# Copyright 2008 LShift Ltd
# Author(s):
# Paul Crowley <paul@lshift.net>
#
# This software may be used and distributed according to the terms
# of the GNU General Public License, incorporated herein by reference.

import sys
import re

allowedchars = "A-Za-z0-9_-"

goodpathre = re.compile("([%s]+/)*[%s]+$" % (allowedchars, allowedchars))
def goodpath(path):
    return goodpathre.match(path) is not None

goodglobre = re.compile("[*/%s]+$" % allowedchars)

def goodglob(pattern):
    return goodglobre.match(pattern) is not None

# Don't put anything except *A-Za-z0-9_- in rule globs or   
# it will match nothing.  No regexp metachars, not even .
# We may fix this later.
def globmatcher(pattern):
    if not goodglob(pattern):
        #fail("Bad glob pattern in auth config: %s" % pattern)
        # FIXME: report it somehow
        return lambda x: False
    # Substitution cunning so ** can be different from *
    pattern = pattern.replace("*", "[]")
    pattern = pattern.replace("[][]", "[/%s]*" % allowedchars)
    pattern = pattern.replace("[]", "[%s]*" % allowedchars)
    rex = re.compile(pattern + "$")
    # None matches everything
    return lambda x: x is None or rex.match(x) is not None

def rule(pairs):
    matchers = [(k, globmatcher(v)) for k, v in pairs]
    def c(**kw):
        for k, m in matchers:
            if k not in kw or not m(kw[k]):
                return False
        return True
    return c

class Ruleset(object):
    '''Class representing the rules in a rule file'''
    
    levels = ["init", "write", "read", "deny"]

    def __init__(self):
        # The user called "root" automatically has the highest
        # privilege
        self.rules = [(self.levels[0], rule([('user', 'root')]))]
        self.preset = {}

    def add(self, action, conditions):
        self.rules.append((action, conditions))


    def set(self, **kw):
        self.preset.update(kw)
        
    def matchrule(self, **kw):
        d = self.preset.copy()
        d.update(**kw)
        for a, c in self.rules:
            if c(**d):
                return a
        return None

    def allow(self, level, **kw):
        a = self.matchrule(**kw)
        return a in self.levels and self.levels.index(a) <= self.levels.index(level)
    
    @classmethod
    def readfile(cls, fn):
        res = cls()
        try:
            f = open(fn)
            try:
                for l in f:
                    l = l.strip()
                    if len(l) == 0 or l.startswith("#"):
                        continue
                    l = l.split()
                    res.add(l[0], rule([c.split("=", 1) for c in l[1:]]))
            finally:
                f.close()
        except Exception, e:
            print >> sys.stderr, "Failure reading rules file:", e
            return cls()
        return res