#! /usr/bin/env python3

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

# (Dec 1991 version).

__all__ = ["encode", "decode", "encodestring", "decodestring"]

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

try:
    from binascii import a2b_qp, b2a_qp
except ImportError:
    a2b_qp = None
    b2a_qp = None


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

    The 'quotetabs' flag indicates whether embedded tabs and spaces should be
    quoted.  Note that line-ending tabs and spaces are always encoded, as per
    RFC 1521.
    """
    assert isinstance(c, bytes)
    if c in b' \t':
        return quotetabs
    # if header, we have to escape _ because _ is used to escape space
    if c == b'_':
        return header
    return c == ESCAPE or not (b' ' <= c <= b'~')

def quote(c):
    """Quote a single character."""
    assert isinstance(c, bytes) and len(c)==1
    c = ord(c)
    return ESCAPE + bytes((HEX[c//16], HEX[c%16]))


def encode(input, output, quotetabs, header=False):
    """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 embedded tabs and spaces should be
    quoted.  Note that line-ending tabs and spaces are always encoded, as per
    RFC 1521.
    The 'header' flag indicates whether we are encoding spaces as _ as per
    RFC 1522.
    """

    if b2a_qp is not None:
        data = input.read()
        odata = b2a_qp(data, quotetabs=quotetabs, header=header)
        output.write(odata)
        return

    def write(s, output=output, lineEnd=b'\n'):
        # RFC 1521 requires that the line ending in a space or tab must have
        # that trailing character encoded.
        if s and s[-1:] in b' \t':
            output.write(s[:-1] + quote(s[-1:]) + lineEnd)
        elif s == b'.':
            output.write(quote(s) + lineEnd)
        else:
            output.write(s + lineEnd)

    prevline = None
    while 1:
        line = input.readline()
        if not line:
            break
        outline = []
        # Strip off any readline induced trailing newline
        stripped = b''
        if line[-1:] == b'\n':
            line = line[:-1]
            stripped = b'\n'
        # Calculate the un-length-limited encoded line
        for c in line:
            c = bytes((c,))
            if needsquoting(c, quotetabs, header):
                c = quote(c)
            if header and c == b' ':
                outline.append(b'_')
            else:
                outline.append(c)
        # First, write out the previous line
        if prevline is not None:
            write(prevline)
        # Now see if we need any soft line breaks because of RFC-imposed
        # length limitations.  Then do the thisline->prevline dance.
        thisline = EMPTYSTRING.join(outline)
        while len(thisline) > MAXLINESIZE:
            # Don't forget to include the soft line break `=' sign in the
            # length calculation!
            write(thisline[:MAXLINESIZE-1], lineEnd=b'=\n')
            thisline = thisline[MAXLINESIZE-1:]
        # Write out the current line
        prevline = thisline
    # Write out the last line, without a trailing newline
    if prevline is not None:
        write(prevline, lineEnd=stripped)

def encodestring(s, quotetabs=False, header=False):
    if b2a_qp is not None:
        return b2a_qp(s, quotetabs=quotetabs, header=header)
    from io import BytesIO
    infp = BytesIO(s)
    outfp = BytesIO()
    encode(infp, outfp, quotetabs, header)
    return outfp.getvalue()


def decode(input, output, header=False):
    """Read 'input', apply quoted-printable decoding, and write to 'output'.
    'input' and 'output' are files with readline() and write() methods.
    If 'header' is true, decode underscore as space (per RFC 1522)."""

    if a2b_qp is not None:
        data = input.read()
        odata = a2b_qp(data, header=header)
        output.write(odata)
        return

    new = b''
    while 1:
        line = input.readline()
        if not line: break
        i, n = 0, len(line)
        if n > 0 and line[n-1:n] == b'\n':
            partial = 0; n = n-1
            # Strip trailing whitespace
            while n > 0 and line[n-1:n] in b" \t\r":
                n = n-1
        else:
            partial = 1
        while i < n:
            c = line[i:i+1]
            if c == b'_' and header:
                new = new + b' '; i = i+1
            elif 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:i+2]) and ishex(line[i+2:i+3]):
                new = new + bytes((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 + b'\n')
            new = b''
    if new:
        output.write(new)

def decodestring(s, header=False):
    if a2b_qp is not None:
        return a2b_qp(s, header=header)
    from io import BytesIO
    infp = BytesIO(s)
    outfp = BytesIO()
    decode(infp, outfp, header=header)
    return outfp.getvalue()


# Other helper functions
def ishex(c):
    """Return true if the byte ordinal 'c' is a hexadecimal digit in ASCII."""
    assert isinstance(c, bytes)
    return b'0' <= c <= b'9' or b'a' <= c <= b'f' or b'A' <= c <= b'F'

def unhex(s):
    """Get the integer value of a hexadecimal number."""
    bits = 0
    for c in s:
        c = bytes((c,))
        if b'0' <= c <= b'9':
            i = ord('0')
        elif b'a' <= c <= b'f':
            i = ord('a')-10
        elif b'A' <= c <= b'F':
            i = ord(b'A')-10
        else:
            assert False, "non-hex digit "+repr(c)
        bits = bits*16 + (ord(c) - i)
    return bits


def main():
    import sys
    import getopt
    try:
        opts, args = getopt.getopt(sys.argv[1:], 'td')
    except getopt.error as 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.buffer
        else:
            try:
                fp = open(file, "rb")
            except IOError as msg:
                sys.stderr.write("%s: can't open (%s)\n" % (file, msg))
                sts = 1
                continue
        try:
            if deco:
                decode(fp, sys.stdout.buffer)
            else:
                encode(fp, sys.stdout.buffer, tabs)
        finally:
            if file != '-':
                fp.close()
    if sts:
        sys.exit(sts)


if __name__ == '__main__':
    main()