"""Simplify adding markup to a piece of text."""


from xml.sax import saxutils

# Helper functions to turn start/end tags into text
def _start_element(tag, attrs):
    s = "<" + tag
    for name, value in attrs.items():
        s += " %s=%s" % (name, saxutils.quoteattr(value))
    return s + ">"

def _end_element(tag):
    return "</%s>" % tag


class MidPoint:
    def __init__(self):
        self.left = []
        self.right = []

class MarkupEditor:
    def __init__(self, text):
        self.text = text
        self._max = len(text)
        self.midpoints = {}

    def _get(self, pos):
        assert 0 <= pos <= self._max, \
               "position (%d) out of range; 0 <= x <= %d" % self._max
        if self.midpoints.has_key(pos):
            return self.midpoints[pos]
        x = MidPoint()
        self.midpoints[pos] = x
        return x
        
    def insert_text(self, pos, text):
        point = self._get(pos)
        point.right.insert(0, saxutils.escape(text))
        
    def insert_raw_text(self, pos, text):
        point = self._get(pos)
        point.right.insert(0, text)

    def insert_element(self, leftpos, rightpos, tag, attrs = {}):
        strleft = _start_element(tag, attrs)
        strright = _end_element(tag)
        if leftpos == rightpos:
            point = self._get(leftpos)
            point.right.insert(0, strleft + strright)
        else:
            assert leftpos < rightpos, (leftpos, rightpos)
            left = self._get(leftpos)
            right = self._get(rightpos)

            left.right.insert(0, strleft)
            right.left.append(strright)

    def insert_singleton(self, pos, tag, attrs = {}):
        point = self._get(pos)
        s = _start_element(tag, attrs)
        point.right.insert(0, s)

    def to_file(self, outfile):
        items = self.midpoints.items()
        items.sort()
        text = self.text
        prevpos = 0
        for pos, midpoint in items:
            outfile.write(text[prevpos:pos])
            for s in midpoint.left:
                outfile.write(s)
            for s in midpoint.right:
                outfile.write(s)
            prevpos = pos
        outfile.write(text[prevpos:])

def _compare(markup, expect):
    from cStringIO import StringIO
    file = StringIO()
    markup.to_file(file)
    s = file.getvalue()
    assert s == expect, (s, expect)

def test():
    markup = MarkupEditor("01234")
    _compare(markup, "01234")
    markup.insert_text(0, "A")
    _compare(markup, "A01234")
    markup.insert_text(5, "Z")
    _compare(markup, "A01234Z")
    markup.insert_text(5, "Y")
    _compare(markup, "A01234YZ")
    markup.insert_text(5, "<")
    _compare(markup, "A01234&lt;YZ")
    markup.insert_raw_text(1, "BCD")
    _compare(markup, "A0BCD1234&lt;YZ")
    markup.insert_raw_text(3, "<P>")
    _compare(markup, "A0BCD12<P>34&lt;YZ")
    markup.insert_element(1, 3, "a", {"tag": "value"})
    _compare(markup, 'A0<a tag="value">BCD12</a><P>34&lt;YZ')
    markup.insert_element(1, 1, "Q", {"R": "S"})
    _compare(markup, 'A0<Q R="S"></Q><a tag="value">BCD12</a><P>34&lt;YZ')
    markup.insert_singleton(3, "br")
    _compare(markup, 'A0<Q R="S"></Q><a tag="value">BCD12</a><br><P>34&lt;YZ')

if __name__ == "__main__":
    test()