# Natural Language Toolkit: Dependency Grammars
#
# Copyright (C) 2001-2010 NLTK Project
# Author: Jason Narad <jason.narad@gmail.com>
#
# URL: <http://www.nltk.org/>
# For license information, see LICENSE.TXT
#

import math

from nltk.grammar import DependencyProduction, DependencyGrammar,\
                 StatisticalDependencyGrammar, parse_dependency_grammar
from dependencygraph import *
from pprint import pformat

#################################################################
# Dependency Span
#################################################################

class DependencySpan(object):
    """
    A contiguous span over some part of the input string representing 
    dependency (head -> modifier) relationships amongst words.  An atomic 
    span corresponds to only one word so it isn't a 'span' in the conventional
    sense, as its _start_index = _end_index = _head_index for concatenation
    purposes.  All other spans are assumed to have arcs between all nodes
    within the start and end indexes of the span, and one head index corresponding
    to the head word for the entire span.  This is the same as the root node if 
    the dependency structure were depicted as a graph.
    """
    def __init__(self, start_index, end_index, head_index, arcs, tags):
        self._start_index = start_index
        self._end_index = end_index
        self._head_index = head_index
        self._arcs = arcs
        self._hash = hash((start_index, end_index, head_index, tuple(arcs)))
        self._tags = tags

    def head_index(self):
        """
        @return: An value indexing the head of the entire C{DependencySpan}.
        @rtype: C{int}.
        """
        return self._head_index
    
    def __repr__(self):
        """
        @return: A concise string representatino of the C{DependencySpan}.
        @rtype: C{string}.
        """
        return 'Span %d-%d; Head Index: %d' % (self._start_index, self._end_index, self._head_index)
    
    def __str__(self):
        """
        @return: A verbose string representation of the C{DependencySpan}.
        @rtype: C{string}.
        """
        str = 'Span %d-%d; Head Index: %d' % (self._start_index, self._end_index, self._head_index)
        for i in range(len(self._arcs)):
            str += '\n%d <- %d, %s' % (i, self._arcs[i], self._tags[i])
        return str

    def __eq__(self, other):
        """
        @return: true if this C{DependencySpan} is equal to C{other}.
        @rtype: C{boolean}.
        """
        return (isinstance(other, self.__class__) and
                self._start_index == other._start_index and
                self._end_index == other._end_index and
                self._head_index == other._head_index and
                self._arcs == other._arcs)

    def __ne__(self, other):
        """
        @return: false if this C{DependencySpan} is equal to C{other}
        @rtype: C{boolean}	
        """
        return not (self == other)

    def __cmp__(self, other):
        """
        @return: -1 if args are of different class.  Otherwise returns the
        cmp() of the two sets of spans.
        @rtype: C{int} 
        """
        if not isinstance(other, self.__class__): return -1
        return cmp((self._start_index, self._start_index, self._head_index), (other._end_index, other._end_index, other._head_index))

    def __hash__(self):
        """
        @return: The hash value of this C{DependencySpan}.
        """
        return self._hash

#################################################################
# Chart Cell
#################################################################

class ChartCell(object):
    """
    A cell from the parse chart formed when performing the CYK algorithm.
    Each cell keeps track of its x and y coordinates (though this will probably
    be discarded), and a list of spans serving as the cell's entries.
    """
    def __init__(self, x, y):
        """
        @param x: This cell's x coordinate.
        @type x: C{int}.
        @param y: This cell's y coordinate.
        @type y: C{int}.
        """
        self._x = x
        self._y = y
        self._entries = set([])
        
    def add(self, span):
        """
        Appends the given span to the list of spans
        representing the chart cell's entries.
        
        @param span: The span to add.
        @type span: C{DependencySpan}.
        """
        self._entries.add(span);

    def __str__(self):
        """
        @return: A verbose string representation of this C{ChartCell}.
        @rtype: C{string}.
        """ 
        return 'CC[%d,%d]: %s' % (self._x, self._y, self._entries)
        
    def __repr__(self):
        """
        @return: A concise string representation of this C{ChartCell}.
        @rtype: C{string}.
        """
        return '%s' % self


#################################################################
# Parsing  with Dependency Grammars
#################################################################


class ProjectiveDependencyParser(object):
    """
    A projective, rule-based, dependency parser.  A ProjectiveDependencyParser
    is created with a DependencyGrammar, a set of productions specifying 
    word-to-word dependency relations.  The parse() method will then 
    return the set of all parses, in tree representation, for a given input
    sequence of tokens.  Each parse must meet the requirements of the both
    the grammar and the projectivity constraint which specifies that the 
    branches of the dependency tree are not allowed to cross.  Alternatively, 
    this can be understood as stating that each parent node and its children 
    in the parse tree form a continuous substring of the input sequence.
    """

    def __init__(self, dependency_grammar):
        """
        Create a new ProjectiveDependencyParser, from a word-to-word
        dependency grammar C{DependencyGrammar}.

        @param dependency_grammar: A word-to-word relation dependencygrammar.
        @type dependency_grammar: A C{DependencyGrammar}.
        """
        self._grammar = dependency_grammar

    def parse(self, tokens):
        """
        Performs a projective dependency parse on the list of tokens using
        a chart-based, span-concatenation algorithm similar to Eisner (1996).
        
        @param tokens: The list of input tokens.
        @type tokens:a C{list} of L{String}
        @return: A list of parse trees.
        @rtype: a C{list} of L{tree}
        """
        self._tokens = list(tokens)
        chart = []
        for i in range(0, len(self._tokens) + 1):
            chart.append([])
            for j in range(0, len(self._tokens) + 1):
                chart[i].append(ChartCell(i,j))
                if i==j+1:
                    chart[i][j].add(DependencySpan(i-1,i,i-1,[-1], ['null']))
        for i in range(1,len(self._tokens)+1):
            for j in range(i-2,-1,-1):
                for k in range(i-1,j,-1):
                    for span1 in chart[k][j]._entries:
                            for span2 in chart[i][k]._entries:
                                for newspan in self.concatenate(span1, span2):
                                    chart[i][j].add(newspan)
        graphs = []
        trees = []
        for parse in chart[len(self._tokens)][0]._entries:
            conll_format = ""
#            malt_format = ""
            for i in range(len(tokens)):
#                malt_format += '%s\t%s\t%d\t%s\n' % (tokens[i], 'null', parse._arcs[i] + 1, 'null')
                conll_format += '\t%d\t%s\t%s\t%s\t%s\t%s\t%d\t%s\t%s\t%s\n' % (i+1, tokens[i], tokens[i], 'null', 'null', 'null', parse._arcs[i] + 1, 'null', '-', '-')
            dg = DependencyGraph(conll_format)
#           if self.meets_arity(dg):
            graphs.append(dg)
            trees.append(dg.tree())
        return trees
            

    def concatenate(self, span1, span2):
        """
        Concatenates the two spans in whichever way possible.  This
        includes rightward concatenation (from the leftmost word of the 
        leftmost span to the rightmost word of the rightmost span) and
        leftward concatenation (vice-versa) between adjacent spans.  Unlike 
        Eisner's presentation of span concatenation, these spans do not 
        share or pivot on a particular word/word-index.

        return: A list of new spans formed through concatenation.
        rtype: A C{list} of L{DependencySpan}
        """
        spans = []
        if span1._start_index == span2._start_index:
            print 'Error: Mismatched spans - replace this with thrown error'
        if span1._start_index > span2._start_index:
            temp_span = span1
            span1 = span2
            span2 = temp_span
        # adjacent rightward covered concatenation
        new_arcs = span1._arcs + span2._arcs
        new_tags = span1._tags + span2._tags
        if self._grammar.contains(self._tokens[span1._head_index], self._tokens[span2._head_index]):
#           print 'Performing rightward cover %d to %d' % (span1._head_index, span2._head_index)
            new_arcs[span2._head_index - span1._start_index] = span1._head_index
            spans.append(DependencySpan(span1._start_index, span2._end_index, span1._head_index, new_arcs, new_tags))
        # adjacent leftward covered concatenation
        new_arcs = span1._arcs + span2._arcs
        if self._grammar.contains(self._tokens[span2._head_index], self._tokens[span1._head_index]):
#           print 'performing leftward cover %d to %d' % (span2._head_index, span1._head_index)
            new_arcs[span1._head_index - span1._start_index] = span2._head_index
            spans.append(DependencySpan(span1._start_index, span2._end_index, span2._head_index, new_arcs, new_tags))
        return spans



#################################################################
# Parsing  with Probabilistic Dependency Grammars
#################################################################

class ProbabilisticProjectiveDependencyParser(object):
    """
    A probabilistic, projective dependency parser.  This parser returns 
    the most probable projective parse derived from the probabilistic 
    dependency grammar derived from the train() method.  The probabilistic 
    model is an implementation of Eisner's (1996) Model C, which conditions 
    on head-word, head-tag, child-word, and child-tag.  The decoding 
    uses a bottom-up chart-based span concatenation algorithm that's 
    identical to the one utilized by the rule-based projective parser.
    """

    def __init__(self):
        """
        Create a new probabilistic dependency parser.  No additional 
        operations are necessary.
        """
        print ''

    def parse(self, tokens):
        """
        Parses the list of tokens subject to the projectivity constraint
        and the productions in the parser's grammar.  This uses a method 
        similar to the span-concatenation algorithm defined in Eisner (1996).
        It returns the most probable parse derived from the parser's 
        probabilistic dependency grammar.
        """
        self._tokens = list(tokens)
        chart = []
        for i in range(0, len(self._tokens) + 1):
            chart.append([])
            for j in range(0, len(self._tokens) + 1):
                chart[i].append(ChartCell(i,j))
                if i==j+1:
                    if self._grammar._tags.has_key(tokens[i-1]):
                        for tag in self._grammar._tags[tokens[i-1]]:
                            chart[i][j].add(DependencySpan(i-1,i,i-1,[-1], [tag]))
                    else:
                        print 'No tag found for input token \'%s\', parse is impossible.' % tokens[i-1]
                        return []
        for i in range(1,len(self._tokens)+1):
            for j in range(i-2,-1,-1):
                for k in range(i-1,j,-1):
                    for span1 in chart[k][j]._entries:
                            for span2 in chart[i][k]._entries:
                                for newspan in self.concatenate(span1, span2):
                                    chart[i][j].add(newspan)
        graphs = []
        trees = []
        max_parse = None
        max_score = 0
        for parse in chart[len(self._tokens)][0]._entries:
            conll_format = ""
            malt_format = ""
            for i in range(len(tokens)):
                malt_format += '%s\t%s\t%d\t%s\n' % (tokens[i], 'null', parse._arcs[i] + 1, 'null')
                conll_format += '\t%d\t%s\t%s\t%s\t%s\t%s\t%d\t%s\t%s\t%s\n' % (i+1, tokens[i], tokens[i], parse._tags[i], parse._tags[i], 'null', parse._arcs[i] + 1, 'null', '-', '-')
            dg = DependencyGraph(conll_format)
            score = self.compute_prob(dg)
            if score > max_score:
                max_parse = dg.tree()
                max_score = score
        return [max_parse, max_score]


    def concatenate(self, span1, span2):
        """
        Concatenates the two spans in whichever way possible.  This
        includes rightward concatenation (from the leftmost word of the 
        leftmost span to the rightmost word of the rightmost span) and
        leftward concatenation (vice-versa) between adjacent spans.  Unlike 
        Eisner's presentation of span concatenation, these spans do not 
        share or pivot on a particular word/word-index.

        return: A list of new spans formed through concatenation.
        rtype: A C{list} of L{DependencySpan}
        """
        spans = []
        if span1._start_index == span2._start_index:
            print 'Error: Mismatched spans - replace this with thrown error'
        if span1._start_index > span2._start_index:
            temp_span = span1
            span1 = span2
            span2 = temp_span
        # adjacent rightward covered concatenation
        new_arcs = span1._arcs + span2._arcs
        new_tags = span1._tags + span2._tags
        if self._grammar.contains(self._tokens[span1._head_index], self._tokens[span2._head_index]):
            new_arcs[span2._head_index - span1._start_index] = span1._head_index
            spans.append(DependencySpan(span1._start_index, span2._end_index, span1._head_index, new_arcs, new_tags))
        # adjacent leftward covered concatenation
        new_arcs = span1._arcs + span2._arcs
        new_tags = span1._tags + span2._tags
        if self._grammar.contains(self._tokens[span2._head_index], self._tokens[span1._head_index]):
            new_arcs[span1._head_index - span1._start_index] = span2._head_index
            spans.append(DependencySpan(span1._start_index, span2._end_index, span2._head_index, new_arcs, new_tags))
        return spans

    def train(self, graphs):
        """
        Trains a StatisticalDependencyGrammar based on the list of input 
        DependencyGraphs.  This model is an implementation of Eisner's (1996)
        Model C, which derives its statistics from head-word, head-tag, 
        child-word, and child-tag relationships.

        param graphs: A list of dependency graphs to train from.
        type: A list of C{DependencyGraph}
        """
        productions = []
        events = {}
        tags = {}
        for dg in graphs:
            for node_index in range(1,len(dg.nodelist)):
                children = dg.nodelist[node_index]['deps']
                nr_left_children = dg.left_children(node_index)
                nr_right_children = dg.right_children(node_index)
                nr_children = nr_left_children + nr_right_children
                for child_index in range(0 - (nr_left_children + 1), nr_right_children + 2):
                    head_word = dg.nodelist[node_index]['word']
                    head_tag = dg.nodelist[node_index]['tag']
                    if tags.has_key(head_word):
                        tags[head_word].add(head_tag)
                    else:
                        tags[head_word] = set([head_tag])
                    child = 'STOP'
                    child_tag = 'STOP'
                    prev_word = 'START'
                    prev_tag = 'START'
                    if child_index < 0:
                        array_index = child_index + nr_left_children
                        if array_index >= 0:
                            child = dg.nodelist[children[array_index]]['word']
                            child_tag = dg.nodelist[children[array_index]]['tag']
                        if child_index != -1:
                            prev_word = dg.nodelist[children[array_index + 1]]['word']
                            prev_tag =  dg.nodelist[children[array_index + 1]]['tag']
                        if child != 'STOP':
                            productions.append(DependencyProduction(head_word, [child]))
                        head_event = '(head (%s %s) (mods (%s, %s, %s) left))' % (child, child_tag, prev_tag, head_word, head_tag)
                        mod_event = '(mods (%s, %s, %s) left))' % (prev_tag, head_word, head_tag)
                        if events.has_key(head_event):
                            events[head_event] += 1
                        else:
                            events[head_event] = 1
                        if events.has_key(mod_event):
                            events[mod_event] += 1
                        else:
                            events[mod_event] = 1
                    elif child_index > 0:
                        array_index = child_index + nr_left_children - 1
                        if array_index < nr_children:
                            child = dg.nodelist[children[array_index]]['word']
                            child_tag = dg.nodelist[children[array_index]]['tag']
                        if child_index != 1:
                            prev_word = dg.nodelist[children[array_index - 1]]['word']
                            prev_tag =  dg.nodelist[children[array_index - 1]]['tag']
                        if child != 'STOP':
                            productions.append(DependencyProduction(head_word, [child]))
                        head_event = '(head (%s %s) (mods (%s, %s, %s) right))' % (child, child_tag, prev_tag, head_word, head_tag)
                        mod_event = '(mods (%s, %s, %s) right))' % (prev_tag, head_word, head_tag)
                        if events.has_key(head_event):
                            events[head_event] += 1
                        else:
                            events[head_event] = 1
                        if events.has_key(mod_event):
                            events[mod_event] += 1
                        else:
                            events[mod_event] = 1
        self._grammar = StatisticalDependencyGrammar(productions, events, tags)
#        print self._grammar
        
    def compute_prob(self, dg):
        """
        Computes the probability of a dependency graph based 
        on the parser's probability model (defined by the parser's
        statistical dependency grammar).

        param dg: A dependency graph to score.
        type dg: a C{DependencyGraph}
        return: The probability of the dependency graph.
        rtype: A number/double.
        """
        prob = 1.0
        for node_index in range(1,len(dg.nodelist)):
            children = dg.nodelist[node_index]['deps']
            nr_left_children = dg.left_children(node_index)
            nr_right_children = dg.right_children(node_index)
            nr_children = nr_left_children + nr_right_children
            for child_index in range(0 - (nr_left_children + 1), nr_right_children + 2):
                head_word = dg.nodelist[node_index]['word']
                head_tag = dg.nodelist[node_index]['tag']
                child = 'STOP'
                child_tag = 'STOP'
                prev_word = 'START'
                prev_tag = 'START'
                if child_index < 0:
                    array_index = child_index + nr_left_children
                    if array_index >= 0:
                        child = dg.nodelist[children[array_index]]['word']
                        child_tag = dg.nodelist[children[array_index]]['tag']
                    if child_index != -1:
                        prev_word = dg.nodelist[children[array_index + 1]]['word']
                        prev_tag =  dg.nodelist[children[array_index + 1]]['tag']
                    head_event = '(head (%s %s) (mods (%s, %s, %s) left))' % (child, child_tag, prev_tag, head_word, head_tag)
                    mod_event = '(mods (%s, %s, %s) left))' % (prev_tag, head_word, head_tag)
                    h_count = self._grammar._events[head_event]
                    m_count = self._grammar._events[mod_event]
                    prob *= (h_count / m_count)
                elif child_index > 0:
                    array_index = child_index + nr_left_children - 1
                    if array_index < nr_children:
                        child = dg.nodelist[children[array_index]]['word']
                        child_tag = dg.nodelist[children[array_index]]['tag']
                    if child_index != 1:
                        prev_word = dg.nodelist[children[array_index - 1]]['word']
                        prev_tag =  dg.nodelist[children[array_index - 1]]['tag']
                    head_event = '(head (%s %s) (mods (%s, %s, %s) right))' % (child, child_tag, prev_tag, head_word, head_tag)
                    mod_event = '(mods (%s, %s, %s) right))' % (prev_tag, head_word, head_tag)
                    h_count = self._grammar._events[head_event]
                    m_count = self._grammar._events[mod_event]
                    prob *= (h_count / m_count)
        return prob


#################################################################
# Demos
#################################################################

def demo():
    projective_rule_parse_demo()
#    arity_parse_demo()
    projective_prob_parse_demo()


def projective_rule_parse_demo():
    """
    A demonstration showing the creation and use of a 
    C{DependencyGrammar} to perform a projective dependency 
    parse.
    """
    grammar = parse_dependency_grammar("""
    'scratch' -> 'cats' | 'walls'
    'walls' -> 'the'
    'cats' -> 'the'
    """)
    print grammar
    pdp = ProjectiveDependencyParser(grammar)
    trees = pdp.parse(['the', 'cats', 'scratch', 'the', 'walls'])
    for tree in trees:
        print tree
    
def arity_parse_demo():
    """
    A demonstration showing the creation of a C{DependencyGrammar} 
    in which a specific number of modifiers is listed for a given 
    head.  This can further constrain the number of possible parses
    created by a C{ProjectiveDependencyParser}.
    """
    print
    print 'A grammar with no arity constraints. Each DependencyProduction'
    print 'specifies a relationship between one head word and only one'
    print 'modifier word.'
    grammar = parse_dependency_grammar("""
    'fell' -> 'price' | 'stock'
    'price' -> 'of' | 'the'
    'of' -> 'stock'
    'stock' -> 'the'
    """)
    print grammar
    
    print
    print 'For the sentence \'The price of the stock fell\', this grammar'
    print 'will produce the following three parses:'    
    pdp = ProjectiveDependencyParser(grammar)
    trees = pdp.parse(['the', 'price', 'of', 'the', 'stock', 'fell'])   
    for tree in trees:
        print tree

    print
    print 'By contrast, the following grammar contains a '
    print 'DependencyProduction that specifies a relationship'
    print 'between a single head word, \'price\', and two modifier'
    print 'words, \'of\' and \'the\'.'
    grammar = parse_dependency_grammar("""
    'fell' -> 'price' | 'stock'
    'price' -> 'of' 'the'
    'of' -> 'stock'
    'stock' -> 'the'
    """)
    print grammar
    
    print
    print 'This constrains the number of possible parses to just one:' # unimplemented, soon to replace
    pdp = ProjectiveDependencyParser(grammar)
    trees = pdp.parse(['the', 'price', 'of', 'the', 'stock', 'fell'])
    for tree in trees:
        print tree

def projective_prob_parse_demo():
    """
    A demo showing the training and use of a projective 
    dependency parser.
    """
    graphs = [DependencyGraph(entry)
              for entry in conll_data2.split('\n\n') if entry]
    ppdp = ProbabilisticProjectiveDependencyParser()
    print 'Training Probabilistic Projective Dependency Parser...'
    ppdp.train(graphs)
    sent = ['Cathy', 'zag', 'hen', 'wild', 'zwaaien', '.']
    print 'Parsing \'', " ".join(sent), '\'...'
    parse = ppdp.parse(sent)
    print 'Parse:'
    print parse[0]


if __name__ == '__main__':
    demo()