#!/usr/bin/python

"""
Bottom up rewrite generator
---------------------------

This script takes as input a description of patterns and outputs a
matcher class that can match trees given the patterns.

Patterns are specified as follows::

     reg -> ADDI32(reg, reg) 2 (. add NT0 NT1 .)
     reg -> MULI32(reg, reg) 3 (. .)

or a multiply add::

    reg -> ADDI32(MULI32(reg, reg), reg) 4 (. muladd $1, $2, $3 .)

The general specification pattern is::

    [result] -> [tree] [cost] [template code]

Trees
-----

A tree is described using parenthesis notation. For example a node X with
three child nodes is described as:

     X(a, b, b)

Trees can be nested:

     X(Y(a, a), a)

The 'a' in the example above indicates an open connection to a next tree
pattern.


In the example above 'reg' is a non-terminal. ADDI32 is a terminal. non-terminals
cannot have child nodes. A special case occurs in this case:

    reg -> rc

where 'rc' is a non-terminal. This is an example of a chain rule. Chain rules
can be used to allow several variants of non-terminals.

The generated matcher uses dynamic programming to find the best match of the
tree. This strategy consists of two steps:

  - label: During this phase the given tree is traversed in a bottom up way.
    each node is labelled with a possible matching rule and the corresponding cost.
  - select: In this step, the tree is traversed again, selecting at each point
    the cheapest way to get to the goal.

"""

import sys
import os
import io
import types
import argparse
from ppci import Token
from pyyacc import ParserException, EOF
import yacc
import baselex
from tree import Tree

# Generate parser on the fly:
spec_file = os.path.join(os.path.dirname(os.path.abspath(__file__)), 'burg.x')
burg_parser = yacc.load_as_module(spec_file)


class BurgLexer:
    def feed(self, txt):
        tok_spec = [
           ('id', r'[A-Za-z][A-Za-z\d_]*', lambda typ, val: (typ, val)),
           ('kw', r'%[A-Za-z][A-Za-z\d_]*', lambda typ, val: (val, val)),
           ('number', r'\d+', lambda typ, val: (typ, int(val))),
           ('STRING', r"'[^']*'", lambda typ, val: ('id', val[1:-1])),
           ('template', r"\(\..*\.\)", lambda typ, val: (typ, val)),
           ('OTHER', r'[:;\|\(\),]', lambda typ, val: (val, val)),
           ('SKIP', r'[ ]', None)
            ]

        lines = txt.split('\n')
        header_lines = []

        def tokenize():
            section = 0
            for line in lines:
                line = line.strip()
                if not line:
                    continue  # Skip empty lines
                elif line == '%%':
                    section += 1
                    if section == 1:
                        yield Token('header', header_lines)
                    yield Token('%%', '%%')
                else:
                    if section == 0:
                        header_lines.append(line)
                    else:
                        yield from baselex.tokenize(tok_spec, line)
            yield Token(EOF, EOF)
        self.tokens = tokenize()
        self.token = self.tokens.__next__()

    def next_token(self):
        t = self.token
        if t.typ != EOF:
            self.token = self.tokens.__next__()
        return t


class Rule:
    """ A rewrite rule. Specifies a tree that can be rewritten into a result
    at a specific cost """
    def __init__(self, non_term, tree, cost, template):
        self.non_term = non_term
        self.tree = tree
        self.cost = cost
        self.template = template
        self.nr = 0

    def __repr__(self):
        return '{} -> {} ${}'.format(self.non_term, self.tree, self.cost)


class Symbol:
    def __init__(self, name):
        self.name = name


class Term(Symbol):
    pass


class Nonterm(Symbol):
    def __init__(self, name):
        super().__init__(name)
        self.chain_rules = []


class BurgSystem:
    def __init__(self):
        self.rules = []
        self.symbols = {}
        self.goal = None

    def symType(self, t):
        return (s.name for s in self.symbols.values() if type(s) is t)

    terminals = property(lambda s: s.symType(Term))

    non_terminals = property(lambda s: s.symType(Nonterm))

    def add_rule(self, non_term, tree, cost, template):
        template = template[2:-2].strip()
        if not template:
            template = 'pass'
        rule = Rule(non_term, tree, cost, template)
        if len(tree.children) == 0 and tree.name not in self.terminals:
            self.non_term(tree.name).chain_rules.append(rule)
        self.non_term(rule.non_term)
        self.rules.append(rule)
        rule.nr = len(self.rules)

    def non_term(self, name):
        if name in self.terminals:
            raise BurgError('Cannot redefine terminal')
        if not self.goal:
            self.goal = name
        return self.install(name, Nonterm)

    def tree(self, name, *args):
        return Tree(name, *args)

    def install(self, name, t):
        assert type(name) is str
        if name in self.symbols:
            assert type(self.symbols[name]) is t
        else:
            self.symbols[name] = t(name)
        return self.symbols[name]

    def add_terminal(self, terminal):
        self.install(terminal, Term)


class BurgError(Exception):
    pass


class BurgParser(burg_parser.Parser):
    """ Derived from automatically generated parser """
    def parse(self, l):
        self.system = BurgSystem()
        super().parse(l)
        return self.system


class BurgGenerator:
    def print(self, *args):
        """ Print helper function that prints to output file """
        print(*args, file=self.output_file)

    def generate(self, system, output_file):
        """ Generate script that implements the burg spec """
        self.output_file = output_file
        self.system = system

        self.print('#!/usr/bin/python')
        self.print('from tree import Tree, BaseMatcher, State')
        for header in self.system.header_lines:
            self.print(header)
        self.print()
        self.print('class Matcher(BaseMatcher):')
        self.print('    def __init__(self):')
        self.print('        self.kid_functions = {}')
        self.print('        self.nts_map = {}')
        self.print('        self.pat_f = {}')
        for rule in self.system.rules:
            kids, dummy = self.compute_kids(rule.tree, 't')
            rule.num_nts = len(dummy)
            lf = 'lambda t: [{}]'.format(', '.join(kids), rule)
            pf = 'self.P{}'.format(rule.nr)
            self.print('        #  {}: {}'.format(rule.nr, rule))
            self.print('        self.kid_functions[{}] = {}'.format(rule.nr, lf))
            self.print('        self.nts_map[{}] = {}'.format(rule.nr, dummy))
            self.print('        self.pat_f[{}] = {}'.format(rule.nr, pf))
        self.print()
        for rule in self.system.rules:
            if rule.num_nts > 0:
                args = ', ' + ', '.join('nt{}'.format(x) for x in range(rule.num_nts))
            else:
                args = ''
            self.print('    def P{}(self, tree{}):'.format(rule.nr, args))
            template = rule.template
            template = template.replace('$$', 'tree')
            for i in range(rule.num_nts):
                template = template.replace('${}'.format(i+1), 'nt{}'.format(i))
            for t in template.split(';'):
                self.print('        {}'.format(t.strip()))
        self.emit_state()
        self.print('    def gen(self, tree):')
        self.print('        self.burm_label(tree)')
        self.print('        if not tree.state.has_goal("{}"):'.format(self.system.goal))
        self.print('          raise Exception("Tree {} not covered".format(tree))')
        self.print('        return self.apply_rules(tree, "{}")'.format(self.system.goal))

    def emit_record(self, rule, state_var):
        # TODO: check for rules fullfilled (by not using 999999)
        self.print('            nts = self.nts({})'.format(rule.nr))
        self.print('            kids = self.kids(tree, {})'.format(rule.nr))
        self.print('            c = sum(x.state.get_cost(y) for x, y in zip(kids, nts)) + {}'.format(rule.cost))
        self.print('            tree.state.set_cost("{}", c, {})'.format(rule.non_term, rule.nr))
        for cr in self.system.symbols[rule.non_term].chain_rules:
            self.print('            # Chain rule: {}'.format(cr))
            self.print('            tree.state.set_cost("{}", c + {}, {})'.format(cr.non_term, cr.cost, cr.nr))

    def emit_state(self):
        """ Emit a function that assigns a new state to a node """
        self.print('    def burm_state(self, tree):')
        self.print('        tree.state = State()')
        for term in self.system.terminals:
            self.emitcase(term)
        self.print()

    def emitcase(self, term):
        rules = [rule for rule in self.system.rules if rule.tree.name == term]
        for rule in rules:
            condition = self.emittest(rule.tree, 'tree')
            self.print('        if {}:'.format(condition))
            self.emit_record(rule, 'state')

    def compute_kids(self, t, root_name):
        """ Compute of a pattern the blanks that must be provided from below in the tree """
        if t.name in self.system.non_terminals:
            return [root_name], [t.name]
        else:
            k = []
            nts = []
            for i, c in enumerate(t.children):
                pfx = root_name + '.children[{}]'.format(i)
                kf, dummy = self.compute_kids(c, pfx)
                nts.extend(dummy)
                k.extend(kf)
            return k, nts


    def emittest(self, tree, prefix):
        """ Generate condition for a tree pattern """
        ct = (c for c in tree.children if c.name not in self.system.non_terminals)
        child_tests = (self.emittest(c, prefix + '.children[{}]'.format(i)) for i, c in enumerate(ct))
        child_tests = ('({})'.format(ct) for ct in child_tests)
        child_tests = ' and '.join(child_tests)
        child_tests = ' and ' + child_tests if child_tests else ''
        tst = '{}.name == "{}"'.format(prefix, tree.name)
        return tst + child_tests


def make_argument_parser():
    """ Constructs an argument parser """
    parser = argparse.ArgumentParser(description='pyburg bottom up rewrite system generator compiler compiler')
    parser.add_argument('source', type=argparse.FileType('r'), \
      help='the parser specification')
    parser.add_argument('-o', '--output', type=argparse.FileType('w'), \
        default=sys.stdout)
    return parser

def load_as_module(filename):
    """ Load a parser spec file, generate LR tables and create module """
    ob = io.StringIO()
    args = argparse.Namespace(source=open(filename), output=ob)
    main(args)

    matcher_mod = types.ModuleType('generated_matcher')
    exec(ob.getvalue(), matcher_mod.__dict__)
    return matcher_mod


def main(args):
    src = args.source.read()
    args.source.close()

    # Parse specification into burgsystem:
    l = BurgLexer()
    p = BurgParser()
    l.feed(src)
    burg_system = p.parse(l)

    # Generate matcher:
    generator = BurgGenerator()
    generator.generate(burg_system, args.output)


if __name__ == '__main__':
    # Parse arguments:
    args = make_argument_parser().parse_args()
    main(args)