added error handler

+
+// # error handler
+
+var _ = require('underscore')
+var util = require('util')
+
+exports = module.exports = function(logger, settings) {
+
+  return function(err, req, res, next) {
+
+    // set default error status code
+    res.statusCode = (_.isNumber(err.status)) ? err.status : 500
+
+    if (!_.isString(err.message))
+      err.message = 'An unknown error has occured, please try again'
+
+    if (_.isObject(err) && _.isNumber(err.code) && err.code === 11000)
+      err.message = 'Duplicate document already exists in database, try making a more unique value'
+
+    // if we pass an error object, then we want to simply return the message...
+    // if we pass an object, then we want to do a stack trace, and then return the object + stack
+    var error = {}
+
+    // set error type
+    error.type = _.isString(err.param) ? 'invalid_request_error' : 'api_error'
+
+    if (error.type === 'invalid_request_error' && res.statusCode === 500)
+      res.statusCode = 400
+
+    // set error message and stack trace
+    if (util.isError(err)) {
+      error.message = err.message
+    } else {
+      _.extend(error, err)
+    }
+
+    // set status code for BadRequestError
+    if (_.isString(error.name) && error.name === 'BadRequestError') {
+      error.type = 'invalid_request_error'
+      res.statusCode = 400
+      delete error.name
+    }
+
+    if (settings.showStack)
+      error.stack = _.isUndefined(err.stack) ? new Error(err.message).stack : err.stack
+
+    // set error level
+    var level = (res.statusCode < 500) ? 'warn' : 'error'
+    logger[level](error)
+
+    // set error back to warning if it was warn
+    // logger level type = "warn"
+    // req.flash messages type = "warning"
+    if (level === 'warn')
+      level = 'warning'
+
+    // if we have a mongoose validation err
+    // then we know to output all the errors
+    if (_.isObject(error.errors) && !_.isEmpty(error.errors)) {
+      var messages = []
+      _.each(error.errors, function(errMsg) {
+        if (_.isString(errMsg.message))
+          messages.push(errMsg.message)
+      })
+      if (!_.isEmpty(messages))
+        error.message = messages.join(' ')
+    }
+
+    res.format({
+      text: function() {
+        res.send(error.message)
+      },
+      html: function() {
+        req.flash(level, error.message)
+        res.redirect('back')
+      },
+      json: function() {
+        res.json({ error: error })
+      }
+    })
+
+  }
+
+}
+
+exports['@singleton'] = true
+exports['@require'] = [ 'logger', 'settings' ]