#!/usr/bin/env python3

from socketserver import TCPServer
from socketserver import BaseRequestHandler
import subprocess
import argparse
import os
import time
import pwd
import grp

class GopherError(BaseException): pass
class RequestError(GopherError): pass

class GopherLine:
    def __init__(self, line):
        self.item = "i"
        self.text = ""
        self.location = "null"
        self.host = "null.host"
        self.port = "0"
        self.line = line
        self.parse()

    def parse(self):
        split = self.line.rstrip().split('\t')
        location = False
        if len(split) == 1:
            self.text = split[0]
            return

        try: self.item = split[0][0]
        except IndexError: pass

        try: self.text = split[0][1:]
        except IndexError: pass

        try:
            self.location = split[1]
            location = True
        except IndexError: pass

        try: self.host = split[2]
        except IndexError:
            if location == True: self.host = host

        try: self.port = split[3]
        except IndexError:
            if location == True: self.port = str(port)

    def render(self):
        return "{}{}\t{}\t{}\t{}".format(
            self.item,
            self.text,
            self.location,
            self.host,
            self.port
        )

class Logger:
    def __init__(self, file=None):
        if file != None: self.fd = open(file, "a+")
        else: self.fd = False

    def time(self):
        return int(time.time())

    def write(self, msg):
        if self.fd: self.fd.write("{}\n")

    def log(self, msg):
        ct = self.time()
        self.write("[{}] {}".format(str(ct), msg))
        print("[{}] {}".format(str(ct), msg))

    def warn(self, msg):
        ct = self.time()
        self.write("! [{}] {}".format(str(ct), msg))
        print("! [{}] {}".format(str(ct), msg))

    def error(self, msg):
        ct = self.time()
        self.write("!! [{}] {}".format(str(ct), msg))
        print("!! [{}] {}".format(str(ct), msg))
        self.close()
        raise SystemExit

    def close(self):
        if self.fd: self.fd.close()

class GopherServerLogic:
    def recieveRequest(self):
        data = b""
        while data[-2:] != b"\r\n":
            data += self.request.recv(1)
        decoded = data[:-2].decode("utf-8")
        return decoded

    def requestParser(self, request):
        if ".." in request: raise RequestError
        try:
            if request[0] == "/": request = request[1:]
        except IndexError: pass
        request = request.replace("?", "\t").split("\t")
        try: return (request[0], request[1])
        except IndexError: return (request[0], "")

    def returnRelative(self, file):
        gph = False
        if file == "":
            ret = "gophermap"
            gph = True
        elif os.path.isdir(file):
            if file[-1] != "/": ret = file + "/gophermap"
            else: ret = file + "gophermap"
            gph = True
        elif os.path.isfile(file):
            ret = file
        else: raise RequestError("unreachable state")
        return (ret, gph)

    def fileSendable(self, file):
        return os.access(file, os.F_OK|os.R_OK)

    def fileCGI(self, file):
        if exempt != None:
            for i in exempt:
                if i in file: return False
        if nocgi:
            return False
        return os.access(file, os.F_OK|os.R_OK|os.X_OK)

    def notFound(self):
        self.request.sendall(
            b"3error: file not found!\r\n.\r\n")

    def invalid(self):
        self.request.sendall(
            b"3error: selector contains '..'!\r\n.\r\n")

    def fileToFileArray(self, file):
        fd = open(file, "r")
        ret = [i.rstrip() for i in fd.readlines()]
        fd.close()
        return ret

    def sendFileArray(self, fileArray):
        [self.request.sendall(
            (i.rstrip() + "\r\n").encode("utf-8")
        ) for i in fileArray]
        self.request.sendall(b".\r\n")

    def cgi(self, file, query):
        env = {}
        env["QUERY_STRING"] = query
        env["SCRIPT_NAME"] = "/" + file
        env["REMOTE_ADDR"] = self.client_address[0]

        proc = subprocess.Popen(
            [os.getcwd() + "/" + file],
            stdout = subprocess.PIPE,
            env = env
        )

        try: out, err = proc.communicate(timeout=10)
        except TimeoutExpired:
            proc.kill()
            out, err = proc.communicate()

        return out.decode("utf-8")\
            .replace("\r", "")\
            .split("\n")

    def gopherRenderer(self, fileArray):
        gopherlines = []
        for i in fileArray:
            gopherlines.append(GopherLine(i))
        returned = []
        for i in gopherlines:
            returned.append(i.render())
        return returned

    def serveFile(self, file, query, gph):
        if self.fileCGI(file):
            fa = self.cgi(file, query)
        elif self.fileSendable(file):
            fa = self.fileToFileArray(file)
        else:
            log.log("selector not found")
            self.notFound()
            return
        if gph: fa = self.gopherRenderer(fa)
        self.sendFileArray(fa)

class GopherHandler(BaseRequestHandler,
    GopherServerLogic):
    def handle(self):
        log.log("request from {}".format(
            self.client_address[0]))
        decoded = self.recieveRequest()
        try: parsed = self.requestParser(decoded)
        except RequestError:
            log.log("request was invalid")
            self.invalid()
            return

        try: file = self.returnRelative(parsed[0])
        except RequestError:
            log.log("selector not found")
            self.notFound()
            return
        log.log("serving {}".format(file[0]))
        self.serveFile(file[0], parsed[1], file[1])

log = Logger()

def parseArgs():
    parse = argparse.ArgumentParser()
    parse.add_argument("-u", "--user", default="nobody",
        help="user to change to on startup")
    parse.add_argument("-g", "--group", default="nobody",
        help="group to change to on startup")
    parse.add_argument("-s", "--host", default="localhost",
        help="host to host on")
    parse.add_argument("-p", "--port", default=70, type=int,
        help="port to host on")
    parse.add_argument("-d", "--dir", default="/var/gopher",
        help="directory to host from")
    parse.add_argument("-ndx", "--direxc",
        action="extend", nargs="*",
        help="make directory-wide exception for file execution")
    parse.add_argument("-nx", "--nocgi", action="store_true",
        help="disable execution of cgi scripts")
    return parse.parse_args()

if __name__ == "__main__":
    args = parseArgs()
    log.log("arguments parsed")

    switchgrp = grp.getgrnam(args.group).gr_gid
    switchusr = pwd.getpwnam(args.user).pw_uid
    host = args.host
    port = args.port
    location = args.dir
    exempt = args.direxc
    nocgi = args.nocgi
    log.log("arguments good")
    try:
        with TCPServer((host, port), GopherHandler) as server:
            os.setgid(switchgrp)
            os.seteuid(switchusr)
            log.log("switch user successful")
            os.chdir(location)
            log.log("change directory successful")
            server.serve_forever()
    except PermissionError: log.error("invalid permissions")
    except OSError: log.error("address already in use")