Couple useful heplers for ghost

heplers.js

var hbs = require('express-hbs'),
    api = require('core/server/api'),
    _ = require('lodash'),
    async = require('express-hbs/lib/async'), // To redefine `registerAsyncHelper`
    registerAsyncHelper;

// Redefine `registerAsyncHelper` from `express-hbs`
registerAsyncHelper = function (name, fn) {
    hbs.handlebars.registerHelper(name, function (context, options) {
        // Pass `[context, options]` as arg instead of `context` only
        return async.resolve(fn.bind(this), [context, options]);
    });
};

module.exports = function () {

    // {{#node_env}} Helper
    //
    // Example:
    // {{#node_env production}}
    //     ...production only 
    // {{/node_env}}
    //
    hbs.registerHelper('node_env', function (env, options) {
        return (options.data.root.settings.env === env) ? options.fn(this) : options.inverse(this)
    });


    // {{#by_tag}} Helper
    //
    // Example:
    // {{#by_tag 'dev'}}
    //    {{#foreach posts}}
    //        {{title}}
    //        {{content}}
    //    {{/foreach}}
    // {{/by_tag}}
    //
    // TODO `page` or smth like this functionality
    //
    registerAsyncHelper('by_tag', function (context_data, callback) {
        var context = context_data[0], // get context and options passed from context_data array
            options = context_data[1],
            parameters = (options || {}).hash || {},
            request = {
                context: {internal: true},
                tag: context
            };

        if (parameters.hasOwnProperty('limit')) {
            request.limit = parameters.limit
        }

        return api.posts.browse(request).then(function (responce) {
            var data;
            if (options !== undefined && typeof options.fn === 'function') {
                data = hbs.handlebars.createFrame(options.data || {});
                data.posts = responce.posts;
                console.log(data);
                callback(options.fn(data))
            } else {
                callback('')
            }
        });
    });

    
    // {{{hello_kitty}}} Sample Helper
    hbs.registerHelper('hello_kitty', function () {
        return new hbs.handlebars.SafeString('Hello =^oo^= Kitty!');
    });
    
};

{{#by_tag}} works fine.But if used twice like.

{{#by_tag 'tag1'}}
//do something
{{/by_tag}}

{{#by_tag 'tag2'}}
//do something
{{/by_tag}}

throws the following error in the server.Please help

ERROR: Can't set headers after they are sent.
registerAsyncThemeHelper: ghost_head

Error: Can't set headers after they are sent.
at ServerResponse.OutgoingMessage.setHeader (_http_outgoing.js:335:11)
at ServerResponse.header (C:\Ghost\ghost-0.7.1\node_modules\express\lib\response.js:700:10)
at ServerResponse.send (C:\Ghost\ghost-0.7.1\node_modules\express\lib\response.js:154:12)
at fn (C:\Ghost\ghost-0.7.1\node_modules\express\lib\response.js:934:10)
at _stackRenderer (C:\Ghost\ghost-0.7.1\node_modules\express-hbs\lib\hbs.js:524:9)
at Waiter.callback (C:\Ghost\ghost-0.7.1\node_modules\express-hbs\lib\hbs.js:501:7)
at Waiter.resolve (C:\Ghost\ghost-0.7.1\node_modules\express-hbs\lib\async.js:43:12)
at C:\Ghost\ghost-0.7.1\node_modules\express-hbs\lib\async.js:84:15
at C:\Ghost\ghost-0.7.1\core\server\helpers\index.js:64:13
at tryCatcher (C:\Ghost\ghost-0.7.1\node_modules\bluebird\js\main\util.js:24:31)
at Promise._settlePromiseFromHandler (C:\Ghost\ghost-0.7.1\node_modules\bluebird\js\main\promise.js:454:31)
at Promise._settlePromiseAt (C:\Ghost\ghost-0.7.1\node_modules\bluebird\js\main\promise.js:530:18)
at Promise._settlePromises (C:\Ghost\ghost-0.7.1\node_modules\bluebird\js\main\promise.js:646:14)
at Async._drainQueue (C:\Ghost\ghost-0.7.1\node_modules\bluebird\js\main\async.js:177:16)
at Async._drainQueues (C:\Ghost\ghost-0.7.1\node_modules\bluebird\js\main\async.js:187:10)
at Immediate.Async.drainQueues as _onImmediate
at processImmediate as _immediateCallback

Unhandled rejection Error: Can't set headers after they are sent.
at ServerResponse.OutgoingMessage.setHeader (_http_outgoing.js:335:11)
at ServerResponse.header (C:\Ghost\ghost-0.7.1\node_modules\express\lib\response.js:700:10)
at ServerResponse.send (C:\Ghost\ghost-0.7.1\node_modules\express\lib\response.js:154:12)
at fn (C:\Ghost\ghost-0.7.1\node_modules\express\lib\response.js:934:10)
at _stackRenderer (C:\Ghost\ghost-0.7.1\node_modules\express-hbs\lib\hbs.js:524:9)
at Waiter.callback (C:\Ghost\ghost-0.7.1\node_modules\express-hbs\lib\hbs.js:501:7)
at Waiter.resolve (C:\Ghost\ghost-0.7.1\node_modules\express-hbs\lib\async.js:43:12)
at C:\Ghost\ghost-0.7.1\node_modules\express-hbs\lib\async.js:84:15
at C:\Ghost\ghost-0.7.1\core\server\helpers\index.js:64:13
at tryCatcher (C:\Ghost\ghost-0.7.1\node_modules\bluebird\js\main\util.js:24:31)
at Promise._settlePromiseFromHandler (C:\Ghost\ghost-0.7.1\node_modules\bluebird\js\main\promise.js:454:31)
at Promise._settlePromiseAt (C:\Ghost\ghost-0.7.1\node_modules\bluebird\js\main\promise.js:530:18)
at Promise._settlePromises (C:\Ghost\ghost-0.7.1\node_modules\bluebird\js\main\promise.js:646:14)
at Async._drainQueue (C:\Ghost\ghost-0.7.1\node_modules\bluebird\js\main\async.js:177:16)
at Async._drainQueues (C:\Ghost\ghost-0.7.1\node_modules\bluebird\js\main\async.js:187:10)
at Immediate.Async.drainQueues as _onImmediate
at processImmediate as _immediateCallback

This code is compatible with ghost 0.7.4 and support multiple tags.

var hbs = require('express-hbs'),
  api = require('./core/server/api'),
  _ = require('lodash'),
  async = require('express-hbs/lib/async'), // To redefine `registerAsyncHelper`
  registerAsyncHelper;

// Redefine `registerAsyncHelper` from `express-hbs`
registerAsyncHelper = function(name, fn) {
  hbs.handlebars.registerHelper(name, function(context, options) {
    // Pass `[context, options]` as arg instead of `context` only
    return async.resolve(fn.bind(this), [context, options]);
  });
};

module.exports = function() {

  // {{#by_tag}} Helper
  //
  // Example:
  // {{#by_tag 'dev,prod' limit=3}}
  //    {{#foreach posts}}
  //        {{title}}
  //        {{content}}
  //    {{/foreach}}
  // {{/by_tag}}
  //
  // TODO `page` or smth like this functionality
  //
  registerAsyncHelper('by_tag', function(context_data, callback) {
    var context = context_data[0], // get context and options passed from context_data array
      options = context_data[1],
      parameters = (options || {}).hash || {},
      request = {
        context: {
          internal: true
        }
      };

    var tags = (context || '').split(',');
    _.each(tags, function(tag, i) {
      tags[i] = 'tag:' + tags[i];
    });
    if (tags.length > 0) {
      request.filter = tags.join(',');
    }

    if (parameters.hasOwnProperty('limit')) {
      request.limit = parameters.limit
    }

    return api.posts.browse(request).then(function(responce) {
      var data;
      if (options !== undefined && typeof options.fn === 'function') {
        data = hbs.handlebars.createFrame(options.data || {});
        data.posts = responce.posts;
        data.pagination = {
          page: 1,
          prev: 0,
          next: 0,
          pages: 1,
          total: request.limit || 100,
          limit: request.limit || 100
        };
        callback(options.fn(data))
      } else {
        callback('')
      }
    });
  });
};