// Transaction
// -------
import Promise from 'bluebird';
import { EventEmitter } from 'events';
import Debug from 'debug'

import makeKnex from './util/make-knex';

const debug = Debug('knex:tx');

import { uniqueId, isUndefined } from 'lodash';

// Acts as a facade for a Promise, keeping the internal state
// and managing any child transactions.
export default class Transaction extends EventEmitter {

  constructor(client, container, config, outerTx) {
    super()

    const 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), (connection) => {

      const trxClient = this.trxClient = makeTxClient(this, client, connection)
      const init = client.transacting ? this.savepoint(connection) : this.begin(connection)

      init.then(() => {
        return makeTransactor(this, connection, trxClient)
      })
      .then((transactor) => {
        // If we've returned a "thenable" from the transaction container, assume
        // the rollback and commit are chained to this object's success / failure.
        // Directly thrown errors are treated as automatic rollbacks.
        let result
        try {
          result = container(transactor)
        } catch (err) {
          result = Promise.reject(err)
        }
        if (result && result.then && typeof result.then === 'function') {
          result.then((val) => {
            return transactor.commit(val)
          })
          .catch((err) => {
            return transactor.rollback(err)
          })
        }
        return null;
      })
      .catch((e) => this._rejecter(e))

      return new Promise((resolver, rejecter) => {
        this._resolver = resolver
        this._rejecter = rejecter
      })
    })

    this._completed  = false

    // If there's a wrapping transaction, we need to wait for any older sibling
    // transactions to settle (commit or rollback) before we can start, and we
    // need to register ourselves with the parent transaction so any younger
    // siblings can wait for us to complete before they can start.
    this._previousSibling = Promise.resolve(true);
    if (outerTx) {
      if (outerTx._lastChild) this._previousSibling = outerTx._lastChild;
      outerTx._lastChild = this._promise;
    }
  }

  isCompleted() {
    return this._completed || this.outerTx && this.outerTx.isCompleted() || false
  }

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

  savepoint(conn) {
    return this.query(conn, `SAVEPOINT ${this.txid};`)
  }

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

  release(conn, value) {
    return this.query(conn, `RELEASE SAVEPOINT ${this.txid};`, 1, value)
  }

  rollback(conn, error) {
    return this.query(conn, 'ROLLBACK;', 2, error)
      .timeout(5000)
      .catch(Promise.TimeoutError, () => {
        this._resolver();
      });
  }

  rollbackTo(conn, error) {
    return this.query(conn, `ROLLBACK TO SAVEPOINT ${this.txid}`, 2, error)
      .timeout(5000)
      .catch(Promise.TimeoutError, () => {
        this._resolver();
      });
  }

  query(conn, sql, status, value) {
    const q = this.trxClient.query(conn, sql)
      .catch((err) => {
        status = 2
        value  = err
        this._completed = true
        debug('%s error running transaction query', this.txid)
      })
      .tap(() => {
        if (status === 1) {
          this._resolver(value)
        }
        if (status === 2) {
          if(isUndefined(value)) {
            value = new Error(`Transaction rejected with non-error: ${value}`)
          }
          this._rejecter(value)
        }
      })
    if (status === 1 || status === 2) {
      this._completed = true
    }
    return q;
  }

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

  // 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(client, config, txid) {
    const configConnection = config && config.connection
    return Promise.try(() => 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) {

  const transactor = makeKnex(trxClient);

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

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

  const trxClient = Object.create(client.constructor.prototype)
  trxClient.config             = client.config
  trxClient.driver             = client.driver
  trxClient.connectionSettings = client.connectionSettings
  trxClient.transacting        = true
  trxClient.valueForUndefined  = client.valueForUndefined

  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)
  })

  trxClient.on('query-response', function(response, obj, builder) {
    trx.emit('query-response', response, obj, builder)
    client.emit('query-response', response, obj, builder)
  })

  const _query = trxClient.query;
  trxClient.query  = function(conn, obj) {
    const 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)
    })
  }
  const _stream = trxClient.stream
  trxClient.stream = function(conn, obj, stream, options) {
    const 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 Promise.resolve(connection)
  }
  trxClient.releaseConnection = function() {
    return Promise.resolve()
  }

  return trxClient
}

function completedError(trx, obj) {
  const 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')
}

const promiseInterface = [
  'then', 'bind', 'catch', 'finally', 'asCallback',
  'spread', 'map', 'reduce', 'tap', 'thenReturn',
  'return', 'yield', 'ensure', 'exec', 'reflect',
  'get', 'mapSeries', 'delay'
]

// 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))
  }
})