/* The reach loader's host under Node, in ECMAScript 5 so that it runs on every Node line
 * the conformance proxies use (0.12 onward).
 *
 *   var H = require('./node-host.js');
 *   H.host          { loadScript(file, cb), fetchBytes(file, cb), importModule(file, cb) }
 *   H.loadLoader(dist)  evaluates dist/wai-load.js as a classic script; returns WaiLoad
 *   H.bytes(file)   the file as a Uint8Array
 */
'use strict';
var fs = require('fs'), vm = require('vm'), path = require('path');

function toBytes(buf) {
  var u;
  try { u = new Uint8Array(buf); if (u.length === buf.length) return u; } catch (e) { /* engines without array-like construction */ }
  u = new Uint8Array(buf.length);
  for (var i = 0; i < buf.length; i++) u[i] = buf[i];
  return u;
}

function bytes(file) { return toBytes(fs.readFileSync(file)); }

function runScript(file) {
  vm.runInThisContext(fs.readFileSync(file, 'utf8'), file);
}

var host = {
  loadScript: function (file, cb) {
    try { runScript(file); } catch (e) { cb(e); return; }
    cb(null);
  },
  fetchBytes: function (file, cb) {
    var u;
    try { u = bytes(file); } catch (e) { cb(e); return; }
    cb(null, u);
  },
  importModule: function (file, cb) {
    var dyn;
    try { dyn = new Function('u', 'return import(u)'); } catch (e) { cb(new Error('no dynamic import on this engine: ' + e.message)); return; }
    var url = 'file://' + path.resolve(file).split(path.sep).join('/');
    dyn(url).then(function (m) { cb(null, m); }, function (e) { cb(e); });
  }
};

function loadLoader(dist) {
  runScript(path.join(dist, 'wai-load.js'));
  return global.WaiLoad;
}

module.exports = { host: host, loadLoader: loadLoader, bytes: bytes, toBytes: toBytes, runScript: runScript };