'use strict';

var esprima;

// Browserified version does not have esprima
//
// 1. For node.js just require module as deps
// 2. For browser try to require mudule via external AMD system.
//    If not found - try to fallback to window.esprima. If not
//    found too - then fail to parse.
//
try {
  esprima = require('esprima');
} catch (_) {
  /*global window */
  if (typeof window !== 'undefined') { esprima = window.esprima; }
}

var Type = require('../../type');

function resolveJavascriptFunction(data) {
  try {
    var source = '(' + data + ')',
        ast    = esprima.parse(source, { range: true }),
        params = [],
        body;

    if ('Program'             !== ast.type         ||
        1                     !== ast.body.length  ||
        'ExpressionStatement' !== ast.body[0].type ||
        'FunctionExpression'  !== ast.body[0].expression.type) {
      return false;
    }

    return true;
  } catch (err) {
    return false;
  }
}

function constructJavascriptFunction(data) {
  /*jslint evil:true*/

  var source = '(' + data + ')',
      ast    = esprima.parse(source, { range: true }),
      params = [],
      body;

  if ('Program'             !== ast.type         ||
      1                     !== ast.body.length  ||
      'ExpressionStatement' !== ast.body[0].type ||
      'FunctionExpression'  !== ast.body[0].expression.type) {
    throw new Error('Failed to resolve function');
  }

  ast.body[0].expression.params.forEach(function (param) {
    params.push(param.name);
  });

  body = ast.body[0].expression.body.range;

  // Esprima's ranges include the first '{' and the last '}' characters on
  // function expressions. So cut them out.
  return new Function(params, source.slice(body[0]+1, body[1]-1));
}

function representJavascriptFunction(object /*, style*/) {
  return object.toString();
}

function isFunction(object) {
  return '[object Function]' === Object.prototype.toString.call(object);
}

module.exports = new Type('tag:yaml.org,2002:js/function', {
  kind: 'scalar',
  resolve: resolveJavascriptFunction,
  construct: constructJavascriptFunction,
  predicate: isFunction,
  represent: representJavascriptFunction
});