import type { Context } from "../context.js";
import type { TypeValue } from "../types.js";
import { NoExplicitTypeError } from "../errors/no-explicit-type.js";
import { ReflectMetadataMissingError } from "../errors/reflect-metadata-missing.js";

/**
 * Asserts that `reflect-metadata` exists.
 */
export function assertReflectMetadata() {
  if (typeof Reflect !== "object" || typeof Reflect.getMetadata !== "function") {
    throw new ReflectMetadataMissingError();
  }
}

export type MetadataKey = "design:type" | "design:returntype" | "design:paramtypes";

export type FindTypeOptions = {
  context: Context;
  metadataKey: MetadataKey;
  prototype: Object;
  propertyKey: string;
};

/**
 * Returns the type inferred from class member.
 */
export function findType({ metadataKey, prototype, propertyKey }: FindTypeOptions) {
  assertReflectMetadata();
  const reflectedType: Function | undefined = Reflect.getMetadata(metadataKey, prototype, propertyKey);

  if (!reflectedType) {
    throw new NoExplicitTypeError(prototype.constructor.name, propertyKey);
  }

  return reflectedType;
}

const IS_THUNK_REG = /^.+=>[\w\d\s\t\n\r]*/;

/**
 * Asserts that a value is a thunk value.
 *
 * @example isThunk('hello') === false
 * @example isThunk(() => 'hello') === true
 */
export function isThunk(value: any): boolean {
  if (typeof value !== "function") {
    return false;
  }

  return Boolean(IS_THUNK_REG.exec(value));
}