# -*- test-case-name: twisted.names.test.test_hosts -*-
# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.

"""
hosts(5) support.
"""

from __future__ import division, absolute_import

from twisted.python.compat import nativeString
from twisted.names import dns
from twisted.python import failure
from twisted.python.filepath import FilePath
from twisted.internet import defer
from twisted.internet.abstract import isIPAddress

from twisted.names import common

def searchFileForAll(hostsFile, name):
    """
    Search the given file, which is in hosts(5) standard format, for an address
    entry with a given name.

    @param hostsFile: The name of the hosts(5)-format file to search.
    @type hostsFile: L{FilePath}

    @param name: The name to search for.
    @type name: C{str}

    @return: C{None} if the name is not found in the file, otherwise a
        C{str} giving the address in the file associated with the name.
    """
    results = []
    try:
        lines = hostsFile.getContent().splitlines()
    except:
        return results

    name = name.lower()
    for line in lines:
        idx = line.find(b'#')
        if idx != -1:
            line = line[:idx]
        if not line:
            continue
        parts = line.split()

        if name.lower() in [s.lower() for s in parts[1:]]:
            results.append(nativeString(parts[0]))
    return results



def searchFileFor(file, name):
    """
    Grep given file, which is in hosts(5) standard format, for an address
    entry with a given name.

    @param file: The name of the hosts(5)-format file to search.

    @param name: The name to search for.
    @type name: C{str}

    @return: C{None} if the name is not found in the file, otherwise a
        C{str} giving the address in the file associated with the name.
    """
    addresses = searchFileForAll(FilePath(file), name)
    if addresses:
        return addresses[0]
    return None



class Resolver(common.ResolverBase):
    """
    A resolver that services hosts(5) format files.
    """
    def __init__(self, file=b'/etc/hosts', ttl = 60 * 60):
        common.ResolverBase.__init__(self)
        self.file = file
        self.ttl = ttl


    def _aRecords(self, name):
        """
        Return a tuple of L{dns.RRHeader} instances for all of the IPv4
        addresses in the hosts file.
        """
        return tuple([
            dns.RRHeader(name, dns.A, dns.IN, self.ttl,
                         dns.Record_A(addr, self.ttl))
            for addr
            in searchFileForAll(FilePath(self.file), name)
            if isIPAddress(addr)])


    def _aaaaRecords(self, name):
        """
        Return a tuple of L{dns.RRHeader} instances for all of the IPv6
        addresses in the hosts file.
        """
        return tuple([
            dns.RRHeader(name, dns.AAAA, dns.IN, self.ttl,
                         dns.Record_AAAA(addr, self.ttl))
            for addr
            in searchFileForAll(FilePath(self.file), name)
            if not isIPAddress(addr)])


    def _respond(self, name, records):
        """
        Generate a response for the given name containing the given result
        records, or a failure if there are no result records.

        @param name: The DNS name the response is for.
        @type name: C{str}

        @param records: A tuple of L{dns.RRHeader} instances giving the results
            that will go into the response.

        @return: A L{Deferred} which will fire with a three-tuple of result
            records, authority records, and additional records, or which will
            fail with L{dns.DomainError} if there are no result records.
        """
        if records:
            return defer.succeed((records, (), ()))
        return defer.fail(failure.Failure(dns.DomainError(name)))


    def lookupAddress(self, name, timeout=None):
        """
        Read any IPv4 addresses from C{self.file} and return them as L{Record_A}
        instances.
        """
        return self._respond(name, self._aRecords(name))


    def lookupIPV6Address(self, name, timeout=None):
        """
        Read any IPv6 addresses from C{self.file} and return them as
        L{Record_AAAA} instances.
        """
        return self._respond(name, self._aaaaRecords(name))

    # Someday this should include IPv6 addresses too, but that will cause
    # problems if users of the API (mainly via getHostByName) aren't updated to
    # know about IPv6 first.
    lookupAllRecords = lookupAddress