resolve-url-loader/lib/join-function.js

/*
 * MIT License http://opensource.org/licenses/MIT
 * Author: Ben Holloway @bholloway
 */
'use strict';

var path     = require('path'),
    fs       = require('fs'),
    compose  = require('compose-function'),
    Iterator = require('es6-iterator');

var PACKAGE_NAME = require('../package.json').name;

var simpleJoin = compose(path.normalize, path.join);

/**
 * The default join function iterates over possible base paths until a suitable join is found.
 *
 * The first base path is used as fallback for the case where none of the base paths can locate the actual file.
 *
 * @type {function}
 */
exports.defaultJoin = createJoinForPredicate(
  function predicate(_, uri, base, i, next) {
    var absolute = simpleJoin(base, uri);
    return fs.existsSync(absolute) ? absolute : next((i === 0) ? absolute : null);
  },
  'defaultJoin'
);

/**
 * Define a join function by a predicate that tests possible base paths from an iterator.
 *
 * The `predicate` is of the form:
 *
 * ```
 * function(filename, uri, base, i, next):string|null
 * ```
 *
 * Given the uri and base it should either return:
 * - an absolute path success
 * - a call to `next(null)` as failure
 * - a call to `next(absolute)` where absolute is placeholder and the iterator continues
 *
 * The value given to `next(...)` is only used if success does not eventually occur.
 *
 * The `file` value is typically unused but useful if you would like to differentiate behaviour.
 *
 * You can write a much simpler function than this if you have specific requirements.
 *
 * @param {function} predicate A function that tests values
 * @param {string} [name] Optional name for the resulting join function
 */
function createJoinForPredicate(predicate, name) {
  /**
   * A factory for a join function with logging.
   *
   * @param {string} filename The current file being processed
   * @param {{debug:function|boolean,root:string}} options An options hash
   */
  function join(filename, options) {
    var log = createDebugLogger(options.debug);

    /**
     * Join function proper.
     *
     * For absolute uri only `uri` will be provided. In this case we substitute any `root` given in options.
     *
     * @param {string} uri A uri path, relative or absolute
     * @param {string|Iterator.<string>} [baseOrIteratorOrAbsent] Optional absolute base path or iterator thereof
     * @return {string} Just the uri where base is empty or the uri appended to the base
     */
    return function joinProper(uri, baseOrIteratorOrAbsent) {
      var iterator =
        (typeof baseOrIteratorOrAbsent === 'undefined') && new Iterator([options.root          ]) ||
        (typeof baseOrIteratorOrAbsent === 'string'   ) && new Iterator([baseOrIteratorOrAbsent]) ||
        baseOrIteratorOrAbsent;

      var result = runIterator([]);
      log(createJoinMsg, [filename, uri, result, result.isFound]);

      return (typeof result.absolute === 'string') ? result.absolute : uri;

      function runIterator(accumulator) {
        var nextItem = iterator.next();
        var base     = !nextItem.done && nextItem.value;
        if (typeof base === 'string') {
          var element = predicate(filename, uri, base, accumulator.length, next);

          if ((typeof element === 'string') && path.isAbsolute(element)) {
            return Object.assign(
              accumulator.concat(base),
              {isFound: true, absolute: element}
            );
          } else if (Array.isArray(element)) {
            return element;
          } else {
            throw new Error('predicate must return an absolute path or the result of calling next()');
          }
        } else {
          return accumulator;
        }

        function next(fallback) {
          return runIterator(Object.assign(
            accumulator.concat(base),
            (typeof fallback === 'string') && {absolute: fallback}
          ));
        }
      }
    };
  }

  function toString() {
    return '[Function: ' + name + ']';
  }

  return Object.assign(join, name && {
    valueOf : toString,
    toString: toString
  });
}

exports.createJoinForPredicate = createJoinForPredicate;

/**
 * Format a debug message.
 *
 * @param {string} file The file being processed by webpack
 * @param {string} uri A uri path, relative or absolute
 * @param {Array.<string>} bases Absolute base paths up to and including the found one
 * @param {boolean} isFound Indicates the last base was correct
 * @return {string} Formatted message
 */
function createJoinMsg(file, uri, bases, isFound) {
  return [PACKAGE_NAME + ': ' + pathToString(file) + ': ' + uri]
    .concat(bases.map(pathToString).filter(Boolean))
    .concat(isFound ? 'FOUND' : 'NOT FOUND')
    .join('\n  ');

  /**
   * If given path is within `process.cwd()` then show relative posix path, otherwise show absolute posix path.
   *
   * @param {string} absolute An absolute path
   * @return {string} A relative or absolute path
   */
  function pathToString(absolute) {
    if (!absolute) {
      return null;
    } else {
      var relative = path.relative(process.cwd(), absolute)
        .split(path.sep);

      return ((relative[0] === '..') ? absolute.split(path.sep) : ['.'].concat(relative).filter(Boolean))
        .join('/');
    }
  }
}

exports.createJoinMsg = createJoinMsg;

/**
 * A factory for a log function predicated on the given debug parameter.
 *
 * The logging function created accepts a function that formats a message and parameters that the function utilises.
 * Presuming the message function may be expensive we only call it if logging is enabled.
 *
 * The log messages are de-duplicated based on the parameters, so it is assumed they are simple types that stringify
 * well.
 *
 * @param {function|boolean} debug A boolean or debug function
 * @return {function(function, array)} A logging function possibly degenerate
 */
function createDebugLogger(debug) {
  var log = !!debug && ((typeof debug === 'function') ? debug : console.log);
  var cache = {};
  return log ? actuallyLog : noop;

  function noop() {}

  function actuallyLog(msgFn, params) {
    var key = JSON.stringify(params);
    if (!cache[key]) {
      cache[key] = true;
      log(msgFn.apply(null, params));
    }
  }
}

exports.createDebugLogger = createDebugLogger;