import os
import json

class MetaDataManager:
    _instance = None

    def __new__(cls, *args, **kwargs):
        if cls._instance is None:
            cls._instance = super().__new__(cls)
        return cls._instance
    def __init__(self):
        # read metadata file from executing directory
        self.metadata_file = os.path.join(os.getcwd(), "metadata.json")
        if os.path.exists(self.metadata_file):
            with open(self.metadata_file, "r") as f:
                self.collections = json.load(f)
        else:
            self.collections = {}
    
    def create_collection(self, name):
        if name in self.collections:
            raise ValueError(f"Collection '{name}' already exists.")
        self.collections[name] = []
        self.save_metadata()
    
    def delete_collection(self, name):
        if name not in self.collections:
            raise ValueError(f"Collection '{name}' does not exist.")
        del self.collections[name]
        self.save_metadata()
    
    def add_clip_to_collection(self, collection_name, clip_metadata):
        if collection_name not in self.collections:
            raise ValueError(f"Collection '{collection_name}' does not exist.")
        self.collections[collection_name].append(clip_metadata)
        self.save_metadata()
    
    def get_collections(self):
        return list(self.collections.keys())
    
    def get_clips_in_collection(self, collection_name):
        if collection_name not in self.collections:
            raise ValueError(f"Collection '{collection_name}' does not exist.")
        return self.collections[collection_name]
    
    def save_metadata(self):
        with open(self.metadata_file, "w") as f:
            json.dump(self.collections, f, indent=4)