import socket
import os
import select
import sys

class SocketFileWrapper:
    """Wraps a socket to a wsgi-compliant file-like object."""
    def __init__(self, sock):
        """@param sock is a socket.socket()"""
        self.sock = sock
        self.buff = ""
    def read(self, size=None):
        """see pep333"""
        if size is None:
            try:
                return self.buff + self.sock.recv()
            except: raise # Yes, this is necessary.
            else:
                self.buff = ""
        if size >= len(self.buff):
            ret, self.buff = self.buff[:size], self.buff[size:]
            return ret
        try:
            return self.buff + self.sock.recv(size)
        except: raise # Yes, this is necessary.
        else:
            self.buff = ""
    def readline(self):
        """see pep333"""
        while True:
            try:
                split = self.buff.index('\n') + 1
                ret, self.buff = self.buff[:split], self.buff[split:]
                return ret
            except ValueError:
                data = self.sock.recv(4096)
                if not data:
                    ret, self.buff = self.buff, ""
                    return ret
                self.buff += data
    def readlines(self):
        """see pep333"""
        data = self.readline()
        while data:
            yield data
            data = self.readline()
    def __iter__(self):
        """see pep333"""
        return self
    def next(self):
        """see pep333"""
        data = self.read(4096)
        if not data:
            raise StopIteration
        return data
    def flush(self):
        """see pep333"""
        pass
    def write(self, data):
        """see pep333"""
        self.sock.send(data)
    def writelines(self, lines):
        """see pep333"""
        map(self.write, lines)

class SCGIServer:
    """Usage: create an SCGIServer object and invoke the run method which will
    then turn this process into an scgi server."""
    class WorkerState:
        """state: 0 means idle and 1 means working.
        These values are also sent as strings '0' and '1' over the socket."""
        def __init__(self, pid, sock, state):
            self.pid = pid
            self.sock = sock
            self.state = state

    def __init__(self, wsgiapp, port, interface="localhost", error=sys.stderr,
                 minworkers=2, maxworkers=32, maxrequests=1000):
        """Parameters:
        wsgiapp is the WSGI application to be run.
        port is the tcp port to listen on
        interface is the interface to bind to (default: "localhost")
        error is a filelike object beeing passed as wsgi.error in environ
        minworkers is the number of worker processes to spawn
        maxworkers is the maximum number of workers that can be spawned on demand
        maxrequests is the number of requests a worker processes before dying
        """
        self.wsgiapp = wsgiapp
        self.port = port
        self.interface = interface
        self.minworkers = minworkers
        self.maxworkers = maxworkers
        self.maxrequests = maxrequests
        self.error = error
        self.server = None # becomes a socket
        # maps filedescriptors to WorkerStates
        self.workers = {}

    def run(self):
        """
        Serve the wsgi application.
        """
        self.server = socket.socket()
        self.server.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
        self.server.bind((self.interface, self.port))
        self.server.listen(5)
        while True:
            while (len(self.workers) < self.minworkers or # less than min
                    (len(self.workers) < self.maxworkers and # less than max
                        not len([w for w in # no inctive
                                 self.workers.values() if w.state == 0]))):
                self.spawnworker()
            rs, _, _ = select.select(self.workers.keys(), [], [])
            for s in rs:
                data = self.workers[s].sock.recv(1)
                if data == '':
                    self.workers[s].sock.close()
                    del self.workers[s]
                elif data in ('0', '1'):
                    self.workers[s].state = int(data)
                else:
                    raise RuntimeError, "unexpected data from worker"
            try:
                pid = 1
                while pid > 0:
                    pid, _ = os.waitpid(0, os.WNOHANG)
            except OSError:
                pass

    def spawnworker(self):
        """
        internal! spawns a single worker
        """
        srvsock, worksock = socket.socketpair()

        pid = os.fork()
        if pid == 0:
            # close unneeded sockets
            srvsock.close()
            for worker in self.workers.values():
                worker.sock.close()
            del self.workers

            self.work(worksock)

            sys.exit()
        elif pid > 0:
            # close unneeded sockets
            worksock.close()

            self.workers[srvsock.fileno()] = SCGIServer.\
                                             WorkerState(pid, srvsock, 0)
        else:
            raise RuntimeError, "fork failed"

    def work(self, worksock):
        """
        internal! serves maxrequests times
        """
        for _ in range(self.maxrequests):
            (con, addr) = self.server.accept()
            worksock.send('1') # tell server we're working
            self.process(con)
            worksock.send('0') # tell server we've finished

    def process(self, con):
        """
        internal! processes a single request on the connection con.
        """
        # This is a little bit ugly:
        # The server has to send the length of the request followed by a colon.
        # We assume that 1. the colon is within the first seven bytes.
        # 2. the packet isn't fragmented.
        # Furthermore 1 implies that the request isn't longer than 999999 bytes.
        # This method however works. :-)
        data = con.recv(7)
        if not ':' in data:
            con.close()
            return
        length, data = data.split(':', 1)
        if not length.isdigit(): # clear protocol violation
            con.close()
            return
        length = long(length)

        while len(data) != length + 1: # read one byte beyond
            t = con.recv(length + 1 - len(data))
            if not t: # request too short
                con.close()
                return
            data += t

        # netstrings!
        data = data.split('\0')
        # the byte beyond has to be a ','.
        # and the number of netstrings excluding the final ',' has to be even
        if data.pop() != ',' or len(data) % 2 != 0:
            con.close()
            return

        environ = {}
        while data:
            key = data.pop(0)
            value = data.pop(0)
            environ[key] = value

        def start_response(status, headers):
            con.send('Status: %s\r\n%s\r\n\r\n' % (status,
                      '\r\n'.join(map("%s: %s".__mod__, headers))))
            return con.send

        environ.update({
            "wsgi.version": (1, 0),
            "wsgi.input": SocketFileWrapper(con),
            "wsgi.errors": self.error,
            "wsgi.url_scheme": "http", # TODO: this is wrong
            "wsgi.multithread": False,
            "wsgi.multiprocess": True,
            "wsgi.run_once": False})
        result = self.wsgiapp(environ, start_response)
        for data in result:
            con.send(data)
        if hasattr(result, "close"):
            result.close()
        con.close()