var capability = require('./capability');
var inherits = require('inherits');
var response = require('./response');
var stream = require('readable-stream');
var toArrayBuffer = require('to-arraybuffer');

var IncomingMessage = response.IncomingMessage;
var rStates = response.readyStates;

function decideMode(preferBinary, useFetch) {
  if (capability.fetch && useFetch) {
    return 'fetch';
  } else if (capability.mozchunkedarraybuffer) {
    return 'moz-chunked-arraybuffer';
  } else if (capability.msstream) {
    return 'ms-stream';
  } else if (capability.arraybuffer && preferBinary) {
    return 'arraybuffer';
  } else if (capability.vbArray && preferBinary) {
    return 'text:vbarray';
  } else {
    return 'text';
  }
}

var ClientRequest = (module.exports = function (opts) {
  var self = this;
  stream.Writable.call(self);

  self._opts = opts;
  self._body = [];
  self._headers = {};
  if (opts.auth) self.setHeader('Authorization', 'Basic ' + new Buffer(opts.auth).toString('base64'));
  Object.keys(opts.headers).forEach(function (name) {
    self.setHeader(name, opts.headers[name]);
  });

  var preferBinary;
  var useFetch = true;
  if (opts.mode === 'disable-fetch' || ('requestTimeout' in opts && !capability.abortController)) {
    // If the use of XHR should be preferred. Not typically needed.
    useFetch = false;
    preferBinary = true;
  } else if (opts.mode === 'prefer-streaming') {
    // If streaming is a high priority but binary compatibility and
    // the accuracy of the 'content-type' header aren't
    preferBinary = false;
  } else if (opts.mode === 'allow-wrong-content-type') {
    // If streaming is more important than preserving the 'content-type' header
    preferBinary = !capability.overrideMimeType;
  } else if (!opts.mode || opts.mode === 'default' || opts.mode === 'prefer-fast') {
    // Use binary if text streaming may corrupt data or the content-type header, or for speed
    preferBinary = true;
  } else {
    throw new Error('Invalid value for opts.mode');
  }
  self._mode = decideMode(preferBinary, useFetch);
  self._fetchTimer = null;

  self.on('finish', function () {
    self._onFinish();
  });
});

inherits(ClientRequest, stream.Writable);

ClientRequest.prototype.setHeader = function (name, value) {
  var self = this;
  var lowerName = name.toLowerCase();
  // This check is not necessary, but it prevents warnings from browsers about setting unsafe
  // headers. To be honest I'm not entirely sure hiding these warnings is a good thing, but
  // http-browserify did it, so I will too.
  if (unsafeHeaders.indexOf(lowerName) !== -1) return;

  self._headers[lowerName] = {
    name: name,
    value: value
  };
};

ClientRequest.prototype.getHeader = function (name) {
  var header = this._headers[name.toLowerCase()];
  if (header) return header.value;
  return null;
};

ClientRequest.prototype.removeHeader = function (name) {
  var self = this;
  delete self._headers[name.toLowerCase()];
};

ClientRequest.prototype._onFinish = function () {
  var self = this;

  if (self._destroyed) return;
  var opts = self._opts;

  var headersObj = self._headers;
  var body = null;
  if (opts.method !== 'GET' && opts.method !== 'HEAD') {
    if (capability.arraybuffer) {
      body = toArrayBuffer(Buffer.concat(self._body));
    } else if (capability.blobConstructor) {
      body = new global.Blob(
        self._body.map(function (buffer) {
          return toArrayBuffer(buffer);
        }),
        {
          type: (headersObj['content-type'] || {}).value || ''
        }
      );
    } else {
      // get utf8 string
      body = Buffer.concat(self._body).toString();
    }
  }

  // create flattened list of headers
  var headersList = [];
  Object.keys(headersObj).forEach(function (keyName) {
    var name = headersObj[keyName].name;
    var value = headersObj[keyName].value;
    if (Array.isArray(value)) {
      value.forEach(function (v) {
        headersList.push([name, v]);
      });
    } else {
      headersList.push([name, value]);
    }
  });

  if (self._mode === 'fetch') {
    var signal = null;
    var fetchTimer = null;
    if (capability.abortController) {
      var controller = new AbortController();
      signal = controller.signal;
      self._fetchAbortController = controller;

      if ('requestTimeout' in opts && opts.requestTimeout !== 0) {
        self._fetchTimer = global.setTimeout(function () {
          self.emit('requestTimeout');
          if (self._fetchAbortController) self._fetchAbortController.abort();
        }, opts.requestTimeout);
      }
    }

    global
      .fetch(self._opts.url, {
        method: self._opts.method,
        headers: headersList,
        body: body || undefined,
        mode: 'cors',
        credentials: opts.withCredentials ? 'include' : 'same-origin',
        signal: signal
      })
      .then(
        function (response) {
          self._fetchResponse = response;
          self._connect();
        },
        function (reason) {
          global.clearTimeout(self._fetchTimer);
          if (!self._destroyed) self.emit('error', reason);
        }
      );
  } else {
    var xhr = (self._xhr = new global.XMLHttpRequest());
    try {
      xhr.open(self._opts.method, self._opts.url, true);
    } catch (err) {
      process.nextTick(function () {
        self.emit('error', err);
      });
      return;
    }

    // Can't set responseType on really old browsers
    if ('responseType' in xhr) xhr.responseType = self._mode.split(':')[0];

    if ('withCredentials' in xhr) xhr.withCredentials = !!opts.withCredentials;

    if (self._mode === 'text' && 'overrideMimeType' in xhr) xhr.overrideMimeType('text/plain; charset=x-user-defined');

    if ('requestTimeout' in opts) {
      xhr.timeout = opts.requestTimeout;
      xhr.ontimeout = function () {
        self.emit('requestTimeout');
      };
    }

    headersList.forEach(function (header) {
      xhr.setRequestHeader(header[0], header[1]);
    });

    self._response = null;
    xhr.onreadystatechange = function () {
      switch (xhr.readyState) {
        case rStates.LOADING:
        case rStates.DONE:
          self._onXHRProgress();
          break;
      }
    };
    // Necessary for streaming in Firefox, since xhr.response is ONLY defined
    // in onprogress, not in onreadystatechange with xhr.readyState = 3
    if (self._mode === 'moz-chunked-arraybuffer') {
      xhr.onprogress = function () {
        self._onXHRProgress();
      };
    }

    xhr.onerror = function () {
      if (self._destroyed) return;
      self.emit('error', new Error('XHR error'));
    };

    try {
      xhr.send(body);
    } catch (err) {
      process.nextTick(function () {
        self.emit('error', err);
      });
      return;
    }
  }
};

/**
 * Checks if xhr.status is readable and non-zero, indicating no error.
 * Even though the spec says it should be available in readyState 3,
 * accessing it throws an exception in IE8
 */
function statusValid(xhr) {
  try {
    var status = xhr.status;
    return status !== null && status !== 0;
  } catch (e) {
    return false;
  }
}

ClientRequest.prototype._onXHRProgress = function () {
  var self = this;

  if (!statusValid(self._xhr) || self._destroyed) return;

  if (!self._response) self._connect();

  self._response._onXHRProgress();
};

ClientRequest.prototype._connect = function () {
  var self = this;

  if (self._destroyed) return;

  self._response = new IncomingMessage(self._xhr, self._fetchResponse, self._mode, self._fetchTimer);
  self._response.on('error', function (err) {
    self.emit('error', err);
  });

  self.emit('response', self._response);
};

ClientRequest.prototype._write = function (chunk, encoding, cb) {
  var self = this;

  self._body.push(chunk);
  cb();
};

ClientRequest.prototype.abort = ClientRequest.prototype.destroy = function () {
  var self = this;
  self._destroyed = true;
  global.clearTimeout(self._fetchTimer);
  if (self._response) self._response._destroyed = true;
  if (self._xhr) self._xhr.abort();
  else if (self._fetchAbortController) self._fetchAbortController.abort();
};

ClientRequest.prototype.end = function (data, encoding, cb) {
  var self = this;
  if (typeof data === 'function') {
    cb = data;
    data = undefined;
  }

  stream.Writable.prototype.end.call(self, data, encoding, cb);
};

ClientRequest.prototype.flushHeaders = function () {};
ClientRequest.prototype.setTimeout = function () {};
ClientRequest.prototype.setNoDelay = function () {};
ClientRequest.prototype.setSocketKeepAlive = function () {};

// Taken from http://www.w3.org/TR/XMLHttpRequest/#the-setrequestheader%28%29-method
var unsafeHeaders = [
  'accept-charset',
  'accept-encoding',
  'access-control-request-headers',
  'access-control-request-method',
  'connection',
  'content-length',
  'cookie',
  'cookie2',
  'date',
  'dnt',
  'expect',
  'host',
  'keep-alive',
  'origin',
  'referer',
  'te',
  'trailer',
  'transfer-encoding',
  'upgrade',
  'user-agent',
  'via'
];
