/**
 * Read-only signal wrappers.
 */

import type { Signal } from './core';

const READONLY_SIGNAL_BRAND: unique symbol = Symbol('bquery.readonlySignal');

/** @internal */
type ReadonlySignalWrapper<T> = ReadonlySignal<T> & {
  readonly [READONLY_SIGNAL_BRAND]: true;
};

/**
 * A readonly wrapper around a signal that prevents writes.
 * Provides read-only access to a signal's value while maintaining reactivity.
 *
 * @template T - The type of the wrapped value
 */
export interface ReadonlySignal<T> {
  /** Gets the current value with dependency tracking. */
  readonly value: T;
  /** Gets the current value without dependency tracking. */
  peek(): T;
}

/**
 * Determines whether a value is a bQuery readonly signal wrapper.
 *
 * @internal
 */
export const isReadonlySignal = <T>(value: unknown): value is ReturnType<typeof readonly<T>> => {
  return (
    typeof value === 'object' &&
    value !== null &&
    Object.prototype.hasOwnProperty.call(value, READONLY_SIGNAL_BRAND)
  );
};

/**
 * Creates a read-only view of a signal.
 * Useful for exposing reactive state without allowing modifications.
 *
 * @template T - The type of the signal value
 * @param sig - The signal to wrap
 * @returns A readonly signal wrapper
 */
export const readonly = <T>(sig: Signal<T>): ReadonlySignalWrapper<T> =>
  Object.defineProperties(
    {},
    {
      value: {
        get(): T {
          return sig.value;
        },
        enumerable: true,
      },
      peek: {
        value(): T {
          return sig.peek();
        },
        enumerable: true,
      },
      [READONLY_SIGNAL_BRAND]: {
        value: true,
        enumerable: false,
        configurable: false,
        writable: false,
      },
    }
  ) as ReadonlySignalWrapper<T>;

/**
 * Branded readonly wrapper type produced by {@link readonly}.
 *
 * Useful for APIs that compose additional behavior on top of a readonly signal
 * without widening to arbitrary structural `{ value, peek }` objects.
 */
export type ReadonlySignalHandle<T> = ReturnType<typeof readonly<T>>;