// Transaction
// -------
'use strict';

var Promise = require('./promise');
var EventEmitter = require('events').EventEmitter;
var inherits = require('inherits');

var makeKnex = require('./util/make-knex');
var assign = require('lodash/object/assign');
var uniqueId = require('lodash/utility/uniqueId');
var debug = require('debug')('knex:tx');

// Acts as a facade for a Promise, keeping the internal state
// and managing any child transactions.
function Transaction(client, container, config, outerTx) {
  var _this = this;

  var txid = this.txid = uniqueId('trx');

  this.client = client;
  this.outerTx = outerTx;
  this.trxClient = undefined;
  this._debug = client.config && client.config.debug;

  debug('%s: Starting %s transaction', txid, outerTx ? 'nested' : 'top level');

  this._promise = Promise.using(this.acquireConnection(client, config, txid), function (connection) {

    var trxClient = _this.trxClient = makeTxClient(_this, client, connection);
    var init = client.transacting ? _this.savepoint(connection) : _this.begin(connection);

    init.then(function () {
      return makeTransactor(_this, connection, trxClient);
    }).then(function (transactor) {

      var result = container(transactor);

      // If we've returned a "thenable" from the transaction container,
      // and it's got the transaction object we're running for this, assume
      // the rollback and commit are chained to this object's success / failure.
      if (result && result.then && typeof result.then === 'function') {
        result.then(function (val) {
          transactor.commit(val);
        })['catch'](function (err) {
          transactor.rollback(err);
        });
      }
    })['catch'](function (e) {
      return _this._rejecter(e);
    });

    return new Promise(function (resolver, rejecter) {
      _this._resolver = resolver;
      _this._rejecter = rejecter;
    });
  });

  this._completed = false;

  // If there is more than one child transaction,
  // we queue them, executing each when the previous completes.
  this._childQueue = [];

  // The queue is a noop unless we have child promises.
  this._queue = this._queue || Promise.resolve(true);

  // If there's a wrapping transaction, we need to see if there are
  // any current children in the pending queue.
  if (outerTx) {

    // If there are other promises pending, we just wait until that one
    // settles (commit or rollback) and then we can continue.
    if (outerTx._childQueue.length > 0) {

      this._queue = this._queue.then(function () {
        return Promise.settle(outerTx._childQueue[outerTx._childQueue.length - 1]);
      });
    }

    // Push the current promise onto the queue of promises.
    outerTx._childQueue.push(this._promise);
  }
}
inherits(Transaction, EventEmitter);

assign(Transaction.prototype, {

  isCompleted: function isCompleted() {
    return this._completed || this.outerTx && this.outerTx.isCompleted() || false;
  },

  begin: function begin(conn) {
    return this.query(conn, 'BEGIN;');
  },

  savepoint: function savepoint(conn) {
    return this.query(conn, 'SAVEPOINT ' + this.txid + ';');
  },

  commit: function commit(conn, value) {
    return this.query(conn, 'COMMIT;', 1, value);
  },

  release: function release(conn, value) {
    return this.query(conn, 'RELEASE SAVEPOINT ' + this.txid + ';', 1, value);
  },

  rollback: function rollback(conn, error) {
    return this.query(conn, 'ROLLBACK;', 2, error);
  },

  rollbackTo: function rollbackTo(conn, error) {
    return this.query(conn, 'ROLLBACK TO SAVEPOINT ' + this.txid, 2, error);
  },

  query: function query(conn, sql, status, value) {
    var _this2 = this;

    var q = this.trxClient.query(conn, sql)['catch'](function (err) {
      status = 2;
      value = err;
      _this2._completed = true;
      debug('%s error running transaction query', _this2.txid);
    }).tap(function () {
      if (status === 1) _this2._resolver(value);
      if (status === 2) _this2._rejecter(value);
    });
    if (status === 1 || status === 2) {
      this._completed = true;
    }
    return q;
  },

  debug: function debug(enabled) {
    this._debug = arguments.length ? enabled : true;
    return this;
  },

  _skipping: function _skipping(sql) {
    return Promise.reject(new Error('Transaction ' + this.txid + ' has already been released skipping: ' + sql));
  },

  // Acquire a connection and create a disposer - either using the one passed
  // via config or getting one off the client. The disposer will be called once
  // the original promise is marked completed.
  acquireConnection: function acquireConnection(client, config, txid) {
    var configConnection = config && config.connection;
    return Promise['try'](function () {
      return configConnection || client.acquireConnection();
    }).disposer(function (connection) {
      if (!configConnection) {
        debug('%s: releasing connection', txid);
        client.releaseConnection(connection);
      } else {
        debug('%s: not releasing external connection', txid);
      }
    });
  }

});

// The transactor is a full featured knex object, with a "commit",
// a "rollback" and a "savepoint" function. The "savepoint" is just
// sugar for creating a new transaction. If the rollback is run
// inside a savepoint, it rolls back to the last savepoint - otherwise
// it rolls back the transaction.
function makeTransactor(trx, connection, trxClient) {

  var transactor = makeKnex(trxClient);

  transactor.transaction = function (container, options) {
    return new trxClient.Transaction(trxClient, container, options, trx);
  };
  transactor.savepoint = function (container, options) {
    return transactor.transaction(container, options);
  };

  if (trx.client.transacting) {
    transactor.commit = function (value) {
      return trx.release(connection, value);
    };
    transactor.rollback = function (error) {
      return trx.rollbackTo(connection, error);
    };
  } else {
    transactor.commit = function (value) {
      return trx.commit(connection, value);
    };
    transactor.rollback = function (error) {
      return trx.rollback(connection, error);
    };
  }

  return transactor;
}

// We need to make a client object which always acquires the same
// connection and does not release back into the pool.
function makeTxClient(trx, client, connection) {

  var trxClient = Object.create(client.constructor.prototype);
  trxClient.config = client.config;
  trxClient.driver = client.driver;
  trxClient.connectionSettings = client.connectionSettings;
  trxClient.transacting = true;

  trxClient.on('query', function (arg) {
    trx.emit('query', arg);
    client.emit('query', arg);
  });

  trxClient.on('query-error', function (err, obj) {
    trx.emit('query-error', err, obj);
    client.emit('query-error', err, obj);
  });

  var _query = trxClient.query;
  trxClient.query = function (conn, obj) {
    var completed = trx.isCompleted();
    return Promise['try'](function () {
      if (conn !== connection) throw new Error('Invalid connection for transaction query.');
      if (completed) completedError(trx, obj);
      return _query.call(trxClient, conn, obj);
    });
  };
  var _stream = trxClient.stream;
  trxClient.stream = function (conn, obj, stream, options) {
    var completed = trx.isCompleted();
    return Promise['try'](function () {
      if (conn !== connection) throw new Error('Invalid connection for transaction query.');
      if (completed) completedError(trx, obj);
      return _stream.call(trxClient, conn, obj, stream, options);
    });
  };
  trxClient.acquireConnection = function () {
    return trx._queue.then(function () {
      return connection;
    });
  };
  trxClient.releaseConnection = function () {
    return Promise.resolve();
  };

  return trxClient;
}

function completedError(trx, obj) {
  var sql = typeof obj === 'string' ? obj : obj && obj.sql;
  debug('%s: Transaction completed: %s', trx.id, sql);
  throw new Error('Transaction query already complete, run with DEBUG=knex:tx for more info');
}

var promiseInterface = ['then', 'bind', 'catch', 'finally', 'asCallback', 'spread', 'map', 'reduce', 'tap', 'thenReturn', 'return', 'yield', 'ensure', 'nodeify', 'exec'];

// Creates a method which "coerces" to a promise, by calling a
// "then" method on the current `Target`
promiseInterface.forEach(function (method) {
  Transaction.prototype[method] = function () {
    return this._promise = this._promise[method].apply(this._promise, arguments);
  };
});

module.exports = Transaction;