var assign = require('object-assign');

exports.injectInto = function injectInto(express) {
  if(express.response.marko) return;

  express.response.marko = function(template, data) {
    if(typeof template === 'string') {
      throw new Error(
        'res.marko does not take a template name or path like res.render.  ' +
        'Instead you should use `require(\'./path/to/template.marko\')` ' +
        'and pass the loaded template to this function.'
      )
    }

    var res = this;
    var req = res.req;
    var app = res.app;
    var $global = assign({ app, req, res }, app.locals, res.locals);

    if (data) {
      data = assign(data, {
        $global: assign($global, data.$global)
      });
    } else {
      data = { $global };
    }

    res.set({ 'content-type': 'text/html; charset=utf-8' });

    template.render(data, res);
  };
};