#! /usr/bin/env python

"""Conversions to/from quoted-printable transport encoding as per RFC-1521."""

# (Dec 1991 version).

ESCAPE = '='
MAXLINESIZE = 76
HEX = '0123456789ABCDEF'

def needsquoting(c, quotetabs):
    """Decide whether a particular character needs to be quoted.

    The 'quotetabs' flag indicates whether tabs should be quoted."""
    if c == '\t':
        return not quotetabs
    return c == ESCAPE or not(' ' <= c <= '~')

def quote(c):
    """Quote a single character."""
    i = ord(c)
    return ESCAPE + HEX[i/16] + HEX[i%16]

def encode(input, output, quotetabs):
    """Read 'input', apply quoted-printable encoding, and write to 'output'.

    'input' and 'output' are files with readline() and write() methods.
    The 'quotetabs' flag indicates whether tabs should be quoted.
        """
    while 1:
        line = input.readline()
        if not line:
            break
        new = ''
        last = line[-1:]
        if last == '\n':
            line = line[:-1]
        else:
            last = ''
        prev = ''
        for c in line:
            if needsquoting(c, quotetabs):
                c = quote(c)
            if len(new) + len(c) >= MAXLINESIZE:
                output.write(new + ESCAPE + '\n')
                new = ''
            new = new + c
            prev = c
        if prev in (' ', '\t'):
            output.write(new + ESCAPE + '\n\n')
        else:
            output.write(new + '\n')

def decode(input, output):
    """Read 'input', apply quoted-printable decoding, and write to 'output'.

    'input' and 'output' are files with readline() and write() methods."""
    new = ''
    while 1:
        line = input.readline()
        if not line: break
        i, n = 0, len(line)
        if n > 0 and line[n-1] == '\n':
            partial = 0; n = n-1
            # Strip trailing whitespace
            while n > 0 and line[n-1] in (' ', '\t'):
                n = n-1
        else:
            partial = 1
        while i < n:
            c = line[i]
            if c != ESCAPE:
                new = new + c; i = i+1
            elif i+1 == n and not partial:
                partial = 1; break
            elif i+1 < n and line[i+1] == ESCAPE:
                new = new + ESCAPE; i = i+2
            elif i+2 < n and ishex(line[i+1]) and ishex(line[i+2]):
                new = new + chr(unhex(line[i+1:i+3])); i = i+3
            else: # Bad escape sequence -- leave it in
                new = new + c; i = i+1
        if not partial:
            output.write(new + '\n')
            new = ''
    if new:
        output.write(new)

def ishex(c):
    """Return true if the character 'c' is a hexadecimal digit."""
    return '0' <= c <= '9' or 'a' <= c <= 'f' or 'A' <= c <= 'F'

def unhex(s):
    """Get the integer value of a hexadecimal number."""
    bits = 0
    for c in s:
        if '0' <= c <= '9':
            i = ord('0')
        elif 'a' <= c <= 'f':
            i = ord('a')-10
        elif 'A' <= c <= 'F':
            i = ord('A')-10
        else:
            break
        bits = bits*16 + (ord(c) - i)
    return bits

def test():
    import sys
    import getopt
    try:
        opts, args = getopt.getopt(sys.argv[1:], 'td')
    except getopt.error, msg:
        sys.stdout = sys.stderr
        print msg
        print "usage: quopri [-t | -d] [file] ..."
        print "-t: quote tabs"
        print "-d: decode; default encode"
        sys.exit(2)
    deco = 0
    tabs = 0
    for o, a in opts:
        if o == '-t': tabs = 1
        if o == '-d': deco = 1
    if tabs and deco:
        sys.stdout = sys.stderr
        print "-t and -d are mutually exclusive"
        sys.exit(2)
    if not args: args = ['-']
    sts = 0
    for file in args:
        if file == '-':
            fp = sys.stdin
        else:
            try:
                fp = open(file)
            except IOError, msg:
                sys.stderr.write("%s: can't open (%s)\n" % (file, msg))
                sts = 1
                continue
        if deco:
            decode(fp, sys.stdout)
        else:
            encode(fp, sys.stdout, tabs)
        if fp is not sys.stdin:
            fp.close()
    if sts:
        sys.exit(sts)

if __name__ == '__main__':
    test()