[Lemon] / mod.js

// 🍋🏷 Lemon ∷ mod.js
// ====================================================================
//
// Copyright © 2022 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 { xhtmlNamespace } from "./names.js";

const {
  /**
   * Create a D·O·M Element from a tagged template.
   *
   * Usage :—
   *
   * ```js
   * Lemon("elementName", "namespace")`content`;
   * // or
   * Lemon("elementName", "namespace")({ attr: "value" })`content`;
   * ```
   *
   * Content may, via substitutions, include additional nodes. As a
   * convenience, if the namespace is not defined, it is the X·H·T·M·L
   * namespace. As a convenience, `Lemon.elementName` is a shorthand
   * for `Lemon("element-name").` As a convenience, substitutions may
   * take the form of an array of nodes.
   *
   * By default, `globalThis.document` is used as the owner document
   * for new nodes. To pick a different document, supply a different
   * `document` on the `this` value when calling. You can use `bind` to
   * simplify this in some cases :—
   *
   * ```js
   * const MyLemon = Lemon.bind({ document });
   * MyLemon.p`words`; // same as Lemon.call({ document }, "p")`words`
   * ```
   */
  Lemon,
} = (() => {
  const lemonProxyHandler = Object.assign(
    Object.create(null),
    {
      /** If `P` doesn’t exist on `O`, calls `O` with `P` instead. */
      get(O, P, Receiver) {
        if (typeof P != "string" || Reflect.has(O, P)) {
          return Reflect.get(O, P, Receiver);
        } else if (typeof O == "function") {
          return O([...function* () {
            for (const character of P) {
              yield /[A-Z]/u.test(character)
                ? `-${character.toLowerCase()}`
                : character;
            }
          }()].join(""));
        } else {
          return undefined;
        }
      },
    },
  );
  return {
    Lemon: new Proxy(
      Object.defineProperties(
        Object.setPrototypeOf(
          function (name, namespace = xhtmlNamespace) {
            return Object.setPrototypeOf(
              nodeTagBuilder.bind({
                context: this ?? globalThis,
                name: `${name}`,
                namespace: `${namespace}`,
              }),
              Lemon.prototype,
            );
          },
          Function,
        ),
        {
          name: { value: "Lemon" },
          prototype: { value: Object.create(Function.prototype) },
          bind: {
            value: Object.defineProperties(
              function (thisArg, ...args) {
                return new Proxy(
                  Function.prototype.bind.call(
                    this,
                    thisArg,
                    ...args,
                  ),
                  lemonProxyHandler,
                );
              },
              { name: { value: "bind" } },
            ),
            writable: true,
            enumerable: false,
            configurable: true,
          },
        },
      ),
      lemonProxyHandler,
    ),
  };
})();
export default Lemon;

/**
 * Creates an Element with `name`, `namespace`, and `attributes` drawn
 * from this object and content determined by the provided strings and
 * expressions.
 */
const createNode = function (strings, ...expressions) {
  const { raw } = strings;
  const { context, name, namespace, attributes } = this;
  const document = context.document ?? globalThis.document;
  const result = document.createElementNS(namespace, name);
  for (const [attName, attValue] of Object.entries(attributes)) {
    result.setAttribute(attName, `${attValue}`);
  }
  const maxIndex = Math.max(raw.length, expressions.length);
  for (let index = 0; index < maxIndex; ++index) {
    result.append(
      ...nodesFromExpression.call(context, raw[index]),
      ...nodesFromExpression.call(context, expressions[index]),
    );
  }
  result.normalize();
  return result;
};

/**
 * Creates a new template tag builder with the provided attributes for
 * for making Element’s with the `name` specified on this.
 *
 * As a shorthand, you can also use this function as a template tag
 * itself, in which case it is treated as though its attributes were
 * empty.
 */
const nodeTagBuilder = function (attrsOrStrings, ...expressions) {
  const { context, name, namespace } = this;
  if (
    Array.isArray(attrsOrStrings) && "raw" in attrsOrStrings &&
    Array.isArray(attrsOrStrings.raw)
  ) {
    // The first argument is usable as a template string.
    return createNode.call(
      { context, name, namespace, attributes: {} },
      attrsOrStrings,
      ...expressions,
    );
  } else {
    // The first argument is not a template string.
    return createNode.bind({
      context,
      name,
      namespace,
      attributes: { ...Object(attrsOrStrings) },
    });
  }
};

/** Processes the provided expression and yields Nodes. */
const nodesFromExpression = function* (expression) {
  const document = this.document ?? globalThis.document;
  const nodePrototype = Object.getPrototypeOf(
    Object.getPrototypeOf(document.createDocumentFragment()),
  );
  if (expression == null) {
    // The expression is nullish.
    /* do nothing */
  } else {
    // The expression is not nullish.
    const expressionIsNode = (() => {
      // Due to how D·O·M‐to‐Ecmascript bindings work, attempting to
      // call a D·O·M method or accessor on a value which is not
      // actually of the appropriate type will throw.
      //
      // This I·I·F·E uses that fact to test whether the provided
      // expression is already a Node.
      try { // throws unless this is a Node
        return !!Reflect.get(nodePrototype, "nodeType", expression);
      } catch {
        return false;
      }
    })();
    if (expressionIsNode) {
      // The expression is already a `Node`.
      yield expression;
    } else if (Array.isArray(expression)) {
      // The expression is an array of expressions.
      for (const subexpression of expression) {
        yield* nodesFromExpression.call(this, subexpression);
      }
    } else {
      // The expression is something else.
      yield document.createTextNode(`${expression}`);
    }
  }
};