#!/usr/bin/env python3

import argparse
import socket
import sys
import threading
import psycopg2
import psycopg2.extras
import queue
import os
import signal
import json
import logging

#
# Errors
#

class InvalidConfigError(Exception):
    pass
class DuplicateMetricVersionError(Exception):
    pass
class UnsupportedMetricVersionError(Exception):
    pass
class RequestTimeoutError(Exception):
    pass

#
# Logging
#

logger = None

# Store the current log file since there is no public method to get the filename
# from a FileHandler object
current_log_file = None

# Handler objects for easy adding/removing/modifying
file_log_handler = None
stderr_log_handler = None

def init_logging(config):
    """
    Initialize (or re-initialize/modify) logging
    """
    global logger
    global file_log_handler
    global stderr_log_handler

    # Get the logger object
    logger = logging.getLogger(__name__)

    # Create a common formatter
    formatter = logging.Formatter('%(asctime)s - %(levelname)s - %(message)s')

    # Set up or modify stderr logging
    if config.stderr_log_level != 'OFF':
        # Create and add the handler if it doesn't exist
        if stderr_log_handler is None:
            stderr_log_handler = logging.StreamHandler()
            logger.addHandler(stderr_log_handler)

        # Set the formatter
        stderr_log_handler.setFormatter(formatter)

        # Set the log level
        level = logging.getLevelName(config.stderr_log_level)
        stderr_log_handler.setLevel(level)
    else:
        if stderr_log_handler is not None:
            logger.removeHandler(stderr_log_handler)
            stderr_log_handler = None

    # Set up or modify file logging
    if config.file_log_level != 'OFF':
        # Create and add the handler if it doesn't exist
        if file_log_handler is None:
            file_log_handler = logging.FileHandler(config.log_file, encoding='utf-8')
            logger.addHandler(file_log_handler)

        # Set the formatter
        file_log_handler.setFormatter(formatter)

        # Set the log level
        level = logging.getLevelName(config.file_log_level)
        file_log_handler.setLevel(level)

        # Note where logs are being written
        print("Logging to {}".format(config.log_file))
    else:
        if file_log_handler is not None:
            logger.removeHandler(file_log_handler)
            file_log_handler = None

#
# PID file handling
#
def write_pid_file(pid_file):
    with open(pid_file, 'w') as f:
        f.write("{}".format(os.getpid()))

def read_pid_file(pid_file):
    with open(pid_file, 'r') as f:
        return int(f.read().strip())

def remove_pid_file(pid_file):
    os.unlink(pid_file)

#
# Global flags for signal handler
#
running = True
reload = False

#
# Signal handler
#
def signal_handler(sig, frame):
    # Restore the original handler
    signal.signal(signal.SIGINT, signal.default_int_handler)

    # Signal everything to shut down
    if sig in [ signal.SIGINT, signal.SIGTERM, signal.SIGQUIT ]:
        logger.info("Shutting down ...")
        global running
        running = False
    elif sig == signal.SIGHUP:
        logger.info("Reloading config ...")
        global reload
        reload = True

#
# Classes
#

class Config:
    """
    Agent configuration
    """
    def __init__(self, config_file, read_metrics = True):
        # Set defaults
        self.pid_file = '/tmp/pgmon.pid'    # PID file

        self.ipc_socket = '/tmp/pgmon.sock' # IPC socket
        self.ipc_timeout = 10               # IPC communication timeout (s)
        self.request_timeout = 10           # Request processing timeout (s)
        self.request_queue_size = 100       # Max size of the request queue before it blocks
        self.request_queue_timeout = 2      # Max time to wait when queueing a request (s)
        self.worker_count = 4               # Number of worker threads

        self.stderr_log_level = 'INFO'      # Log level for stderr logging (or 'off')
        self.file_log_level = 'INFO'        # Log level for file logging (od 'off')
        self.log_file = 'pgmon.log'         # Log file

        self.host = 'localhost'             # DB host
        self.port = 5432                    # DB port
        self.user = 'postgres'              # DB user
        self.password = None                # DB password
        self.dbname = 'postgres'            # DB name

        self.metrics = {}                   # Metrics

        # Dynamic values
        self.pg_version = None              # PostgreSQL version

        # Read config
        self.read_file(config_file, read_metrics)

    def read_file(self, config_file, read_metrics = True):
        with open(config_file, 'r') as f:
            for line in f:
                line = line.strip()

                if line.startswith('#'):
                    continue
                elif line == '':
                    continue

                (key, value) = line.split('=', 1)
                if value is None:
                    raise InvalidConfigError("{}: {}", config_file, line)

                if key == 'include':
                    self.read_file(value, read_metrics)
                elif key == 'pid_file':
                    self.pid_file = value
                elif key == 'ipc_socket':
                    self.ipc_socket = value
                elif key == 'ipc_timeout':
                    self.ipc_timeout = float(value)
                elif key == 'request_timeout':
                    self.request_timeout = float(value)
                elif key == 'request_queue_size':
                    self.request_queue_size = int(value)
                elif key == 'request_queue_timeout':
                    self.request_queue_timeout = float(value)
                elif key == 'worker_count':
                    self.worker_count = int(value)
                elif key == 'stderr_log_level':
                    self.stderr_log_level = value.upper()
                elif key == 'file_log_level':
                    self.file_log_level = value.upper()
                elif key == 'log_file':
                    self.log_file = value
                elif key == 'host':
                    self.host = value
                elif key == 'port':
                    self.port = int(value)
                elif key == 'user':
                    self.user = value
                elif key == 'password':
                    self.password = value
                elif key == 'dbname':
                    self.dbname = value
                elif key == 'metric':
                    if read_metrics:
                        self.add_metric(value)
                else:
                    raise InvalidConfigError("WARNING: Unknown config: {}".format(key))

    def add_metric(self, metric_def):
        (name, ret_type, version, sql) = metric_def.split(':', 3)
        if sql is None:
            raise InvalidConfigError

        if sql.startswith('file:'):
            (_,path) = sql.split(':', 1)
            with open(path, 'r') as f:
                sql = f.read()

        if version == '':
            version = 0

        try:
            metric = self.metrics[name]
        except KeyError:
            metric = Metric(name, ret_type)
            self.metrics[name] = metric

        metric.add_version(int(version), sql)

    def get_pg_version(self):
        if self.pg_version is None:
            db = DB(self)
            self.pg_version = int(db.query('SHOW server_version_num')[0]['server_version_num'])
            db.close()
        return self.pg_version


class DB:
    """
    Database access
    """
    def __init__(self, config, dbname=None):
        if dbname is None:
            dbname = config.dbname
        self.conn = psycopg2.connect(
            host = config.host,
            port = config.port,
            user = config.user,
            password = config.password,
            dbname = dbname);
        self.conn.set_session(readonly=True, autocommit=True)

    def query(self, sql, args=[]):
        with self.conn.cursor(cursor_factory=psycopg2.extras.RealDictCursor) as cur:
            cur.execute(sql, args)
            return(cur.fetchall())

    def close(self):
        try:
            if self.conn is not None:
                self.conn.close()
        except psycopg2.Error as e:
            logger.warning("Caught an error when closing a connection: {}".format(e))
        self.conn = None


class Request:
    """
    A metric request
    """
    def __init__(self, metric_name, args = {}):
        self.metric_name = metric_name
        self.args = args
        self.result = None

        # Add a lock to indicate when the request is complete
        self.complete = threading.Lock()
        self.complete.acquire()

    def set_result(self, result):
        self.result = result

        # Release the lock
        self.complete.release()

    def get_result(self, timeout = -1):
        # Wait until the request has been completed
        if self.complete.acquire(timeout = timeout):
            return self.result
        else:
            raise RequestTimeoutError


class Metric:
    """
    A metric
    """
    def __init__(self, name, ret_type):
        self.name = name
        self.versions = {}
        self.type = ret_type
        self.cached = None
        self.cached_version = None

    def add_version(self, version, sql):
        if version in self.versions:
            raise DuplicateMetricVersionError
        self.versions[version] = MetricVersion(sql)

    def get_version(self, version):
        # Since we're usually going to keep asking for the same version,
        # we cache the metric version and only search through the versions
        # again if the PostgreSQL version changes
        if self.cached is None or self.cached_version != version:
            self.cached = None
            self.cached_version = None
            for v in reversed(sorted(self.versions.keys())):
                if version >= v:
                    self.cached = self.versions[v]
                    self.cached_version = version
                    break
            if self.cached is None:
                raise UnsupportedMetricVersionError

        return self.cached


class MetricVersion:
    """
    A version of a metric
    """
    def __init__(self, sql):
        self.sql = sql

    def get_sql(self, args):
        return self.sql.format(**args)


class IPC:
    """
    IPC handler
    """
    def __init__(self, config, mode):
        self.config = config
        self.mode = mode
        self.reconnect()

    def reconnect(self):
        if self.mode == 'server':
            # Try to clean up the socket if it exists
            try:
                os.unlink(self.config.ipc_socket)
            except OSError:
                if os.path.exists(self.config.ipc_socket):
                    raise

            # Create the socket
            self.socket = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
            # Set a timeout for accepting connections to be able to catch signals
            self.socket.settimeout(1)
            self.socket.bind(self.config.ipc_socket)
            self.socket.listen(1)

        elif self.mode == 'agent':
            # Connect to the socket
            self.conn = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
            self.conn.settimeout(self.config.ipc_timeout)

        else:
            raise RuntimeError

    def connect(self):
        """
        Establish a connection to a socket
        """
        self.conn.connect(self.config.ipc_socket)
        return self.conn

    def accept(self):
        """
        Accept a connection
        """
        (conn, _) = self.socket.accept()
        conn.settimeout(self.config.ipc_timeout)
        return conn

    def send(self, conn, msg):
        msg_bytes = msg.encode("utf-8")
        msg_len = len(msg_bytes)
        msg_len_bytes = msg_len.to_bytes(4, byteorder='big')
        conn.sendall(msg_len_bytes + msg_bytes)

    def recv(self, conn, timeout=-1):
        # Read at least the length
        buffer = []
        msg_len = -4
        while msg_len < 0:
            buffer += conn.recv(1024)
            msg_len = len(buffer) - 4

        msg_len_bytes = buffer[:4]
        msg_len = int.from_bytes(msg_len_bytes, byteorder='big')

        while len(buffer) < msg_len + 4:
            buffer += conn.recv(1024)

        return bytes(buffer[4:]).decode("utf-8")


class Agent:
    """
    The agent side of the connector
    """
    @staticmethod
    def run(config_file, key):
        config = Config(config_file, read_metrics = False)

        # Connect to the socket
        ipc = IPC(config, 'agent')
        try:
            conn = ipc.connect()

            # Send a request
            ipc.send(conn, key)

            # Wait for a response
            res = ipc.recv(conn)

        except:
            print("IPC error")
            sys.exit(1)

        # Output the response
        print(res)


class Server:
    """
    The server side of the connector
    """

    def __init__(self, config_file):
        self.config_file = config_file

        # Load config
        self.config = Config(config_file)

        # Write pid file
        # Note: we record the PID file here so it can't be changed with reload
        self.pid_file = self.config.pid_file
        write_pid_file(self.pid_file)

        # Initialize logging
        init_logging(self.config)

        # Set up the signal handler
        signal.signal(signal.SIGINT, signal_handler)
        signal.signal(signal.SIGHUP, signal_handler)

        # Create reqest queue
        self.req_queue = queue.Queue(self.config.request_queue_size)

        # Spawn worker threads
        self.workers = self.spawn_workers(self.config)

    def spawn_workers(self, config):
        logger.info("Spawning {} workers".format(config.worker_count))

        workers = [None] * config.worker_count
        for i in range(config.worker_count):
            workers[i] = Worker(config, self.req_queue)
            workers[i].start()

        return workers

    def retire_workers(self, workers):
        logger.info("Retiring {} workers".format(len(workers)))

        for worker in workers:
            worker.active = False

        for worker in workers:
            worker.join()

    def reload_config(self):
        # Clear the reload flag
        global reload
        reload = False

        # Read new config
        new_config = Config(self.config_file)

        # Re-init logging in case settings changed
        init_logging(new_config)

        # Spawn new workers
        new_workers = self.spawn_workers(new_config)

        # Replace workers
        old_workers = self.workers
        self.workers = new_workers

        # Retire old workers
        self.retire_workers(old_workers)

        # Adjust other settings
        # TODO

        self.config = new_config

    def run(self):
        logger.info("Server starting")

        # Listen on ipc socket
        ipc = IPC(self.config, 'server')

        while True:
            # Wait for a request connection
            try:
                conn = ipc.accept()
            except socket.timeout:
                conn = None

            # See if we should exit
            if not running:
                break

            # Check if we're supposed to reload the config
            if reload:
                try:
                    self.reload_config()
                except Exceptioin as e:
                    logger.ERROR("Reload failed: {}".format(e))

            # If we just timed out waiting for a request, go back to waiting
            if conn is None:
                continue

            # Get the request string (csv)
            key = ipc.recv(conn)

            # Parse ipc request (csv)
            try:
                parts = key.split(',', 1)
                metric_name = parts[0]
                args_dict = {}

                if len(parts) > 1:
                    for arg in parts[1].split(','):
                        if arg != '':
                            (k, v) = arg.split('=', 1)
                            args_dict[k] = v
            except socket.timeout:
                logger.warning("IPC communication timeout receiving request")
                conn.close()
                continue
            except Exception:
                logger.warning("Received invalid request: '{}'".format(key))
                ipc.send(conn, "ERROR: Invalid key")
                conn.close()
                continue

            # Create request object
            req = Request(metric_name, args_dict)

            # Queue the request
            try:
                self.req_queue.put(req, timeout=self.config.request_queue_timeout)
            except:
                logger.warning("Failed to queue request")
                req.set_result("ERROR: Queue timeout")
                continue

            # Spawn a thread to wait for the result
            r = Responder(self.config, ipc, conn, req)
            r.start()

        # Join worker threads
        self.retire_workers(self.workers)

        # Clean up the PID file
        remove_pid_file(self.pid_file)

        logger.info("Good bye")


class Worker(threading.Thread):
    """
    Worker thread that processes requests (ie: queries the database)
    """
    def __init__(self, config, queue):
        super(Worker, self).__init__()

        self.config = config
        self.queue = queue

        self.active = True

    def run(self):
        while True:
            # Wait for a request
            try:
                req = self.queue.get(timeout=1)
            except queue.Empty:
                req = None

            # Check if we're supposed to exit
            if not self.active:
                logger.info("Worker exiting: tid={}".format(self.native_id))
                break

            # If we got here because we waited too long for a request, go back to waiting
            if req is None:
                continue

            # Find the requested metrtic
            try:
                metric = self.config.metrics[req.metric_name]
            except KeyError:
                req.set_result("ERROR: Unknown key '{}'".format(req.metric_name))
                continue

            # Get the DB version
            try:
                pg_version = self.config.get_pg_version()
            except Exception as e:
                req.set_result("Failed to retrieve database version")
                logger.error("Failed to get Postgresql version: {}".format(e))
                continue

            # Get the query to use
            try:
                mv = metric.get_version(pg_version)
            except UnsupportedMetricVersionError:
                req.set_result("Unsupported PosgreSQL version for metric")
                continue

            # Query the database
            try:
                dbname = req.args['db']
            except KeyError:
                dbname = None

            try:
                db = DB(self.config, dbname)
                res = db.query(mv.get_sql(req.args))
                db.close()
            except Exception as e:
                # Make sure the database connectin is closed (ie: if the query timed out)
                try:
                    db.close()
                except:
                    pass
                req.set_result("Failed to query database")
                logger.error("Database error: {}".format(e))
                continue

            # Set the result on the request
            if len(res) == 0:
                req.set_result("Empty result set")
            elif metric.type == 'value':
                req.set_result("{}".format(list(res[0].values())[0]))
            elif metric.type == 'row':
                req.set_result(json.dumps(res[0]))
            elif metric.type == 'column':
                req.set_result(json.dumps([list(r.values())[0] for r in res]))
            elif metric.type == 'set':
                req.set_result(json.dumps(res))

            try:
                db.close()
            except Exception as e:
                logger.debug("Failed to close database connection: {}".format(e))

class Responder(threading.Thread):
    """
    Thread responsible for replying to requests
    """
    def __init__(self, config, ipc, conn, req):
        super(Responder, self).__init__()

        # Wait for a result
        result = req.get_result()

        # Send the result back to the client
        ipc.send(conn, result)

def main():
    parser = argparse.ArgumentParser(
                prog='pgmon',
                description='A briidge between monitoring tools and PostgreSQL')

    # General options
    parser.add_argument('-c', '--config', default='pgmon.cfg')
    parser.add_argument('-v', '--verbose', action='store_true')

    # Operational mode
    parser.add_argument('-s', '--server', action='store_true')
    parser.add_argument('-r', '--reload', action='store_true')

    # Agent options
    parser.add_argument('key', nargs='?')

    args = parser.parse_args()

    if args.server:
        server = Server(args.config)
        server.run()
    elif args.reload:
        config = Config(args.config, read_metrics = False)
        pid = read_pid_file(config.pid_file)
        os.kill(pid, signal.SIGHUP)
    else:
        Agent.run(args.config, args.key)


if __name__ == '__main__':
    main()

##
# Tests
##
class TestConfig:
    pass

class TestDB:
    pass

class TestRequest:
    def test_request_creation(self):
        # Create result with no args
        req1 = Request('foo', {})
        assert req1.metric_name == 'foo'
        assert len(req1.args) == 0
        assert req1.complete.locked()

        # Create result with args
        req2 = Request('foo', {'arg1': 'value1', 'arg2': 'value2'})
        assert req2.metric_name == 'foo'
        assert len(req2.args) == 2
        assert req2.complete.locked()

    def test_request_lock(self):
        req1 = Request('foo', {})
        assert req1.complete.locked()
        req1.set_result('blah')
        assert not req1.complete.locked()
        assert 'blah' == req1.get_result()



class TestMetric:
    def test_metric_creation(self):
        # Test basic creation
        m1 = Metric('foo', 'value')
        assert m1.name == 'foo'
        assert len(m1.versions) == 0
        assert m1.type == 'value'
        assert m1.cached is None
        assert m1.cached_version is None

    def test_metric_add_version(self):
        # Test adding versions
        m1 = Metric('foo', 'value')
        assert len(m1.versions) == 0
        m1.add_version(0, 'default')
        assert len(m1.versions) == 1
        m1.add_version(120003, 'v12.3')
        assert len(m1.versions) == 2

        # Make sure added versions are correct
        assert m1.versions[0].sql == 'default'
        assert m1.versions[120003].sql == 'v12.3'

    def test_metric_get_version(self):
        # Test retrieving metric versions
        m1 = Metric('foo', 'value')
        m1.add_version(100000, 'v10.0')
        m1.add_version(120000, 'v12.0')

        # Make sure cache is initially empty
        assert m1.cached is None
        assert m1.cached_version is None

        assert m1.get_version(110003).sql == 'v10.0'

        # Make sure cache is set
        assert m1.cached is not None
        assert m1.cached_version == 110003

        # Make sure returned value changes with version
        assert m1.get_version(120000).sql == 'v12.0'
        assert m1.get_version(150005).sql == 'v12.0'

        # Make sure an error is thrown when no version matches
        with pytest.raises(UnsupportedMetricVersionError):
            m1.get_version(90603)

        # Add a default version
        m1.add_version(0, 'default')
        assert m1.get_version(90603).sql == 'default'
        assert m1.get_version(110003).sql == 'v10.0'
        assert m1.get_version(120000).sql == 'v12.0'
        assert m1.get_version(150005).sql == 'v12.0'

class TestMetricVersion:
    def test_metric_version_creation(self):
        mv1 = MetricVersion('test')
        assert mv1.sql == 'test'

    def test_metric_version_templating(self):
        mv1 = MetricVersion('foo')
        assert mv1.get_sql({}) == 'foo'

        mv2 = MetricVersion('foo {a1} {a3} {a2}')
        assert mv2.get_sql({'a1': 'bar', 'a2': 'blah blah blah', 'a3': 'baz'}) == 'foo bar baz blah blah blah'


class TestIPC:
    pass

class TestAgent:
    pass

class TestServer:
    pass

class TestWorker:
    pass

class TestResponder:
    pass