import base64
import hashlib
import os
import uuid
from collections.abc import Generator, Sequence  # Changed Iterator to Generator
from contextlib import contextmanager, suppress
from tempfile import NamedTemporaryFile
from typing import Literal
from zipfile import ZIP_DEFLATED, ZipFile

from sqlalchemy import Engine, select
from sqlalchemy.orm import Session, sessionmaker
from werkzeug.exceptions import NotFound

from configs import dify_config
from constants import (
    AUDIO_EXTENSIONS,
    DOCUMENT_EXTENSIONS,
    IMAGE_EXTENSIONS,
    VIDEO_EXTENSIONS,
)
from core.rag.extractor.extract_processor import ExtractProcessor
from extensions.ext_database import db
from extensions.ext_storage import storage
from extensions.storage.storage_type import StorageType
from graphon.file import helpers as file_helpers
from libs.datetime_utils import naive_utc_now
from libs.helper import extract_tenant_id
from models import Account
from models.enums import CreatorUserRole
from models.model import EndUser, UploadFile

from .errors.file import BlockedFileExtensionError, FileTooLargeError, UnsupportedFileTypeError

PREVIEW_WORDS_LIMIT = 3000


class FileService:
    _session_maker: sessionmaker[Session]

    def __init__(self, session_factory: sessionmaker | Engine | None = None):
        if isinstance(session_factory, Engine):
            self._session_maker = sessionmaker(bind=session_factory)
        elif isinstance(session_factory, sessionmaker):
            self._session_maker = session_factory
        else:
            raise AssertionError("must be a sessionmaker or an Engine.")

    def upload_file(
        self,
        *,
        filename: str,
        content: bytes,
        mimetype: str,
        user: Account | EndUser,
        source: Literal["datasets"] | None = None,
        source_url: str = "",
    ) -> UploadFile:
        # get file extension
        extension = os.path.splitext(filename)[1].lstrip(".").lower()

        # Only reject path separators here. The original filename is stored as metadata,
        # while the storage key is UUID-based.
        if any(c in filename for c in ["/", "\\"]):
            raise ValueError("Filename contains invalid characters")

        if len(filename) > 200:
            filename = filename.split(".")[0][:200] + "." + extension

        # check if extension is in blacklist
        if extension and extension in dify_config.UPLOAD_FILE_EXTENSION_BLACKLIST:
            raise BlockedFileExtensionError(f"File extension '.{extension}' is not allowed for security reasons")

        if source == "datasets" and extension not in DOCUMENT_EXTENSIONS:
            raise UnsupportedFileTypeError()

        # get file size
        file_size = len(content)

        # check if the file size is exceeded
        if not FileService.is_file_size_within_limit(extension=extension, file_size=file_size):
            raise FileTooLargeError

        # generate file key
        file_uuid = str(uuid.uuid4())

        current_tenant_id = extract_tenant_id(user)

        file_key = "upload_files/" + (current_tenant_id or "") + "/" + file_uuid + "." + extension

        # save file to storage
        storage.save(file_key, content)

        # save file to db
        upload_file = UploadFile(
            tenant_id=current_tenant_id or "",
            storage_type=StorageType(dify_config.STORAGE_TYPE),
            key=file_key,
            name=filename,
            size=file_size,
            extension=extension,
            mime_type=mimetype,
            created_by_role=(CreatorUserRole.ACCOUNT if isinstance(user, Account) else CreatorUserRole.END_USER),
            created_by=user.id,
            created_at=naive_utc_now(),
            used=False,
            hash=hashlib.sha3_256(content).hexdigest(),
            source_url=source_url,
        )

        with self._session_maker(expire_on_commit=False) as session:
            session.add(upload_file)
            session.commit()

        if not upload_file.source_url:
            upload_file.source_url = file_helpers.get_signed_file_url(upload_file_id=upload_file.id)

        return upload_file

    @staticmethod
    def is_file_size_within_limit(*, extension: str, file_size: int) -> bool:
        if extension in IMAGE_EXTENSIONS:
            file_size_limit = dify_config.UPLOAD_IMAGE_FILE_SIZE_LIMIT * 1024 * 1024
        elif extension in VIDEO_EXTENSIONS:
            file_size_limit = dify_config.UPLOAD_VIDEO_FILE_SIZE_LIMIT * 1024 * 1024
        elif extension in AUDIO_EXTENSIONS:
            file_size_limit = dify_config.UPLOAD_AUDIO_FILE_SIZE_LIMIT * 1024 * 1024
        else:
            file_size_limit = dify_config.UPLOAD_FILE_SIZE_LIMIT * 1024 * 1024

        return file_size <= file_size_limit

    def get_file_base64(self, file_id: str) -> str:
        with self._session_maker(expire_on_commit=False) as session:
            upload_file = session.scalar(select(UploadFile).where(UploadFile.id == file_id).limit(1))
            if not upload_file:
                raise NotFound("File not found")
            upload_file_key = upload_file.key

        blob = storage.load_once(upload_file_key)
        return base64.b64encode(blob).decode()

    def upload_text(self, text: str, text_name: str, user_id: str, tenant_id: str) -> UploadFile:
        if len(text_name) > 200:
            text_name = text_name[:200]
        # user uuid as file name
        file_uuid = str(uuid.uuid4())
        file_key = "upload_files/" + tenant_id + "/" + file_uuid + ".txt"

        # save file to storage
        storage.save(file_key, text.encode("utf-8"))

        # save file to db
        upload_file = UploadFile(
            tenant_id=tenant_id,
            storage_type=StorageType(dify_config.STORAGE_TYPE),
            key=file_key,
            name=text_name,
            size=len(text),
            extension="txt",
            mime_type="text/plain",
            created_by=user_id,
            created_by_role=CreatorUserRole.ACCOUNT,
            created_at=naive_utc_now(),
            used=True,
            used_by=user_id,
            used_at=naive_utc_now(),
        )

        with self._session_maker(expire_on_commit=False) as session:
            session.add(upload_file)
            session.commit()

        return upload_file

    def get_file_preview(self, file_id: str, tenant_id: str):
        """
        Return a short text preview extracted from a document file.
        """
        with self._session_maker(expire_on_commit=False) as session:
            upload_file = session.scalar(
                select(UploadFile).where(UploadFile.id == file_id, UploadFile.tenant_id == tenant_id).limit(1)
            )

        if not upload_file:
            raise NotFound("File not found")

        # extract text from file
        extension = upload_file.extension
        if extension.lower() not in DOCUMENT_EXTENSIONS:
            raise UnsupportedFileTypeError()

        text = ExtractProcessor.load_from_upload_file(upload_file, return_text=True)
        text = text[0:PREVIEW_WORDS_LIMIT] if text else ""

        return text

    def get_image_preview(self, file_id: str, timestamp: str, nonce: str, sign: str):
        result = file_helpers.verify_image_signature(
            upload_file_id=file_id, timestamp=timestamp, nonce=nonce, sign=sign
        )
        if not result:
            raise NotFound("File not found or signature is invalid")
        with self._session_maker(expire_on_commit=False) as session:
            upload_file = session.scalar(select(UploadFile).where(UploadFile.id == file_id).limit(1))

        if not upload_file:
            raise NotFound("File not found or signature is invalid")

        # extract text from file
        extension = upload_file.extension
        if extension.lower() not in IMAGE_EXTENSIONS:
            raise UnsupportedFileTypeError()

        generator = storage.load(upload_file.key, stream=True)

        return generator, upload_file.mime_type

    def get_file_generator_by_file_id(self, file_id: str, timestamp: str, nonce: str, sign: str):
        result = file_helpers.verify_file_signature(upload_file_id=file_id, timestamp=timestamp, nonce=nonce, sign=sign)
        if not result:
            raise NotFound("File not found or signature is invalid")

        with self._session_maker(expire_on_commit=False) as session:
            upload_file = session.scalar(select(UploadFile).where(UploadFile.id == file_id).limit(1))

        if not upload_file:
            raise NotFound("File not found or signature is invalid")

        generator = storage.load(upload_file.key, stream=True)

        return generator, upload_file

    def get_public_image_preview(self, file_id: str):
        with self._session_maker(expire_on_commit=False) as session:
            upload_file = session.scalar(select(UploadFile).where(UploadFile.id == file_id).limit(1))

        if not upload_file:
            raise NotFound("File not found or signature is invalid")

        # extract text from file
        extension = upload_file.extension
        if extension.lower() not in IMAGE_EXTENSIONS:
            raise UnsupportedFileTypeError()

        generator = storage.load(upload_file.key)

        return generator, upload_file.mime_type

    def get_file_content(self, file_id: str) -> str:
        with self._session_maker(expire_on_commit=False) as session:
            upload_file: UploadFile | None = session.scalar(select(UploadFile).where(UploadFile.id == file_id).limit(1))

        if not upload_file:
            raise NotFound("File not found")
        content = storage.load(upload_file.key)

        return content.decode("utf-8")

    def delete_file(self, file_id: str):
        with self._session_maker() as session, session.begin():
            upload_file = session.scalar(select(UploadFile).where(UploadFile.id == file_id))

            if not upload_file:
                return
            storage.delete(upload_file.key)
            session.delete(upload_file)

    @staticmethod
    def get_upload_files_by_ids(tenant_id: str, upload_file_ids: Sequence[str]) -> dict[str, UploadFile]:
        """
        Fetch `UploadFile` rows for a tenant in a single batch query.

        This is a generic `UploadFile` lookup helper (not dataset/document specific), so it lives in `FileService`.
        """
        if not upload_file_ids:
            return {}

        # Normalize and deduplicate ids before using them in the IN clause.
        upload_file_id_list: list[str] = [str(upload_file_id) for upload_file_id in upload_file_ids]
        unique_upload_file_ids: list[str] = list(set(upload_file_id_list))

        # Fetch upload files in one query for efficient batch access.
        upload_files: Sequence[UploadFile] = db.session.scalars(
            select(UploadFile).where(
                UploadFile.tenant_id == tenant_id,
                UploadFile.id.in_(unique_upload_file_ids),
            )
        ).all()
        return {str(upload_file.id): upload_file for upload_file in upload_files}

    @staticmethod
    def _sanitize_zip_entry_name(name: str) -> str:
        """
        Sanitize a ZIP entry name to avoid path traversal and weird separators.

        We keep this conservative: the upload flow already rejects `/` and `\\`, but older rows (or imported data)
        could still contain unsafe names.
        """
        # Drop any directory components and prevent empty names.
        base = os.path.basename(name).strip() or "file"

        # ZIP uses forward slashes as separators; remove any residual separator characters.
        return base.replace("/", "_").replace("\\", "_")

    @staticmethod
    def _dedupe_zip_entry_name(original_name: str, used_names: set[str]) -> str:
        """
        Return a unique ZIP entry name, inserting suffixes before the extension.
        """
        # Keep the original name when it's not already used.
        if original_name not in used_names:
            return original_name

        # Insert suffixes before the extension (e.g., "doc.txt" -> "doc (1).txt").
        stem, extension = os.path.splitext(original_name)
        suffix = 1
        while True:
            candidate = f"{stem} ({suffix}){extension}"
            if candidate not in used_names:
                return candidate
            suffix += 1

    @staticmethod
    @contextmanager
    def build_upload_files_zip_tempfile(
        *,
        upload_files: Sequence[UploadFile],
    ) -> Generator[str, None, None]:  # Changed from Iterator[str]
        """
        Build a ZIP from `UploadFile`s and yield a tempfile path.

        We yield a path (rather than an open file handle) to avoid "read of closed file" issues when Flask/Werkzeug
        streams responses. The caller is expected to keep this context open until the response is fully sent, then
        close it (e.g., via `response.call_on_close(...)`) to delete the tempfile.
        """
        used_names: set[str] = set()

        # Build a ZIP in a temp file and keep it on disk until the caller finishes streaming it.
        tmp_path: str | None = None
        try:
            with NamedTemporaryFile(mode="w+b", suffix=".zip", delete=False) as tmp:
                tmp_path = tmp.name
                with ZipFile(tmp, mode="w", compression=ZIP_DEFLATED) as zf:
                    for upload_file in upload_files:
                        # Ensure the entry name is safe and unique.
                        safe_name = FileService._sanitize_zip_entry_name(upload_file.name)
                        arcname = FileService._dedupe_zip_entry_name(safe_name, used_names)
                        used_names.add(arcname)

                        # Stream file bytes from storage into the ZIP entry.
                        with zf.open(arcname, "w") as entry:
                            for chunk in storage.load(upload_file.key, stream=True):
                                entry.write(chunk)

                # Flush so `send_file(path, ...)` can re-open it safely on all platforms.
                tmp.flush()

            assert tmp_path is not None
            yield tmp_path
        finally:
            # Remove the temp file when the context is closed (typically after the response finishes streaming).
            if tmp_path is not None:
                with suppress(FileNotFoundError):
                    os.remove(tmp_path)
