mjackson/mach

var Location = require('../Location');
var createProxy = require('../utils/createProxy');
var isRegExp = require('../utils/isRegExp');

function returnTrue() {
  return true;
}

/**
 * A middleware that forwards requests that pass the given test function
 * to the given target. If the target is not an app, it should be a string
 * or options hash that is used to create a proxy.
 *
 * Example:
 *
 *   var mach = require('mach');
 *   var app = mach.stack();
 *
 *   // Forward all requests to example.com.
 *   app.use(mach.proxy, 'http://www.example.com');
 *
 *   // Forward all requests that match "/images/*.jpg" to S3.
 *   app.use(mach.proxy, 'http://s3.amazon.com/my-bucket', /\/images/*.jpg/);
 *   
 *   mach.serve(app);
 */
function proxy(app, target, test) {
  test = test || returnTrue;

  if (isRegExp(test)) {
    var pattern = test;
    test = function (conn) {
      return pattern.test(conn.href);
    };
  } else if (typeof test !== 'function') {
    throw new Error('mach.proxy needs a test function');
  }

  var targetApp;
  if (typeof target === 'function') {
    targetApp = target;
  } else if (typeof target === 'string' || target instanceof Location) {
    targetApp = createProxy(target);
  } else {
    throw new Error('mach.proxy needs a target app');
  }

  return function (conn) {
    return conn.call(test(conn) ? targetApp : app);
  };
}

module.exports = proxy;