Prototype of formatter for tcomb errors

formatter.js

'use strict';
var xtend = require('xtend');
var op = require('object-path');

var isMeta = /^meta\./;

module.exports = function formatErrors (errors, options) {
  options = options || {};
  var byPath = options.paths || {};
  var byType = options.types || {};

  return errors.map(function (error) {
    var formatString = getFormatString(error.path, error.expected);

    return xtend(error, {
      message: formatString.replace(/{([\w. _-]+)}/g, function (_, key) {
        switch (key) {
          case 'path': return error.path.join('.');
          case 'jsonPath': return JSON.stringify(path);
        }

        debugger
        var root = isMeta.test(key) ? error.expected : error;

        return op.get(root, key);
      })
    });
  });

  // Precedence for format string is:
  //
  //  1. path-specific override
  //  2. type-specific override
  //  3. type-meta default
  //  4. global default
  function getFormatString (path, type) {
    var pathOpts = byPath[path.join('.')];
    if (pathOpts && 'message' in pathOpts) {
      return pathOpts.message;
    }

    var typeOpts = byType[type.meta.name];
    if (typeOpts && 'message' in typeOpts) {
      return typeOpts.message;
    }

    if ('message' in type.meta) {
      return type.meta.message;
    }

    return 'value "{actual}" at {path} was expected to be a {meta.name}';
  }
};

test.js

var T = require('tcomb');

var formatErrors = require('./formatter');

var errors = [{
  actual: 'toast',
  expected: T.Num,
  path: ['count']
}, {
  actual: 'beer',
  expected: T.Num,
  path: ['people', 'count']
}];

var messages = formatErrors(errors, {
  types: {
    Num: {
      message: '{path} should be a {meta.name}, was "{actual}"'
    }
  },

  paths: {
    'people.count': { 
      message: 'The count of people must be a {meta.name}, was "{actual}"'
    }
  }
}).map(function (formatted) {
  return formatted.message;
});

require('assert').deepEqual(messages, [
  'count should be a Num, was "toast"',
  'The count of people must be a Num, was "beer"'
]);