import { deserializeFromBinary, serializeToBinary } from '@og/binary-struct';
import { VirtualMethodNotImplementedError } from '@og/error-utils';
import { pluralize } from 'inflection';
import fs from 'node:fs/promises';
import path from 'node:path';

/**
 * @abstract
 * @class
 * @classdesc Represents a key-value storage interface.
 */
export class BaseKeyValueStorage {
	/**
	 * Sets a value for the given class and primary key.
	 * @param {string} cls - The class identifier.
	 * @param {string} pk - The primary key.
	 * @param {ArrayBuffer} val - The value to set.
	 * @abstruct
	 * @async
	 */
	async set(cls, pk, val) {
		throw new VirtualMethodNotImplementedError();
	}

	/**
	 * Retrieves the value associated with the given class and primary key.
	 * @param {string} cls - The class identifier.
	 * @param {string} pk - The primary key.
	 * @abstruct
	 * @async
	 * @returns {Promise<ArrayBuffer|null>} - The value associated with the class and primary key, or null if not found.
	 */
	async get(cls, pk) {
		throw new VirtualMethodNotImplementedError();
	}

	/**
	 * Checks whether a value exists for the given class and primary key.
	 * @param {string} cls - The class identifier.
	 * @param {string} pk - The primary key.
	 * @abstruct
	 * @async
	 * @returns {Promise<boolean>} - True if the value exists, otherwise false.
	 */
	async has(cls, pk) {
		throw new VirtualMethodNotImplementedError();
	}

	/**
	 * Deletes the value associated with the given class and primary key.
	 * @param {string} cls - The class identifier.
	 * @param {string} pk - The primary key.
	 * @abstruct
	 * @async
	 */
	async destroy(cls, pk) {
		throw new VirtualMethodNotImplementedError();
	}

	/**
	 * Initializes or updates the class.
	 * @param {string} cls - The class identifier.
	 * @abstruct
	 * @async
	 */
	async touchClass(cls) { }
}

/**
 * Represents a key-value storage implementation using the file system.
 * @class
 * @extends {BaseKeyValueStorage}
 */
export class FileSystemKeyValueStorage extends BaseKeyValueStorage {
	/**
	 * Creates an instance of FileSystemKeyValueStorage.
	 * @param {string} root - The root directory where key-value data will be stored.
	 */
	constructor(root) {
		super();
		/** @private @type {string} */
		this.root = root;
	}

	/**
	 * Sets a value for the given class and primary key.
	 * @param {string} cls - The class identifier.
	 * @param {string} pk - The primary key.
	 * @param {ArrayBuffer} val - The value to set.
	 * @abstruct
	 */
	async set(cls, pk, val) {
		const filePath = this._getFilePath(cls, pk);
		await fs.writeFile(filePath, Buffer.from(val));
	}

	/**
	 * Retrieves the value associated with the given class and primary key.
	 * @param {string} cls - The class identifier.
	 * @param {string} pk - The primary key.
	 * @abstruct
	 * @returns {Promise<ArrayBuffer|null>} - The value associated with the class and primary key, or null if not found.
	 */
	async get(cls, pk) {
		const filepath = this._getFilePath(cls, pk);
		try {
			const data = await fs.readFile(filepath);
			return data.buffer;
		} catch (error) {
			if (error.code === 'ENOENT') { // File not found
				return null;
			} else {
				throw error;
			}
		}
	}

	/**
	 * Checks whether a value exists for the given class and primary key.
	 * @param {string} cls - The class identifier.
	 * @param {string} pk - The primary key.
	 * @abstruct
	 * @returns {Promise<boolean>} - True if the value exists, otherwise false.
	 */
	async has(cls, pk) {
		const filepath = this._getFilePath(cls, pk);
		try {
			await fs.access(filepath);
			return true;
		} catch {
			return false;
		}
	}

	/**
	 * Deletes the value associated with the given class and primary key.
	 * @param {string} cls - The class identifier.
	 * @param {string} pk - The primary key.
	 * @abstruct
	 */
	async destroy(cls, pk) {
		const filepath = this._getFilePath(cls, pk);
		await fs.unlink(filepath);
	}

	/**
	 * Initializes or updates the class by creating a folder for it if it doesn't exist.
	 * @param {string} cls - The class identifier.
	 * @abstruct
	 */
	async touchClass(cls) {
		const cls_dir = path.join(this.root, cls);
		await fs.mkdir(cls_dir, { recursive: true });
	}

	/**
	 * Constructs the file path for a given class and primary key.
	 * @private
	 * @param {string} cls - The class identifier.
	 * @param {string} pk - The primary key.
	 * @returns {string} - The file path.
	 */
	_getFilePath(cls, pk) {
		const cls_dir = path.join(this.root, cls);
		return path.join(cls_dir, pk);
	}
}


/**
 * Abstract base class for all models.
 * @abstract
 * @class
 */
export class BaseModel {
	/**
	 * Gets the primary key of the model.
	 * @abstract
	 * @returns {string|null} The primary key value or null if not applicable.
	 */
	get pk() {
		throw new VirtualMethodNotImplementedError();
	}

	/**
	 * Asynchronously saves the current model instance to the key-value storage.
	 * @throws {Error} - Throws an error if the primary key is not set.
	 * @returns {Promise<void>}
	 * @abstract
	 */
	async save() {
		throw new VirtualMethodNotImplementedError();
	}

	/**
	 * Asynchronously destroys the current model instance in the key-value storage.
	 * @throws {Error} - Throws an error if the primary key is not set.
	 * @returns {Promise<void>}
	 * @abstract
	 */
	async destroy() {
		throw new VirtualMethodNotImplementedError();
	}

	/**
	 * Asynchronously checks if the current model instance can be created in the key-value storage.
	 * @returns {Promise<boolean>} - True if the model can be created, false otherwise.
	 * @abstract
	 */
	async canCreate() {
		throw new VirtualMethodNotImplementedError();
	}

	/**
	 * Asynchronously loads a model instance from the key-value storage based on its primary key.
	 * @param {string} pk - The primary key of the model to load.
	 * @returns {Promise<*>} The loaded model instance or null if not found.
	 * @abstract
	 */
	static async load(pk) {
		throw new VirtualMethodNotImplementedError();
	}
}

/**
 * A mixin function that creates a model class with basic CRUD operations and storage methods.
 *
 * @param {string} name - The name of the model.
 * @param {BaseKeyValueStorage} kv - The key-value storage for data persistence.
 * @returns {Function} - The generated model class.
 */
export function Model(name, kv) {
	const cls = pluralize(name);

	/**
	 * @class
	 * @extends BaseModel
	 */
	return class extends BaseModel {
		/**
		 * Asynchronously saves the current model instance to the key-value storage.
		 * @throws {Error} - Throws an error if the primary key is not set.
		 * @returns {Promise<void>}
		 */
		async save() {
			const pk = this.pk;
			if (pk == null) {
				throw new PrimaryKeyNotSetError();
			}

			const buf = serializeToBinary(this, this.constructor);
			await kv.set(cls, pk, buf);
		}

		/**
		 * Asynchronously destroys the current model instance in the key-value storage.
		 * @throws {Error} - Throws an error if the primary key is not set.
		 * @returns {Promise<void>}
		 */
		async destroy() {
			const pk = this.pk;
			if (pk == null) {
				throw new PrimaryKeyNotSetError();
			}

			await kv.destroy(cls, pk);
		}

		/**
		 * Asynchronously checks if the current model instance can be created in the key-value storage.
		 * @returns {Promise<boolean>} - True if the model can be created, false otherwise.
		 */
		async canCreate() {
			const pk = this.pk;
			if (pk == null) {
				return false;
			}

			return !(await kv.has(cls, pk));
		}

		/**
		 * Asynchronously loads a model instance from the key-value storage based on its primary key.
		 * @param {string} pk - The primary key of the model to load.
		 * @returns {Promise<*>} - The loaded model instance or null if not found.
		 */
		static async load(pk) {
			const buf = await kv.get(cls, pk);
			if (buf == null) {
				return null;
			}

			return deserializeFromBinary(new DataView(buf), this);
		}

		/**
		 * Initializes the key-value storage for the current class.
		 */
		static {
			kv.touchClass(cls);
		}
	};
}

/**
 * Represents an error that is thrown when the primary key of an object is not set.
 * @class
 * @extends {Error}
 */
class PrimaryKeyNotSetError extends Error {
	/**
	 * Constructs a new PrimaryKeyNotSetError instance with a default error message.
	 * @constructor
	 */
	constructor() {
		super('pk() returns null');
	}
};