# ========= Copyright 2026 @ Strukto.AI All Rights Reserved. =========
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# ========= Copyright 2026 @ Strukto.AI All Rights Reserved. =========

from collections.abc import AsyncIterator
from contextlib import AsyncExitStack
from typing import Any

from mirage.accessor.s3 import S3Accessor
from mirage.cache.index import NULL_INDEX, IndexCacheStore
from mirage.core.s3.client import _client_kwargs, _key, async_session
from mirage.core.s3.read import _fp_rev_from_response, read_bytes
from mirage.observe.context import record_stream, revision_for
from mirage.types import PathSpec
from mirage.utils.errors import enoent


def _is_not_found(exc: Exception) -> bool:
    if hasattr(exc, "response"):
        code = exc.response.get("Error", {}).get("Code")
        return code in ("404", "NoSuchKey")
    return False


async def read_stream(
    accessor: S3Accessor,
    path_spec: PathSpec,
    index: IndexCacheStore = NULL_INDEX,
    chunk_size: int = 8192,
) -> AsyncIterator[bytes]:
    """Async generator yielding chunks of an S3 object.

    Args:
        accessor (S3Accessor): S3 accessor.
        path_spec (PathSpec): Object path.
        index: Index cache store.
        chunk_size (int): Size of each chunk in bytes.
    """
    virtual = path_spec.virtual
    path = path_spec.mount_path
    pinned_revision = revision_for(virtual)
    config = accessor.config
    rec = record_stream("read", path, "s3")
    session = async_session(config)
    async with session.client(**_client_kwargs(config)) as client:
        kwargs: dict[str, Any] = {
            "Bucket": config.bucket,
            "Key": _key(path, config)
        }
        if pinned_revision is not None:
            kwargs["VersionId"] = pinned_revision
        try:
            response = await client.get_object(**kwargs)
        except Exception as exc:
            if _is_not_found(exc):
                raise enoent(virtual) from exc
            raise
        if rec is not None:
            fingerprint, revision = _fp_rev_from_response(response)
            rec.fingerprint = fingerprint
            rec.revision = revision
        body = response["Body"]
        async with AsyncExitStack() as stack:
            if hasattr(body, "__aenter__") and hasattr(body, "__aexit__"):
                await stack.enter_async_context(body)
            else:
                close = getattr(body, "close", None)
                if close is not None:
                    stack.callback(close)
            async for chunk in body.iter_chunks(chunk_size):
                if rec is not None:
                    rec.bytes += len(chunk)
                yield chunk


async def range_read(accessor: S3Accessor, path_spec: PathSpec, start: int,
                     end: int) -> bytes:
    """Read a byte range, in the resource API's end-exclusive spelling.

    Args:
        accessor (S3Accessor): S3 accessor.
        path_spec (PathSpec): Object path_spec.
        start (int): first byte to read.
        end (int): one past the last byte to read.
    """
    return await read_bytes(accessor,
                            path_spec,
                            offset=start,
                            size=end - start)
