# (c) 2012, Zettar Inc.
# Written by Chin Fang <fangchin@zettar.com>
#
# This file is part of Ansible
#
# This module is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This software 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 General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this software.  If not, see <http://www.gnu.org/licenses/>.
#

'''
This module is for enhancing ansible's inventory parsing capability such
that it can deal with hostnames specified using a simple pattern in the
form of [beg:end], example: [1:5], [a:c], [D:G]. If beg is not specified,
it defaults to 0.

If beg is given and is left-zero-padded, e.g. '001', it is taken as a
formatting hint when the range is expanded. e.g. [001:010] is to be
expanded into 001, 002 ...009, 010.

Note that when beg is specified with left zero padding, then the length of
end must be the same as that of beg, else a exception is raised.
'''
import string

from ansible import errors

def detect_range(line = None):
    '''
    A helper function that checks a given host line to see if it contains
    a range pattern descibed in the docstring above.

    Returnes True if the given line contains a pattern, else False.
    '''
    if (not line.startswith("[") and
        line.find("[") != -1 and
        line.find(":") != -1 and
        line.find("]") != -1 and
        line.index("[") < line.index(":") < line.index("]")):
        return True
    else:
        return False

def expand_hostname_range(line = None):
    '''
    A helper function that expands a given line that contains a pattern
    specified in top docstring, and returns a list that consists of the
    expanded version.

    The '[' and ']' characters are used to maintain the pseudo-code
    appearance. They are replaced in this function with '|' to ease
    string splitting.

    References: http://ansible.github.com/patterns.html#hosts-and-groups
    '''
    all_hosts = []
    if line:
        # A hostname such as db[1:6]-node is considered to consists
        # three parts:
        # head: 'db'
        # nrange: [1:6]; range() is a built-in. Can't use the name
        # tail: '-node'

        # Add support for multiple ranges in a host so:
        # db[01:10:3]node-[01:10]
        # - to do this we split off at the first [...] set, getting the list
        #   of hosts and then repeat until none left.
        # - also add an optional third parameter which contains the step. (Default: 1)
        #   so range can be [01:10:2] -> 01 03 05 07 09
        # FIXME: make this work for alphabetic sequences too.

        (head, nrange, tail) = line.replace('[','|',1).replace(']','|',1).split('|')
        bounds = nrange.split(":")
        if len(bounds) != 2 and len(bounds) != 3:
            raise errors.AnsibleError("host range incorrectly specified")
        beg = bounds[0]
        end = bounds[1]
        if len(bounds) == 2:
            step = 1
        else:
            step = bounds[2]
        if not beg:
            beg = "0"
        if not end:
            raise errors.AnsibleError("host range end value missing")
        if beg[0] == '0' and len(beg) > 1:
            rlen = len(beg) # range length formatting hint
            if rlen != len(end):
                raise errors.AnsibleError("host range format incorrectly specified!")
            fill = lambda _: str(_).zfill(rlen)  # range sequence
        else:
            fill = str

        try:
            i_beg = string.ascii_letters.index(beg)
            i_end = string.ascii_letters.index(end)
            if i_beg > i_end:
                raise errors.AnsibleError("host range format incorrectly specified!")
            seq = string.ascii_letters[i_beg:i_end+1]
        except ValueError:  # not a alpha range
            seq = range(int(beg), int(end)+1, int(step))

        for rseq in seq:
            hname = ''.join((head, fill(rseq), tail))

            if detect_range(hname):
                all_hosts.extend( expand_hostname_range( hname ) )
            else:
                all_hosts.append(hname)

        return all_hosts
