ruler.js

/**
 * Ruler is a helper class for building responsibility chains from
 * parse rules. It allows:
 *
 *   - easy stack rules chains
 *   - getting main chain and named chains content (as arrays of functions)
 *
 * Helper methods, should not be used directly.
 * @api private
 */

export default function Ruler() {
  // List of added rules. Each element is:
  //
  // { name: XXX,
  //   enabled: Boolean,
  //   fn: Function(),
  //   alt: [ name2, name3 ] }
  //
  this.__rules__ = [];

  // Cached rule chains.
  //
  // First level - chain name, '' for default.
  // Second level - digital anchor for fast filtering by charcodes.
  //
  this.__cache__ = null;
}

/**
 * Find the index of a rule by `name`.
 *
 * @param  {String} `name`
 * @return {Number} Index of the given `name`
 * @api private
 */

Ruler.prototype.__find__ = function (name) {
  var len = this.__rules__.length;
  var i = -1;

  while (len--) {
    if (this.__rules__[++i].name === name) {
      return i;
    }
  }
  return -1;
};

/**
 * Build the rules lookup cache
 *
 * @api private
 */

Ruler.prototype.__compile__ = function () {
  var self = this;
  var chains = [ '' ];

  // collect unique names
  self.__rules__.forEach(function (rule) {
    if (!rule.enabled) {
      return;
    }

    rule.alt.forEach(function (altName) {
      if (chains.indexOf(altName) < 0) {
        chains.push(altName);
      }
    });
  });

  self.__cache__ = {};

  chains.forEach(function (chain) {
    self.__cache__[chain] = [];
    self.__rules__.forEach(function (rule) {
      if (!rule.enabled) {
        return;
      }

      if (chain && rule.alt.indexOf(chain) < 0) {
        return;
      }
      self.__cache__[chain].push(rule.fn);
    });
  });
};

/**
 * Ruler public methods
 * ------------------------------------------------
 */

/**
 * Replace rule function
 *
 * @param  {String} `name` Rule name
 * @param  {Function `fn`
 * @param  {Object} `options`
 * @api private
 */

Ruler.prototype.at = function (name, fn, options) {
  var idx = this.__find__(name);
  var opt = options || {};

  if (idx === -1) {
    throw new Error('Parser rule not found: ' + name);
  }

  this.__rules__[idx].fn = fn;
  this.__rules__[idx].alt = opt.alt || [];
  this.__cache__ = null;
};

/**
 * Add a rule to the chain before given the `ruleName`.
 *
 * @param  {String}   `beforeName`
 * @param  {String}   `ruleName`
 * @param  {Function} `fn`
 * @param  {Object}   `options`
 * @api private
 */

Ruler.prototype.before = function (beforeName, ruleName, fn, options) {
  var idx = this.__find__(beforeName);
  var opt = options || {};

  if (idx === -1) {
    throw new Error('Parser rule not found: ' + beforeName);
  }

  this.__rules__.splice(idx, 0, {
    name: ruleName,
    enabled: true,
    fn: fn,
    alt: opt.alt || []
  });

  this.__cache__ = null;
};

/**
 * Add a rule to the chain after the given `ruleName`.
 *
 * @param  {String}   `afterName`
 * @param  {String}   `ruleName`
 * @param  {Function} `fn`
 * @param  {Object}   `options`
 * @api private
 */

Ruler.prototype.after = function (afterName, ruleName, fn, options) {
  var idx = this.__find__(afterName);
  var opt = options || {};

  if (idx === -1) {
    throw new Error('Parser rule not found: ' + afterName);
  }

  this.__rules__.splice(idx + 1, 0, {
    name: ruleName,
    enabled: true,
    fn: fn,
    alt: opt.alt || []
  });

  this.__cache__ = null;
};

/**
 * Add a rule to the end of chain.
 *
 * @param  {String}   `ruleName`
 * @param  {Function} `fn`
 * @param  {Object}   `options`
 * @return {String}
 */

Ruler.prototype.push = function (ruleName, fn, options) {
  var opt = options || {};

  this.__rules__.push({
    name: ruleName,
    enabled: true,
    fn: fn,
    alt: opt.alt || []
  });

  this.__cache__ = null;
};

/**
 * Enable a rule or list of rules.
 *
 * @param  {String|Array} `list` Name or array of rule names to enable
 * @param  {Boolean} `strict` If `true`, all non listed rules will be disabled.
 * @api private
 */

Ruler.prototype.enable = function (list, strict) {
  list = !Array.isArray(list)
    ? [ list ]
    : list;

  // In strict mode disable all existing rules first
  if (strict) {
    this.__rules__.forEach(function (rule) {
      rule.enabled = false;
    });
  }

  // Search by name and enable
  list.forEach(function (name) {
    var idx = this.__find__(name);
    if (idx < 0) {
      throw new Error('Rules manager: invalid rule name ' + name);
    }
    this.__rules__[idx].enabled = true;
  }, this);

  this.__cache__ = null;
};


/**
 * Disable a rule or list of rules.
 *
 * @param  {String|Array} `list` Name or array of rule names to disable
 * @api private
 */

Ruler.prototype.disable = function (list) {
  list = !Array.isArray(list)
    ? [ list ]
    : list;

  // Search by name and disable
  list.forEach(function (name) {
    var idx = this.__find__(name);
    if (idx < 0) {
      throw new Error('Rules manager: invalid rule name ' + name);
    }
    this.__rules__[idx].enabled = false;
  }, this);

  this.__cache__ = null;
};

/**
 * Get a rules list as an array of functions.
 *
 * @param  {String} `chainName`
 * @return {Object}
 * @api private
 */

Ruler.prototype.getRules = function (chainName) {
  if (this.__cache__ === null) {
    this.__compile__();
  }
  return this.__cache__[chainName] || [];
};