import hashlib
import logging
from typing import BinaryIO, Tuple, Optional, Dict, Any, Generator
import boto3
from botocore.config import Config
from botocore.exceptions import ClientError

from .config import get_settings

settings = get_settings()
logger = logging.getLogger(__name__)

# Threshold for multipart upload (100MB)
MULTIPART_THRESHOLD = 100 * 1024 * 1024
# Chunk size for multipart upload (10MB)
MULTIPART_CHUNK_SIZE = 10 * 1024 * 1024
# Chunk size for streaming hash computation
HASH_CHUNK_SIZE = 8 * 1024 * 1024


class S3Storage:
    def __init__(self):
        config = Config(s3={"addressing_style": "path"} if settings.s3_use_path_style else {})

        self.client = boto3.client(
            "s3",
            endpoint_url=settings.s3_endpoint if settings.s3_endpoint else None,
            region_name=settings.s3_region,
            aws_access_key_id=settings.s3_access_key_id,
            aws_secret_access_key=settings.s3_secret_access_key,
            config=config,
        )
        self.bucket = settings.s3_bucket
        # Store active multipart uploads for resumable support
        self._active_uploads: Dict[str, Dict[str, Any]] = {}

    def store(self, file: BinaryIO, content_length: Optional[int] = None) -> Tuple[str, int, str]:
        """
        Store a file and return its SHA256 hash, size, and s3_key.
        Content-addressable: if the file already exists, just return the hash.
        Uses multipart upload for files larger than MULTIPART_THRESHOLD.
        """
        # For small files or unknown size, use the simple approach
        if content_length is None or content_length < MULTIPART_THRESHOLD:
            return self._store_simple(file)
        else:
            return self._store_multipart(file, content_length)

    def _store_simple(self, file: BinaryIO) -> Tuple[str, int, str]:
        """Store a small file using simple put_object"""
        # Read file and compute hash
        content = file.read()
        sha256_hash = hashlib.sha256(content).hexdigest()
        size = len(content)

        # Check if already exists
        s3_key = f"fruits/{sha256_hash[:2]}/{sha256_hash[2:4]}/{sha256_hash}"

        if not self._exists(s3_key):
            self.client.put_object(
                Bucket=self.bucket,
                Key=s3_key,
                Body=content,
            )

        return sha256_hash, size, s3_key

    def _store_multipart(self, file: BinaryIO, content_length: int) -> Tuple[str, int, str]:
        """Store a large file using S3 multipart upload with streaming hash computation"""
        # First pass: compute hash by streaming through file
        hasher = hashlib.sha256()
        size = 0

        # Read file in chunks to compute hash
        while True:
            chunk = file.read(HASH_CHUNK_SIZE)
            if not chunk:
                break
            hasher.update(chunk)
            size += len(chunk)

        sha256_hash = hasher.hexdigest()
        s3_key = f"fruits/{sha256_hash[:2]}/{sha256_hash[2:4]}/{sha256_hash}"

        # Check if already exists (deduplication)
        if self._exists(s3_key):
            return sha256_hash, size, s3_key

        # Seek back to start for upload
        file.seek(0)

        # Start multipart upload
        mpu = self.client.create_multipart_upload(Bucket=self.bucket, Key=s3_key)
        upload_id = mpu["UploadId"]

        try:
            parts = []
            part_number = 1

            while True:
                chunk = file.read(MULTIPART_CHUNK_SIZE)
                if not chunk:
                    break

                response = self.client.upload_part(
                    Bucket=self.bucket,
                    Key=s3_key,
                    UploadId=upload_id,
                    PartNumber=part_number,
                    Body=chunk,
                )
                parts.append({
                    "PartNumber": part_number,
                    "ETag": response["ETag"],
                })
                part_number += 1

            # Complete multipart upload
            self.client.complete_multipart_upload(
                Bucket=self.bucket,
                Key=s3_key,
                UploadId=upload_id,
                MultipartUpload={"Parts": parts},
            )

            return sha256_hash, size, s3_key

        except Exception as e:
            # Abort multipart upload on failure
            logger.error(f"Multipart upload failed: {e}")
            self.client.abort_multipart_upload(
                Bucket=self.bucket,
                Key=s3_key,
                UploadId=upload_id,
            )
            raise

    def store_streaming(self, chunks: Generator[bytes, None, None]) -> Tuple[str, int, str]:
        """
        Store a file from a stream of chunks.
        First accumulates to compute hash, then uploads.
        For truly large files, consider using initiate_resumable_upload instead.
        """
        # Accumulate chunks and compute hash
        hasher = hashlib.sha256()
        all_chunks = []
        size = 0

        for chunk in chunks:
            hasher.update(chunk)
            all_chunks.append(chunk)
            size += len(chunk)

        sha256_hash = hasher.hexdigest()
        s3_key = f"fruits/{sha256_hash[:2]}/{sha256_hash[2:4]}/{sha256_hash}"

        # Check if already exists
        if self._exists(s3_key):
            return sha256_hash, size, s3_key

        # Upload based on size
        if size < MULTIPART_THRESHOLD:
            content = b"".join(all_chunks)
            self.client.put_object(Bucket=self.bucket, Key=s3_key, Body=content)
        else:
            # Use multipart for large files
            mpu = self.client.create_multipart_upload(Bucket=self.bucket, Key=s3_key)
            upload_id = mpu["UploadId"]

            try:
                parts = []
                part_number = 1
                buffer = b""

                for chunk in all_chunks:
                    buffer += chunk
                    while len(buffer) >= MULTIPART_CHUNK_SIZE:
                        part_data = buffer[:MULTIPART_CHUNK_SIZE]
                        buffer = buffer[MULTIPART_CHUNK_SIZE:]

                        response = self.client.upload_part(
                            Bucket=self.bucket,
                            Key=s3_key,
                            UploadId=upload_id,
                            PartNumber=part_number,
                            Body=part_data,
                        )
                        parts.append({
                            "PartNumber": part_number,
                            "ETag": response["ETag"],
                        })
                        part_number += 1

                # Upload remaining buffer
                if buffer:
                    response = self.client.upload_part(
                        Bucket=self.bucket,
                        Key=s3_key,
                        UploadId=upload_id,
                        PartNumber=part_number,
                        Body=buffer,
                    )
                    parts.append({
                        "PartNumber": part_number,
                        "ETag": response["ETag"],
                    })

                self.client.complete_multipart_upload(
                    Bucket=self.bucket,
                    Key=s3_key,
                    UploadId=upload_id,
                    MultipartUpload={"Parts": parts},
                )

            except Exception as e:
                logger.error(f"Streaming multipart upload failed: {e}")
                self.client.abort_multipart_upload(
                    Bucket=self.bucket,
                    Key=s3_key,
                    UploadId=upload_id,
                )
                raise

        return sha256_hash, size, s3_key

    def initiate_resumable_upload(self, expected_hash: str) -> Dict[str, Any]:
        """
        Initiate a resumable upload session.
        Returns upload session info including upload_id.
        """
        s3_key = f"fruits/{expected_hash[:2]}/{expected_hash[2:4]}/{expected_hash}"

        # Check if already exists
        if self._exists(s3_key):
            return {
                "upload_id": None,
                "s3_key": s3_key,
                "already_exists": True,
                "parts": [],
            }

        mpu = self.client.create_multipart_upload(Bucket=self.bucket, Key=s3_key)
        upload_id = mpu["UploadId"]

        session = {
            "upload_id": upload_id,
            "s3_key": s3_key,
            "already_exists": False,
            "parts": [],
            "expected_hash": expected_hash,
        }
        self._active_uploads[upload_id] = session
        return session

    def upload_part(self, upload_id: str, part_number: int, data: bytes) -> Dict[str, Any]:
        """
        Upload a part for a resumable upload.
        Returns part info including ETag.
        """
        session = self._active_uploads.get(upload_id)
        if not session:
            raise ValueError(f"Unknown upload session: {upload_id}")

        response = self.client.upload_part(
            Bucket=self.bucket,
            Key=session["s3_key"],
            UploadId=upload_id,
            PartNumber=part_number,
            Body=data,
        )

        part_info = {
            "PartNumber": part_number,
            "ETag": response["ETag"],
        }
        session["parts"].append(part_info)
        return part_info

    def complete_resumable_upload(self, upload_id: str) -> Tuple[str, str]:
        """
        Complete a resumable upload.
        Returns (sha256_hash, s3_key).
        """
        session = self._active_uploads.get(upload_id)
        if not session:
            raise ValueError(f"Unknown upload session: {upload_id}")

        # Sort parts by part number
        sorted_parts = sorted(session["parts"], key=lambda x: x["PartNumber"])

        self.client.complete_multipart_upload(
            Bucket=self.bucket,
            Key=session["s3_key"],
            UploadId=upload_id,
            MultipartUpload={"Parts": sorted_parts},
        )

        # Clean up session
        del self._active_uploads[upload_id]

        return session["expected_hash"], session["s3_key"]

    def abort_resumable_upload(self, upload_id: str):
        """Abort a resumable upload"""
        session = self._active_uploads.get(upload_id)
        if session:
            self.client.abort_multipart_upload(
                Bucket=self.bucket,
                Key=session["s3_key"],
                UploadId=upload_id,
            )
            del self._active_uploads[upload_id]

    def list_upload_parts(self, upload_id: str) -> list:
        """List uploaded parts for a resumable upload (for resume support)"""
        session = self._active_uploads.get(upload_id)
        if not session:
            raise ValueError(f"Unknown upload session: {upload_id}")

        response = self.client.list_parts(
            Bucket=self.bucket,
            Key=session["s3_key"],
            UploadId=upload_id,
        )
        return response.get("Parts", [])

    def get(self, s3_key: str) -> bytes:
        """Retrieve a file by its S3 key"""
        response = self.client.get_object(Bucket=self.bucket, Key=s3_key)
        return response["Body"].read()

    def get_stream(self, s3_key: str, range_header: Optional[str] = None):
        """
        Get a streaming response for a file.
        Supports range requests for partial downloads.
        Returns (stream, content_length, content_range, accept_ranges)
        """
        kwargs = {"Bucket": self.bucket, "Key": s3_key}

        if range_header:
            kwargs["Range"] = range_header

        response = self.client.get_object(**kwargs)

        content_length = response.get("ContentLength", 0)
        content_range = response.get("ContentRange")

        return response["Body"], content_length, content_range

    def get_object_info(self, s3_key: str) -> Dict[str, Any]:
        """Get object metadata without downloading content"""
        try:
            response = self.client.head_object(Bucket=self.bucket, Key=s3_key)
            return {
                "size": response.get("ContentLength", 0),
                "content_type": response.get("ContentType"),
                "last_modified": response.get("LastModified"),
                "etag": response.get("ETag"),
            }
        except ClientError:
            return None

    def _exists(self, s3_key: str) -> bool:
        """Check if an object exists"""
        try:
            self.client.head_object(Bucket=self.bucket, Key=s3_key)
            return True
        except ClientError:
            return False

    def delete(self, s3_key: str) -> bool:
        """Delete an object"""
        try:
            self.client.delete_object(Bucket=self.bucket, Key=s3_key)
            return True
        except ClientError:
            return False


# Singleton instance
_storage = None


def get_storage() -> S3Storage:
    global _storage
    if _storage is None:
        _storage = S3Storage()
    return _storage