;(function(){
  /*
    Security, Encryption, and Authorization: SEA.js
  */

  // NECESSARY PRE-REQUISITE: http://gun.js.org/explainers/data/security.html

  /* THIS IS AN EARLY ALPHA!!! */

  var nodeCrypto = require('crypto');
  var ecCrypto = require('eccrypto');

  var Gun = (typeof window !== 'undefined' ? window : global).Gun || require('./gun');

  // Following enable Web Cryptography API use in NodeJS
  var crypto = (typeof window !== 'undefined' && window.crypto)
  || { subtle: require('subtle') };

  var TextEncoder = (typeof window !== 'undefined' && window.TextEncoder)
  || require('text-encoding').TextEncoder;
  var TextDecoder = (typeof window !== 'undefined' && window.TextDecoder)
  || require('text-encoding').TextDecoder;

  if(typeof Buffer === 'undefined'){
    var Buffer = require('buffer').Buffer;
  }

  var pbkdf2 = {
    hash: 'SHA-256',  // Was 'SHA-1'
    iter: 50000,
    ks: 64
  };
  var ecdh = {
    enc: (typeof window !== 'undefined' && 'secp256r1') || 'prime256v1'
  };
  var aes = {
    enc: 'aes-256-cbc'
  };

  // let's extend the gun chain with a `user` function.
  // only one user can be logged in at a time, per gun instance.
  Gun.chain.user = function(){
    var root = this.back(-1); // always reference the root gun instance.
    var user = root._.user || (root._.user = root.chain()); // create a user context.
    user.create = User.create; // attach a factory method to it.
    user.auth = User.auth; // and a login method.
    user.remember = User.remember; // and a credentials persisting method.
    return user; // return the user!
  }

  // EXAMPLE! Use it this way:
  ;(function(){return;
    localStorage.clear();

    var gun = Gun();
    var user = gun.user();

    Gun.on('auth', function(at){
      // do something once logged in.
    });
    Gun.on('secure', function(at){
      // enforce some rules about shared app level data
      var no;
      if(no){ return }
      this.to.next(at);
    });

    user.create("test", "password"); // create a user from a username alias and a password phrase.
    user.auth("test", "password"); // authenticate and log in the user!

  }());

  // How does it work?
  function User(){};
  // Well first we have to actually create a user. That is what this function does.
  User.create = function(alias, pass, cb){
    var root = this.back(-1);
    var doCreate = function(resolve, reject){
      // Because more than 1 user might have the same username, we treat the alias as a list of those users.
      root.get('alias/'+alias).get(function(at, ev){
        ev.off();
        if(at.put){
          // If we can enforce that a user name is already taken, it might be nice to try, but this is not guaranteed.
          var err = 'User already created!';
          Gun.log(err);
          return reject({err: err});
        }
        var user = {alias: alias, salt: Gun.text.random(64)};
        // pseudo-randomly create a salt, then use CryptoJS's PBKDF2 function to extend the password with it.
        SEA.proof(pass, user.salt).then(function(proof){
          // this will take some short amount of time to produce a proof, which slows brute force attacks.
          SEA.pair().then(function(pair){
            // now we have generated a brand new ECDSA key pair for the user account.
            user.pub = pair.pub;
            // the user's public key doesn't need to be signed. But everything else needs to be signed with it!
            SEA.write(alias, pair.priv).then(function(sAlias){
              user.alias = sAlias;
              return SEA.write(user.salt, pair.priv);
            }).then(function(sSalt){
              user.salt = sSalt;
              // to keep the private key safe, we AES encrypt it with the proof of work!
              return SEA.en(pair.priv, proof);
            }).then(function(encVal){
              return SEA.write(encVal, pair.priv);
            }).then(function(sAuth){
              user.auth = sAuth;
              var tmp = 'pub/'+pair.pub;
              //console.log("create", user, pair.pub);
              // awesome, now we can actually save the user with their public key as their ID.
              root.get(tmp).put(user);
              // next up, we want to associate the alias with the public key. So we add it to the alias list.
              var ref = root.get('alias/'+alias).put(Gun.obj.put({}, tmp, Gun.val.rel.ify(tmp)));
              // callback that the user has been created. (Note: ok = 0 because we didn't wait for disk to ack)
              resolve({ok: 0, pub: pair.pub});
            });
          });
        });
      });
    };
    if (cb){doCreate(cb, cb)} else {return new Promise(doCreate)}
  };
  // now that we have created a user, we want to authenticate them!
  User.auth = function(props, cb){
    var alias = props.alias, pass = props.pass, newpass = props.newpass;
    var root = this.back(-1);
    var doAuth = function(resolve, reject){
      // load all public keys associated with the username alias we want to log in with.
      root.get('alias/'+alias).get(function(at, ev){
        ev.off();
        if(!at.put){
          // if no user, don't do anything.
          var err = 'No user!';
          Gun.log(err);
          return reject({err: err});
        }
        // then attempt to log into each one until we find ours!
        // (if two users have the same username AND the same password... that would be bad)
        Gun.obj.map(at.put, function(val, key){
          // grab the account associated with this public key.
          root.get(key).get(function(at, ev){
            key = key.slice(4);
            ev.off();
            if(!at.put){return}
            // attempt to PBKDF2 extend the password with the salt. (Verifying the signature gives us the plain text salt.)
            SEA.read(at.put.salt, key).then(function(salt){
              return SEA.proof(pass, salt);
            }).then(function(proof){
              // the proof of work is evidence that we've spent some time/effort trying to log in, this slows brute force.
              return SEA.read(at.put.auth, key).then(function(auth){
                return SEA.de(auth, proof);
              });
            }).then(function(priv){
              // now we have AES decrypted the private key, from when we encrypted it with the proof at registration.
              if(priv){ // if we were successful, then that means...
                // we're logged in!
                function doLogin(){
                  var user = root._.user;
                  // add our credentials in-memory only to our root gun instance
                  user._ = at.gun._;
                  // so that way we can use the credentials to encrypt/decrypt data
                  user._.is = user.is = {};
                  // that is input/output through gun (see below)
                  user._.sea = priv;
                  user._.pub = key;
                  //console.log("authorized", user._);
                  // callbacks success with the user data credentials.
                  resolve(user._);
                  // emit an auth event, useful for page redirects and stuff.
                  Gun.on('auth', user._);
                }
                if(newpass) {
                  // password update so encrypt private key using new pwd + salt
                  var newsalt = Gun.text.random(64);
                  SEA.proof(newpass, newsalt).then(function(proof){
                    SEA.en(priv, proof).then(function(encVal){
                      return SEA.write(encVal, priv).then(function(sAuth){
                        return { pub: key, auth: sAuth };
                      });
                    }).then(function(user){
                      return SEA.write(alias, priv).then(function(sAlias){
                        user.alias = sAlias; return user;
                      });
                    }).then(function(user){
                      return SEA.write(newsalt, priv).then(function(sSalt){
                        user.salt = sSalt; return user;
                      });
                    }).then(function(user){
                      var tmp = 'pub/'+key;
                      // awesome, now we can update the user using public key ID.
                      root.get(tmp).put(user);
                      // then we're done
                      doLogin();
                    });
                  });
                } else {
                  doLogin();
                }
                return;
              }
              // Or else we failed to log in...
            }).catch(function(e){
              Gun.log('Failed to sign in!');
              reject({err: 'Attempt failed'});
            });
          });
          // if (!found) {
          //   reject({err: 'Public key does not exist!'})
          // }
        });
      });
    };
    if (cb){doAuth(cb, cb)} else {return new Promise(doAuth)}
  };
  // now that we have created a user, we want to authenticate them!
  User.remember = function(props, cb){
    var doRemember = function(resolve, reject){
      Gun.log('User.remember is TODO: still');
      reject({ err: 'Not implemented.' });
    }
    if (cb){doRemember(cb, cb)} else {return new Promise(doRemember)}
  };

  // After we have a GUN extension to make user registration/login easy, we then need to handle everything else.

  // We do this with a GUN adapter, we first listen to when a gun instance is created (and when its options change)
  Gun.on('opt', function(at){
    if(!at.sea){ // only add SEA once per instance, on the "at" context.
      at.sea = {own: {}};
      at.gun.on('in', security, at); // now listen to all input data, acting as a firewall.
      at.gun.on('out', signature, at); // and output listeners, to encrypt outgoing data.
    }
    this.to.next(at); // make sure to call the "next" middleware adapter.
  });

  // Alright, this next adapter gets run at the per node level in the graph database.
  // This will let us verify that every property on a node has a value signed by a public key we trust.
  // If the signature does not match, the data is just `undefined` so it doesn't get passed on.
  // If it does match, then we transform the in-memory "view" of the data into its plain value (without the signature).
  // Now NOTE! Some data is "system" data, not user data. Example: List of public keys, aliases, etc.
  // This data is self-enforced (the value can only match its ID), but that is handled in the `security` function.
  // From the self-enforced data, we can see all the edges in the graph that belong to a public key.
  // Example: pub/ASDF is the ID of a node with ASDF as its public key, signed alias and salt, and
  // its encrypted private key, but it might also have other signed values on it like `profile = <ID>` edge.
  // Using that directed edge's ID, we can then track (in memory) which IDs belong to which keys.
  // Here is a problem: Multiple public keys can "claim" any node's ID, so this is dangerous!
  // This means we should ONLY trust our "friends" (our key ring) public keys, not any ones.
  // I have not yet added that to SEA yet in this alpha release. That is coming soon, but beware in the meanwhile!
  Gun.on('node', function(at){ // TODO: Warning: Need to switch to `gun.on('node')`! Do not use `Gun.on('node'` in your apps!
    var own = (at.gun.back(-1)._).sea.own, soul = at.get, pub = own[soul] || soul.slice(4), vertex = (at.gun._).put;
    Gun.node.is(at.put, function(val, key, node){ // for each property on the node.
      SEA.read(val, pub).then(function(data){
        vertex[key] = node[key] = val = data; // verify signature and get plain value.
        if(val && val['#'] && (key = Gun.val.rel.is(val))){ // if it is a relation / edge
          if('alias/' === soul.slice(0,6)){ return } // if it is itself
          own[key] = pub; // associate the public key with a node
        }
      });
    });
  })

  // signature handles data output, it is a proxy to the security function.
  function signature(at){
    at.user = at.gun.back(-1)._.user;
    security.call(this, at);
  }

  // okay! The security function handles all the heavy lifting.
  // It needs to deal read and write of input and output of system data, account/public key data, and regular data.
  // This is broken down into some pretty clear edge cases, let's go over them:
  function security(at){
    var cat = this.as, sea = cat.sea, to = this.to;
    if(at.get){
      // if there is a request to read data from us, then...
      var soul = at.get['#'];
      if(soul){ // for now, only allow direct IDs to be read.
        if('alias' === soul){ // Allow reading the list of usernames/aliases in the system?
          return to.next(at); // yes.
        } else
        if('alias/' === soul.slice(0,6)){ // Allow reading the list of public keys associated with an alias?
          return to.next(at); // yes.
        } else { // Allow reading everything?
          return to.next(at); // yes // TODO: No! Make this a callback/event that people can filter on.
        }
      }
    }
    if(at.put){
      // if there is a request to write data to us, then...
      var no, tmp, u;
      Gun.obj.map(at.put, function(node, soul){ // for each over every node in the graph
        if(no){ return no = true }
        if(Gun.obj.empty(node, '_')){ return } // ignore empty updates, don't reject them.
        if('alias' === soul){ // special case for shared system data, the list of aliases.
          Gun.obj.map(node, function(val, key){ // for each over the node to look at each property/value.
            if('_' === key){ return } // ignore meta data
            if(!val){ return no = true } // data MUST exist
            if('alias/'+key !== Gun.val.rel.is(val)){ // in fact, it must be EXACTLY equal to itself
              return no = true; // if it isn't, reject.
            }
          });
        } else
        if('alias/' === soul.slice(0,6)){ // special case for shared system data, the list of public keys for an alias.
          Gun.obj.map(node, function(val, key){ // for each over the node to look at each property/value.
            if('_' === key){ return } // ignore meta data
            if(!val){ return no = true } // data MUST exist
            if(key === Gun.val.rel.is(val)){ return } // and the ID must be EXACTLY equal to its property
            return no = true; // that way nobody can tamper with the list of public keys.
          });
        } else
        if('pub/' === soul.slice(0,4)){ // special case, account data for a public key.
          tmp = soul.slice(4); // ignore the 'pub/' prefix on the public key.
          Gun.obj.map(node, function(val, key){ // for each over the account data, looking at each property/value.
            if('_' === key){ return } // ignore meta data.
            if('pub' === key){
              if(val === tmp){ return } // the account MUST have a `pub` property that equals the ID of the public key.
              return no = true; // if not, reject the update.
            }
            if(at.user){ // if we are logged in
              if(tmp === at.user._.pub){ // as this user
                SEA.write(val, at.user._.sea).then(function(data){
                  val = node[key] = data; // then sign our updates as we output them.
                });
              } // (if we are lying about our signature, other peer's will reject our update)
            }
            // TODO: this likely isn't working as expected
            SEA.read(val, tmp).then(function(data){
              if(u === (val = data)){ // make sure the signature matches the account it claims to be on.
                return no = true; // reject any updates that are signed with a mismatched account.
              }
            });
          });
        } else
        if(at.user && (tmp = at.user._.sea)){ // not special case, if we are logged in, then
          Gun.obj.map(node, function(val, key){ // any data we output needs to
            if('_' === key){ return }
            SEA.write(val, tmp).then(function(data){
              node[key] = data; // be signed by our logged in account.
            });
          });
        } else // TODO: BUG! These two if-statements are not exclusive to each other!!!
        if(tmp = sea.own[soul]){ // not special case, if we receive an update on an ID associated with a public key, then
          Gun.obj.map(node, function(val, key){ // for each over the property/values
            if('_' === key){ return }
            // TODO: this likely isn't working as expected
            SEA.read(val, tmp).then(function(data){
              if(u === (val = data)){ // and verify they were signed by the associated public key!
                return no = true; // reject the update if it fails to match.
              }
            });
          });
        } else { // reject any/all other updates by default.
          return no = true;
        }
      });
      if(no){ // if we got a rejection then...
        if(!at || !Gun.tag.secure){ return }
        Gun.on('secure', function(at){ // (below) emit a special event for the developer to handle security.
          this.off();
          if(!at){ return }
          to.next(at); // and if they went ahead and explicitly called "next" (to us) with data, then approve.
        });
        Gun.on('secure', at);
        return; // else wise, reject.
      }
      //console.log("SEA put", at.put);
      // if we did not get a rejection, then pass forward to the "next" adapter middleware.
      return to.next(at);
    }
    to.next(at); // pass forward any data we do not know how to handle or process (this allows custom security protocols).
  };

  // Does enc/dec key like OpenSSL - works with CryptoJS encryption/decryption
  function makeKey(p, s) {
    var ps = Buffer.concat([ new Buffer(p, 'utf8'), s ]);
    var h128 = new Buffer(nodeCrypto.createHash('md5').update(ps).digest('hex'), 'hex');
    // TODO: 'md5' is insecure, do we need OpenSSL compatibility anymore ?
    return Buffer.concat([
      h128,
      new Buffer(nodeCrypto.createHash('md5').update(
        Buffer.concat([ h128, ps ]).toString('base64'), 'base64'
      ).digest('hex'), 'hex')
    ]);
  }

  var nHash = pbkdf2.hash.replace('-', '').toLowerCase();

  // These SEA functions support both callback AND Promises
  var SEA = {};
  // create a wrapper library around NodeJS crypto & ecCrypto and Web Crypto API.
  // now wrap the various AES, ECDSA, PBKDF2 functions we called above.
  SEA.proof = function(pass,salt,cb){
    var doProof = (typeof window !== 'undefined' && function(resolve, reject){
      crypto.subtle.importKey(  // For browser crypto.subtle works fine
        'raw', new TextEncoder().encode(pass), {name: 'PBKDF2'}, false, ['deriveBits']
      ).then(function(key){
        return crypto.subtle.deriveBits({
          name: 'PBKDF2',
          iterations: pbkdf2.iter,
          salt: new TextEncoder().encode(salt),
          hash: pbkdf2.hash,
        }, key, pbkdf2.ks*8);
      }).then(function(result){
        return new Buffer(result, 'binary').toString('base64');
      }).then(resolve).catch(function(e){Gun.log(e); reject(e)});
    }) || function(resolve, reject){  // For NodeJS crypto.pkdf2 rocks
      nodeCrypto.pbkdf2(pass,new Buffer(salt, 'utf8'),pbkdf2.iter,pbkdf2.ks,nHash,function(err,hash){
        resolve(!err && hash && hash.toString('base64'));
      });
    };
    if(cb){doProof(cb, function(){cb()})} else {return new Promise(doProof)}
  };
  SEA.pair = function(cb){
    var doPair = function(resolve, reject){
      var priv = nodeCrypto.randomBytes(32);
      resolve({
        pub: new Buffer(ecCrypto.getPublic(priv), 'binary').toString('hex'),
        priv: new Buffer(priv, 'binary').toString('hex')
      });
    };
    if(cb){doPair(cb, function(){cb()})} else {return new Promise(doPair)}
  };
  SEA.derive = function(m,p,cb){
    var doDerive = function(resolve, reject){
      ecCrypto.derive(new Buffer(p, 'hex'), new Buffer(m, 'hex'))
      .then(function(secret){
        resolve(new Buffer(secret, 'binary').toString('hex'));
      }).catch(function(e){Gun.log(e); reject(e)});
    };
    if(cb){doDerive(cb, function(){cb()})} else {return new Promise(doDerive)}
  };
  SEA.sign = function(m, p, cb){
    var doSign = function(resolve, reject){
      ecCrypto.sign(
        new Buffer(p, 'hex'),
        nodeCrypto.createHash(nHash).update(JSON.stringify(m), 'utf8').digest()
      ).then(function(sig){
        resolve(new Buffer(sig, 'binary').toString('hex'));
      }).catch(function(e){Gun.log(e); reject(e)});
    };
    if(cb){doSign(cb, function(){cb()})} else {return new Promise(doSign)}
  };
  SEA.verify = function(m, p, s, cb){
    var doVerify = function(resolve, reject){
      ecCrypto.verify(
        new Buffer(p, 'hex'),
        nodeCrypto.createHash(nHash).update(JSON.stringify(m), 'utf8').digest(),
        new Buffer(s, 'hex')
      ).then(function(){resolve(true)}).catch(function(e){Gun.log(e);reject(e)})
    };
    if(cb){doVerify(cb, function(){cb()})} else {return new Promise(doVerify)}
  };
  SEA.en = function(m,p,cb){
    var doEncrypt = function(resolve, reject){
      var s = nodeCrypto.randomBytes(8);
      var iv = nodeCrypto.randomBytes(16);
      var r = {iv: iv.toString('hex'), s: s.toString('hex')};
      var key = makeKey(p, s);
      if (typeof window !== 'undefined'){ // Browser doesn't run createCipheriv
        crypto.subtle.importKey('raw', key, 'AES-CBC', false, ['encrypt'])
        .then(function(aesKey){
          crypto.subtle.encrypt({
            name: 'AES-CBC', iv: iv
          }, aesKey, new TextEncoder().encode(JSON.stringify(m))).then(function(ct){
            r.ct = new Buffer(ct, 'binary').toString('base64');
            return JSON.stringify(r);
          }).then(resolve).catch(function(e){Gun.log(e); reject(e)});
        }).catch(function(e){Gun.log(e); reject(e)});
      } else {  // NodeJS doesn't support crypto.subtle.importKey properly
        try{
          var cipher = nodeCrypto.createCipheriv(aes.enc, key, iv);
          r.ct = cipher.update(m, 'utf8', 'base64');
          r.ct += cipher.final('base64');
        }catch(e){Gun.log(e); return reject(e)}
        resolve(JSON.stringify(r));
      }
    };
    if(cb){doEncrypt(cb, function(){cb()})} else {return new Promise(doEncrypt)}
  };
  SEA.de = function(m,p,cb){
    var doDecrypt = function(resolve, reject){
      var d = JSON.parse(m);
      var key = makeKey(p, new Buffer(d.s, 'hex'));
      var iv = new Buffer(d.iv, 'hex');
      if (typeof window !== 'undefined'){ // Browser doesn't run createDecipheriv
        crypto.subtle.importKey('raw', key, 'AES-CBC', false, ['decrypt'])
        .then(function(aesKey){
          crypto.subtle.decrypt({
            name: 'AES-CBC', iv: iv
          }, aesKey, new Buffer(d.ct, 'base64')).then(function(ct){
            var ctUtf8 = new TextDecoder('utf8').decode(ct);
            var ret = JSON.parse(ctUtf8);
            return ret;
          }).then(resolve).catch(function(e){Gun.log(e); reject(e)});
        }).catch(function(e){Gun.log(e); reject(e)});
      } else {  // NodeJS doesn't support crypto.subtle.importKey properly
        try{
          var decipher = nodeCrypto.createDecipheriv(aes.enc, key, iv);
          r = decipher.update(d.ct, 'base64', 'utf8') + decipher.final('utf8');
        }catch(e){Gun.log(e); return reject(e)}
        resolve(r);
      }
    };
    if(cb){doDecrypt(cb, function(){cb()})} else {return new Promise(doDecrypt)}
  };
  SEA.write = function(m,p,cb){
    var doSign = function(resolve, reject) {
      SEA.sign(m, p).then(function(signature){
        resolve('SEA'+JSON.stringify([m,signature]));
      }).catch(function(e){Gun.log(e); reject(e)});
    };
    if(cb){doSign(cb, function(){cb()})} else {return new Promise(doSign)}
    // TODO: what's this ?
    // return JSON.stringify([m,SEA.sign(m,p)]);
  };
  SEA.read = function(m,p,cb){
    var doRead = function(resolve, reject) {
      if(!m){ return resolve(); }
      if(!m.slice || 'SEA[' !== m.slice(0,4)){ return resolve(m); }
      m = m.slice(3);
      try{m = JSON.parse(m);
      }catch(e){ return reject(e); }
      m = m || '';
      SEA.verify(m[0], p, m[1]).then(function(ok){
        resolve(ok && m[0]);
      });
    };
    if(cb){doRead(cb, function(){cb()})} else {return new Promise(doRead)}
  };

  Gun.SEA = SEA;

  // all done!
  // Obviously it is missing MANY necessary features. This is only an alpha release.
  // Please experiment with it, audit what I've done so far, and complain about what needs to be added.
  // SEA should be a full suite that is easy and seamless to use.
  // Again, scroll naer the top, where I provide an EXAMPLE of how to create a user and sign in.
  // Once logged in, the rest of the code you just read handled automatically signing/validating data.
  // But all other behavior needs to be equally easy, like opinionated ways of
  // Adding friends (trusted public keys), sending private messages, etc.
  // Cheers! Tell me what you think.

  module.exports = SEA;
}());