# encoding=UTF-8
# Copyright © 2008, 2009 Jakub Wilk <jwilk@jwilk.net>
#
# This package 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; version 2 dated June, 1991.
#
# This package 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.

class Operation(object):

    def __init__(self, cost):
        self.cost = cost

    def __cmp__(self, other):
        return cmp(self.cost, other.cost)

    def __repr__(self):
        return '%s(cost=%r)' % (self.__class__.__name__, self.cost)

    def __add__(self, other):
        return self.cost + other

class Delete(Operation): pass
class Insert(Operation): pass
class Substitute(Operation): pass
class Drop(Operation): pass
class Append(Operation): pass

def distance(s, t):
    len_s = len(s)
    len_t = len(t)
    d = [[None for j in xrange(len_t + 1)] for i in xrange(len_s + 1)]
    for i in xrange(len_s + 1): d[i][0] = Drop(i)
    for j in xrange(len_t + 1): d[0][j] = Append(j)
    for i in xrange(1, len_s + 1):
        for j in xrange(1, len_t + 1):
            subst_cost = int(s[i-1] != t[j-1])
            d[i][j] = min(
                Delete(d[i-1][j] + 1),
                Insert(d[i][j-1] + 1),
                Substitute(d[i-1][j-1] + subst_cost)
            )
    i = len_s
    j = len_t
    ops = []
    while True:
        op = d[i][j]
        if isinstance(op, Delete):
            i -= 1
            ops += (i, s[i], ''),
        elif isinstance(op, Insert):
            j -= 1
            ops += (i, '', t[j]),
        elif isinstance(op, Substitute):
            i -= 1
            j -= 1
            if s[i] != t[j]:
                ops += (i, s[i], t[j],),
        elif isinstance(op, Append):
            ops += ((i, '', t[jj]) for jj in xrange(j-1, -1, -1))
            break
        elif isinstance(op, Drop):
            ops += ((ii, s[ii], '') for ii in xrange(i-1, -1, -1))
            break
    return reversed(ops)

__all__ = 'distance',

# vim:ts=4 sw=4 et
