@metalsmith/default-values/lib/index.js

A metalsmith plugin for setting default values to file metadata.

import { Buffer } from 'buffer';
import get from 'dlv';
import { dset } from 'dset';

/**
 * Sets defaults for object values
 * @param {Array<Array<*>>} defaults
 * @param {'keep'|'overwrite'} strategy
 * @return {import('.').DefaultSetter} Takes an object and sets defaults
 */
function set_defaults(defaults, strategy) {
  return (item, context) => {
    const delta = {};
    defaults.forEach(([key, defaultValue]) => {
      const value = get(item, key);
      if (strategy === 'overwrite' || value === void 0 || value === null || Buffer.isBuffer(value) && value.toString().trim().length === 0) {
        if (typeof defaultValue === 'function') defaultValue = defaultValue(item, context);
        if (Buffer.isBuffer(value) && !Buffer.isBuffer(defaultValue)) defaultValue = Buffer.from(defaultValue);
        dset(item, key, defaultValue);
        dset(delta, key, defaultValue);
      }
    });
    return delta;
  };
}

/**
 * @callback DefaultSetter
 * @param {import('metalsmith').File} file
 * @param {Object<string, *>} metadata
 */

/**
 * @typedef {Object} DefaultsSet
 * @property {string|string[]} [pattern="**"] 1 or more glob patterns to match files. Defaults to `'**'` (all).
 * @property {Object<string, *>} [defaults={}] an object whose keys will be set as file metadata keys
 * @property {'keep'|'overwrite'} [strategy="keep"] Strategy to handle setting defaults to keys that are aleady defined. Defaults to `'keep'`
 */

/** @type {DefaultsSet} */
const defaultDefaultsSet = {
  defaults: {},
  strategy: 'keep',
  pattern: '**'
};

/**
 * Set `defaults` to file metadata matching `pattern`'s.
 *
 * @param  {DefaultsSet|DefaultsSet[]} options an array of defaults sets to add to files matched by pattern
 * @return {import('metalsmith').Plugin}
 * 
 * @example
 * metalsmith.use(defaultValues({
    pattern: 'posts/*.md',
    defaults: {
      layout: 'post.hbs',
      draft: false,
      date(post) {
        return post.stats.ctime
      }
    }
  }))
 **/

function defaultValues(options) {
  return function defaultValues(files, metalsmith, done) {
    const debug = metalsmith.debug('@metalsmith/default-values');
    if (!Array.isArray(options) && typeof options === 'object' && options !== null) {
      options = [options];
    }
    debug('Running with options: %O ', options);
    const defaultSets = (options || []).map(defaultsSet => Object.assign({}, defaultDefaultsSet, defaultsSet));

    // Loop through configurations
    defaultSets.forEach(function ({
      pattern,
      defaults,
      strategy
    }) {
      const matches = metalsmith.match(pattern, Object.keys(files));
      const defaultsEntries = Object.entries(defaults);
      debug.info('Matched %s files to pattern "%s": %o', matches.length, pattern, matches);
      if (matches.length) {
        const setDefaults = set_defaults(defaultsEntries, strategy);
        matches.forEach(file => {
          const changed = setDefaults(files[file], metalsmith.metadata());
          debug.info('Values set for file "%s": %O', file, changed);
        });
      } else {
        debug.warn('No matches for pattern "%s"', pattern);
      }
    });
    done();
  };
}

export { defaultValues as default };