"""
###############################################################################
split lines on fixed columns or at delimiters before a column;
see also: related but different textwrap standard library module (2.3+);
4E caveat: this assumes str; supporting bytes might help avoid some decodes; 
###############################################################################
"""

defaultsize = 80

def wrapLinesSimple(lineslist, size=defaultsize):
    "split at fixed position size"
    wraplines = []
    for line in lineslist:
        while True:
            wraplines.append(line[:size])         # OK if len < size
            line = line[size:]                    # split without analysis
            if not line: break
    return wraplines

def wrapLinesSmart(lineslist, size=defaultsize, delimiters='.,:\t '):
    "wrap at first delimiter left of size"
    wraplines = []
    for line in lineslist:
        while True:
            if len(line) <= size:
                wraplines += [line]
                break
            else:
                for look in range(size-1, size // 2, -1):       # 3.0: need // not /
                    if line[look] in delimiters:
                        front, line = line[:look+1], line[look+1:]
                        break
                else:
                    front, line = line[:size], line[size:]
                wraplines += [front]
    return wraplines

###############################################################################
# common use case utilities
###############################################################################

def wrapText1(text, size=defaultsize):         # better for line-based txt: mail
    "when text read all at once"               # keeps original line brks struct
    lines = text.split('\n')                   # split on newlines
    lines = wrapLinesSmart(lines, size)        # wrap lines on delimiters
    return '\n'.join(lines)                    # put back together

def wrapText2(text, size=defaultsize):         # more uniform across lines
    "same, but treat as one long line"         # but loses original line struct
    text  = text.replace('\n', ' ')            # drop newlines if any
    lines = wrapLinesSmart([text], size)       # wrap single line on delimiters
    return lines                               # caller puts back together

def wrapText3(text, size=defaultsize):
    "same, but put back together"
    lines = wrapText2(text, size)              # wrap as single long line
    return '\n'.join(lines) + '\n'             # make one string with newlines

def wrapLines1(lines, size=defaultsize):
    "when newline included at end"
    lines = [line[:-1] for line in lines]      # strip off newlines (or .rstrip)
    lines = wrapLinesSmart(lines, size)        # wrap on delimiters
    return [(line + '\n') for line in lines]   # put them back

def wrapLines2(lines, size=defaultsize):       # more uniform across lines
    "same, but concat as one long line"        # but loses original structure
    text  = ''.join(lines)                     # put together as 1 line
    lines = wrapText2(text)                    # wrap on delimiters
    return [(line + '\n') for line in lines]   # put newlines on ends

###############################################################################
# self-test
###############################################################################

if __name__ == '__main__':
    lines = ['spam ham ' * 20 + 'spam,ni' * 20,
             'spam ham ' * 20,
             'spam,ni'   * 20,
             'spam ham.ni' * 20,
             '',
             'spam'*80,
             ' ',
             'spam ham eggs']

    sep = '-' * 30
    print('all', sep)
    for line in lines: print(repr(line))
    print('simple', sep)
    for line in wrapLinesSimple(lines): print(repr(line))
    print('smart', sep)
    for line in wrapLinesSmart(lines): print(repr(line))

    print('single1', sep)
    for line in wrapLinesSimple([lines[0]], 60): print(repr(line))
    print('single2', sep)
    for line in wrapLinesSmart([lines[0]], 60): print(repr(line))
    print('combined text', sep)
    for line in wrapLines2(lines): print(repr(line))
    print('combined lines', sep)
    print(wrapText1('\n'.join(lines)))

    assert ''.join(lines) == ''.join(wrapLinesSimple(lines, 60))
    assert ''.join(lines) == ''.join(wrapLinesSmart(lines, 60))
    print(len(''.join(lines)), end=' ')
    print(len(''.join(wrapLinesSimple(lines))), end=' ')
    print(len(''.join(wrapLinesSmart(lines))), end=' ')
    print(len(''.join(wrapLinesSmart(lines, 60))), end=' ')
    input('Press enter')   # pause if clicked