# Copyright 2014 The Chromium OS Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

"""Continuous Integration Database Library."""

from __future__ import print_function

import datetime
import glob
import logging
import os
import re
try:
  import sqlalchemy
  import sqlalchemy.exc
  import sqlalchemy.interfaces
  from sqlalchemy import MetaData
except ImportError:
  raise AssertionError(
      'Unable to import sqlalchemy. Please install this package by running '
      '`sudo apt-get install python-sqlalchemy` or similar.')

from chromite.cbuildbot import constants
from chromite.lib import retry_stats
from chromite.lib import clactions

CIDB_MIGRATIONS_DIR = os.path.join(constants.CHROMITE_DIR, 'cidb',
                                   'migrations')

_RETRYABLE_OPERATIONAL_ERROR_CODES = (
    1053,   # 'Server shutdown in progress'
    2003,   # 'Can't connect to MySQL server'
    2006,   # Error code 2006 'MySQL server has gone away' indicates that
            # the connection used was closed or dropped
    2013,   # 'Lost connection to MySQL server during query'
            # TODO(akeshet): consider only retrying UPDATE queries against
            # this error code, not INSERT queries, since we don't know
            # whether the query completed before or after the connection
            # lost.
    2026,   # 'SSL connection error: unknown error number'
)


def _IsRetryableException(e):
  """Determine whether a query should be retried based on exception.

  Intended for use as a handler for retry_util.

  Args:
    e: The exception to be filtered.

  Returns:
    True if the query should be retried, False otherwise.
  """
  if isinstance(e, sqlalchemy.exc.OperationalError):
    error_code = e.orig.args[0]
    if error_code in _RETRYABLE_OPERATIONAL_ERROR_CODES:
      return True

  return False


class DBException(Exception):
  """General exception class for this module."""


class UnsupportedMethodException(DBException):
  """Raised when a call is made that the database does not support."""


def minimum_schema(min_version):
  """Generate a decorator to specify a minimum schema version for a method.

  This decorator should be applied only to instance methods of
  SchemaVersionedMySQLConnection objects.
  """

  def decorator(f):
    def wrapper(self, *args, **kwargs):
      if self.schema_version < min_version:
        raise UnsupportedMethodException()
      return f(self, *args, **kwargs)
    return wrapper
  return decorator


class StrictModeListener(sqlalchemy.interfaces.PoolListener):
  """This listener ensures that STRICT_ALL_TABLES for all connections."""
  # pylint: disable=W0613
  def connect(self, dbapi_con, *args, **kwargs):
    cur = dbapi_con.cursor()
    cur.execute("SET SESSION sql_mode='STRICT_ALL_TABLES'")
    cur.close()


class SchemaVersionedMySQLConnection(object):
  """Connection to a database that is aware of its schema version."""

  SCHEMA_VERSION_TABLE_NAME = 'schemaVersionTable'
  SCHEMA_VERSION_COL = 'schemaVersion'

  def __init__(self, db_name, db_migrations_dir, db_credentials_dir):
    """SchemaVersionedMySQLConnection constructor.

    Args:
      db_name: Name of the database to connect to.
      db_migrations_dir: Absolute path to directory of migration scripts
                         for this database.
      db_credentials_dir: Absolute path to directory containing connection
                          information to the database. Specifically, this
                          directory should contain files names user.txt,
                          password.txt, host.txt, client-cert.pem,
                          client-key.pem, and server-ca.pem
    """
    # None, or a sqlalchemy.MetaData instance
    self._meta = None

    # pid of process on which _engine was created
    self._engine_pid = None

    self._engine = None

    self.db_migrations_dir = db_migrations_dir
    self.db_credentials_dir = db_credentials_dir
    self.db_name = db_name

    with open(os.path.join(db_credentials_dir, 'password.txt')) as f:
      password = f.read().strip()
    with open(os.path.join(db_credentials_dir, 'host.txt')) as f:
      host = f.read().strip()
    with open(os.path.join(db_credentials_dir, 'user.txt')) as f:
      user = f.read().strip()

    cert = os.path.join(db_credentials_dir, 'client-cert.pem')
    key = os.path.join(db_credentials_dir, 'client-key.pem')
    ca = os.path.join(db_credentials_dir, 'server-ca.pem')
    self._ssl_args = {'ssl': {'cert': cert, 'key': key, 'ca': ca}}

    connect_url = sqlalchemy.engine.url.URL('mysql', username=user,
                                            password=password,
                                            host=host)

    # Create a temporary engine to connect to the mysql instance, and check if
    # a database named |db_name| exists. If not, create one. We use a temporary
    # engine here because the real engine will be opened with a default
    # database name given by |db_name|.
    temp_engine = sqlalchemy.create_engine(connect_url,
                                           connect_args=self._ssl_args,
                                           listeners=[StrictModeListener()])
    databases = self._ExecuteWithEngine('SHOW DATABASES',
                                        temp_engine).fetchall()
    if (db_name,) not in databases:
      self._ExecuteWithEngine('CREATE DATABASE %s' % db_name, temp_engine)
      logging.info('Created database %s', db_name)

    temp_engine.dispose()

    # Now create the persistent connection to the database named |db_name|.
    # If there is a schema version table, read the current schema version
    # from it. Otherwise, assume schema_version 0.
    self._connect_url = sqlalchemy.engine.url.URL('mysql', username=user,
                                                  password=password,
                                                  host=host, database=db_name)

    self.schema_version = self.QuerySchemaVersion()

    logging.info('Created a SchemaVersionedMySQLConnection, '
                 'sqlalchemy version %s', sqlalchemy.__version__)

  def DropDatabase(self):
    """Delete all data and tables from database, and drop database.

    Use with caution. All data in database will be deleted. Invalidates
    this database connection instance.
    """
    self._meta = None
    self._Execute('DROP DATABASE %s' % self.db_name)
    self._InvalidateEngine()

  def QuerySchemaVersion(self):
    """Query the database for its current schema version number.

    Returns:
      The current schema version from the database's schema version table,
      as an integer, or 0 if the table is empty or nonexistent.
    """
    tables = self._Execute('SHOW TABLES').fetchall()
    if (self.SCHEMA_VERSION_TABLE_NAME,) in tables:
      r = self._Execute('SELECT MAX(%s) from %s' % (
          self.SCHEMA_VERSION_COL, self.SCHEMA_VERSION_TABLE_NAME))
      return r.fetchone()[0] or 0
    else:
      return 0

  def _GetMigrationScripts(self):
    """Look for migration scripts and return their versions and paths."

    Returns:
      A list of (schema_version, script_path) tuples of the migration
      scripts for this database, sorted in ascending schema_version order.
    """
    # Look for migration script files in the migration script directory,
    # with names of the form [number]*.sql, and sort these by number.
    migration_scripts = glob.glob(os.path.join(self.db_migrations_dir, '*.sql'))
    migrations = []
    for script in migration_scripts:
      match = re.match(r'([0-9]*).*', os.path.basename(script))
      if match:
        migrations.append((int(match.group(1)), script))

    migrations.sort()
    return migrations

  def ApplySchemaMigrations(self, maxVersion=None):
    """Apply pending migration scripts to database, in order.

    Args:
      maxVersion: The highest version migration script to apply. If
                  unspecified, all migrations found will be applied.
    """
    migrations = self._GetMigrationScripts()

    # Execute the migration scripts in order, asserting that each one
    # updates the schema version to the expected number. If maxVersion
    # is specified stop early.
    for (number, script) in migrations:
      if maxVersion is not None and number > maxVersion:
        break

      if number > self.schema_version:
        # Invalidate self._meta, then run script and ensure that schema
        # version was increased.
        self._meta = None
        logging.info('Running migration script %s', script)
        self.RunQueryScript(script)
        self.schema_version = self.QuerySchemaVersion()
        if self.schema_version != number:
          raise DBException('Migration script %s did not update '
                            'schema version to %s as expected. ' % (number,
                                                                    script))

  def RunQueryScript(self, script_path):
    """Run a .sql script file located at |script_path| on the database."""
    with open(script_path, 'r') as f:
      script = f.read()
    queries = [q.strip() for q in script.split(';') if q.strip()]
    for q in queries:
      # This is intentionally not wrapped in retries.
      self._GetEngine().execute(q)

  def _ReflectToMetadata(self):
    """Use sqlalchemy reflection to construct MetaData model of database.

    If self._meta is already populated, this does nothing.
    """
    if self._meta is not None:
      return
    self._meta = MetaData()
    self._meta.reflect(bind=self._GetEngine())

  def _Insert(self, table, values):
    """Create and execute a one-row INSERT query.

    Args:
      table: Table name to insert to.
      values: Dictionary of column values to insert.

    Returns:
      Integer primary key of the inserted row.
    """
    self._ReflectToMetadata()
    ins = self._meta.tables[table].insert().values(values)
    r = self._Execute(ins)
    return r.inserted_primary_key[0]

  def _InsertMany(self, table, values):
    """Create and execute an multi-row INSERT query.

    Args:
      table: Table name to insert to.
      values: A list of value dictionaries to insert multiple rows.

    Returns:
      The number of inserted rows.
    """
    # sqlalchemy 0.7 and prior has a bug in which it does not always
    # correctly unpack a list of rows to multi-insert if the list contains
    # only one item.
    if len(values) == 1:
      self._Insert(table, values[0])
      return 1

    self._ReflectToMetadata()
    ins = self._meta.tables[table].insert()
    r = self._Execute(ins, *values)
    return r.rowcount

  def _GetPrimaryKey(self, table):
    """Gets the primary key column of |table|.

    This function requires that the given table have a 1-column promary key.

    Args:
      table: Name of table to primary key for.

    Returns:
      A sqlalchemy.sql.schema.Column representing the primary key column.

    Raises:
      DBException if the table does not have a single column primary key.
   """
    self._ReflectToMetadata()
    t = self._meta.tables[table]

    # TODO(akeshet): between sqlalchemy 0.7 and 0.8, a breaking change was
    # made to how t.columns and t.primary_key are stored, and in sqlalchemy
    # 0.7 t.columns does not have a .values() method. Hence this clumsy way
    # of extracting the primary key column. Currently, our builders have 0.7
    # installed. Once we drop support for 0.7, this code can be simply replaced
    # by:
    # key_columns = t.primary_key.columns.values()
    col_names = t.columns.keys()
    cols = [t.columns[n] for n in col_names]
    key_columns = [c for c in cols if c.primary_key]

    if len(key_columns) != 1:
      raise DBException('Table %s does not have a 1-column primary '
                        'key.' % table)
    return key_columns[0]

  def _Update(self, table, row_id, values):
    """Create and execute an UPDATE query by primary key.

    Args:
      table: Table name to update.
      row_id: Primary key value of row to update.
      values: Dictionary of column values to update.

    Returns:
      The number of rows that were updated (0 or 1).
    """
    self._ReflectToMetadata()
    primary_key = self._GetPrimaryKey(table)
    upd = self._meta.tables[table].update().where(
        primary_key == row_id).values(values)
    r = self._Execute(upd)
    return r.rowcount

  def _UpdateWhere(self, table, where, values):
    """Create and execute an update query with a custom where clause.

    Args:
      table: Table name to update.
      where: Raw SQL for the where clause, in string form, e.g.
             'build_id = 1 and board = "tomato"'
      values: dictionary of column values to update.

    Returns:
      The number of rows that were updated.
    """
    self._ReflectToMetadata()
    upd = self._meta.tables[table].update().where(where)
    r = self._Execute(upd, values)
    return r.rowcount

  def _Select(self, table, row_id, columns):
    """Create and execute a one-row one-table SELECT query by primary key.

    Args:
      table: Table name to select from.
      row_id: Primary key value of row to select.
      columns: List of column names to select.

    Returns:
      A column name to column value dict for the row found, if a row was found.
      None if no row was.
    """
    self._ReflectToMetadata()
    primary_key = self._GetPrimaryKey(table)
    table_m = self._meta.tables[table]
    columns_m = [table_m.c[col_name] for col_name in columns]
    sel = sqlalchemy.sql.select(columns_m).where(primary_key == row_id)
    r = self._Execute(sel).fetchall()
    if r:
      assert len(r) == 1, 'Query by primary key returned more than 1 row.'
      return dict(zip(columns, r[0]))
    else:
      return None

  def _SelectWhere(self, table, where, columns):
    """Create and execute a one-table SELECT query with a custom where clause.

    Args:
      table: Table name to update.
      where: Raw SQL for the where clause, in string form, e.g.
             'build_id = 1 and board = "tomato"'
      columns: List of column names to select.

    Returns:
      A list of column name to column value dictionaries each representing
      a row that was selected.
    """
    self._ReflectToMetadata()
    table_m = self._meta.tables[table]
    columns_m = [table_m.c[col_name] for col_name in columns]
    sel = sqlalchemy.sql.select(columns_m).where(where)
    r = self._Execute(sel)
    return [dict(zip(columns, values)) for values in r.fetchall()]

  def _Execute(self, query, *args, **kwargs):
    """Execute a query with retries.

    This method executes a query using the engine credentials that
    were set up in the constructor for this object. If necessary,
    a new engine unique to this pid will be created.

    Args:
      query: Query to execute, of type string, or sqlalchemy.Executible,
             or other sqlalchemy-executible statement (see sqlalchemy
             docs).
      *args: Additional args passed along to .execute(...)
      **kwargs: Additional args passed along to .execute(...)

    Returns:
      The result of .execute(...)
    """
    return self._ExecuteWithEngine(query, self._GetEngine(),
                                   *args, **kwargs)

  def _ExecuteWithEngine(self, query, engine, *args, **kwargs):
    """Execute a query using |engine|, with retires.

    This method wraps execution of a query against an engine in retries.
    The engine will automatically create new connections if a prior connection
    was dropped.

    Args:
      query: Query to execute, of type string, or sqlalchemy.Executible,
             or other sqlalchemy-executible statement (see sqlalchemy
             docs).
      engine: sqlalchemy.engine to use.
      *args: Additional args passed along to .execute(...)
      **kwargs: Additional args passed along to .execute(...)

    Returns:
      The result of .execute(...)
    """
    f = lambda: engine.execute(query, *args, **kwargs)
    logging.info('Running cidb query on pid %s, repr(query) starts with %s',
                 os.getpid(), repr(query)[:100])
    return retry_stats.RetryWithStats(
        retry_stats.CIDB,
        handler=_IsRetryableException,
        max_retry=8,
        sleep=4,
        backoff_factor=2,
        functor=f)

  def _GetEngine(self):
    """Get the sqlalchemy engine for this process.

    This method creates a new sqlalchemy engine if necessary, and
    returns an engine that is unique to this process.

    Returns:
      An sqlalchemy.engine instance for this database.
    """
    pid = os.getpid()
    if pid == self._engine_pid and self._engine:
      return self._engine
    else:
      e = sqlalchemy.create_engine(self._connect_url,
                                   connect_args=self._ssl_args,
                                   listeners=[StrictModeListener()])
      self._engine = e
      self._engine_pid = pid
      logging.info('Created cidb engine %s@%s for pid %s', e.url.username,
                   e.url.host, pid)
      return self._engine

  def _InvalidateEngine(self):
    """Dispose of an sqlalchemy engine."""
    try:
      pid = os.getpid()
      if pid == self._engine_pid and self._engine:
        self._engine.dispose()
    finally:
      self._engine = None
      self._meta = None


class CIDBConnection(SchemaVersionedMySQLConnection):
  """Connection to a Continuous Integration database."""

  _SQL_FETCH_ACTIONS = (
      'SELECT c.id, b.id, action, c.reason, build_config, '
      'change_number, patch_number, change_source, timestamp FROM '
      'clActionTable c JOIN buildTable b ON build_id = b.id ')

  def __init__(self, db_credentials_dir):
    super(CIDBConnection, self).__init__('cidb', CIDB_MIGRATIONS_DIR,
                                         db_credentials_dir)

  def GetTime(self):
    """Gets the current time, according to database.

    Returns:
      datetime.datetime instance.
    """
    return self._Execute('SELECT NOW()').fetchall()[0][0]

  @minimum_schema(32)
  def InsertBuild(self, builder_name, waterfall, build_number,
                  build_config, bot_hostname, master_build_id=None,
                  timeout_seconds=None):
    """Insert a build row.

    Args:
      builder_name: buildbot builder name.
      waterfall: buildbot waterfall name.
      build_number: buildbot build number.
      build_config: cbuildbot config of build
      bot_hostname: hostname of bot running the build
      master_build_id: (Optional) primary key of master build to this build.
      timeout_seconds: (Optional) If provided, total time allocated for this
          build. A deadline is recorded in cidb for the current build to end.
    """
    values = {
        'builder_name': builder_name,
        'buildbot_generation': constants.BUILDBOT_GENERATION,
        'waterfall': waterfall,
        'build_number': build_number,
        'build_config': build_config,
        'bot_hostname': bot_hostname,
        'start_time': sqlalchemy.func.current_timestamp(),
        'master_build_id': master_build_id}
    if timeout_seconds is not None:
      now = self.GetTime()
      duration = datetime.timedelta(seconds=timeout_seconds)
      values.update({'deadline': now + duration})

    return self._Insert('buildTable', values)

  @minimum_schema(3)
  def InsertCLActions(self, build_id, cl_actions):
    """Insert a list of |cl_actions|.

    If |cl_actions| is empty, this function does nothing.

    Args:
      build_id: primary key of build that performed these actions.
      cl_actions: A list of CLAction objects.

    Returns:
      Number of actions inserted.
    """
    if not cl_actions:
      return 0

    values = []
    for cl_action in cl_actions:
      change_number = cl_action.change_number
      patch_number = cl_action.patch_number
      change_source = cl_action.change_source
      action = cl_action.action
      reason = cl_action.reason
      values.append({
          'build_id': build_id,
          'change_source': change_source,
          'change_number': change_number,
          'patch_number': patch_number,
          'action': action,
          'reason': reason})

    return self._InsertMany('clActionTable', values)

  @minimum_schema(6)
  def InsertBoardPerBuild(self, build_id, board):
    """Inserts a board-per-build entry into database.

    Args:
      build_id: primary key of the build in the buildTable
      board: String board name.
    """
    self._Insert('boardPerBuildTable', {'build_id': build_id,
                                        'board': board})

  @minimum_schema(7)
  def InsertChildConfigPerBuild(self, build_id, child_config):
    """Insert a child-config-per-build entry into database.

    Args:
      build_id: primary key of the build in the buildTable
      child_config: String child_config name.
    """
    self._Insert('childConfigPerBuildTable', {'build_id': build_id,
                                              'child_config': child_config})

  @minimum_schema(28)
  def InsertBuildStage(self, build_id, name, board=None,
                       status=constants.BUILDER_STATUS_PLANNED):
    """Insert a build stage entry into database.

    Args:
      build_id: primary key of the build in buildTable
      name: Full name of build stage.
      board: (Optional) board name, if this is a board-specific stage.
      status: (Optional) stage status, one of constants.BUILDER_ALL_STATUSES.
              Default constants.BUILDER_STATUS_PLANNED.

    Returns:
      Integer primary key of inserted stage, i.e. build_stage_id
    """
    return self._Insert('buildStageTable', {'build_id': build_id,
                                            'name': name,
                                            'board': board,
                                            'status': status})

  @minimum_schema(29)
  def InsertFailure(self, build_stage_id, exception,
                    exception_category=constants.EXCEPTION_CATEGORY_UNKNOWN,
                    outer_failure_id=None,
                    extra_info=None):
    """Insert a failure description into database.

    Args:
      build_stage_id: primary key, in buildStageTable, of the stage where
                      failure occured.
      exception: Exception instance that occured.
      exception_category: (Optional) one of
                          constants.EXCEPTION_CATEGORY_ALL_CATEGORIES,
                          Default: 'unknown'.
      outer_failure_id: (Optional) primary key of outer failure which contains
                        this failure. Used to store CompoundFailure
                        relationship.
      extra_info: (Optional) extra category-specific string description giving
                  failure details. Used for programmatic triage.
    """
    values = {'build_stage_id': build_stage_id,
              'exception_type': type(exception).__name__,
              'exception_message': exception.message,
              'exception_category': exception_category,
              'outer_failure_id': outer_failure_id,
              'extra_info': extra_info}

    return self._Insert('failureTable', values)

  @minimum_schema(2)
  def UpdateMetadata(self, build_id, metadata):
    """Update the given metadata row in database.

    Args:
      build_id: id of row to update.
      metadata: CBuildbotMetadata instance to update with.

    Returns:
      The number of build rows that were updated (0 or 1).
    """
    d = metadata.GetDict()
    versions = d.get('version') or {}
    return self._Update('buildTable', build_id,
                        {'chrome_version': versions.get('chrome'),
                         'milestone_version': versions.get('milestone'),
                         'platform_version': versions.get('platform'),
                         'full_version': versions.get('full'),
                         'sdk_version': d.get('sdk-versions'),
                         'toolchain_url': d.get('toolchain-url'),
                         'build_type': d.get('build_type')})

  @minimum_schema(32)
  def ExtendDeadline(self, build_id, timeout_seconds):
    """Extend the deadline for this build.

    Args:
      build_id: primary key, in buildTable, of the build for which deadline
          should be extended.
      timeout_seconds: Time remaining for the deadline from the current time.

    Returns:
      Number of rows updated (1 for success, 0 for failure)
      Deadline extension can fail if
        (1) The deadline is already past, or
        (2) The new deadline requested is earlier than the original deadline.
    """
    return self._Execute(
        'UPDATE buildTable SET deadline = NOW() + INTERVAL %s SECOND WHERE '
        'id = %s AND '
        '(deadline = 0 OR deadline > NOW()) AND '
        'NOW() + INTERVAL %s SECOND > deadline',
        timeout_seconds, build_id, timeout_seconds).rowcount

  @minimum_schema(6)
  def UpdateBoardPerBuildMetadata(self, build_id, board, board_metadata):
    """Update the given board-per-build metadata.

    Args:
      build_id: id of the build
      board: board to update
      board_metadata: per-board metadata dict for this board
    """
    update_dict = {
        'main_firmware_version': board_metadata.get('main-firmware-version'),
        'ec_firmware_version': board_metadata.get('ec-firmware-version'),
    }
    return self._UpdateWhere(
        'boardPerBuildTable',
        'build_id = %s and board = "%s"' % (build_id, board),
        update_dict)

  @minimum_schema(28)
  def StartBuildStage(self, build_stage_id):
    """Marks a build stage as inflight, in the database.

    Args:
      build_stage_id: primary key of the build stage in buildStageTable.
    """
    current_timestamp = sqlalchemy.func.current_timestamp()
    return self._Update(
        'buildStageTable',
        build_stage_id,
        {'status': constants.BUILDER_STATUS_INFLIGHT,
         'start_time': current_timestamp})

  @minimum_schema(28)
  def FinishBuildStage(self, build_stage_id, status):
    """Marks a build stage as finished, in the database.

    Args:
      build_stage_id: primary key of the build stage in buildStageTable.
      status: one of constants.BUILDER_COMPLETED_STATUSES
    """
    current_timestamp = sqlalchemy.func.current_timestamp()
    return self._Update(
        'buildStageTable',
        build_stage_id,
        {'status': status,
         'finish_time': current_timestamp,
         'final': True})

  @minimum_schema(25)
  def FinishBuild(self, build_id, status=None, summary=None, metadata_url=None):
    """Update the given build row, marking it as finished.

    This should be called once per build, as the last update to the build.
    This will also mark the row's final=True.

    Args:
      build_id: id of row to update.
      status: Final build status, one of
              constants.BUILDER_COMPLETED_STATUSES.
      summary: A summary of the build (failures) collected from all slaves.
      metadata_url: google storage url to metadata.json file for this build,
                    e.g. ('gs://chromeos-image-archive/master-paladin/'
                          'R39-6225.0.0-rc1/metadata.json')
    """
    self._ReflectToMetadata()
    if summary:
      summary = summary[:1024]
    # The current timestamp is evaluated on the database, not locally.
    current_timestamp = sqlalchemy.func.current_timestamp()
    self._Update('buildTable', build_id, {'finish_time': current_timestamp,
                                          'status': status,
                                          'summary': summary,
                                          'metadata_url': metadata_url,
                                          'final': True})


  @minimum_schema(16)
  def FinishChildConfig(self, build_id, child_config, status=None):
    """Marks the given child config as finished with |status|.

    This should be called before FinishBuild, on all child configs that
    were used in a build.

    Args:
      build_id: primary key of the build in the buildTable
      child_config: String child_config name.
      status: Final child_config status, one of
              constants.BUILDER_COMPLETED_STATUSES or None
              for default "inflight".
    """
    self._Execute(
        'UPDATE childConfigPerBuildTable '
        'SET status="%s", final=1 '
        'WHERE (build_id, child_config) = (%s, "%s")' %
        (status, build_id, child_config))


  @minimum_schema(2)
  def GetBuildStatus(self, build_id):
    """Gets the status of the build.

    Args:
      build_id: build id to fetch.

    Returns:
      Dictionary for a single build (see GetBuildStatuses for keys) or
      None if no build with this id was found.
    """
    statuses = self.GetBuildStatuses([build_id])
    return statuses[0] if statuses else None

  @minimum_schema(2)
  def GetBuildStatuses(self, build_ids):
    """Gets the statuses of the builds.

    Args:
      build_ids: A list of build id to fetch.

    Returns:
      A list of dictionary with keys (id, build_config, start_time,
      finish_time, status, waterfall, build_number, builder_name, full_version),
      or None if no build with this id was found.
    """
    return self._SelectWhere(
        'buildTable',
        'id IN (%s)' % ','.join(str(x) for x in build_ids),
        ['id', 'build_config', 'start_time', 'finish_time', 'status',
         'waterfall', 'build_number', 'builder_name', 'full_version'])

  @minimum_schema(2)
  def GetSlaveStatuses(self, master_build_id):
    """Gets the statuses of slave builders to given build.

    Args:
      master_build_id: build id of the master build to fetch the slave
                       statuses for.

    Returns:
      A list containing, for each slave build (row) found, a dictionary
      with keys (id, build_config, start_time, finish_time, status).
    """
    return self._SelectWhere('buildTable',
                             'master_build_id = %s' % master_build_id,
                             ['id', 'build_config', 'start_time',
                              'finish_time', 'status'])

  @minimum_schema(32)
  def GetTimeToDeadline(self, build_id):
    """Gets the time remaining till the deadline for given build_id.

    Always use this function to find time remaining to a deadline. This function
    computes all times on the database. You run the risk of hitting timezone
    issues if you compute remaining time locally.

    Args:
      build_id: The build_id of the build to query.

    Returns:
      The time remaining to the deadline in seconds.
      0 if the deadline is already past.
      None if no deadline is found.
    """
    # Sign information is lost in the timediff coercion into python
    # datetime.timedelta type. So, we must find out if the deadline is past
    # separately.
    r = self._Execute(
        'SELECT deadline >= NOW(), TIMEDIFF(deadline, NOW()) '
        'from buildTable where id = %s' % build_id).fetchall()
    if not r:
      return None

    time_remaining = r[0][1]
    if time_remaining is None:
      return None

    deadline_past = (r[0][0] == 0)
    return 0 if deadline_past else abs(time_remaining.total_seconds())

  @minimum_schema(2)
  def GetLastBuildStatuses(self, build_config, number):
    """Returns basic information about most recent builds.

    Args:
      build_config: config name of the build.
      number: number of builds to search back.

    Returns:
      A sorted list of dicts containining up to |number| dictionaries for
      build statuses in descending order. Dictionaries contain
      id, build_config, start_time, finish_time, full_version and status.
    """
    results = self._Execute(
        'SELECT id, build_config, start_time, finish_time, full_version, status'
        ' FROM buildTable'
        ' WHERE build_config = "%s"'
        ' ORDER BY id DESC LIMIT %d' % (build_config, number)).fetchall()
    columns = ['id', 'build_config', 'start_time', 'finish_time',
               'full_version', 'status']
    return [dict(zip(columns, values)) for values in results]

  @minimum_schema(11)
  def GetActionsForChanges(self, changes):
    """Gets all the actions for the given changes.

    Note, this includes all patches of the given changes.

    Args:
      changes: A list of GerritChangeTuple, GerritPatchTuple or GerritPatch
               specifying the changes to whose actions should be fetched.

    Returns:
      A list of CLAction instances, in action id order.
    """
    if not changes:
      return []

    clauses = []
    # Note: We are using a string of OR statements rather than a 'WHERE IN'
    # style clause, because 'WHERE IN' does not make use of multi-column
    # indexes, and therefore has poor performance with a large table.
    for change in changes:
      change_number = int(change.gerrit_number)
      change_source = 'internal' if change.internal else 'external'
      clauses.append('(change_number, change_source) = (%s, "%s")' %
                     (change_number, change_source))
    clause = ' OR '.join(clauses)
    results = self._Execute(
        '%s WHERE %s' % (self._SQL_FETCH_ACTIONS, clause)).fetchall()
    return [clactions.CLAction(*values) for values in results]

  @minimum_schema(11)
  def GetActionHistory(self, start_date, end_date=None):
    """Get the action history of CLs in the specified range.

    This will get the full action history of any patches that were touched
    by the CQ or Pre-CQ during the specified time range. Note: Since this
    includes the full action history of these patches, it may include actions
    outside the time range.

    Args:
      start_date: The first date on which you want action history.
      end_date: The last date on which you want action history.
    """
    values = {'start_date': str(start_date),
              'end_date': str(end_date)}

    # Enforce start and end date.
    conds = 'timestamp >= %(start_date)s'
    if end_date:
      conds += ' AND timestamp <= %(end_date)s'

    changes = ('SELECT DISTINCT change_number, patch_number, change_source '
               'FROM clActionTable WHERE %s' % conds)
    query = '%s NATURAL JOIN (%s) as w' % (self._SQL_FETCH_ACTIONS, changes)
    results = self._Execute(query, values).fetchall()
    return [clactions.CLAction(*values) for values in results]


class CIDBConnectionFactory(object):
  """Factory class used by builders to fetch the appropriate cidb connection"""

  # A call to one of the Setup methods below is necessary before using the
  # GetCIDBConnectionForBuilder Factory. This ensures that unit tests do not
  # accidentally use one of the live database instances.

  _ConnectionIsSetup = False
  _ConnectionType = None
  _ConnectionCredsPath = None
  _MockCIDB = None
  _CachedCIDB = None

  _CONNECTION_TYPE_PROD = 'prod'   # production database
  _CONNECTION_TYPE_DEBUG = 'debug' # debug database, used by --debug builds
  _CONNECTION_TYPE_MOCK = 'mock'   # mock connection, not backed by database
  _CONNECTION_TYPE_NONE = 'none'   # explicitly no connection
  _CONNECTION_TYPE_INV = 'invalid' # invalidated connection


  @classmethod
  def IsCIDBSetup(cls):
    """Returns True iff GetCIDBConnectionForBuilder is ready to be called."""
    return cls._ConnectionIsSetup

  @classmethod
  def GetCIDBConnectionType(cls):
    """Returns the type of db connection that is set up.

    Returns:
      One of ('prod', 'debug', 'mock', 'none', 'invalid', None)
    """
    return cls._ConnectionType

  @classmethod
  def InvalidateCIDBSetup(cls):
    """Invalidate the CIDB connection factory.

    This method may be called at any time, even after a setup method. Once
    this is called, future calls to GetCIDBConnectionForBuilder will raise
    an assertion error.
    """
    cls._ConnectionType = cls._CONNECTION_TYPE_INV
    cls._CachedCIDB = None

  @classmethod
  def SetupProdCidb(cls):
    """Sets up CIDB to use the prod instance of the database.

    May be called only once, and may not be called after any other CIDB Setup
    method, otherwise it will raise an AssertionError.
    """
    assert not cls._ConnectionIsSetup, 'CIDB is already set up.'
    assert not cls._ConnectionType == cls._CONNECTION_TYPE_MOCK, (
        'CIDB set for mock use.')
    cls._ConnectionType = cls._CONNECTION_TYPE_PROD
    cls._ConnectionCredsPath = constants.CIDB_PROD_BOT_CREDS
    cls._ConnectionIsSetup = True


  @classmethod
  def SetupDebugCidb(cls):
    """Sets up CIDB to use the debug instance of the database.

    May be called only once, and may not be called after any other CIDB Setup
    method, otherwise it will raise an AssertionError.
    """
    assert not cls._ConnectionIsSetup, 'CIDB is already set up.'
    assert not cls._ConnectionType == cls._CONNECTION_TYPE_MOCK, (
        'CIDB set for mock use.')
    cls._ConnectionType = cls._CONNECTION_TYPE_DEBUG
    cls._ConnectionCredsPath = constants.CIDB_DEBUG_BOT_CREDS
    cls._ConnectionIsSetup = True


  @classmethod
  def SetupMockCidb(cls, mock_cidb=None):
    """Sets up CIDB to use a mock object. May be called more than once.

    Args:
      mock_cidb: (optional) The mock cidb object to be returned by
                 GetCIDBConnection. If not supplied, then CIDB will be
                 considered not set up, but future calls to set up a
                 non-(mock or None) connection will fail.
    """
    if cls._ConnectionIsSetup:
      assert cls._ConnectionType == cls._CONNECTION_TYPE_MOCK, (
          'A non-mock CIDB is already set up.')
    cls._ConnectionType = cls._CONNECTION_TYPE_MOCK
    if mock_cidb:
      cls._ConnectionIsSetup = True
      cls._MockCIDB = mock_cidb


  @classmethod
  def SetupNoCidb(cls):
    """Sets up CIDB to use an explicit None connection.

    May be called more than once, or after SetupMockCidb.
    """
    if cls._ConnectionIsSetup:
      assert (cls._ConnectionType == cls._CONNECTION_TYPE_MOCK or
              cls._ConnectionType == cls._CONNECTION_TYPE_NONE), (
                  'A non-mock CIDB is already set up.')
    cls._ConnectionType = cls._CONNECTION_TYPE_NONE
    cls._ConnectionIsSetup = True


  @classmethod
  def ClearMock(cls):
    """Clear a mock CIDB object.

    This method clears a cidb mock object, but leaves the connection factory
    in _CONNECTION_TYPE_MOCK, so that future calls to set up a non-mock
    cidb will fail.
    """
    assert cls._ConnectionType == cls._CONNECTION_TYPE_MOCK, (
        'CIDB is not set for mock use.')
    cls._ConnectionIsSetup = False
    cls._MockCIDB = None


  @classmethod
  def GetCIDBConnectionForBuilder(cls):
    """Get a CIDBConnection.

    A call to one of the CIDB Setup methods must have been made before calling
    this factory method.

    Returns:
      A CIDBConnection instance connected to either the prod or debug
      instance of the database, or a mock connection, depending on which
      Setup method was called. Returns None if CIDB has been explicitly
      set up for that using SetupNoCidb.
    """
    assert cls._ConnectionIsSetup, 'CIDB has not be set up with a Setup call.'
    assert cls._ConnectionType != cls._CONNECTION_TYPE_INV, (
        'CIDB Connection factory has been invalidated.')
    if cls._ConnectionType == cls._CONNECTION_TYPE_MOCK:
      return cls._MockCIDB
    elif cls._ConnectionType == cls._CONNECTION_TYPE_NONE:
      return None
    else:
      if not cls._CachedCIDB:
        cls._CachedCIDB = CIDBConnection(cls._ConnectionCredsPath)
      return cls._CachedCIDB

  @classmethod
  def _ClearCIDBSetup(cls):
    """Clears the CIDB Setup state. For testing purposes only."""
    cls._ConnectionIsSetup = False
    cls._ConnectionType = None
    cls._ConnectionCredsPath = None
    cls._MockCIDB = None
    cls._CachedCIDB = None