import { defineMetadata, getMetadata } from "muddle/metadata";

export const HYDRATE_METADATA_KEY = "muddle:orm:hydrated";

export interface HydrateOptions<Value = any> {
	/** Computes the value from the raw database row. */
	decode?: (row: Record<string, unknown>) => Value;
	/** Column the value is derived from, handed to `decode` as second argument. */
	column?: string;
}

export interface HydrateDescriptor {
	property: string;
	options: HydrateOptions;
}

/** Declares a hydrated (computed) property. */
export function Hydrate<Value = any>(
	options: HydrateOptions<Value> = {},
): PropertyDecorator {
	return (target, propertyKey) => {
		const constructor = target.constructor as object;
		const hydrated = getHydratedProperties(constructor);
		hydrated.set(String(propertyKey), {
			property: String(propertyKey),
			options: options as HydrateOptions,
		});
	};
}

/** Reads the hydrated properties declared on a model class. */
export function getHydratedProperties(
	target: object,
): Map<string, HydrateDescriptor> {
	const existing = getMetadata(HYDRATE_METADATA_KEY, target) as
		| Map<string, HydrateDescriptor>
		| undefined;
	if (existing) return existing;
	const hydrated = new Map<string, HydrateDescriptor>();
	defineMetadata(HYDRATE_METADATA_KEY, hydrated, target);
	return hydrated;
}