'use strict';

module.exports = {
  setup: setupAsync,
  compile: compileAsync
};


var util = require('./compile/util');

var ASYNC = {
  '*': checkGenerators,
  'co*': checkGenerators,
  'es7': checkAsyncFunction
};

var TRANSPILE = {
  'nodent': getNodent,
  'regenerator': getRegenerator
};

var MODES = [
  { async: 'co*' },
  { async: 'es7', transpile: 'nodent' },
  { async: 'co*', transpile: 'regenerator' }
];


var regenerator, nodent;


function setupAsync(opts, required) {
  if (required !== false) required = true;
  var async = opts.async
    , transpile = opts.transpile
    , check;

  switch (typeof transpile) {
    case 'string':
      var get = TRANSPILE[transpile];
      if (!get) throw new Error('bad transpiler: ' + transpile);
      return (opts._transpileFunc = get(opts, required));
    case 'undefined':
    case 'boolean':
      if (typeof async == 'string') {
        check = ASYNC[async];
        if (!check) throw new Error('bad async mode: ' + async);
        return (opts.transpile = check(opts, required));
      }

      for (var i=0; i<MODES.length; i++) {
        var _opts = MODES[i];
        if (setupAsync(_opts, false)) {
          util.copy(_opts, opts);
          return opts.transpile;
        }
      }
      /* istanbul ignore next */
      throw new Error('generators, nodent and regenerator are not available');
    case 'function':
      return (opts._transpileFunc = opts.transpile);
    default:
      throw new Error('bad transpiler: ' + transpile);
  }
}


function checkGenerators(opts, required) {
  /* jshint evil: true */
  try {
    eval('(function*(){})()');
    return true;
  } catch(e) {
    /* istanbul ignore next */
    if (required) throw new Error('generators not supported');
  }
}


function checkAsyncFunction(opts, required) {
  /* jshint evil: true */
  try {
    eval('(async function(){})()');
    /* istanbul ignore next */
    return true;
  } catch(e) {
    if (required) throw new Error('es7 async functions not supported');
  }
}


function getRegenerator(opts, required) {
  try {
    if (!regenerator) {
      regenerator = require('' + 'regenerator');
      regenerator.runtime();
    }
    if (!opts.async || opts.async === true)
      opts.async = 'es7';
    return regeneratorTranspile;
  } catch(e) {
    /* istanbul ignore next */
    if (required) throw new Error('regenerator not available');
  }
}


function regeneratorTranspile(code) {
  return regenerator.compile(code).code;
}


function getNodent(opts, required) {
  /* jshint evil: true */
  try {
    if (!nodent) nodent = require('' + 'nodent')({ log: false, dontInstallRequireHook: true });
    if (opts.async != 'es7') {
      if (opts.async && opts.async !== true) console.warn('nodent transpiles only es7 async functions');
      opts.async = 'es7';
    }
    return nodentTranspile;
  } catch(e) {
    /* istanbul ignore next */
    if (required) throw new Error('nodent not available');
  }
}


function nodentTranspile(code) {
  return nodent.compile(code, '', { promises: true, sourcemap: false }).code;
}


/**
 * Creates validating function for passed schema with asynchronous loading of missing schemas.
 * `loadSchema` option should be a function that accepts schema uri and node-style callback.
 * @this  Ajv
 * @param {Object}   schema schema object
 * @param {Function} callback node-style callback, it is always called with 2 parameters: error (or null) and validating function.
 */
function compileAsync(schema, callback) {
  /* eslint no-shadow: 0 */
  /* jshint validthis: true */
  var schemaObj;
  var self = this;
  try {
    schemaObj = this._addSchema(schema);
  } catch(e) {
    setTimeout(function() { callback(e); });
    return;
  }
  if (schemaObj.validate) {
    setTimeout(function() { callback(null, schemaObj.validate); });
  } else {
    if (typeof this._opts.loadSchema != 'function')
      throw new Error('options.loadSchema should be a function');
    _compileAsync(schema, callback, true);
  }


  function _compileAsync(schema, callback, firstCall) {
    var validate;
    try { validate = self.compile(schema); }
    catch(e) {
      if (e.missingSchema) loadMissingSchema(e);
      else deferCallback(e);
      return;
    }
    deferCallback(null, validate);

    function loadMissingSchema(e) {
      var ref = e.missingSchema;
      if (self._refs[ref] || self._schemas[ref])
        return callback(new Error('Schema ' + ref + ' is loaded but ' + e.missingRef + ' cannot be resolved'));
      var _callbacks = self._loadingSchemas[ref];
      if (_callbacks) {
        if (typeof _callbacks == 'function')
          self._loadingSchemas[ref] = [_callbacks, schemaLoaded];
        else
          _callbacks[_callbacks.length] = schemaLoaded;
      } else {
        self._loadingSchemas[ref] = schemaLoaded;
        self._opts.loadSchema(ref, function (err, sch) {
          var _callbacks = self._loadingSchemas[ref];
          delete self._loadingSchemas[ref];
          if (typeof _callbacks == 'function') {
            _callbacks(err, sch);
          } else {
            for (var i=0; i<_callbacks.length; i++)
              _callbacks[i](err, sch);
          }
        });
      }

      function schemaLoaded(err, sch) {
        if (err) return callback(err);
        if (!(self._refs[ref] || self._schemas[ref])) {
          try {
            self.addSchema(sch, ref);
          } catch(e) {
            callback(e);
            return;
          }
        }
        _compileAsync(schema, callback);
      }
    }

    function deferCallback(err, validate) {
      if (firstCall) setTimeout(function() { callback(err, validate); });
      else return callback(err, validate);
    }
  }
}