#!/usr/bin/env python3
# A Sigma to SIEM converter
# Copyright 2016-2017 Thomas Patzke, Florian Roth

# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Lesser General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.

# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU Lesser General Public License for more details.

# You should have received a copy of the GNU Lesser General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

import sys
import argparse
import yaml
import json
import pathlib
import itertools
import logging
from sigma.parser.collection import SigmaCollectionParser
from sigma.parser.exceptions import SigmaCollectionParseError, SigmaParseError
from sigma.configuration import SigmaConfiguration, SigmaConfigurationChain
from sigma.config.collection import SigmaConfigurationManager
from sigma.config.exceptions import SigmaConfigParseError, SigmaRuleFilterParseException
from sigma.filter import SigmaRuleFilter
import sigma.backends.discovery as backends
from sigma.backends.base import BackendOptions
from sigma.backends.exceptions import BackendError, NotSupportedError, PartialMatchError, FullMatchError
import codecs

sys.stdout = codecs.getwriter('utf-8')(sys.stdout.detach())

logger = logging.getLogger(__name__)

# Error codes

ERR_OUTPUT              = 1
ERR_INVALID_YAML        = 3
ERR_SIGMA_PARSING       = 4
ERR_OPEN_SIGMA_RULE     = 5
ERR_OPEN_CONFIG_FILE    = 5
ERR_CONFIG_INVALID_YAML = 6
ERR_CONFIG_PARSING      = 6
ERR_BACKEND             = 8
ERR_NOT_SUPPORTED       = 9
ERR_NO_TARGET           = 10
ERR_RULE_FILTER_PARSING = 11
ERR_CONFIG_REQUIRED     = 20
ERR_CONFIG_ORDER        = 21
ERR_CONFIG_BACKEND      = 22
ERR_NOT_IMPLEMENTED     = 42
ERR_PARTIAL_FIELD_MATCH = 80
ERR_FULL_FIELD_MATCH    = 90

def print_verbose(*args, **kwargs):
    if cmdargs.verbose or cmdargs.debug:
        print(*args, **kwargs)

def print_debug(*args, **kwargs):   # pragme: no cover
    if cmdargs.debug:
        print(*args, **kwargs)

def alliter(path):
    for sub in path.iterdir():
        if sub.name.startswith("."):
            continue
        if sub.is_dir():
            yield from alliter(sub)
        else:
            yield sub

def get_inputs(paths, recursive):
    if paths == ['-']:
        return [sys.stdin]

    if recursive:
        return list(itertools.chain.from_iterable([list(alliter(pathlib.Path(p))) for p in paths]))
    else:
        return [pathlib.Path(p) for p in paths]

class SigmacArgumentParser(argparse.ArgumentParser):
    def format_help(self):
        helptext = super().format_help() + "\nBackend options:\n"

        for backend in backends.getBackendList():
            if len(backend.options) > 0:
                helptext += "  " + backend.identifier + "\n"
                for option, default, help, _ in backend.options:
                    helptext += "    {:10}: {} (default: {})".format(option, help, default) + "\n"

        return helptext

argparser = SigmacArgumentParser(description="Convert Sigma rules into SIEM signatures.")
argparser.add_argument("--recurse", "-r", action="store_true", help="Use directory as input (recurse into subdirectories is not implemented yet)")
argparser.add_argument("--filter", "-f", help="""
Define comma-separated filters that must match (AND-linked) to rule to be processed.
Valid filters: level<=x, level>=x, level=x, status=y, logsource=z, tag=t.
x is one of: low, medium, high, critical.
y is one of: experimental, testing, stable.
z is a word appearing in an arbitrary log source attribute.
t is a tag that must appear in the rules tag list, case-insensitive matching.
Multiple log source specifications are AND linked.
        """)
argparser.add_argument("--target", "-t", choices=backends.getBackendDict().keys(), help="Output target format")
argparser.add_argument("--lists", "-l", action="store_true", help="List available output target formats and configurations")
argparser.add_argument("--config", "-c", action="append", help="Configurations with field name and index mapping for target environment. Multiple configurations are merged into one. Last config is authorative in case of conflicts.")
argparser.add_argument("--output", "-o", default=None, help="Output file or filename prefix if multiple files are generated")
argparser.add_argument("--backend-option", "-O", action="append", help="Options and switches that are passed to the backend")
argparser.add_argument("--backend-config", help="Configuration file containing options to pass to the backend")
argparser.add_argument("--defer-abort", "-d", action="store_true", help="Don't abort on parse or conversion errors, proceed with next rule. The exit code from the last error is returned")
argparser.add_argument("--ignore-backend-errors", "-I", action="store_true", help="Only return error codes for parse errors and ignore errors for rules that cause backend errors. Useful, when you want to get as much queries as possible.")
argparser.add_argument("--shoot-yourself-in-the-foot", action="store_true", help=argparse.SUPPRESS)
argparser.add_argument("--verbose", "-v", action="store_true", help="Be verbose")
argparser.add_argument("--debug", "-D", action="store_true", help="Debugging output")
argparser.add_argument("inputs", nargs="*", help="Sigma input files ('-' for stdin)")
cmdargs = argparser.parse_args()

scm = SigmaConfigurationManager()

if cmdargs.debug:   # pragma: no cover
    logger.setLevel(logging.DEBUG)

if cmdargs.lists:
    print("Backends:")
    for backend in backends.getBackendList():
        print("%10s: %s" % (backend.identifier, backend.__doc__))

    print()
    print("Configurations:")
    for conf_id, title in scm.list():
        print("{:>30} : {}".format(conf_id, title))
    sys.exit(0)
elif len(cmdargs.inputs) == 0:
    print("Nothing to do!")
    argparser.print_usage()
    sys.exit(0)

if cmdargs.target is None:
    print("No target selected, select one with -t/--target")
    argparser.print_usage()
    sys.exit(ERR_NO_TARGET)

rulefilter = None
if cmdargs.filter:
    try:
        rulefilter = SigmaRuleFilter(cmdargs.filter)
    except SigmaRuleFilterParseException as e:
        print("Parse error in Sigma rule filter expression: %s" % str(e), file=sys.stderr)
        sys.exit(ERR_RULE_FILTER_PARSING)

sigmaconfigs = SigmaConfigurationChain()
if cmdargs.config:
    order = 0
    for conf_name in cmdargs.config:
        try:
            sigmaconfig = scm.get(conf_name)
            if sigmaconfig.order is not None:
                if sigmaconfig.order <= order and not cmdargs.shoot_yourself_in_the_foot:
                    print("The configurations were provided in the wrong order (order key check in config file)", file=sys.stderr)
                    sys.exit(ERR_CONFIG_ORDER)
                order = sigmaconfig.order

            try:
                if cmdargs.target not in sigmaconfig.config["backends"]:
                    print("The configuration '{}' is not valid for backend '{}'. Valid choices are: {}".format(conf_name, cmdargs.target, ", ".join(sigmaconfig.config["backends"])), file=sys.stderr)
                    sys.exit(ERR_CONFIG_ORDER)
            except KeyError:
                pass

            sigmaconfigs.append(sigmaconfig)
        except OSError as e:
            print("Failed to open Sigma configuration file %s: %s" % (conf_name, str(e)), file=sys.stderr)
            exit(ERR_OPEN_CONFIG_FILE)
        except (yaml.parser.ParserError, yaml.scanner.ScannerError) as e:
            print("Sigma configuration file %s is no valid YAML: %s" % (conf_name, str(e)), file=sys.stderr)
            exit(ERR_CONFIG_INVALID_YAML)
        except SigmaConfigParseError as e:
            print("Sigma configuration parse error in %s: %s" % (conf_name, str(e)), file=sys.stderr)
            exit(ERR_CONFIG_PARSING)

backend_options = BackendOptions(cmdargs.backend_option, cmdargs.backend_config)
backend = backends.getBackend(cmdargs.target)(sigmaconfigs, backend_options)
if backend.config_required and cmdargs.config is None and not cmdargs.shoot_yourself_in_the_foot:
    print("The backend you want to use usually requires a configuration to generate valid results. Please provide one.", file=sys.stderr)
    sys.exit(ERR_CONFIG_REQUIRED)

filename = cmdargs.output
if filename:
    try:
        out = open(filename, "w", encoding='utf-8')
    except (IOError, OSError) as e:
        print("Failed to open output file '%s': %s" % (filename, str(e)), file=sys.stderr)
        exit(ERR_OUTPUT)
else:
    out = sys.stdout

error = 0
for sigmafile in get_inputs(cmdargs.inputs, cmdargs.recurse):
    print_verbose("* Processing Sigma input %s" % (sigmafile))
    try:
        if cmdargs.inputs == ['-']:
            f = sigmafile
        else:
            f = sigmafile.open(encoding='utf-8')
        parser = SigmaCollectionParser(f, sigmaconfigs, rulefilter)
        results = parser.generate(backend)
        for result in results:
            print(result, file=out)
    except OSError as e:
        print("Failed to open Sigma file %s: %s" % (sigmafile, str(e)), file=sys.stderr)
        error = ERR_OPEN_SIGMA_RULE
    except (yaml.parser.ParserError, yaml.scanner.ScannerError) as e:
        print("Sigma file %s is no valid YAML: %s" % (sigmafile, str(e)), file=sys.stderr)
        error = ERR_INVALID_YAML
        if not cmdargs.defer_abort:
            sys.exit(error)
    except (SigmaParseError, SigmaCollectionParseError) as e:
        print("Sigma parse error in %s: %s" % (sigmafile, str(e)), file=sys.stderr)
        error = ERR_SIGMA_PARSING
        if not cmdargs.defer_abort:
            sys.exit(error)
    except NotSupportedError as e:
        print("The Sigma rule requires a feature that is not supported by the target system: " + str(e), file=sys.stderr)
        if not cmdargs.ignore_backend_errors:
            error = ERR_NOT_SUPPORTED
            if not cmdargs.defer_abort:
                sys.exit(error)
    except BackendError as e:
        print("Backend error in %s: %s" % (sigmafile, str(e)), file=sys.stderr)
        if not cmdargs.ignore_backend_errors:
            error = ERR_BACKEND
            if not cmdargs.defer_abort:
                sys.exit(error)
    except NotImplementedError as e:
        print("An unsupported feature is required for this Sigma rule (%s): " % (sigmafile) + str(e), file=sys.stderr)
        print("Feel free to contribute for fun and fame, this is open source :) -> https://github.com/Neo23x0/sigma", file=sys.stderr)
        if not cmdargs.ignore_backend_errors:
            error = ERR_NOT_IMPLEMENTED
            if not cmdargs.defer_abort:
                sys.exit(error)
    except PartialMatchError as e:
        print("Partial field match error: %s" % str(e), file=sys.stderr)
        if not cmdargs.ignore_backend_errors:
            error = ERR_PARTIAL_FIELD_MATCH
            if not cmdargs.defer_abort:
                sys.exit(error)
    except FullMatchError as e:
        print("Full field match error", file=sys.stderr)
        if not cmdargs.ignore_backend_errors:
            error = ERR_FULL_FIELD_MATCH
            if not cmdargs.defer_abort:
                sys.exit(error)                
    finally:
        try:
            f.close()
        except:
            pass

result = backend.finalize()
if result:
    print(result, file=out)
out.close()

sys.exit(error)