var fs = require('graceful-fs');
var Writable = require('readable-stream').Writable;
var util = require('util');
var MurmurHash3 = require('imurmurhash');
var iferr = require('iferr');
var crypto = require('crypto');
var threadId = require('./thread-id');

function murmurhex() {
  var hash = MurmurHash3('');
  for (var ii = 0; ii < arguments.length; ++ii) {
    hash.hash('' + arguments[ii]);
  }
  return hash.result();
}

var invocations = 0;
function getTmpname(filename) {
  return (
    filename + '.' + murmurhex(__filename, process.pid, threadId, ++invocations)
  );
}

var setImmediate = global.setImmediate || setTimeout;

module.exports = WriteStreamAtomic;

// Requirements:
//   1. Write everything written to the stream to a temp file.
//   2. If there are no errors:
//      a. moves the temp file into its final destination
//      b. emits `finish` & `closed` ONLY after the file is
//         fully flushed and renamed.
//   3. If there's an error, removes the temp file.

util.inherits(WriteStreamAtomic, Writable);
function WriteStreamAtomic(path, options) {
  if (!(this instanceof WriteStreamAtomic)) {
    return new WriteStreamAtomic(path, options);
  }
  Writable.call(this, options);

  this.__isWin =
    options && options.hasOwnProperty('isWin')
      ? options.isWin
      : process.platform === 'win32';

  this.__atomicTarget = path;
  this.__atomicTmp = getTmpname(path);

  this.__atomicChown = options && options.chown;

  this.__atomicClosed = false;

  this.__atomicStream = fs.WriteStream(this.__atomicTmp, options);

  this.__atomicStream.once('open', handleOpen(this));
  this.__atomicStream.once('close', handleClose(this));
  this.__atomicStream.once('error', handleError(this));
}

// We have to suppress default finish emitting, because ordinarily it
// would happen as soon as `end` is called on us and all of the
// data has been written to our target stream. So we suppress
// finish from being emitted here, and only emit it after our
// target stream is closed and we've moved everything around.
WriteStreamAtomic.prototype.emit = function(event) {
  if (event === 'finish') return this.__atomicStream.end();
  return Writable.prototype.emit.apply(this, arguments);
};

WriteStreamAtomic.prototype._write = function(buffer, encoding, cb) {
  var flushed = this.__atomicStream.write(buffer, encoding);
  if (flushed) return cb();
  this.__atomicStream.once('drain', cb);
};

function handleOpen(writeStream) {
  return function(fd) {
    writeStream.emit('open', fd);
  };
}

function handleClose(writeStream) {
  return function() {
    if (writeStream.__atomicClosed) return;
    writeStream.__atomicClosed = true;
    if (writeStream.__atomicChown) {
      var uid = writeStream.__atomicChown.uid;
      var gid = writeStream.__atomicChown.gid;
      return fs.chown(
        writeStream.__atomicTmp,
        uid,
        gid,
        iferr(cleanup, moveIntoPlace),
      );
    } else {
      moveIntoPlace();
    }
  };

  function moveIntoPlace() {
    fs.rename(
      writeStream.__atomicTmp,
      writeStream.__atomicTarget,
      iferr(trapWindowsEPERM, end),
    );
  }

  function trapWindowsEPERM(err) {
    if (
      writeStream.__isWin &&
      err.syscall &&
      err.syscall === 'rename' &&
      err.code &&
      err.code === 'EPERM'
    ) {
      checkFileHashes(err);
    } else {
      cleanup(err);
    }
  }

  function checkFileHashes(eperm) {
    var inprocess = 2;
    var tmpFileHash = crypto.createHash('sha512');
    var targetFileHash = crypto.createHash('sha512');

    fs.createReadStream(writeStream.__atomicTmp)
      .on('data', function(data, enc) {
        tmpFileHash.update(data, enc);
      })
      .on('error', fileHashError)
      .on('end', fileHashComplete);
    fs.createReadStream(writeStream.__atomicTarget)
      .on('data', function(data, enc) {
        targetFileHash.update(data, enc);
      })
      .on('error', fileHashError)
      .on('end', fileHashComplete);

    function fileHashError() {
      if (inprocess === 0) return;
      inprocess = 0;
      cleanup(eperm);
    }

    function fileHashComplete() {
      if (inprocess === 0) return;
      if (--inprocess) return;
      if (tmpFileHash.digest('hex') === targetFileHash.digest('hex')) {
        return cleanup();
      } else {
        return cleanup(eperm);
      }
    }
  }

  function cleanup(err) {
    fs.unlink(writeStream.__atomicTmp, function() {
      if (err) {
        writeStream.emit('error', err);
        writeStream.emit('close');
      } else {
        end();
      }
    });
  }

  function end() {
    // We have to use our parent class directly because we suppress `finish`
    // events fired via our own emit method.
    Writable.prototype.emit.call(writeStream, 'finish');

    // Delay the close to provide the same temporal separation a physical
    // file operation would have– that is, the close event is emitted only
    // after the async close operation completes.
    setImmediate(function() {
      writeStream.emit('close');
    });
  }
}

function handleError(writeStream) {
  return function(er) {
    cleanupSync();
    writeStream.emit('error', er);
    writeStream.__atomicClosed = true;
    writeStream.emit('close');
  };
  function cleanupSync() {
    try {
      fs.unlinkSync(writeStream.__atomicTmp);
    } finally {
      return;
    }
  }
}