<?php

namespace Addr;

use Alert\Reactor;

class Client
{
    /**
     * @var Reactor
     */
    private $reactor;

    /**
     * @var RequestBuilder
     */
    private $requestBuilder;

    /**
     * @var ResponseInterpreter
     */
    private $responseInterpreter;

    /**
     * @var \Addr\Cache
     */
    private $cache;

    /**
     * @var resource
     */
    private $socket;

    /**
     * @var int
     */
    private $requestTimeout;

    /**
     * @var int
     */
    private $readWatcherId;

    /**
     * @var array
     */
    private $pendingLookups = [];

    /**
     * @var array
     */
    private $pendingRequestsByNameAndType = [];

    /**
     * @var array
     */
    private $pendingRequestsById = [];

    /**
     * @var int
     */
    private $requestIdCounter = 0;

    /**
     * @var int
     */
    private $lookupIdCounter = 0;

    /**
     * Constructor
     *
     * @param Reactor $reactor
     * @param RequestBuilder $requestBuilder
     * @param ResponseInterpreter $responseInterpreter
     * @param Cache $cache
     * @param string $serverAddress
     * @param int $serverPort
     * @param int $requestTimeout
     * @throws \RuntimeException
     */
    public function __construct(
        Reactor $reactor,
        RequestBuilder $requestBuilder,
        ResponseInterpreter $responseInterpreter,
        Cache $cache = null,
        $serverAddress = null,
        $serverPort = null,
        $requestTimeout = null
    ) {
        $this->reactor = $reactor;
        $this->requestBuilder = $requestBuilder;
        $this->responseInterpreter = $responseInterpreter;
        $this->cache = $cache;

        $serverAddress = $serverAddress !== null ? (string)$serverAddress : '8.8.8.8';
        $serverPort = $serverPort !== null ? (int)$serverPort : 53;
        $requestTimeout = $requestTimeout !== null ? (int)$requestTimeout : 2000;

        $address = sprintf('udp://%s:%d', $serverAddress, $serverPort);
        $this->socket = stream_socket_client($address, $errNo, $errStr);
        if (!$this->socket) {
            throw new \RuntimeException("Creating socket {$address} failed: {$errNo}: {$errStr}");
        }

        stream_set_blocking($this->socket, 0);
        $this->requestTimeout = $requestTimeout;
    }

    /**
     * Get the next available request ID
     *
     * @return int
     */
    private function getNextFreeRequestId()
    {
        do {
            $result = $this->requestIdCounter++;

            if ($this->requestIdCounter >= 65536) {
                $this->requestIdCounter = 0;
            }
        } while(isset($this->pendingRequestsById[$result]));

        return $result;
    }

    /**
     * Get the next available lookup ID
     *
     * @return int
     */
    private function getNextFreeLookupId()
    {
        do {
            $result = $this->lookupIdCounter++;

            if ($this->lookupIdCounter >= PHP_INT_MAX) {
                $this->lookupIdCounter = 0;
            }
        } while(isset($this->pendingLookups[$result]));

        return $result;
    }

    /**
     * Get a list of requests to execute for a given mode mask
     *
     * @param int $mode
     * @return array
     */
    private function getRequestList($mode)
    {
        $result = [];

        if ($mode & AddressModes::PREFER_INET6) {
            if ($mode & AddressModes::INET6_ADDR) {
                $result[] = AddressModes::INET6_ADDR;
            }
            if ($mode & AddressModes::INET4_ADDR) {
                $result[] = AddressModes::INET4_ADDR;
            }
        } else {
            if ($mode & AddressModes::INET4_ADDR) {
                $result[] = AddressModes::INET4_ADDR;
            }
            if ($mode & AddressModes::INET6_ADDR) {
                $result[] = AddressModes::INET6_ADDR;
            }
        }

        return $result;
    }

    /**
     * Send a request to the server
     *
     * @param array $request
     */
    private function sendRequest($request)
    {
        $packet = $this->requestBuilder->buildRequest($request['id'], $request['name'], $request['type']);

        $bytesWritten = fwrite($this->socket, $packet);
        if ($bytesWritten < strlen($packet)) {
            $this->completeRequest($request, null, ResolutionErrors::ERR_REQUEST_SEND_FAILED);
            return;
        }

        $request['timeout_id'] = $this->reactor->once(function() use($request) {
            unset($this->pendingRequestsByNameAndType[$request['name']][$request['type']]);
            $this->completeRequest($request, null, ResolutionErrors::ERR_SERVER_TIMEOUT);
        }, $this->requestTimeout);

        if ($this->readWatcherId === null) {
            $this->readWatcherId = $this->reactor->onReadable($this->socket, function() {
                $this->onSocketReadable();
            });
        }

        $this->pendingRequestsById[$request['id']] = $request;
        $this->pendingRequestsByNameAndType[$request['name']][$request['type']] = &$this->pendingRequestsById[$request['id']];
    }

    /**
     * Handle data waiting to be read from the socket
     */
    private function onSocketReadable()
    {
        $packet = fread($this->socket, 512);

        // Decode the response and clean up the pending requests list
        $decoded = $this->responseInterpreter->decode($packet);
        if ($decoded === null) {
            return;
        }

        list($id, $response) = $decoded;
        $request = $this->pendingRequestsById[$id];
        $name = $request['name'];

        $this->reactor->cancel($request['timeout_id']);
        unset($this->pendingRequestsById[$id], $this->pendingRequestsByNameAndType[$name][$request['type']]);
        if (!$this->pendingRequestsById) {
            $this->reactor->cancel($this->readWatcherId);
            $this->readWatcherId = null;
        }

        // Interpret the response and make sure we have at least one resource record
        $interpreted = $this->responseInterpreter->interpret($response, $request['type']);
        if ($interpreted === null) {
            foreach ($request['lookups'] as $id => $lookup) {
                $this->processPendingLookup($id);
            }

            return;
        }

        // Distribute the result to the appropriate lookup routine
        list($type, $addr, $ttl) = $interpreted;
        if ($type === AddressModes::CNAME) {
            foreach ($request['lookups'] as $id => $lookup) {
                $this->redirectPendingLookup($id, $addr);
            }
        } else if ($addr !== null) {
            $this->store($name, $addr, $type, $ttl);
            $this->completeRequest($request, $addr, $type);
        } else {
            foreach ($request['lookups'] as $id => $lookup) {
                $this->processPendingLookup($id);
            }
        }
    }

    /**
     * Generates the cache key used to store the result for hostname and type.
     *
     * @param string $name
     * @param int $type
     * @return string
     */
    private function generateCacheKey($name, $type)
    {
        return 'Name:'.$name.',Type:'.$type;
    }

    /**
     * Store an address mapping in the cache
     *
     * @param string $name
     * @param string $addr
     * @param int $type
     * @param int $ttl
     */
    public function store($name, $addr, $type, $ttl)
    {
        $key = $this->generateCacheKey($name, $type);
        $this->cache->store($key, $addr, $ttl);
    }

    /**
     * Call a response callback with the result
     *
     * @param int $id
     * @param string $addr
     * @param int $type
     */
    private function completePendingLookup($id, $addr, $type)
    {
        if (isset($this->pendingLookups[$id])) {
            call_user_func($this->pendingLookups[$id]['callback'], $addr, $type);
        }

        unset($this->pendingLookups[$id]);
    }

    /**
     * Complete all lookups in a request
     *
     * @param array $request
     * @param string|null $addr
     * @param int $type
     */
    private function completeRequest($request, $addr, $type)
    {
        foreach ($request['lookups'] as $id => $lookup) {
            $this->completePendingLookup($id, $addr, $type);
        }
    }

    /**
     * Lookup name in cache and send request to server on failure
     *
     * @param int $id
     */
    private function processPendingLookup($id)
    {
        if (!$this->pendingLookups[$id]['requests']) {
            $this->completePendingLookup($id, null, ResolutionErrors::ERR_NO_RECORD);
            return;
        }

        $name = $this->pendingLookups[$id]['name'];
        $type = array_shift($this->pendingLookups[$id]['requests']);

        $key = $this->generateCacheKey($name, $type);
        list($cacheHit, $addr) = $this->cache->get($key);

        if ($cacheHit === true) {
            $this->completePendingLookup($id, $addr, $type);
        } else {
            $this->dispatchRequest($id, $name, $type);
        }
    }

    /**
     * Send a request to the server
     *
     * @param int $id
     * @param string $name
     * @param int $type
     */
    private function dispatchRequest($id, $name, $type)
    {
        $this->pendingLookups[$id]['last_type'] = $type;
        $this->pendingRequestsByNameAndType[$name][$type]['lookups'][$id] = $this->pendingLookups[$id];

        if (count($this->pendingRequestsByNameAndType[$name][$type]) === 1) {
            $request = [
                'id'          => $this->getNextFreeRequestId(),
                'name'        => $name,
                'type'        => $type,
                'lookups'     => [$id => $this->pendingLookups[$id]],
                'timeout_id'  => null,
            ];

            $this->sendRequest($request);
        }
    }

    /**
     * Redirect a lookup to search for another name
     *
     * @param int $id
     * @param string $name
     */
    private function redirectPendingLookup($id, $name)
    {
        array_unshift($this->pendingLookups[$id]['requests'], $this->pendingLookups[$id]['last_type']);
        $this->pendingLookups[$id]['last_type'] = null;
        $this->pendingLookups[$id]['name'] = $name;

        $this->processPendingLookup($id);
    }

    /**
     * Resolve a name from a server
     *
     * @param string $name
     * @param int $mode
     * @param callable $callback
     */
    public function resolve($name, $mode, callable $callback)
    {
        $id = $this->getNextFreeLookupId();

        $this->pendingLookups[$id] = [
            'name'        => $name,
            'requests'    => $this->getRequestList($mode),
            'last_type'   => null,
            'callback'    => $callback,
        ];

        $this->processPendingLookup($id);
    }

    /**
     * Set the request timeout
     *
     * @param int $timeout
     */
    public function setRequestTimeout($timeout)
    {
        $this->requestTimeout = (int)$timeout;
    }
}