac
import json
import time
from collections import OrderedDict
from dataclasses import dataclass, field

LINE_SIGNATURE_HEADER = "x-line-signature"
LINE_WEBHOOK_MAX_BODY_BYTES = 64 * 1024

_REPLAY_WINDOW_SECONDS = 600
_REPLAY_CACHE_MAX_ENTRIES = 4096


class RetryableError(Exception):
    pass


class ReplayDetectedError(RetryableError):
    pass


class WebhookBodyTooLargeError(Exception):
    pass


class WebhookParseError(Exception):
    pass


class ConcurrentRequestRejectedError(Exception):
    pass


def validate_line_signature(raw_body: bytes, signature: str, channel_secret: str) -> bool:
    if not signature or not channel_secret:
        return False
    if len(raw_body) > LINE_WEBHOOK_MAX_BODY_BYTES:
        return False

    try:
        computed = hmac.new(
            key=channel_secret.encode("utf-8"),
            msg=raw_body if isinstance(raw_body, bytes) else raw_body.encode("utf-8"),
            digestmod=hashlib.sha256,
        ).digest()

        computed_b64 = base64.b64encode(computed).decode("utf-8")
        return hmac.compare_digest(computed_b64, signature)
    except Exception:
        return False


def parse_webhook_body(raw_body: bytes) -> list[dict] | None:
    try:
        body_str = raw_body.decode("utf-8") if isinstance(raw_body, bytes) else raw_body
        data = json.loads(body_str)
        return data.get("events", [])
    except (json.JSONDecodeError, UnicodeDecodeError):
        return None


@dataclass
class WebhookReplayGuard:
    _window_seconds: float = _REPLAY_WINDOW_SECONDS
    _max_entries: int = _REPLAY_CACHE_MAX_ENTRIES
    _seen_hashes: OrderedDict = field(default_factory=OrderedDict)

    def check_and_claim(self, signature_hash: str) -> None:
        now = time.time()
        cutoff = now - self._window_seconds

        expired = [k for k, ts in self._seen_hashes.items() if ts < cutoff]
        for k in expired:
            self._seen_hashes.pop(k, None)

        if signature_hash in self._seen_hashes:
            raise ReplayDetectedError(f"Replay detected for signature {signature_hash[:16]}...")

        self._seen_hashes[signature_hash] = now

        while len(self._seen_hashes) > self._max_entries:
            self._seen_hashes.popitem(last=False)

    def clear(self) -> None:
        self._seen_hashes.clear()


@dataclass
class MultiAccountSignatureRouter:
    _secrets: OrderedDict = field(default_factory=OrderedDict)

    def register_account(self, account_id: str, channel_secret: str) -> None:
        self._secrets[account_id] = channel_secret

    def unregister_account(self, account_id: str) -> None:
        self._secrets.pop(account_id, None)

    def list_accounts(self) -> list[str]:
        return list(self._secrets.keys())

    def match_signature(self, raw_body: bytes, signature: str) -> str | None:
        for account_id, secret in self._secrets.items():
            if validate_line_signature(raw_body, signature, secret):
                return account_id
        return None

    def clear(self) -> None:
        self._secrets.clear()


@dataclass
class WebhookConcurrencyGuard:
    _max_concurrent: int = 1
    _semaphores: dict[str, asyncio.Semaphore] = field(default_factory=dict)

    async def acquire(self, path: str) -> bool:
        if path not in self._semaphores:
            self._semaphores[path] = asyncio.Semaphore(self._max_concurrent)
        return await self._semaphores[path].acquire()

    def release(self, path: str) -> None:
        if path in self._semaphores:
            try:
                self._semaphores[path].release()
            except ValueError:
                pass

    def in_flight_count(self, path: str | None = None) -> int:
        if path:
            sem = self._semaphores.get(path)
            if sem is None:
                return 0
            return self._max_concurrent - sem._value
        return sum(self._max_concurrent - sem._value for sem in self._semaphores.values())

    def clear(self) -> None:
        self._semaphores.clear()