"""Vector backend configuration.

Default is ``disabled`` for lightweight local startup. Install optional local
RAG dependencies and set RAG_VECTOR_BACKEND=chroma to restore local vectors.
"""
from __future__ import annotations

import importlib.util
import json
import os
from pathlib import Path
from ..config import DATA_DIR


def settings():
    path = DATA_DIR / 'rag-backend.json'
    try:
        config = json.loads(path.read_text(encoding='utf-8'))
        if not isinstance(config, dict):
            raise ValueError('知识索引配置必须是对象')
    except FileNotFoundError:
        config = {}
    value = os.environ.get('RAG_VECTOR_BACKEND', config.get('backend', 'disabled'))
    backend_name = str(value or 'disabled').strip().lower()
    if backend_name not in {'disabled', 'chroma', 'qdrant'}:
        raise ValueError('知识索引后端配置无效')
    return {**config, 'backend': backend_name}


def configured_backend() -> str:
    return settings()['backend']


def local_chroma_available() -> bool:
    return importlib.util.find_spec('chromadb') is not None


def effective_backend() -> str:
    """Return the backend that can actually run in this installation."""
    value = configured_backend()
    if value == 'chroma' and not local_chroma_available():
        return 'disabled'
    return value


def is_disabled() -> bool:
    return effective_backend() == 'disabled'


def is_qdrant():
    return effective_backend() == 'qdrant'


def qdrant_settings():
    config = settings()
    url = str(os.environ.get('QDRANT_URL', config.get('url', ''))).rstrip('/')
    if not url.startswith(('http://', 'https://')):
        raise ValueError('请配置 Qdrant 服务地址')
    key = os.environ.get('QDRANT_API_KEY', '')
    if not key and config.get('api_key_file'):
        key = Path(config['api_key_file']).read_text(encoding='utf-8').strip()
    if not key:
        raise ValueError('请配置 Qdrant API 密钥')
    prefix = str(config.get('collection_prefix', 'yawan_'))
    if not prefix or not all(c.isalnum() or c in '_-' for c in prefix):
        raise ValueError('Qdrant 知识库命名空间无效')
    return url, key, prefix


def namespace():
    value = effective_backend()
    if value == 'qdrant':
        config = settings()
        return json.dumps(['qdrant', str(os.environ.get('QDRANT_URL', config.get('url', ''))).rstrip('/'),
                           str(config.get('collection_prefix', 'yawan_'))], separators=(',', ':'))
    if value == 'disabled':
        return 'disabled'
    return 'chroma' if local_chroma_available() else 'chroma-missing'