var util = require('util');
var events = require('events');
var stream = require('stream');
var assert = process.assert;


var debugLevel = parseInt(process.env.NODE_DEBUG, 16);
var debug;
if (debugLevel & 0x2) {
  debug = function() { util.error.apply(this, arguments); };
} else {
  debug = function() { };
}


/* Lazy Loaded crypto object */
var SecureStream = null;

/**
 * Provides a pair of streams to do encrypted communication.
 */

function SecurePair(credentials, isServer, shouldVerifyPeer) {
  if (!(this instanceof SecurePair)) {
    return new SecurePair(credentials, isServer, shouldVerifyPeer);
  }

  var self = this;

  try {
    SecureStream = process.binding('crypto').SecureStream;
  }
  catch (e) {
    throw new Error('node.js not compiled with openssl crypto support.');
  }

  events.EventEmitter.call(this);

  this._secureEstablished = false;
  this._isServer = isServer ? true : false;
  this._encWriteState = true;
  this._clearWriteState = true;
  this._done = false;

  var crypto = require('crypto');

  if (!credentials) {
    this.credentials = crypto.createCredentials();
  } else {
    this.credentials = credentials;
  }

  if (!this._isServer) {
    // For clients, we will always have either a given ca list or be using
    // default one
    shouldVerifyPeer = true;
  }

  this._secureEstablished = false;
  this._encInPending = [];
  this._clearInPending = [];

  this._ssl = new SecureStream(this.credentials.context,
                               this._isServer ? true : false,
                               shouldVerifyPeer ? true : false);


  /* Acts as a r/w stream to the cleartext side of the stream. */
  this.cleartext = new stream.Stream();
  this.cleartext.readable = true;
  this.cleartext.writable = true;

  /* Acts as a r/w stream to the encrypted side of the stream. */
  this.encrypted = new stream.Stream();
  this.encrypted.readable = true;
  this.encrypted.writable = true;

  this.cleartext.write = function(data) {
    if (typeof data == 'string') data = Buffer(data);
    debug('clearIn data');
    self._clearInPending.push(data);
    self._cycle();
    return self._cleartextWriteState;
  };

  this.cleartext.pause = function() {
    debug('paused cleartext');
    self._cleartextWriteState = false;
  };

  this.cleartext.resume = function() {
    debug('resumed cleartext');
    self._cleartextWriteState = true;
  };

  this.cleartext.end = function(err) {
    debug('cleartext end');
    if (!self._done) {
      self._ssl.shutdown();
      self._cycle();
    }
    self._destroy(err);
  };

  this.encrypted.write = function(data) {
    debug('encIn data');
    self._encInPending.push(data);
    self._cycle();
    return self._encryptedWriteState;
  };

  this.encrypted.pause = function() {
    if (typeof data == 'string') data = Buffer(data);
    debug('pause encrypted');
    self._encryptedWriteState = false;
  };

  this.encrypted.resume = function() {
    debug('resume encrypted');
    self._encryptedWriteState = true;
  };

  this.encrypted.end = function(err) {
    debug('encrypted end');
    if (!self._done) {
      self._ssl.shutdown();
      self._cycle();
    }
    self._destroy(err);
  };

  this.cleartext.on('end', function(err) {
    debug('clearIn end');
    if (!self._done) {
      self._ssl.shutdown();
      self._cycle();
    }
    self._destroy(err);
  });

  this.cleartext.on('close', function() {
    debug('source close');
    self.emit('close');
    self._destroy();
  });

  this.encrypted.on('end', function() {
    if (!self._done) {
      self._error(
          new Error('Encrypted stream ended before secure pair was done'));
    }
  });

  this.encrypted.on('close', function() {
    if (!self._done) {
      self._error(
          new Error('Encrypted stream closed before secure pair was done'));
    }
  });

  this.cleartext.on('drain', function() {
    debug('source drain');
    self._cycle();
    self.encrypted.resume();
  });

  this.encrypted.on('drain', function() {
    debug('target drain');
    self._cycle();
    self.cleartext.resume();
  });

  process.nextTick(function() {
    self._ssl.start();
    self._cycle();
  });
}

util.inherits(SecurePair, events.EventEmitter);


exports.createSecurePair = function(credentials, isServer, shouldVerifyPeer) {
  var pair = new SecurePair(credentials, isServer, shouldVerifyPeer);
  return pair;
};


/**
 * Attempt to cycle OpenSSLs buffers in various directions.
 *
 * An SSL Connection can be viewed as four separate piplines,
 * interacting with one has no connection to the behavoir of
 * any of the other 3 -- This might not sound reasonable,
 * but consider things like mid-stream renegotiation of
 * the ciphers.
 *
 * The four pipelines, using terminology of the client (server is just
 * reversed):
 *  (1) Encrypted Output stream (Writing encrypted data to peer)
 *  (2) Encrypted Input stream (Reading encrypted data from peer)
 *  (3) Cleartext Output stream (Decrypted content from the peer)
 *  (4) Cleartext Input stream (Cleartext content to send to the peer)
 *
 * This function attempts to pull any available data out of the Cleartext
 * input stream (4), and the Encrypted input stream (2).  Then it pushes any
 * data available from the cleartext output stream (3), and finally from the
 * Encrypted output stream (1)
 *
 * It is called whenever we do something with OpenSSL -- post reciving
 * content, trying to flush, trying to change ciphers, or shutting down the
 * connection.
 *
 * Because it is also called everywhere, we also check if the connection has
 * completed negotiation and emit 'secure' from here if it has.
 */
SecurePair.prototype._cycle = function() {
  if (this._done) {
    return;
  }

  var self = this;
  var rv;
  var tmp;
  var bytesRead;
  var bytesWritten;
  var chunkBytes;
  var chunk = null;
  var pool = null;

  // Pull in incoming encrypted data from the socket.
  // This arrives via some code like this:
  //
  //   socket.on('data', function (d) {
  //     pair.encrypted.write(d)
  //   });
  //
  while (this._encInPending.length > 0) {
    tmp = this._encInPending.shift();

    try {
      debug('writing from encIn');
      rv = this._ssl.encIn(tmp, 0, tmp.length);
    } catch (e) {
      return this._error(e);
    }

    if (rv === 0) {
      this._encInPending.unshift(tmp);
      break;
    }

    assert(rv === tmp.length);
  }

  // Pull in any clear data coming from the application.
  // This arrives via some code like this:
  //
  //   pair.cleartext.write("hello world");
  //
  while (this._clearInPending.length > 0) {
    tmp = this._clearInPending.shift();
    try {
      debug('writng from clearIn');
      rv = this._ssl.clearIn(tmp, 0, tmp.length);
    } catch (e) {
      return this._error(e);
    }

    if (rv === 0) {
      this._clearInPending.unshift(tmp);
      break;
    }

    assert(rv === tmp.length);
  }

  function mover(reader, writer, checker) {
    var bytesRead;
    var pool;
    var chunkBytes;
    do {
      bytesRead = 0;
      chunkBytes = 0;
      pool = new Buffer(4096);
      pool.used = 0;

      do {
        try {
          chunkBytes = reader(pool,
                              pool.used + bytesRead,
                              pool.length - pool.used - bytesRead);
        } catch (e) {
          return self._error(e);
        }
        if (chunkBytes >= 0) {
          bytesRead += chunkBytes;
        }
      } while ((chunkBytes > 0) && (pool.used + bytesRead < pool.length));

      if (bytesRead > 0) {
        chunk = pool.slice(0, bytesRead);
        writer(chunk);
      }
    } while (checker(bytesRead));
  }

  // Move decryptoed, clear data out into the application.
  // From the user's perspective this occurs as a 'data' event
  // on the pair.cleartext.
  mover(
      function(pool, offset, length) {
        debug('reading from clearOut');
        return self._ssl.clearOut(pool, offset, length);
      },
      function(chunk) {
        self.cleartext.emit('data', chunk);
      },
      function(bytesRead) {
        return bytesRead > 0 && self._cleartextWriteState === true;
      });

  // Move encrypted data to the stream. From the user's perspective this
  // occurs as a 'data' event on the pair.encrypted. Usually the application
  // will have some code which pipes the stream to a socket:
  //
  //   pair.encrypted.on('data', function (d) {
  //     socket.write(d);
  //   });
  //
  mover(
      function(pool, offset, length) {
        debug('reading from encOut');
        return self._ssl.encOut(pool, offset, length);
      },
      function(chunk) {
        self.encrypted.emit('data', chunk);
      },
      function(bytesRead) {
        return bytesRead > 0 && self._encryptedWriteState === true;
      });

  if (!this._secureEstablished && this._ssl.isInitFinished()) {
    this._secureEstablished = true;
    debug('secure established');
    this.emit('secure');
    this._cycle();
  }
};


SecurePair.prototype._destroy = function(err) {
  if (!this._done) {
    this._done = true;
    this._ssl.close();
    this._ssl = null;
    this.emit('end', err);
  }
};


SecurePair.prototype._error = function(err) {
  this.emit('error', err);
};


SecurePair.prototype.getPeerCertificate = function(err) {
  if (this._ssl) {
    return this._ssl.getPeerCertificate();
  } else {
    return null;
  }
};


SecurePair.prototype.getCipher = function(err) {
  if (this._ssl) {
    return this._ssl.getCurrentCipher();
  } else {
    return null;
  }
};