class Database {
    private static instance: Database;
    private db: IDBDatabase | null = null;
    private dbName: string = '4nk';
    private dbVersion: number = 1;
    private storeDefinitions = {
        AnkUser: {
            name: "user",
            options: {'keyPath': 'pre_id'},
            indices: []
        },
        AnkSession: {
            name: "session",
            options: {},
            indices: []
        },
        AnkProcess: {
            name: "process",
            options: {'keyPath': 'id'},
            indices: [{
                name: 'by_name',
                keyPath: 'name',
                options: {
                    'unique': true
                }
            }]
        },
        AnkMessages: {
            name: "messages",
            options: {'keyPath': 'id'},
            indices: []
        }
    }

    // Private constructor to prevent direct instantiation from outside
    private constructor() {}

    // Method to access the singleton instance of Database
    public static async getInstance(): Promise<Database> {
        if (!Database.instance) {
            Database.instance = new Database();
            await Database.instance.init();
        }
        return Database.instance;
    }

    // Initialize the database
    private async init(): Promise<void> {
        return new Promise((resolve, reject) => {
            const request = indexedDB.open(this.dbName, this.dbVersion);

            request.onupgradeneeded = () => {
                const db = request.result;
                
                Object.values(this.storeDefinitions).forEach(({name, options, indices}) => {
                    if (!db.objectStoreNames.contains(name)) {
                        let store = db.createObjectStore(name, options);

                        indices.forEach(({name, keyPath, options}) => {
                            store.createIndex(name, keyPath, options);
                        })
                    }
                });
            };

            request.onsuccess = () => {
                this.db = request.result;
                resolve();
            };

            request.onerror = () => {
                console.error("Database error:", request.error);
                reject(request.error);
            };
        });
    }

    public async getDb(): Promise<IDBDatabase> {
        if (!this.db) {
            await this.init();
        }
        return this.db!;
    }

    public getStoreList(): {[key: string]: string} {
        const objectList: {[key: string]: string} = {};
        Object.keys(this.storeDefinitions).forEach(key => {
            objectList[key] = this.storeDefinitions[key as keyof typeof this.storeDefinitions].name;
        });
        return objectList;
    }

    public writeObject(db: IDBDatabase, storeName: string, obj: any, key: IDBValidKey | null): Promise<IDBRequest> {
        return new Promise((resolve, reject) => {
            const transaction = db.transaction(storeName, 'readwrite');
            const store = transaction.objectStore(storeName);
            let request: IDBRequest<any>;
            if (key) {
                request = store.add(obj, key);
            } else {
                request = store.add(obj);
            }

            request.onerror = () => reject(request.error);
            request.onsuccess = () => resolve(request.result);
        });
    }

    public getObject<T>(db: IDBDatabase, storeName: string, key: IDBValidKey): Promise<T> {
        return new Promise((resolve, reject) => {
            const transaction = db.transaction(storeName, 'readonly');
            const store = transaction.objectStore(storeName);
            const request = store.get(key);

            request.onerror = () => reject(request.error);
            request.onsuccess = () => resolve(request.result);
        });
    }

    public rmObject(db: IDBDatabase, storeName: string, key: IDBValidKey): Promise<void> {
        return new Promise((resolve, reject) => {
            const transaction = db.transaction(storeName, 'readwrite');
            const store = transaction.objectStore(storeName);
            const request = store.delete(key);

            request.onerror = () => reject(request.error);
            request.onsuccess = () => resolve(request.result);
        });
    }

    public getFirstMatchWithIndex<T>(db: IDBDatabase, storeName: string, indexName: string, lookup: string): Promise<T | null> {
        return new Promise((resolve, reject) => {
            const transaction = db.transaction(storeName, 'readonly');
            const store = transaction.objectStore(storeName);
            const index = store.index(indexName);
            const request = index.openCursor(IDBKeyRange.only(lookup));

            request.onerror = () => reject(request.error);
            request.onsuccess = () => {
                const cursor = request.result;
                if (cursor) {
                    resolve(cursor.value);
                } else {
                    resolve(null)
                }
            } 
        });
    }

    public setObject(db: IDBDatabase, storeName: string, obj: any, key: string | null): Promise<IDBRequest> {
        return new Promise((resolve, reject) => {
            const transaction = db.transaction(storeName, 'readwrite');
            const store = transaction.objectStore(storeName);
            let request: IDBRequest<any>;
            if (key) {
                request = store.put(obj, key);
            } else {
                request = store.put(obj);
            }

            request.onerror = () => reject(request.error);
            request.onsuccess = () => resolve(request.result);
        });
    }

    public getAll<T>(db: IDBDatabase, storeName: string): Promise<T[]> {
        return new Promise((resolve, reject) => {
            const transaction = db.transaction(storeName, 'readonly');
            const store = transaction.objectStore(storeName);
            const request = store.getAll();

            request.onerror = () => reject(request.error);
            request.onsuccess = () => resolve(request.result);
        });
    }
}

export default Database;