formatter.py

"""Generic output formatting.

Formatter objects transform an abstract flow of formatting events into
specific output events on writer objects. Formatters manage several stack
structures to allow various properties of a writer object to be changed and
restored; writers need not be able to handle relative changes nor any sort
of ``change back'' operation. Specific writer properties which may be
controlled via formatter objects are horizontal alignment, font, and left
margin indentations. A mechanism is provided which supports providing
arbitrary, non-exclusive style settings to a writer as well. Additional
interfaces facilitate formatting events which are not reversible, such as
paragraph separation.

Writer objects encapsulate device interfaces. Abstract devices, such as
file formats, are supported as well as physical devices. The provided
implementations all work with abstract devices. The interface makes
available mechanisms for setting the properties which formatter objects
manage and inserting data into the output.
"""

import sys


AS_IS = None


class NullFormatter:
    """A formatter which does nothing.

    If the writer parameter is omitted, a NullWriter instance is created.
    No methods of the writer are called by NullFormatter instances.

    Implementations should inherit from this class if implementing a writer
    interface but don't need to inherit any implementation.

    """

    def __init__(self, writer=None):
        if writer is None:
            writer = NullWriter()
        self.writer = writer
    def end_paragraph(self, blankline): pass
    def add_line_break(self): pass
    def add_hor_rule(self, *args, **kw): pass
    def add_label_data(self, format, counter, blankline=None): pass
    def add_flowing_data(self, data): pass
    def add_literal_data(self, data): pass
    def flush_softspace(self): pass
    def push_alignment(self, align): pass
    def pop_alignment(self): pass
    def push_font(self, x): pass
    def pop_font(self): pass
    def push_margin(self, margin): pass
    def pop_margin(self): pass
    def set_spacing(self, spacing): pass
    def push_style(self, *styles): pass
    def pop_style(self, n=1): pass
    def assert_line_data(self, flag=1): pass


class AbstractFormatter:
    """The standard formatter.

    This implementation has demonstrated wide applicability to many writers,
    and may be used directly in most circumstances.  It has been used to
    implement a full-featured World Wide Web browser.

    """

    #  Space handling policy:  blank spaces at the boundary between elements
    #  are handled by the outermost context.  "Literal" data is not checked
    #  to determine context, so spaces in literal data are handled directly
    #  in all circumstances.

    def __init__(self, writer):
        self.writer = writer            # Output device
        self.align = None               # Current alignment
        self.align_stack = []           # Alignment stack
        self.font_stack = []            # Font state
        self.margin_stack = []          # Margin state
        self.spacing = None             # Vertical spacing state
        self.style_stack = []           # Other state, e.g. color
        self.nospace = 1                # Should leading space be suppressed
        self.softspace = 0              # Should a space be inserted
        self.para_end = 1               # Just ended a paragraph
        self.parskip = 0                # Skipped space between paragraphs?
        self.hard_break = 1             # Have a hard break
        self.have_label = 0

    def end_paragraph(self, blankline):
        if not self.hard_break:
            self.writer.send_line_break()
            self.have_label = 0
        if self.parskip < blankline and not self.have_label:
            self.writer.send_paragraph(blankline - self.parskip)
            self.parskip = blankline
            self.have_label = 0
        self.hard_break = self.nospace = self.para_end = 1
        self.softspace = 0

    def add_line_break(self):
        if not (self.hard_break or self.para_end):
            self.writer.send_line_break()
            self.have_label = self.parskip = 0
        self.hard_break = self.nospace = 1
        self.softspace = 0

    def add_hor_rule(self, *args, **kw):
        if not self.hard_break:
            self.writer.send_line_break()
        self.writer.send_hor_rule(*args, **kw)
        self.hard_break = self.nospace = 1
        self.have_label = self.para_end = self.softspace = self.parskip = 0

    def add_label_data(self, format, counter, blankline = None):
        if self.have_label or not self.hard_break:
            self.writer.send_line_break()
        if not self.para_end:
            self.writer.send_paragraph((blankline and 1) or 0)
        if isinstance(format, str):
            self.writer.send_label_data(self.format_counter(format, counter))
        else:
            self.writer.send_label_data(format)
        self.nospace = self.have_label = self.hard_break = self.para_end = 1
        self.softspace = self.parskip = 0

    def format_counter(self, format, counter):
        label = ''
        for c in format:
            if c == '1':
                label = label + ('%d' % counter)
            elif c in 'aA':
                if counter > 0:
                    label = label + self.format_letter(c, counter)
            elif c in 'iI':
                if counter > 0:
                    label = label + self.format_roman(c, counter)
            else:
                label = label + c
        return label

    def format_letter(self, case, counter):
        label = ''
        while counter > 0:
            counter, x = divmod(counter-1, 26)
            # This makes a strong assumption that lowercase letters
            # and uppercase letters form two contiguous blocks, with
            # letters in order!
            s = chr(ord(case) + x)
            label = s + label
        return label

    def format_roman(self, case, counter):
        ones = ['i', 'x', 'c', 'm']
        fives = ['v', 'l', 'd']
        label, index = '', 0
        # This will die of IndexError when counter is too big
        while counter > 0:
            counter, x = divmod(counter, 10)
            if x == 9:
                label = ones[index] + ones[index+1] + label
            elif x == 4:
                label = ones[index] + fives[index] + label
            else:
                if x >= 5:
                    s = fives[index]
                    x = x-5
                else:
                    s = ''
                s = s + ones[index]*x
                label = s + label
            index = index + 1
        if case == 'I':
            return label.upper()
        return label

    def add_flowing_data(self, data):
        if not data: return
        # The following looks a bit convoluted but is a great improvement over
        # data = regsub.gsub('[' + string.whitespace + ']+', ' ', data)
        prespace = data[:1].isspace()
        postspace = data[-1:].isspace()
        data = " ".join(data.split())
        if self.nospace and not data:
            return
        elif prespace or self.softspace:
            if not data:
                if not self.nospace:
                    self.softspace = 1
                    self.parskip = 0
                return
            if not self.nospace:
                data = ' ' + data
        self.hard_break = self.nospace = self.para_end = \
                          self.parskip = self.have_label = 0
        self.softspace = postspace
        self.writer.send_flowing_data(data)

    def add_literal_data(self, data):
        if not data: return
        if self.softspace:
            self.writer.send_flowing_data(" ")
        self.hard_break = data[-1:] == '\n'
        self.nospace = self.para_end = self.softspace = \
                       self.parskip = self.have_label = 0
        self.writer.send_literal_data(data)

    def flush_softspace(self):
        if self.softspace:
            self.hard_break = self.para_end = self.parskip = \
                              self.have_label = self.softspace = 0
            self.nospace = 1
            self.writer.send_flowing_data(' ')

    def push_alignment(self, align):
        if align and align != self.align:
            self.writer.new_alignment(align)
            self.align = align
            self.align_stack.append(align)
        else:
            self.align_stack.append(self.align)

    def pop_alignment(self):
        if self.align_stack:
            del self.align_stack[-1]
        if self.align_stack:
            self.align = align = self.align_stack[-1]
            self.writer.new_alignment(align)
        else:
            self.align = None
            self.writer.new_alignment(None)

    def push_font(self, (size, i, b, tt)):
        if self.softspace:
            self.hard_break = self.para_end = self.softspace = 0
            self.nospace = 1
            self.writer.send_flowing_data(' ')
        if self.font_stack:
            csize, ci, cb, ctt = self.font_stack[-1]
            if size is AS_IS: size = csize
            if i is AS_IS: i = ci
            if b is AS_IS: b = cb
            if tt is AS_IS: tt = ctt
        font = (size, i, b, tt)
        self.font_stack.append(font)
        self.writer.new_font(font)

    def pop_font(self):
        if self.font_stack:
            del self.font_stack[-1]
        if self.font_stack:
            font = self.font_stack[-1]
        else:
            font = None
        self.writer.new_font(font)

    def push_margin(self, margin):
        self.margin_stack.append(margin)
        fstack = filter(None, self.margin_stack)
        if not margin and fstack:
            margin = fstack[-1]
        self.writer.new_margin(margin, len(fstack))

    def pop_margin(self):
        if self.margin_stack:
            del self.margin_stack[-1]
        fstack = filter(None, self.margin_stack)
        if fstack:
            margin = fstack[-1]
        else:
            margin = None
        self.writer.new_margin(margin, len(fstack))

    def set_spacing(self, spacing):
        self.spacing = spacing
        self.writer.new_spacing(spacing)

    def push_style(self, *styles):
        if self.softspace:
            self.hard_break = self.para_end = self.softspace = 0
            self.nospace = 1
            self.writer.send_flowing_data(' ')
        for style in styles:
            self.style_stack.append(style)
        self.writer.new_styles(tuple(self.style_stack))

    def pop_style(self, n=1):
        del self.style_stack[-n:]
        self.writer.new_styles(tuple(self.style_stack))

    def assert_line_data(self, flag=1):
        self.nospace = self.hard_break = not flag
        self.para_end = self.parskip = self.have_label = 0


class NullWriter:
    """Minimal writer interface to use in testing & inheritance.

    A writer which only provides the interface definition; no actions are
    taken on any methods.  This should be the base class for all writers
    which do not need to inherit any implementation methods.

    """
    def __init__(self): pass
    def flush(self): pass
    def new_alignment(self, align): pass
    def new_font(self, font): pass
    def new_margin(self, margin, level): pass
    def new_spacing(self, spacing): pass
    def new_styles(self, styles): pass
    def send_paragraph(self, blankline): pass
    def send_line_break(self): pass
    def send_hor_rule(self, *args, **kw): pass
    def send_label_data(self, data): pass
    def send_flowing_data(self, data): pass
    def send_literal_data(self, data): pass


class AbstractWriter(NullWriter):
    """A writer which can be used in debugging formatters, but not much else.

    Each method simply announces itself by printing its name and
    arguments on standard output.

    """

    def new_alignment(self, align):
        print "new_alignment(%s)" % `align`

    def new_font(self, font):
        print "new_font(%s)" % `font`

    def new_margin(self, margin, level):
        print "new_margin(%s, %d)" % (`margin`, level)

    def new_spacing(self, spacing):
        print "new_spacing(%s)" % `spacing`

    def new_styles(self, styles):
        print "new_styles(%s)" % `styles`

    def send_paragraph(self, blankline):
        print "send_paragraph(%s)" % `blankline`

    def send_line_break(self):
        print "send_line_break()"

    def send_hor_rule(self, *args, **kw):
        print "send_hor_rule()"

    def send_label_data(self, data):
        print "send_label_data(%s)" % `data`

    def send_flowing_data(self, data):
        print "send_flowing_data(%s)" % `data`

    def send_literal_data(self, data):
        print "send_literal_data(%s)" % `data`


class DumbWriter(NullWriter):
    """Simple writer class which writes output on the file object passed in
    as the file parameter or, if file is omitted, on standard output.  The
    output is simply word-wrapped to the number of columns specified by
    the maxcol parameter.  This class is suitable for reflowing a sequence
    of paragraphs.

    """

    def __init__(self, file=None, maxcol=72):
        self.file = file or sys.stdout
        self.maxcol = maxcol
        NullWriter.__init__(self)
        self.reset()

    def reset(self):
        self.col = 0
        self.atbreak = 0

    def send_paragraph(self, blankline):
        self.file.write('\n'*blankline)
        self.col = 0
        self.atbreak = 0

    def send_line_break(self):
        self.file.write('\n')
        self.col = 0
        self.atbreak = 0

    def send_hor_rule(self, *args, **kw):
        self.file.write('\n')
        self.file.write('-'*self.maxcol)
        self.file.write('\n')
        self.col = 0
        self.atbreak = 0

    def send_literal_data(self, data):
        self.file.write(data)
        i = data.rfind('\n')
        if i >= 0:
            self.col = 0
            data = data[i+1:]
        data = data.expandtabs()
        self.col = self.col + len(data)
        self.atbreak = 0

    def send_flowing_data(self, data):
        if not data: return
        atbreak = self.atbreak or data[0].isspace()
        col = self.col
        maxcol = self.maxcol
        write = self.file.write
        for word in data.split():
            if atbreak:
                if col + len(word) >= maxcol:
                    write('\n')
                    col = 0
                else:
                    write(' ')
                    col = col + 1
            write(word)
            col = col + len(word)
            atbreak = 1
        self.col = col
        self.atbreak = data[-1].isspace()


def test(file = None):
    w = DumbWriter()
    f = AbstractFormatter(w)
    if file is not None:
        fp = open(file)
    elif sys.argv[1:]:
        fp = open(sys.argv[1])
    else:
        fp = sys.stdin
    while 1:
        line = fp.readline()
        if not line:
            break
        if line == '\n':
            f.end_paragraph(1)
        else:
            f.add_flowing_data(line)
    f.end_paragraph(0)


if __name__ == '__main__':
    test()