Mime.js

'use strict';

/**
 * @param typeMap [Object] Map of MIME type -> Array[extensions]
 * @param ...
 */
function Mime() {
  this._types = Object.create(null);
  this._extensions = Object.create(null);

  for (var i = 0; i < arguments.length; i++) {
    this.define(arguments[i]);
  }

  this.define = this.define.bind(this);
  this.getType = this.getType.bind(this);
  this.getExtension = this.getExtension.bind(this);
}

/**
 * Define mimetype -> extension mappings.  Each key is a mime-type that maps
 * to an array of extensions associated with the type.  The first extension is
 * used as the default extension for the type.
 *
 * e.g. mime.define({'audio/ogg', ['oga', 'ogg', 'spx']});
 *
 * If a type declares an extension that has already been defined, an error will
 * be thrown.  To suppress this error and force the extension to be associated
 * with the new type, pass `force`=true.  Alternatively, you may prefix the
 * extension with "*" to map the type to extension, without mapping the
 * extension to the type.
 *
 * e.g. mime.define({'audio/wav', ['wav']}, {'audio/x-wav', ['*wav']});
 *
 *
 * @param map (Object) type definitions
 * @param force (Boolean) if true, force overriding of existing definitions
 */
Mime.prototype.define = function(typeMap, force) {
  for (var type in typeMap) {
    var extensions = typeMap[type].map(function(t) {return t.toLowerCase()});
    type = type.toLowerCase();

    for (var i = 0; i < extensions.length; i++) {
      var ext = extensions[i];

      // '*' prefix = not the preferred type for this extension.  So fixup the
      // extension, and skip it.
      if (ext[0] == '*') {
        continue;
      }

      if (!force && (ext in this._types)) {
        throw new Error(
          'Attempt to change mapping for "' + ext +
          '" extension from "' + this._types[ext] + '" to "' + type +
          '". Pass `force=true` to allow this, otherwise remove "' + ext +
          '" from the list of extensions for "' + type + '".'
        );
      }

      this._types[ext] = type;
    }

    // Use first extension as default
    if (force || !this._extensions[type]) {
      var ext = extensions[0];
      this._extensions[type] = (ext[0] != '*') ? ext : ext.substr(1)
    }
  }
};

/**
 * Lookup a mime type based on extension
 */
Mime.prototype.getType = function(path) {
  path = String(path);
  var last = path.replace(/^.*[/\\]/, '').toLowerCase();
  var ext = last.replace(/^.*\./, '').toLowerCase();

  var hasPath = last.length < path.length;
  var hasDot = ext.length < last.length - 1;

  return (hasDot || !hasPath) && this._types[ext] || null;
};

/**
 * Return file extension associated with a mime type
 */
Mime.prototype.getExtension = function(type) {
  type = /^\s*([^;\s]*)/.test(type) && RegExp.$1;
  return type && this._extensions[type.toLowerCase()] || null;
};

module.exports = Mime;