# Source code for hypothesis.extra.lark

    # This file is part of Hypothesis, which may be found at
    # https://github.com/HypothesisWorks/hypothesis/
    #
    # Copyright the Hypothesis Authors.
    # Individual contributors are listed in AUTHORS.rst and the git log.
    #
    # This Source Code Form is subject to the terms of the Mozilla Public License,
    # v. 2.0. If a copy of the MPL was not distributed with this file, You can
    # obtain one at https://mozilla.org/MPL/2.0/.

    """
    ----------------
    hypothesis[lark]
    ----------------

    This extra can be used to generate strings matching any context-free grammar,
    using the `Lark parser library <https://github.com/lark-parser/lark>`_.

    It currently only supports Lark's native EBNF syntax, but we plan to extend
    this to support other common syntaxes such as ANTLR and :rfc:`5234` ABNF.
    Lark already `supports loading grammars
    <https://lark-parser.readthedocs.io/en/latest/nearley.html>`_
    from `nearley.js <https://nearley.js.org/>`_, so you may not have to write
    your own at all.

    Note that as Lark is at version 0.x, this module *may* break API compatibility
    in minor releases if supporting the latest version of Lark would otherwise be
    infeasible.  We may also be quite aggressive in bumping the minimum version of
    Lark, unless someone volunteers to either fund or do the maintenance.
    """

    from inspect import getfullargspec
    from typing import Dict, Optional

    import attr
    import lark
    from lark.grammar import NonTerminal, Terminal  # type: ignore

    from hypothesis import strategies as st
    from hypothesis.errors import InvalidArgument
    from hypothesis.internal.conjecture.utils import calc_label_from_name
    from hypothesis.internal.validation import check_type
    from hypothesis.strategies._internal.utils import cacheable, defines_strategy

    __all__ = ["from_lark"]

    @attr.s()
    class DrawState:
        """Tracks state of a single draw from a lark grammar.

        Currently just wraps a list of tokens that will be emitted at the
        end, but as we support more sophisticated parsers this will need
        to track more state for e.g. indentation level.
        """

        # The text output so far as a list of string tokens resulting from
        # each draw to a non-terminal.
        result = attr.ib(default=attr.Factory(list))

    def get_terminal_names(terminals, rules, ignore_names):
        """Get names of all terminals in the grammar.

        The arguments are the results of calling ``Lark.grammar.compile()``,
        so you would think that the ``terminals`` and ``ignore_names`` would
        have it all... but they omit terminals created with ``@declare``,
        which appear only in the expansion(s) of nonterminals.
        """
        names = {t.name for t in terminals} | set(ignore_names)
        for rule in rules:
            names |= {t.name for t in rule.expansion if isinstance(t, Terminal)}
        return names

    class LarkStrategy(st.SearchStrategy):
        """Low-level strategy implementation wrapping a Lark grammar.

        See ``from_lark`` for details.
        """

        def __init__(self, grammar, start, explicit):
            assert isinstance(grammar, lark.lark.Lark)
            if start is None:
                start = grammar.options.start
            if not isinstance(start, list):
                start = [start]
            self.grammar = grammar

            # This is a total hack, but working around the changes is a nicer user
            # experience than breaking for anyone who doesn't instantly update their
            # installation of Lark alongside Hypothesis.
            compile_args = getfullargspec(grammar.grammar.compile).args
            if "terminals_to_keep" in compile_args:
                terminals, rules, ignore_names = grammar.grammar.compile(start, ())
            elif "start" in compile_args:  # pragma: no cover
                # Support lark <= 0.10.0, without the terminals_to_keep argument.
                terminals, rules, ignore_names = grammar.grammar.compile(start)
            else:  # pragma: no cover
                # This branch is to support lark <= 0.7.1, without the start argument.
                terminals, rules, ignore_names = grammar.grammar.compile()

            self.names_to_symbols = {}

            for r in rules:
                t = r.origin
                self.names_to_symbols[t.name] = t

            for t in terminals:
                self.names_to_symbols[t.name] = Terminal(t.name)

            self.start = st.sampled_from([self.names_to_symbols[s] for s in start])

            self.ignored_symbols = tuple(self.names_to_symbols[n] for n in ignore_names)

            self.terminal_strategies = {
                t.name: st.from_regex(t.pattern.to_regexp(), fullmatch=True)
                for t in terminals
            }
            unknown_explicit = set(explicit) - get_terminal_names(
                terminals, rules, ignore_names
            )
            if unknown_explicit:
                raise InvalidArgument(
                    "The following arguments were passed as explicit_strategies, "
                    "but there is no such terminal production in this grammar: "
                    + repr(sorted(unknown_explicit))
                )
            self.terminal_strategies.update(explicit)

            nonterminals = {}

            for rule in rules:
                nonterminals.setdefault(rule.origin.name, []).append(tuple(rule.expansion))

            for v in nonterminals.values():
                v.sort(key=len)

            self.nonterminal_strategies = {
                k: st.sampled_from(v) for k, v in nonterminals.items()
            }

            self.__rule_labels = {}

        def do_draw(self, data):
            state = DrawState()
            start = data.draw(self.start)
            self.draw_symbol(data, start, state)
            return "".join(state.result)

        def rule_label(self, name):
            try:
                return self.__rule_labels[name]
            except KeyError:
                return self.__rule_labels.setdefault(
                    name, calc_label_from_name(f"LARK:{name}")
                )

        def draw_symbol(self, data, symbol, draw_state):
            if isinstance(symbol, Terminal):
                try:
                    strategy = self.terminal_strategies[symbol.name]
                except KeyError:
                    raise InvalidArgument(
                        "Undefined terminal %r. Generation does not currently support "
                        "use of %%declare unless you pass `explicit`, a dict of "
                        'names-to-strategies, such as `{%r: st.just("")}`'
                        % (symbol.name, symbol.name)
                    ) from None
                draw_state.result.append(data.draw(strategy))
            else:
                assert isinstance(symbol, NonTerminal)
                data.start_example(self.rule_label(symbol.name))
                expansion = data.draw(self.nonterminal_strategies[symbol.name])
                for e in expansion:
                    self.draw_symbol(data, e, draw_state)
                    self.gen_ignore(data, draw_state)
                data.stop_example()

        def gen_ignore(self, data, draw_state):
            if self.ignored_symbols and data.draw_bits(2) == 3:
                emit = data.draw(st.sampled_from(self.ignored_symbols))
                self.draw_symbol(data, emit, draw_state)

        def calc_has_reusable_values(self, recur):
            return True

    def check_explicit(name):
        def inner(value):
            check_type(str, value, "value drawn from " + name)
            return value

        return inner

    @cacheable
    @defines_strategy(force_reusable_values=True)
    def from_lark(
        grammar: lark.lark.Lark,
        *,
        start: Optional[str] = None,
        explicit: Optional[Dict[str, st.SearchStrategy[str]]] = None,
    ) -> st.SearchStrategy[str]:
        """A strategy for strings accepted by the given context-free grammar.

        ``grammar`` must be a ``Lark`` object, which wraps an EBNF specification.
        The Lark EBNF grammar reference can be found
        `here <https://lark-parser.readthedocs.io/en/latest/grammar.html>`_.

        ``from_lark`` will automatically generate strings matching the
        nonterminal ``start`` symbol in the grammar, which was supplied as an
        argument to the Lark class.  To generate strings matching a different
        symbol, including terminals, you can override this by passing the
        ``start`` argument to ``from_lark``.  Note that Lark may remove unreachable
        productions when the grammar is compiled, so you should probably pass the
        same value for ``start`` to both.

        Currently ``from_lark`` does not support grammars that need custom lexing.
        Any lexers will be ignored, and any undefined terminals from the use of
        ``%declare`` will result in generation errors.  To define strategies for
        such terminals, pass a dictionary mapping their name to a corresponding
        strategy as the ``explicit`` argument.

        The :pypi:`hypothesmith` project includes a strategy for Python source,
        based on a grammar and careful post-processing.
        """
        check_type(lark.lark.Lark, grammar, "grammar")
        if explicit is None:
            explicit = {}
        else:
            check_type(dict, explicit, "explicit")
            explicit = {
                k: v.map(check_explicit(f"explicit[{k!r}]={v!r}"))
                for k, v in explicit.items()
            }
        return LarkStrategy(grammar, start, explicit)