#!@python@/bin/python

import asyncio
from concurrent.futures import ThreadPoolExecutor
import functools
from typing import Any, AsyncIterable, Awaitable, Callable, Optional, TypeVar
from typing import cast
from os import path, listdir
import json

import boto3
from botocore.response import StreamingBody

ENDPOINT_URL: str = "https://s3.us-west-000.backblazeb2.com"
BUCKET_NAME: str = "cache-chir-rs"

executor: ThreadPoolExecutor = ThreadPoolExecutor()

F = TypeVar('F', bound=Callable[..., Any])
T = TypeVar('T')


def with_backoff(
        f: Callable[..., Awaitable[T]]) -> Callable[..., Awaitable[T]]:

    async def with_backoff_wrapper(*args: Any, **kwargs: Any) -> T:
        last_delay = 2
        while True:
            try:
                return await f(*args, **kwargs)
            except Exception as e:
                print(f"{e}")
                if last_delay >= 120:
                    raise
                await asyncio.sleep(last_delay)
                last_delay *= last_delay

    return with_backoff_wrapper


def aio(f: Callable[..., T]) -> Callable[..., Awaitable[T]]:

    async def aio_wrapper(*args: Any, **kwargs: Any) -> T:
        f_bound: Callable[[], T] = functools.partial(f, *args, **kwargs)
        loop: asyncio.AbstractEventLoop = asyncio.get_running_loop()
        return await loop.run_in_executor(executor, f_bound)

    return aio_wrapper


@aio
def exists_locally(store_path: str) -> bool:
    return path.exists(store_path)


class NarInfo(object):

    def __init__(self, narinfo: str) -> None:
        self.compression = "bzip2"
        for narinfo_line in narinfo.splitlines():
            key, value = narinfo_line.split(": ", 1)
            if key == "StorePath":
                self.store_path = value
            elif key == "URL":
                self.url = value
            elif key == "Compression":
                self.compression = value
            elif key == "FileHash":
                self.file_hash = value
            elif key == "FileSize":
                self.file_size = int(value)
            elif key == "NarHash":
                self.nar_hash = value
            elif key == "NarSize":
                self.nar_size = int(value)
            elif key == "References":
                self.references = value.split()
            elif key == "Deriver":
                self.deriver = value
            elif key == "System":
                self.system = value
            elif key == "Sig":
                self.sig = value
            elif key == "CA":
                self.ca = value

    async def exists_locally(self) -> bool:
        return await exists_locally(self.store_path)


s3 = boto3.client("s3", endpoint_url=ENDPOINT_URL)


@with_backoff
@aio
def get_object(Key: str) -> str:
    obj = s3.get_object(Bucket=BUCKET_NAME, Key=Key)
    if "Body" not in obj:
        raise Exception("No Body")
    if isinstance(obj["Body"], StreamingBody):
        return obj["Body"].read().decode("utf-8")
    raise Exception("Not StreamingBody")


async def list_cache_objects() -> AsyncIterable[str]:

    @with_backoff
    @aio
    def list_objects_v2(ContinuationToken: Optional[str]) -> dict[str, Any]:
        if ContinuationToken is not None:
            return s3.list_objects_v2(Bucket=BUCKET_NAME,
                                      ContinuationToken=ContinuationToken)
        else:
            return s3.list_objects_v2(Bucket=BUCKET_NAME)

    cont_token = None
    while True:
        objs = await list_objects_v2(cont_token)
        if "Contents" not in objs:
            raise Exception("No Contents")
        if isinstance(objs["Contents"], list):
            for obj in cast(list[Any], objs["Contents"]):
                if not isinstance(obj, dict):
                    raise Exception("Not dict")
                obj = cast(dict[str, Any], obj)
                yield obj["Key"]

        if "NextContinuationToken" not in objs:
            break
        cont_token = objs["NextContinuationToken"]


@with_backoff
@aio
def delete_object(key: str) -> None:
    s3.delete_object(Bucket=BUCKET_NAME, Key=key)


def get_store_hashes() -> set[str]:
    hashes = set()
    for obj in listdir("/nix/store"):
        hashes.add(obj.split("-")[0])
    return hashes


async def main() -> None:
    nars_to_delete = set()
    nars_to_keep = set()
    async for obj_key in list_cache_objects():
        if obj_key.endswith(".narinfo"):
            # check if we have the hash locally
            narinfo = await get_object(obj_key)
            narinfo = NarInfo(narinfo)
            if not await narinfo.exists_locally():
                print(f"Found unused NAR for {narinfo.store_path}")
                await delete_object(obj_key)
                nars_to_delete.add(narinfo.url)
            else:
                nars_to_keep.add(narinfo.url)
        if obj_key.startswith("realisations/"):
            realisation = await get_object(obj_key)
            realisation = json.loads(realisation)
            if not isinstance(realisation, dict):
                continue
            if "outPath" not in realisation:
                continue
            if not await exists_locally("/nix/store/" +
                                        realisation["outPath"]):
                print(f"Found unused realisation for {realisation['outPath']}")
                await delete_object(obj_key)
        if obj_key.startswith("nar/"):
            nars_to_delete.add(obj_key)
    for nar in nars_to_delete:
        if nar in nars_to_keep:
            continue
        print(f"Deleting unused NAR {nar}")
        await delete_object(nar)


if __name__ == "__main__":
    asyncio.get_event_loop().run_until_complete(main())