Define names for LazyLoader getters & setters

[Pisces] / object.js

// ♓🌟 Piscēs ∷ object.js
// ====================================================================
//
// Copyright © 2022–2023 Lady [@ Lady’s Computer].
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at <https://mozilla.org/MPL/2.0/>.

import { bind, call, toFunctionName } from "./function.js";
import { ITERATOR, SPECIES, toPrimitive, type } from "./value.js";

/**
 * An object whose properties are lazy‐loaded from the methods on the
 * own properties of the provided object.
 *
 * This is useful when you are looking to reference properties on
 * objects which, due to module dependency graphs, cannot be guaranteed
 * to have been initialized yet.
 *
 * The resulting properties will have the same attributes (regarding
 * configurability, enumerability, and writability) as the
 * corresponding properties on the methods object. If a property is
 * marked as writable, the method will never be called if it is set
 * before it is gotten. By necessity, the resulting properties are all
 * configurable before they are accessed for the first time.
 *
 * Methods will be called with the resulting object as their this
 * value.
 *
 * `LazyLoader` objects have the same prototype as the passed methods
 * object.
 */
export class LazyLoader extends null {
  /**
   * Constructs a new `LazyLoader` object.
   *
   * ☡ This function throws if the provided value is not an object.
   */
  constructor(loadMethods) {
    if (type(loadMethods) !== "object") {
      // The provided value is not an object; throw an error.
      throw new TypeError(
        `Piscēs: Cannot construct LazyLoader: Provided argument is not an object: ${loadMethods}.`,
      );
    } else {
      // The provided value is an object; process it and build the
      // result.
      const result = objectCreate(getPrototype(loadMethods));
      const methodKeys = getOwnPropertyKeys(loadMethods);
      for (let index = 0; index < methodKeys.length; ++index) {
        // Iterate over the property keys of the provided object and
        // define getters and setters appropriately on the result.
        const methodKey = methodKeys[index];
        const { configurable, enumerable, writable } =
          getOwnPropertyDescriptor(loadMethods, methodKey);
        defineOwnProperty(result, methodKey, {
          configurable: true,
          enumerable,
          get: defineOwnProperty(
            () => {
              const value = call(loadMethods[methodKey], result, []);
              defineOwnProperty(result, methodKey, {
                configurable,
                enumerable,
                value,
                writable,
              });
              return value;
            },
            "name",
            { value: toFunctionName(methodKey, "get") },
          ),
          set: writable
            ? defineOwnProperty(
              ($) =>
                defineOwnProperty(result, methodKey, {
                  configurable,
                  enumerable,
                  value: $,
                  writable,
                }),
              "name",
              { value: toFunctionName(methodKey, "set") },
            )
            : void {},
        });
      }
      return result;
    }
  }
}

/**
 * A property descriptor object.
 *
 * Actually constructing a property descriptor object using this class
 * is only necessary if you need strict guarantees about the types of
 * its properties; the resulting object is proxied to ensure the types
 * match what one would expect from composing FromPropertyDescriptor
 * and ToPropertyDescriptor in the Ecmascript specification.
 *
 * Otherwise, the instance properties and methods are generic.
 */
export const { PropertyDescriptor } = (() => {
  class PropertyDescriptor extends null {
    /**
     * Constructs a new property descriptor object from the provided
     * object.
     *
     * The resulting object is proxied to enforce types (for example,
     * its `.enumerable` property, if defined, will always be a
     * boolean).
     */
    constructor(O) {
      if (type(O) !== "object") {
        // The provided value is not an object.
        throw new TypeError(
          `Piscēs: Cannot convert primitive to property descriptor: ${O}.`,
        );
      } else {
        // The provided value is an object.
        const desc = objectCreate(propertyDescriptorPrototype);
        if ("enumerable" in O) {
          // An enumerable property is specified.
          desc.enumerable = !!O.enumerable;
        } else {
          // An enumerable property is not specified.
          /* do nothing */
        }
        if ("configurable" in O) {
          // A configurable property is specified.
          desc.configurable = !!O.configurable;
        } else {
          // A configurable property is not specified.
          /* do nothing */
        }
        if ("value" in O) {
          // A value property is specified.
          desc.value = O.value;
        } else {
          // A value property is not specified.
          /* do nothing */
        }
        if ("writable" in O) {
          // A writable property is specified.
          desc.writable = !!O.writable;
        } else {
          // A writable property is not specified.
          /* do nothing */
        }
        if ("get" in O) {
          // A get property is specified.
          const getter = O.get;
          if (getter !== undefined && typeof getter !== "function") {
            // The getter is not callable.
            throw new TypeError("Piscēs: Getters must be callable.");
          } else {
            // The getter is callable.
            desc.get = getter;
          }
        } else {
          // A get property is not specified.
          /* do nothing */
        }
        if ("set" in O) {
          // A set property is specified.
          const setter = O.set;
          if (setter !== undefined && typeof setter !== "function") {
            // The setter is not callable.
            throw new TypeError("Piscēs: Setters must be callable.");
          } else {
            // The setter is callable.
            desc.set = setter;
          }
        } else {
          // A set property is not specified.
          /* do nothing */
        }
        if (
          ("get" in desc || "set" in desc) &&
          ("value" in desc || "writable" in desc)
        ) {
          // Both accessor and data attributes have been defined.
          throw new TypeError(
            "Piscēs: Property descriptors cannot specify both accessor and data attributes.",
          );
        } else {
          // The property descriptor is valid.
          return new Proxy(desc, propertyDescriptorProxyHandler);
        }
      }
    }

    /**
     * Completes this property descriptor by setting missing values to
     * their defaults.
     *
     * This method modifies this object and returns undefined.
     */
    complete() {
      if (this !== undefined && !("get" in this || "set" in this)) {
        // This is a generic or data descriptor.
        if (!("value" in this)) {
          // `value` is not defined on this.
          this.value = undefined;
        } else {
          // `value` is already defined on this.
          /* do nothing */
        }
        if (!("writable" in this)) {
          // `writable` is not defined on this.
          this.writable = false;
        } else {
          // `writable` is already defined on this.
          /* do nothing */
        }
      } else {
        // This is not a generic or data descriptor.
        if (!("get" in this)) {
          // `get` is not defined on this.
          this.get = undefined;
        } else {
          // `get` is already defined on this.
          /* do nothing */
        }
        if (!("set" in this)) {
          // `set` is not defined on this.
          this.set = undefined;
        } else {
          // `set` is already defined on this.
          /* do nothing */
        }
      }
      if (!("enumerable" in this)) {
        // `enumerable` is not defined on this.
        this.enumerable = false;
      } else {
        // `enumerable` is already defined on this.
        /* do nothing */
      }
      if (!("configurable" in this)) {
        // `configurable` is not defined on this.
        this.configurable = false;
      } else {
        // `configurable` is already defined on this.
        /* do nothing */
      }
    }

    /** Gets whether this is an accessor descrtiptor. */
    get isAccessorDescriptor() {
      return this !== undefined && ("get" in this || "set" in this);
    }

    /** Gets whether this is a data descrtiptor. */
    get isDataDescriptor() {
      return this !== undefined &&
        ("value" in this || "writable" in this);
    }

    /** Gets whether this is a fully‐populated property descriptor. */
    get isFullyPopulated() {
      return this !== undefined &&
        ("value" in this && "writable" in this ||
          "get" in this && "set" in this) &&
        "enumerable" in this && "configurable" in this;
    }

    /**
     * Gets whether this is a generic (not accessor or data)
     * descrtiptor.
     */
    get isGenericDescriptor() {
      return this !== undefined &&
        !("get" in this || "set" in this || "value" in this ||
          "writable" in this);
    }
  }

  const coercePropertyDescriptorValue = (P, V) => {
    switch (P) {
      case "configurable":
      case "enumerable":
      case "writable":
        return !!V;
      case "value":
        return V;
      case "get":
        if (V !== undefined && typeof V !== "function") {
          throw new TypeError(
            "Piscēs: Getters must be callable.",
          );
        } else {
          return V;
        }
      case "set":
        if (V !== undefined && typeof V !== "function") {
          throw new TypeError(
            "Piscēs: Setters must be callable.",
          );
        } else {
          return V;
        }
      default:
        return V;
    }
  };

  const {
    prototype: propertyDescriptorPrototype,
  } = PropertyDescriptor;

  const propertyDescriptorProxyHandler = Object.assign(
    Object.create(null),
    {
      defineProperty(O, P, Desc) {
        if (
          P === "configurable" || P === "enumerable" ||
          P === "writable" || P === "value" ||
          P === "get" || P === "set"
        ) {
          // P is a property descriptor attribute.
          const desc = new PropertyDescriptor(Desc);
          if ("get" in desc || "set" in desc) {
            // Desc is an accessor property descriptor.
            throw new TypeError(
              "Piscēs: Property descriptor attributes must be data properties.",
            );
          } else if ("value" in desc || !(P in O)) {
            // Desc has a value or P does not already exist on O.
            desc.value = coercePropertyDescriptorValue(P, desc.value);
          } else {
            // Desc is not an accessor property descriptor and has no
            // value.
            /* do nothing */
          }
          const isAccessorDescriptor = "get" === P || "set" === P ||
            "get" in O || "set" in O;
          const isDataDescriptor = "value" === P || "writable" === P ||
            "value" in O || "writable" in O;
          if (isAccessorDescriptor && isDataDescriptor) {
            // Both accessor and data attributes will be present on O
            // after defining P.
            throw new TypeError(
              "Piscēs: Property descriptors cannot specify both accessor and data attributes.",
            );
          } else {
            // P can be safely defined on O.
            return defineOwnProperty(O, P, desc);
          }
        } else {
          // P is not a property descriptor attribute.
          return defineOwnProperty(O, P, Desc);
        }
      },
      set(O, P, V, Receiver) {
        if (
          P === "configurable" || P === "enumerable" ||
          P === "writable" || P === "value" ||
          P === "get" || P === "set"
        ) {
          // P is a property descriptor attribute.
          const newValue = coercePropertyDescriptorValue(P, V);
          const isAccessorDescriptor = "get" === P || "set" === P ||
            "get" in O || "set" in O;
          const isDataDescriptor = "value" === P || "writable" === P ||
            "value" in O || "writable" in O;
          if (isAccessorDescriptor && isDataDescriptor) {
            // Both accessor and data attributes will be present on O
            // after defining P.
            throw new TypeError(
              "Piscēs: Property descriptors cannot specify both accessor and data attributes.",
            );
          } else {
            // P can be safely defined on O.
            //
            // ☡ Receiver will be the *proxied* object, so passing it
            // through to setPropertyValue here would produce an
            // infinite loop.
            //
            // ☡ This has implications on objects with a proxied
            // PropertyDescriptor in their prototype.
            return setPropertyValue(O, P, newValue, O);
          }
        } else {
          return setPropertyValue(O, P, V, Receiver);
        }
      },
      setPrototypeOf(O, V) {
        if (V !== propertyDescriptorPrototype) {
          // V is not the property descriptor prototype.
          return false;
        } else {
          // V is the property descriptor prototype.
          return setPrototype(O, V);
        }
      },
    },
  );

  return { PropertyDescriptor };
})();

export const {
  /**
   * Defines own properties on the provided object using the
   * descriptors on the enumerable own properties of the provided
   * additional objects.
   *
   * ※ This differs from `Object.defineProperties` in that it can take
   * multiple source objects.
   */
  defineOwnProperties,
} = (() => {
  const { defineProperties } = Object;
  const { forEach: arrayForEach } = Array.prototype;
  return {
    defineOwnProperties: (O, ...sources) => {
      call(
        arrayForEach,
        sources,
        [(source) => defineProperties(O, source)],
      );
      return O;
    },
  };
})();

export const {
  /**
   * Defines an own property on the provided object on the provided
   * property key using the provided property descriptor.
   *
   * ※ This is an alias for `Object.defineProperty`.
   */
  defineProperty: defineOwnProperty,

  /**
   * Marks the provided object as non·extensible and marks all its
   * properties as nonconfigurable and (if data properties)
   * nonwritable, and returns the object.
   *
   * ※ This is an alias for `Object.freeze`.
   */
  freeze,

  /**
   * Returns the property descriptor for the own property with the
   * provided property key on the provided object, or null if none
   * exists.
   *
   * ※ This is an alias for `Object.getOwnPropertyDescriptor`.
   */
  getOwnPropertyDescriptor,

  /**
   * Returns the property descriptors for the own properties on the
   * provided object.
   *
   * ※ This is an alias for `Object.getOwnPropertyDescriptors`.
   */
  getOwnPropertyDescriptors,

  /**
   * Returns an array of string‐valued own property keys on the
   * provided object.
   *
   * ☡ This includes both enumerable and non·enumerable properties.
   *
   * ※ This is an alias for `Object.getOwnPropertyNames`.
   */
  getOwnPropertyNames: getOwnPropertyStrings,

  /**
   * Returns an array of symbol‐valued own property keys on the
   * provided object.
   *
   * ☡ This includes both enumerable and non·enumerable properties.
   *
   * ※ This is an alias for `Object.getOwnPropertySymbols`.
   */
  getOwnPropertySymbols,

  /**
   * Returns the prototype of the provided object.
   *
   * ※ This is an alias for `Object.getPrototypeOf`.
   */
  getPrototypeOf: getPrototype,

  /**
   * Returns whether the provided object has an own property with the
   * provided property key.
   *
   * ※ This is an alias for `Object.hasOwn`.
   */
  hasOwn: hasOwnProperty,

  /**
   * Returns whether the provided object is extensible.
   *
   * ※ This is an alias for `Object.isExtensible`.
   */
  isExtensible: isExtensibleObject,

  /**
   * Returns whether the provided object is frozen.
   *
   * ※ This is an alias for `Object.isFrozen`.
   */
  isFrozen: isFrozenObject,

  /**
   * Returns whether the provided object is sealed.
   *
   * ※ This is an alias for `Object.isSealed`.
   */
  isSealed: isSealedObject,

  /**
   * Returns an array of key~value pairs for the enumerable,
   * string‐valued property keys on the provided object.
   *
   * ※ This is an alias for `Object.entries`.
   */
  entries: namedEntries,

  /**
   * Returns an array of the enumerable, string‐valued property keys on
   * the provided object.
   *
   * ※ This is an alias for `Object.keys`.
   */
  keys: namedKeys,

  /**
   * Returns an array of property values for the enumerable,
   * string‐valued property keys on the provided object.
   *
   * ※ This is an alias for `Object.values`.
   */
  values: namedValues,

  /**
   * Returns a new object with the provided prototype and property
   * descriptors.
   *
   * ※ This is an alias for `Object.create`.
   */
  create: objectCreate,

  /**
   * Returns a new object with the provided property keys and values.
   *
   * ※ This is an alias for `Object.fromEntries`.
   */
  fromEntries: objectFromEntries,

  /**
   * Marks the provided object as non·extensible, and returns the
   * object.
   *
   * ※ This is an alias for `Object.preventExtensions`.
   */
  preventExtensions,

  /**
   * Marks the provided object as non·extensible and marks all its
   * properties as nonconfigurable, and returns the object.
   *
   * ※ This is an alias for `Object.seal`.
   */
  seal,

  /**
   * Sets the values of the enumerable own properties of the provided
   * additional objects on the provided object.
   *
   * ※ This is an alias for `Object.assign`.
   */
  assign: setPropertyValues,

  /**
   * Sets the prototype of the provided object to the provided value
   * and returns the object.
   *
   * ※ This is an alias for `Object.setPrototypeOf`.
   */
  setPrototypeOf: setPrototype,
} = Object;

export const {
  /**
   * Removes the provided property key from the provided object and
   * returns the object.
   *
   * ※ This function differs from `Reflect.deleteProperty` and the
   * `delete` operator in that it throws if the deletion is
   * unsuccessful.
   *
   * ☡ This function throws if the first argument is not an object.
   */
  deleteOwnProperty,

  /**
   * Returns an array of property keys on the provided object.
   *
   * ※ This is effectively an alias for `Reflect.ownKeys`, except that
   * it does not require that the argument be an object.
   */
  getOwnPropertyKeys,

  /**
   * Returns the value of the provided property key on the provided
   * object.
   *
   * ※ This is effectively an alias for `Reflect.get`, except that it
   * does not require that the argument be an object.
   */
  getPropertyValue,

  /**
   * Returns whether the provided property key exists on the provided
   * object.
   *
   * ※ This is effectively an alias for `Reflect.has`, except that it
   * does not require that the argument be an object.
   *
   * ※ This includes properties present on the prototype chain.
   */
  hasProperty,

  /**
   * Sets the provided property key to the provided value on the
   * provided object and returns the object.
   *
   * ※ This function differs from `Reflect.set` in that it throws if
   * the setting is unsuccessful.
   *
   * ☡ This function throws if the first argument is not an object.
   */
  setPropertyValue,
} = (() => {
  const { deleteProperty, get, has, ownKeys, set } = Reflect;

  return {
    deleteOwnProperty: (O, P) => {
      if (type(O) !== "object") {
        throw new TypeError(
          `Piscēs: Tried to set property but provided value was not an object: ${V}`,
        );
      } else if (!deleteProperty(O, P)) {
        throw new TypeError(
          `Piscēs: Tried to delete property from object but [[Delete]] returned false: ${P}`,
        );
      } else {
        return O;
      }
    },
    getOwnPropertyKeys: (O) => ownKeys(toObject(O)),
    getPropertyValue: (O, P, Receiver = O) =>
      get(toObject(O), P, Receiver),
    hasProperty: (O, P) => has(toObject(O), P),
    setPropertyValue: (O, P, V, Receiver = O) => {
      if (type(O) !== "object") {
        throw new TypeError(
          `Piscēs: Tried to set property but provided value was not an object: ${V}`,
        );
      } else if (!set(O, P, V, Receiver)) {
        throw new TypeError(
          `Piscēs: Tried to set property on object but [[Set]] returned false: ${P}`,
        );
      } else {
        return O;
      }
    },
  };
})();

export const {
  /**
   * Returns a new frozen shallow copy of the enumerable own properties
   * of the provided object, according to the following rules :—
   *
   * - For data properties, create a nonconfigurable, nonwritable
   *   property with the same value.
   *
   * - For accessor properties, create a nonconfigurable accessor
   *   property with the same getter *and* setter.
   *
   * The prototype for the resulting object will be taken from the
   * `.prototype` property of the provided constructor, or the
   * `.prototype` of the `.constructor` of the provided object if the
   * provided constructor is undefined. If the used constructor has a
   * nonnullish `.[Symbol.species]`, that will be used instead. If the
   * used constructor or species is nullish or does not have a
   * `.prototype` property, the prototype is set to null.
   *
   * ※ The prototype of the provided object itself is ignored.
   */
  frozenCopy,
} = (() => {
  const {
    next: generatorIteratorNext,
  } = getPrototype(function* () {}.prototype);
  const propertyDescriptorEntryIterablePrototype = {
    [ITERATOR]() {
      return {
        next: bind(generatorIteratorNext, this.generator(), []),
      };
    },
  };
  return {
    frozenCopy: (O, constructor = O?.constructor) => {
      if (O == null) {
        // O is null or undefined.
        throw new TypeError(
          "Piscēs: Cannot copy properties of null or undefined.",
        );
      } else {
        // O is not null or undefined.
        //
        // (If not provided, the constructor will be the value of
        // getting the `.constructor` property of O.)
        const species = constructor?.[SPECIES] ?? constructor;
        return preventExtensions(
          objectCreate(
            species == null || !("prototype" in species)
              ? null
              : species.prototype,
            objectFromEntries(
              objectCreate(
                propertyDescriptorEntryIterablePrototype,
                {
                  generator: {
                    value: function* () {
                      const ownPropertyKeys = getOwnPropertyKeys(O);
                      for (
                        let i = 0;
                        i < ownPropertyKeys.length;
                        ++i
                      ) {
                        const P = ownPropertyKeys[i];
                        const Desc = getOwnPropertyDescriptor(O, P);
                        if (Desc.enumerable) {
                          // P is an enumerable property.
                          yield [
                            P,
                            "get" in Desc || "set" in Desc
                              ? {
                                configurable: false,
                                enumerable: true,
                                get: Desc.get,
                                set: Desc.set,
                              }
                              : {
                                configurable: false,
                                enumerable: true,
                                value: Desc.value,
                                writable: false,
                              },
                          ];
                        } else {
                          // P is not an enumerable property.
                          /* do nothing */
                        }
                      }
                    },
                  },
                },
              ),
            ),
          ),
        );
      }
    },
  };
})();

/**
 * Returns the function on the provided value at the provided property
 * key.
 *
 * ☡ This function throws if the provided property key does not have an
 * associated value which is callable.
 */
export const getMethod = (V, P) => {
  const func = getPropertyValue(V, P);
  if (func == null) {
    return undefined;
  } else if (typeof func !== "function") {
    throw new TypeError(`Piscēs: Method not callable: ${P}`);
  } else {
    return func;
  }
};

/**
 * Returns the provided value converted to an object.
 *
 * Existing objects are returned with no modification.
 *
 * ☡ This function throws if its argument is null or undefined.
 */
export const { toObject } = (() => {
  const makeObject = Object;
  return {
    toObject: ($) => {
      if ($ == null) {
        throw new TypeError(
          `Piscēs: Cannot convert ${$} into an object.`,
        );
      } else {
        return makeObject($);
      }
    },
  };
})();

/**
 * Returns the property key (symbol or string) corresponding to the
 * provided value.
 */
export const toPropertyKey = ($) => {
  const key = toPrimitive($, "string");
  return typeof key == "symbol" ? key : `${key}`;
};