import os
import hashlib
import shutil
from pathlib import Path
from typing import BinaryIO, Optional, Tuple
from fastapi import UploadFile, HTTPException
from app.core.config import settings


class FileStorageService:
    """Service for handling file storage operations."""

    def __init__(self):
        self.base_dir = Path(settings.UPLOAD_DIR)
        self._ensure_base_dir()

    def _ensure_base_dir(self):
        """Ensure the base upload directory exists."""
        self.base_dir.mkdir(parents=True, exist_ok=True)

    def _get_file_path(self, project_id: str, task_id: str, attachment_id: str, version: int) -> Path:
        """Generate the file path for an attachment version."""
        return self.base_dir / project_id / task_id / attachment_id / str(version)

    @staticmethod
    def calculate_checksum(file: BinaryIO) -> str:
        """Calculate SHA-256 checksum of a file."""
        sha256_hash = hashlib.sha256()
        # Read in chunks to handle large files
        for chunk in iter(lambda: file.read(8192), b""):
            sha256_hash.update(chunk)
        file.seek(0)  # Reset file position
        return sha256_hash.hexdigest()

    @staticmethod
    def get_extension(filename: str) -> str:
        """Get file extension in lowercase."""
        return filename.rsplit(".", 1)[-1].lower() if "." in filename else ""

    @staticmethod
    def validate_file(file: UploadFile) -> Tuple[str, str]:
        """
        Validate file size and type.
        Returns (extension, mime_type) if valid.
        Raises HTTPException if invalid.
        """
        # Check file size
        file.file.seek(0, 2)  # Seek to end
        file_size = file.file.tell()
        file.file.seek(0)  # Reset

        if file_size > settings.MAX_FILE_SIZE:
            raise HTTPException(
                status_code=400,
                detail=f"File too large. Maximum size is {settings.MAX_FILE_SIZE_MB}MB"
            )

        if file_size == 0:
            raise HTTPException(status_code=400, detail="Empty file not allowed")

        # Get extension
        extension = FileStorageService.get_extension(file.filename or "")

        # Check blocked extensions
        if extension in settings.BLOCKED_EXTENSIONS:
            raise HTTPException(
                status_code=400,
                detail=f"File type '.{extension}' is not allowed for security reasons"
            )

        # Check allowed extensions (if whitelist is enabled)
        if settings.ALLOWED_EXTENSIONS and extension not in settings.ALLOWED_EXTENSIONS:
            raise HTTPException(
                status_code=400,
                detail=f"File type '.{extension}' is not supported"
            )

        mime_type = file.content_type or "application/octet-stream"
        return extension, mime_type

    async def save_file(
        self,
        file: UploadFile,
        project_id: str,
        task_id: str,
        attachment_id: str,
        version: int
    ) -> Tuple[str, int, str]:
        """
        Save uploaded file to storage.
        Returns (file_path, file_size, checksum).
        """
        # Validate file
        extension, _ = self.validate_file(file)

        # Calculate checksum first
        checksum = self.calculate_checksum(file.file)

        # Create directory structure
        dir_path = self._get_file_path(project_id, task_id, attachment_id, version)
        dir_path.mkdir(parents=True, exist_ok=True)

        # Save file with original extension
        filename = f"file.{extension}" if extension else "file"
        file_path = dir_path / filename

        # Get file size
        file.file.seek(0, 2)
        file_size = file.file.tell()
        file.file.seek(0)

        # Write file in chunks (streaming)
        with open(file_path, "wb") as buffer:
            shutil.copyfileobj(file.file, buffer)

        return str(file_path), file_size, checksum

    def get_file(
        self,
        project_id: str,
        task_id: str,
        attachment_id: str,
        version: int
    ) -> Optional[Path]:
        """
        Get the file path for an attachment version.
        Returns None if file doesn't exist.
        """
        dir_path = self._get_file_path(project_id, task_id, attachment_id, version)

        if not dir_path.exists():
            return None

        # Find the file in the directory
        files = list(dir_path.iterdir())
        if not files:
            return None

        return files[0]

    def get_file_by_path(self, file_path: str) -> Optional[Path]:
        """Get file by stored path. Handles both absolute and relative paths."""
        path = Path(file_path)

        # If path is absolute and exists, return it directly
        if path.is_absolute() and path.exists():
            return path

        # If path is relative, try prepending base_dir
        full_path = self.base_dir / path
        if full_path.exists():
            return full_path

        # Fallback: check if original path exists (e.g., relative from current dir)
        if path.exists():
            return path

        return None

    def delete_file(
        self,
        project_id: str,
        task_id: str,
        attachment_id: str,
        version: Optional[int] = None
    ) -> bool:
        """
        Delete file(s) from storage.
        If version is None, deletes all versions.
        Returns True if successful.
        """
        if version is not None:
            # Delete specific version
            dir_path = self._get_file_path(project_id, task_id, attachment_id, version)
        else:
            # Delete all versions (attachment directory)
            dir_path = self.base_dir / project_id / task_id / attachment_id

        if dir_path.exists():
            shutil.rmtree(dir_path)
            return True
        return False

    def delete_task_files(self, project_id: str, task_id: str) -> bool:
        """Delete all files for a task."""
        dir_path = self.base_dir / project_id / task_id
        if dir_path.exists():
            shutil.rmtree(dir_path)
            return True
        return False


# Singleton instance
file_storage_service = FileStorageService()