"""HTML Diff: http://www.aaronsw.com/2002/diff
Rough code, badly documented. Send me comments and patches."""

__author__ = 'Aaron Swartz <me@aaronsw.com>'
__copyright__ = '(C) 2003 Aaron Swartz. GNU GPL 2.'
__version__ = '0.22'

import difflib, string

def isTag(x): return x[0] == "<" and x[-1] == ">"

def textDiff(a, b, 
            ins_start='<ins>', ins_end = '</ins>',
            del_start='<del>', del_end='</del>'
        ):
    """Takes in strings a and b and returns a human-readable HTML diff."""

    out = []
    a, b = html2list(a), html2list(b)
    s = difflib.SequenceMatcher(None, a, b)
    for e in s.get_opcodes():
        if e[0] == "replace":
            # @@ need to do something more complicated here
            # call textDiff but not for html, but for some html... ugh
            # gonna cop-out for now
            out.append(del_start + ''.join(a[e[1]:e[2]]) + 
                del_end + ins_start + ''.join(b[e[3]:e[4]])+ ins_end
            )
        elif e[0] == "delete":
            out.append(del_start + ''.join(a[e[1]:e[2]]) + del_end)
        elif e[0] == "insert":
            out.append(ins_start + ''.join(b[e[3]:e[4]]) + ins_end)
        elif e[0] == "equal":
            out.append(''.join(b[e[3]:e[4]]))
        else: 
            raise "Um, something's broken. I didn't expect a '" + `e[0]` + "'."
    return ''.join(out)

def html2list(x, b=0):
    mode = 'char'
    cur = ''
    out = []
    for c in x:
        if mode == 'tag':
            if c == '>': 
                if b: 
                    cur += ']'
                else: 
                    cur += c
                out.append(cur)
                cur = ''
                mode = 'char'
            else: cur += c
        elif mode == 'char':
            if c == '<': 
                out.append(cur)
                if b:
                    cur = '['
                else:
                    cur = c
                mode = 'tag'
            elif c in string.whitespace:
                out.append(cur+c);
                cur = ''
            else:
                cur += c
    out.append(cur)
    return filter(lambda x: x is not '', out)

if __name__ == '__main__':
    import sys
    try:
        a, b = sys.argv[1:3]
    except ValueError:
        print "htmldiff: highlight the differences between two html files"
        print "usage: " + sys.argv[0] + " a b"
        sys.exit(1)
    print textDiff(open(a).read(), open(b).read())