# parser.py - simple top-down operator precedence parser for mercurial

#

# Copyright 2010 Matt Mackall <mpm@selenic.com>

#

# This software may be used and distributed according to the terms of the

# GNU General Public License version 2 or any later version.

# see http://effbot.org/zone/simple-top-down-parsing.htm and

# http://eli.thegreenplace.net/2010/01/02/top-down-operator-precedence-parsing/

# for background

# takes a tokenizer and elements

# tokenizer is an iterator that returns (type, value, pos) tuples

# elements is a mapping of types to binding strength, prefix, infix and

# suffix actions

# an action is a tree node name, a tree label, and an optional match

# __call__(program) parses program into a labeled tree

import error

from i18n import _

class parser(object):

    def __init__(self, elements, methods=None):

        self._elements = elements

        self._methods = methods

        self.current = None

    def _advance(self):

        'advance the tokenizer'

        t = self.current

        self.current = next(self._iter, None)

        return t

    def _match(self, m):

        'make sure the tokenizer matches an end condition'

        if self.current[0] != m:

            raise error.ParseError(_("unexpected token: %s") % self.current[0],

                                   self.current[2])

        self._advance()

    def _parseoperand(self, bind, m=None):

        'gather right-hand-side operand until an end condition or binding met'

        if m and self.current[0] == m:

            expr = None

        else:

            expr = self._parse(bind)

        if m:

            self._match(m)

        return expr

    def _parse(self, bind=0):

        token, value, pos = self._advance()

        # handle prefix rules on current token

        prefix = self._elements[token][1]

        if not prefix:

            raise error.ParseError(_("not a prefix: %s") % token, pos)

        if len(prefix) == 1:

            expr = (prefix[0], value)

        else:

            expr = (prefix[0], self._parseoperand(*prefix[1:]))

        # gather tokens until we meet a lower binding strength

        while bind < self._elements[self.current[0]][0]:

            token, value, pos = self._advance()

            infix, suffix = self._elements[token][2:]

            # check for suffix - next token isn't a valid prefix

                expr = (suffix[0], expr)

            else:

                # handle infix rules

                if not infix:

                    raise error.ParseError(_("not an infix: %s") % token, pos)

                expr = (infix[0], expr, self._parseoperand(*infix[1:]))

        return expr

    def parse(self, tokeniter):

        'generate a parse tree from tokens'

        self._iter = tokeniter

        self._advance()

        res = self._parse()

        token, value, pos = self.current

        return res, pos

    def eval(self, tree):

        'recursively evaluate a parse tree using node methods'

        if not isinstance(tree, tuple):

            return tree

        return self._methods[tree[0]](*[self.eval(t) for t in tree[1:]])

    def __call__(self, tokeniter):

        'parse tokens into a parse tree and evaluate if methods given'

        t = self.parse(tokeniter)

        if self._methods:

            return self.eval(t)

        return t

def buildargsdict(trees, funcname, keys, keyvaluenode, keynode):

    """Build dict from list containing positional and keyword arguments

    Invalid keywords or too many positional arguments are rejected, but

    missing arguments are just omitted.

    """

    if len(trees) > len(keys):

        raise error.ParseError(_("%(func)s takes at most %(nargs)d arguments")

                               % {'func': funcname, 'nargs': len(keys)})

    args = {}

    # consume positional arguments

    for k, x in zip(keys, trees):

        if x[0] == keyvaluenode:

            break

        args[k] = x

    # remainder should be keyword arguments

    for x in trees[len(args):]:

        if x[0] != keyvaluenode or x[1][0] != keynode:

            raise error.ParseError(_("%(func)s got an invalid argument")

                                   % {'func': funcname})

        k = x[1][1]

        if k not in keys:

            raise error.ParseError(_("%(func)s got an unexpected keyword "

                                     "argument '%(key)s'")

                                   % {'func': funcname, 'key': k})

        if k in args:

            raise error.ParseError(_("%(func)s got multiple values for keyword "

                                     "argument '%(key)s'")

                                   % {'func': funcname, 'key': k})

        args[k] = x[2]

    return args

def _prettyformat(tree, leafnodes, level, lines):

    if not isinstance(tree, tuple) or tree[0] in leafnodes:

        lines.append((level, str(tree)))

    else:

        lines.append((level, '(%s' % tree[0]))

        for s in tree[1:]:

            _prettyformat(s, leafnodes, level + 1, lines)

        lines[-1:] = [(lines[-1][0], lines[-1][1] + ')')]

def prettyformat(tree, leafnodes):

    lines = []

    _prettyformat(tree, leafnodes, 0, lines)

    output = '\n'.join(('  ' * l + s) for l, s in lines)

    return output

def simplifyinfixops(tree, targetnodes):

    """Flatten chained infix operations to reduce usage of Python stack

    >>> def f(tree):

    ...     print prettyformat(simplifyinfixops(tree, ('or',)), ('symbol',))

    >>> f(('or',

    ...     ('or',

    ...       ('symbol', '1'),

    ...       ('symbol', '2')),

    ...     ('symbol', '3')))

    (or

      ('symbol', '1')

      ('symbol', '2')

      ('symbol', '3'))

    >>> f(('func',

    ...     ('symbol', 'p1'),

    ...     ('or',

    ...       ('or',

    ...         ('func',

    ...           ('symbol', 'sort'),

    ...           ('list',

    ...             ('or',

    ...               ('or',

    ...                 ('symbol', '1'),

    ...                 ('symbol', '2')),

    ...               ('symbol', '3')),

    ...             ('negate',

    ...               ('symbol', 'rev')))),

    ...         ('and',

    ...           ('symbol', '4'),

    ...           ('group',

    ...             ('or',

    ...               ('or',

    ...                 ('symbol', '5'),

    ...                 ('symbol', '6')),

    ...               ('symbol', '7'))))),

    ...       ('symbol', '8'))))

    (func

      ('symbol', 'p1')

      (or

        (func

          ('symbol', 'sort')

          (list

            (or

              ('symbol', '1')

              ('symbol', '2')

              ('symbol', '3'))

            (negate

              ('symbol', 'rev'))))

        (and

          ('symbol', '4')

          (group

            (or

              ('symbol', '5')

              ('symbol', '6')

              ('symbol', '7'))))

        ('symbol', '8')))

    """

    if not isinstance(tree, tuple):

        return tree

    op = tree[0]

    if op not in targetnodes:

        return (op,) + tuple(simplifyinfixops(x, targetnodes) for x in tree[1:])

    # walk down left nodes taking each right node. no recursion to left nodes

    # because infix operators are left-associative, i.e. left tree is deep.

    # e.g. '1 + 2 + 3' -> (+ (+ 1 2) 3) -> (+ 1 2 3)

    simplified = []

    x = tree

    while x[0] == op:

        l, r = x[1:]

        simplified.append(simplifyinfixops(r, targetnodes))

        x = l

    simplified.append(simplifyinfixops(x, targetnodes))

    simplified.append(op)

    return tuple(reversed(simplified))